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In this work, the physical, mechanical, and fracturing properties of three different types of rock (shale, sandstone, and coal) are studied through three-point bending tests. The fracturing characteristics are further investigated by acoustic emission (AE) and digital image correlation (DIC). The modified fracture mechanics (MFM) theory, which considers the influence of fracture process zone (FPZ) length, is constructed to calculate the fracture toughness with greater accuracy than that obtained using standard linear elastic fracture mechanics (LEFM). The experimental results indicate that the coal shows more significant nonlinear fracture behaviour than sandstone and shale. For the geometry of the FPZ, coal has the largest FPZ area, and the FPZ length-to-width ratios for shale, sandstone, and coal are 0.86, 1.96, and 1.93, respectively. Furthermore, the FPZ length varies dramatically, while the FPZ width is almost stable among the three types of rock. Using the proposed MFM approach, the average fracture toughness values of shale, sandstone, and coal are 1.019, 0.419, and 0.058 MPa × m0.5, respectively, which are much lower than those calculated by the standard LEFM. For the average fracture energy, sandstone exhibits the largest value (236.55 J/m2), while coal exhibits the lowest value (42.99 J/m2). These newly observed fracture toughness and fracture energy differences among the three materials provide a theoretical basis for the implementation of hydraulic fracturing in the joint exploitation of shale gas, tight sandstone gas, and coalbed methane.

The preparation of lightweight and high-performance material is of great significance for developing stab-resistant clothing. This paper proposes a stab-resistant composite structure combining lightweight polylactic acid (PLA) and carbon fiber reinforced polymer (CFRP). The effect of stacking sequence and filling density on the puncture resistance of composite structures was investigated by dynamic puncture and quasi-static puncture. Puncture load, energy and depth are studied as key parameters of puncture resistance. This paper investigated composite structures' failure process and damage morphology using high-speed camera photography and microscopic imaging techniques. The results show that the composite structure exhibits the strongest puncture resistance when CFRP is designed on the top layer of PLA. The higher the filling density, the lower the puncture depth of the composite structure, but the increase in the overall weight eventually leads to a decrease in the puncture specific energy (PSE). The introduction of the bottom PLA delays the penetration point of the composite structure and increases the absorption of the penetration energy by the CFRP before penetration. The final damage modes of composite structures include fiber fracture, slip and pull-out, matrix fracture and peel damage, as well as fracture damage and plastic deformation of PLA materials.

Sequentially timed all-optical mapping photography (STAMP) is a promising technology for observing ultrafast phenomena. Increasing the frame number during one shot is critical to enhance the capability of STAMP, but the rearrangement of the frames significantly intensifies the complexity of the system. In this work, we design a spectrum-slicing method, allowing for the separation and arrangement of the frames simultaneously in a two-dimensional manner. The experimental results show that our system can capture 25 images in one shot with a spatial resolution of 2.46 μm and a frame rate of 2.5 Tfps, indicating its potential for the observation of highly dynamic events

Concrete constructions commonly contain cracks or defects during forming and service, repair operations are necessary in many situations. However, limited investigations conducted on the dynamic fracture toughness (DFT) of repaired concrete structures. This paper investigates the cracking behavior of concrete structures through notched dynamic semi-circular bend (NSCB) tests performed using a split Hopkinson pressure bar (SHPB) apparatus with two measurement techniques, namely digital image correlation (DIC) and crack propagation gauge (CPG), to capture the flying half angular velocity and crack propagation speed of NSCB concrete specimens under various loads. The results demonstrate a linear increase in both DFT and crack propagation speed of concrete with the loading rate. Additionally, a threshold value exists beyond which the crack speed stabilizes, and the DFT is not evidently influenced by the notch depths. The cracks propagate along the aggregates and remain mostly intact under a relatively low loading rate. With an increased loading rate, the damage pattern of some otherwise deflected aggregates changes resulting in crack penetration and significantly reducing the fracture surface roughness. Repaired specimens exhibit greater energy dissipation at the same loading rate, thereby producing flying fragments with lower kinetic energy, which can prevent secondary damage to internal personnel and structures.

Hypothesis - The use of monoolein/water mixtures in serial crystallography experiments using high-viscosity injectors (HVI) results in significant departures from equilibrium behaviour. This is expected to include changes in phase, viscosity, and associated flow behaviour. It should be possible to detect these changes, in-situ, using a combination of polarisation and rheology characterisation techniques. Experiments - A systematic study was performed using monoolein, varying the water content to create a range of mixtures. Injection induced phase changes within the HVI flow were established using real-time cross-polarization measurements. Dynamic flow characteristics and viscosity was characterized by particle tracking and rheology. Findings - HVI injection induces deformation and phase changes within monoolein (MO)/water mixtures which can be detected through variations in the transmitted intensity during in-situ polarisation studies. The heterogeneity of the extruded sample results in a highly viscous cubic phase in the central region of the stream and a less viscous lamellar-rich phase at the edges adjacent to the walls. The extent of these variations depends on sample composition and injection conditions. Shear-thinning behaviour and increasing heterogeneity in the vicinity of the capillary walls under dynamic flow conditions. This is the first report observing injection induced dynamical behaviour in MO/water mixtures under realistic flow conditions.

Gas fluidization is an efficient method to process nanoparticles. In this study, we employ 3D printing to fabricate a hollow stirring structure of blades with jet holes and position it in a vibrating fluidized bed to realize an integration of vibration, stirring and jetting assistance methods, without increasing structural complexity. The fluidization of SiO2, Al2O3 and TiO2 nanoparticle agglomerates with different primary particle sizes and surface properties are investigated. The combination of vibration and stirring improves the bed expansion obviously, while a further addition of the gas jets at a velocity of a few meters per second allows a further small improvement of bed expansion. The jets slightly reduce the agglomerate size in the dense bed, the agglomerate size at the bed outlet, and the elutriation rate. By combining vibration, stirring and jets, the fluidization is enhanced while the elutriation is kept low during fluidization lasting for a few hours.

Understanding the scale effect in the behavior of solid materials is important when small-scale models are used to predict the behavior of real structures. Tremendous efforts have been devoted to investigating the scale effect in the strength of quasi-brittle materials. However, limited studies have focused on the whether there is a scale effect in bursting failure, which is a typical failure pattern of quasi-brittle structures. Here, we conduct a series of unconfined compression tests on coal samples using a specialized designed loading machine to produce bursting failure in the laboratory. We use cubic coal samples with a large range of sizes from 50 to 300 mm to investigate the scale effect in bursting failure of quasi-brittle materials. We use acoustic emission technology to monitor microcreaking within the samples and a high-speed camera to capture the bursting failure process. We demonstrate that there is a strong scale effect in bursting failure of quasi-brittle materials in terms of mechanical properties including compressive strength and deformability, strain energy density, bursting severity, and precursor time. We found that ejection of localized pieces from the skin of the structure is a precursor of catastrophic bursting failure of quasi-brittle materials. We conclude that the relationship between the precursor time (T) and structure size (M) of bursting failure is logarithmic and can be described as logT = a + bM where a and b are constants. This relationship provides a guideline when models obtained from laboratory tests are used to predict strength and behavior at the intermediate (mines and rock slopes) and large scales (earthquakes).

The increasing demand for contacting applications in electric components such as batteries, power electronics and electric drives is boosting the use of laser-based copper processing. Laser beam welding is a key for an efficient and high-quality electric vehicle production due to its local, non-contact energy input and high automation capability enabling reproducible weld quality. Nevertheless, a major challenge in process design is the combination of energy-efficiency and precise process guidance with regard to weld seam depth and defect prevention (i.e. spatter, melt ejections), partly caused by the high thermal conductivity of copper. High power lasers in the near infrared range and emerging visible laser beam sources with excellent beam quality can provide a suitable joining solution for this purpose. However, the underlying physical phenomena are currently only partly understood and a reflection on the challenges of laser beam welding of copper compared to well researched steel processing has not yet been carried out. In order to improve the understanding of the effect of the different material properties and the influence of process parameters on the vapor capillary and melt pool geometry in laser beam welding, in situ synchrotron investigations on Cu-ETP and S235 using 515 and 1030 nm laser sources were conducted. The material phase contrast analysis was successfully used to distinguish vapor capillary and melt pool phase boundaries during the welding process with high spatial and temporal resolution up to 5 kHz. A significantly different vapor capillary geometry and sensitivity to parameter variation were found between the steel and copper material. In addition, the visualization of characteristic melt flows revealed different melt pool dynamics and a pronounced eddy close to the melt pool surface for copper, which is assumed to be causal for the observation of pronounced spatter formation during copper welding in a certain process window.

The combustion characteristics of a swirl-radial-injection composite fuel grain were experimentally and numerically investigated. This composite grain permits swirl-radial oxidizer injection based on three hollow helical blades, each having a constant hollow space allowing uniform oxidizer injection into the main chamber along the axial direction. The oxidizer enters from channel inlets located along a hollow outer wall. This wall, together with the three blades, is fabricated as one piece from acrylonitrile-butadiene-styrene using three-dimensional printing. Paraffin-based fuel is embedded in the spaces between adjacent blades. Firing tests were conducted with gaseous oxygen as the oxidizer, using oxidizer mass flow rates ranging from 7.45 to 30.68 g/s. Paraffin-based fuel grains using conventional fore-end injection were used for comparison. Regression rate boundaries were determined taking into account the erosion of the oxidizer channels. The data show that the regression rate was significantly increased even at the lower limit. Images of the combustion chamber flame and of the exhaust plume were also acquired. The flame was found to be concentrated in the main chamber and a smoky plume was observed, consistent with the high regression rate. A three-dimensional simulation was employed. The present design was found to improve fuel/oxidizer mixing and combustion efficiency compared with a fuel grain using fore-end injection. Both the experimental results and numerical simulations confirmed the potential of this swirl-radial-injection fuel grain.

Objective To study the effect of Er:YAG laserirrigation on root canal system with different mechanical preparation tapers. Methods Er:YAG laser irrigation process was conducted in different prepared resin tooth models(15/. 05, 20/. 06 and 25/. 08). The bubble oscillation in root canal was recorded by a high speed camera and the gray scale integral of the bubbles was calculated. The third molars with vital pulp were collected and divided into three groups for different taper root canal preparation(13/. 02, 15/. 05, 20/. 06 and 25/. 08)after extraction. The root canals were prepared by Er:YAG laser irrigation, hand empty needle washing and 5.25% NaClO, respectively. The specimens were fixed, decalcified, embedded, sectioned and stained by HE. The residual pulp tissue was observed and analyzed statistically. Results Under the same mono-pulse energy, the gray scale integral of air bubbles in root canals of 15/. 05 group was significantly less than 20/. 06 and 25/. 08 group(P<0.05); there was no significant difference between 20/. 06 and 25/. 08 groups(P>0.05). The pathological results showed that the risk of residual pulp in Er:YAG laser group was lower than that of empty needle group under the same condition(P<0.05). Compared with 25/. 08 group, 15/. 05 group had a higher residual risk of residual pulp(P<0.05), but 20/. 06 group had no significant difference(P>0.05). Conclusion Under same parameters, the effect of Er:YAG laser on root canal system has no significant difference between 20/. 06 and 25/. 08 group, but both groups have better cleaningeffects than 15/. 05 group.

Adjuvants can effectively enhance the utilization rate of pesticides, but the application of adjuvants in plant growth regulators is rarely studied.MethodsThis work explored the effects of adjuvants dioctyl sulfosuccinate sodium salt (AOT) and methyl oleate (MO) on lime sulfur (LS), especially the drop behavior on flower and paraffin surface. Results The results showed that the addition of AOT and AOT+MO can significantly reduce the static and dynamic surface tension of LS from 72mN/m to 28mN/m and 32mN/m respectively, and increase the spreading factor from 0.18 to 1.83 and 3.10 respectively, reduce the bounce factor from 2.72 to 0.37 and 0.27 respectively. The fluorescence tracer test showed that the addition of adjuvants could promote the spreading and permeation of droplets. The field test results revealed that the flower thinning rate of adjuvant and non-adjuvant were 80.55% and 54.4% respectively, and the flower thinning effect of adding adjuvant was the same as that of artificial which the flower thinning rate was 84.77%. The quality of apples treated with adjuvants was similar to that treated with artificial, and the weight of single fruit increased by 24.08% compared with CK (spray water).

In a liquid kerosene rotating detonation engine (RDE), detonation waves often exhibit different propagation modes. The propagation characteristics with different modes are worthy of further study. To further investigate the propagation characteristics, a series of experiments was conducted, and the flow field characteristics under different modes were comparatively studied using high-speed photography and pressure sensors. The modal features and mode change trends obtained in the experiments were simulated using numerical methods. Based on this, the combustion efficiencies of the different modes were quantitatively characterized. The results showed that with increasing propellant mass flux, the detonation wave gradually changes from the two-counter wave mode to the single-wave mode, and the interim mode is a hybrid mode. Compared with the two-counter wave mode, the velocity deficit of a single wave is smaller, and the reaction zone is more compact. Numerical simulations show that a higher proportion of fuel is consumed by more violent chemical reactions in the single-wave mode; that is, the combustion efficiency in the single-wave mode is higher than that in the two-wave mode. The results provide a reference for further understanding the liquid fuel detonation phenomenon and improving fuel combustion efficiency.

The combination of electrical wire explosion and low sensitivity energetic materials is an efficient and practical method to generate controllable strong pressure waves, which is a potential alternative to explosives in directional fracturing applications. In this paper, a new configuration of hybrid load is proposed to generate synchronized pressure waves for directional fracturing, with the advantages of lower energy storage and smaller blast-hole diameters. The pressure wave of hybrid load explosion is measured, and the explosion synchronicity of the two loads at the microsecond level is verified by self-illumination images. Then, two-hole granite cylinders are used to verify the feasibility of directional fracturing, and the results show that the double loads explosion formed directional fractures connecting the two holes and a horizontal failure plane. The fracturing process, including fracture initiation, propagation, and connection, is recorded with a high-speed camera and is reproduced in numerical simulation. Based on the experimental and numerical results, the fracture morphology is characterized as four areas, and the fracturing mechanism is analyzed.

Membrane distillation (MD) is a promising green separation technology for the treatment of high salinity wastewater attributed to excellent salt rejection, which is significant in relevant environmental and chemical engineering application. However, membrane scaling is an inevitable issue during long-term membrane distillation process. Thus, we developed a membrane flux response technology with data processing method to in-situ monitor the membrane scaling according to the reduction of permeate flux. By real-time analyzing the derivative of deviation between theoretical and experimental fluxes, early warning of initial membrane surface scaling was observed at initial nucleation stage. Besides, such timely detection was also achieved under different temperatures and flow velocities of feed solution, even for the poor light transmittance aqueous solution (such as NiSO4 and CoSO4 solution), which exhibited wide application potential on diverse high salinity wastewater systems. In addition, the metastable zone width of salt solution within MD system was obtained for the efficient operation design. To sum up, membrane flux response technology provides an early warning at imminent membrane scaling, which will maintain the great separation effect for a fresh feed solution after a facile cleaning by pure water, indicating the extension of device lifetime.

Walnut shell is lightweight material with high-strength and toughening characteristics, but it is different from other nut shells’ microstructure with two or three short sclerotic cell layers and long bundle fibers. It is essential to explore the fracture resistance biomechanism of lightweight walnut shell and how to prevent damage of bionic structure. In this study, it is found that the asymmetric mass center and geometric center dissipated impact energy to the whole shell without loading concentration in the loading area. Diaphragma juglandis is a special structure improved walnut shell's toughening. The S-shape gradient porosity/elastic modulus distribution combined with pits on single auxetic sclerotic cells requires higher energy to crack expansion, then decreases its fracture behavior. These fantastic findings inspire to design fracture resistance devices including helmets, armor, automobile anti-collision beams, and re-entry capsule in spacecraft.

In this work, droplets bouncing on curved surfaces with elevated temperatures are reported. The bouncing and depositing phenomena of different lubricant droplets are confirmed. The influence of initial diameter, tangential velocity, and surface roughness on the impact dynamics of silicone oil droplets on wetted curved surfaces is investigated, and the temperature dependence of the bouncing phenomenon is highlighted. Bouncing and depositing thresholds under various conditions are summarized. It is found that surface roughness has the most significant negative effect on the bounceable velocity range, followed by initial diameter and tangential velocity. A theoretical model and force analysis are established to explain the bouncing mechanism. The modified Bond numbers and Ohnesorge numbers are introduced to predict the bouncing thresholds. This work provides sufficient experimental and theoretical insights into manipulating droplets bouncing on wetted and curved surfaces with elevated temperatures.

Rayleigh’s equation has been widely used to determine surface tension from oscillating droplets. In this study, the use of a drop-on-demand droplet generator is proposed to create free-falling, oscillating, molten metal droplets for this purpose. To examine the applicability of the droplet generator, extensive numerical simulations in three and two-dimensions were performed. The effect of gravity, initial velocity and initial deformation on the frequency and pattern of the droplet oscillation was investigated. The use of this generator enables the creation of thousands of droplets in the course of a single experiment and the droplets have a much shorter exposure time to possible unwanted contaminations, due to a rapid measurement principle. Furthermore, the adjustable nozzle size of the generator provides flexibility in terms of droplet size, which affects the range of validity of Rayleigh’s method. To validate the method, the surface tension of molten copper in an argon atmosphere was determined over a temperature range of 1400–1620 K. The determined linear relation is expressed as σ [mN m−1] = (1307 ± 98) − (0.22 ± 0.015) (T−1356) (T in K).

Both snap-shot as well as time-resolved PIV (TR-PIV) measurements are performed on a transonic com- pressor cascade to elucidate the underlying shock-boundary layer interaction process. In order to align both the instantaneous passage shock and the boundary layer along with its separation downstream of the shock foot, shadowgraph imagery is acquired synchronous with TR-PIV recordings. Statistics from PIV snapshots reveal that the passage shock fluctuates by up to 13% of the chord. Frequencies of shock motion lay in a range between 500 and 600 Hz with an additional specific tone near 1142 Hz. With TR-PIV, the velocity field in the interaction region is sampled at 20 kHz, which temporally resolves the motion of the shock foot and captures size variations of the separation region. The thickness of the laminar boundary layer (BL) is found to grow as the shock moves downstream. A rapid upstream motion of the shock leads to even higher BL growth rates and large scale flow separation downstream. Proper orthogonal decomposition (POD) of the snap-shot PIV data reveals that 50% of the energy is contained in the first 4 modes. The corresponding POD eigenvalue spectrum exhibits a -11/9 decay slope as predicted in literature for the inertial range of inhomogeneous turbulence.

In a rotating detonation engine (RDE), specifically a low-activity liquid fuel RDE, ensuring the continuous and stable propagation of detonation waves is important. In the RDE experiment with oxygen-enriched air as the oxidant and liquid kerosene as the fuel at room temperature, the stability of the rotating detonation wave (RDW) is found to be extremely inadequate. This inadequacy is manifested by more than 10 times of quenching and re-initiation within 500 ms. This frequent quenching and re-initiation phenomena considerably differ from those of the gaseous fuel RDE. Consequently, the velocity deficit of the detonation wave increased and the propulsion performance of the RDE was affected. In a further study using pressure sensors and high-speed cameras, the quenching phenomenon was found to be related to the supply state of the propellant, and the re-initiation phenomenon was related to the chemical reaction zone in the combustion chamber. To verify the foregoing, a special control test was performed. After improving the supply state of the corresponding propellant, the unstable characteristic of liquid fuel was effectively suppressed and a stable RDW with a velocity of 1321 m/s was obtained. The results of this study reveal the mechanism of liquid fuel quenching and re-initiation. This mechanism significantly restrains the instability of liquid fuel detonation waves.

A lateral-approaching and horizontal-pushing transplanting manipulator for greenhouse seedlings was developed to minimize the damage of their stems and leaves during transplanting. The manipulator is composed of a pick-up robotic arm, an end-effector, two conveyors, and a control system. The robotic arm liking a spatial 3-DoF displacement mechanism to achieve a point-to-point circuitous locomotion of the end-effector was designed with the mechanism combination innovation method, which consisted of two crossing high-speed linear modules and a pushing slide cylinder. The end-effector of a pincette-type mechanism uses two cylinder fingers and four pins to pick up and release the seedlings. Each conveyor adopts a flat-belt transmission mode to move the plug tray/growth pot to the working position of the end-effector. The control system coordinates the flexible automation of each component. A physical prototype of the manipulator was constructed and its performance was tested under laboratory conditions. Through the high-speed camera test, the end-effector could approach plug seedling in lateral sliding way to effectively shelter the seedling plants. On the whole, the maximum holding angles of these seedling plants were larger than 45° with little effects on the subsequent growth. The corresponding performance tests showed that the average success ratios for automatic transplanting were up to 97.57% for typical pepper and cabbage seedlings. The lateral-approaching and horizontal-pushing transplanting performance was satisfactory.

In this work, physical dealloying was explored as a simple and green method to microstructure the surface of commercial brass for pool boiling heat transfer coefficient enhancement. Three samples were dealloyed for 0.5, 1 and 3 hours at 650 ℃, turning the smooth surface into a porous one with a depth of 175, 200 and 223 μm. The boiling experiments carried out in ethanol at 78 ℃ have shown, that the maximum enhancement of heat transfer coefficient between 110 and 150% was achieved for the sample dealloyed for 0.5 h. Longer intervals of dealloying reduce boiling performance, but it is still much higher compared to smooth brass. This simple method can be customized for various thermal management equipment, such as conventional, plate and micro heat exchangers, all types of heat pipes, HVAC equipment etc., where the heat transfer occurs with phase change.

We studied the layer structure of bubbles just below water/air and water/EPE (Expand aple poly ephylene) interfaces using high-speed photography. The layer structure was generated by floating spherical clusters, the source bubbles of which were identified to come from the attachment of bubble nuclei at the interface, the floating of bubbles in the bulk liquid, or bubbles generated on the surface of the ultrasonic transducer. The boundary shape affected the layer structure, which assumed a similar profile below the water/EPE interface. We developed a simplified model composed of a bubble column and bubble chain to describe interface impacts and the interaction of bubbles in a typical branching structure. We found that the resonant frequency of the bubbles is smaller than that of an isolated single bubble. Moreover, the primary acoustic field plays an important role in the generation of the structure. A higher acoustic frequency and pressure were found to shorten the distance between the structure and the interface. A hat-like layer structure of bubbles was more likely to exist in the low-frequency (28 and 40 kHz) intense inertial cavitation field, in which bubbles oscillate violently. By contrast, structures composed of discrete spherical clusters were more likely to form in the relatively weak cavitation field at 80 kHz, in which stable and inertial cavitation coexisted. The theoretical predictions were in good agreement with the experimental observations.

Ferrite paint are commonly used on the surface of aluminum alloys. It contains metal oxide particles, significantly affecting laser paint removal when a nanosecond pulsed laser was used to clean the ferrite paint. In this paper, we experimentally investigate and analyze the plume ejection characteristics and the product during the laser cleaning of the paint. Driven by ablative gas recoil pressure, the ferrite paint was vaporized by the laser pulse into a mixture of molten droplets, resin residual particles, and carbides, and they were then ejected from the laser scanning area with the plume to form a black spatter powder on the cleaned surface. A physical model for calculating the ejection angle of the laser-cleaning plume is established. The results show that the thermal diffusion rate of paint and substrate, laser pulse duration, and laser scanning speed determine the plume ejection angle. Optimizing laser defocus distance and lap rate could significantly reduce surface spatter and improve cleaning quality. Furthermore, through the analysis of XPS, we found that the valence state of the residual ferrite paint changes after the laser cleaning and may affect the residual paint's microwave-absorbing performance. Therefore, removing the ferrite paint layer completely and then re-spray rather than only removing a certain paint depth is necessary.

The effects of the spraying thickness and the position on the response of aluminum plates under impact loading were studied. The impact tests and numerical simulation were conducted for the penetration process of polyurea-coated 2024 aluminum plates with tungsten sphere impacts. The results indicate the impact resistance performance is similar at slower impact velocity (500–1000 m/s), and the front (or double-side) coating has a smaller advantage. When the impact velocity rises to 1500 m/s, the back coating has a better energy-absorbing performance. The polyurea perform more efficiently with the increase in the impact velocity because the elastomer has large-scale deformation. By comparing the different thicknesses of the back coating, the residual velocity of the fragment has small changes and the impact energy absorption increased with the increase in the coating thickness. The separated phenomenon is serious in front of the bonding face with shear compression failure. In the back polyurea layer, the stripping area is smaller than the front bonding face, and the petaloid cracking is formed with tensile failure.

Surfactants are widely used in industrial and agricultural production, especially as agrochemicals. However, the improvement of pesticide utilization by surfactants as the synergist should be achieved without adverse effects on crops, non-target organisms and related ecological environment, which is a lack of attention. Herein, the influence of the nonionic surfactant Triton X (TX) series with different hydrophilic chain lengths on the “Pesticide-Crop-Ecology” system was systematically studied. The impact behavior of TX droplets on the scallion leaf surface was predicted first by molecular dynamics (MD) simulation. Then the impact behavior, adhesion properties and foliar retention of TX droplets on the scallion leaf were investigated by physical experiments. The results showed that the TX-102 structure could increase leaf retention of pyraclostrobin (PYR) by 15.66% due to its fast molecular migration rate, strong adhesion and appropriate wettability with leaves. Furthermore, the environmental effect of the selected TX-102 was fully evaluated, and it was found that TX-102 was relatively safe for both Vicia faba cells and human 293t cells, although it slightly promoted the effect of PYR on cell apoptosis. Importantly, TX-102 has a potential repair effect on the damage to dominant soil bacteria caused by PYR. This study provides a new strategy for the development of efficient and environment-friendly pesticide synergists and sustainable agricultural development.

Experimental and numerical studies were conducted to investigate the effects of drop height on the ignition mechanism of NEPE nitrate ester plasticized polyether-based propellants. A modified drop-weight system was equipped with a high-speed camera to capture the ignition response images during the whole impact process. A macro-mesoscopic thermomechanical model considering the microcrack and viscous shear flow hotspot formation mechanism was established. The experimental results showed that the ignition responses of the propellants heavily depended on drop height, and the main ignition mechanism was viscous shear flow. The whole loading process could be summarized into three stages: radial extension (viscous shear flow), macroscopic crack initiation and ultimate failure (multiple macroscopic cracks or ignition). The ignition threshold was 35 cm. The posttest scanning electron microscopy (SEM) images further revealed that viscous shear flow played an important role in the ignition of propellants. The numerical simulation results indicated that viscous shear flow was the dominant ignition mechanism compared with the microcrack hotspot mechanism. Point A (along L1) was the most dangerous location under the drop-weight experiment. The predicted features of ignition evolution were consistent with the experimental results and prove that the critical drop height of ignition was 35 cm.

Fabrication of hole-free aluminum structures through metal droplet-based 3D printing is an important channel for high-performance aluminum parts in aerospace applications. Unfortunately, completely eliminating bottom hole defects has proven challenging due to the narrow printing temperature range and complex hole defect evolution rules. In this work, by tailoring the overlap ratio (η) and substrate temperature (Ts), we proposed a novel strategy to eliminate bottom hole defects of overlapping droplets in a broad temperature range. Combining the high-speed sequence images and the numerical simulation model, the evolution mechanism of bottom hole defects with distinct overlap ratios was revealed. The result demonstrats that the bottom hole defect evolution is dominated by the droplet spreading order and the competition of inertial and capillary forces. Moreover, a regime map was summarized, where the substrate temperature window for the hole-free region at the valley (η = 0) is expanded by 114% compared to the peak (η = 0.6). Finally, a simple and effective strategy was presented, which could enlarge the printing temperature range for eliminating bottom hole defects. This work might provide theoretical guidance for the low-cost and high-quality droplet printing of multitudinous metal components.

The important role of local mine stiffness (LMS) on rock strainbursts has been extensively recognized. Understanding the evolution of LMS as mining proceeds is of significance to rockburst prevention. Existing studies on this topic, however, are limited to theoretical and numerical methods. In this study, an experimental study is performed using in-house built equipment to produce strainbursts resulting from excavation-induced stress concentration and LMS decreasing. The process of excavations and their resultant disturbance is produced using real coal blocks in the laboratory. A novel method is proposed for calculating LMS, based on which the evolution of LMS with excavations is quantitatively evaluated. The influence of initial LMS on the strainbursts is also investigated. The experimental result demonstrated that there is a critical threshold value of LMS below which the coal pillar fails with a bursting pattern. The threshold is related to the post-peak stiffness of the coal pillar. The experimental study proposes a novel method for producing strainbursts and evaluating LMS in the laboratory.

Digital photography of cavitation in narrow gap flows, e.g., lubrication films in journal bearings or squeeze film dampers, demands a high time-resolution and a solution to approaching the particular spatial restrictions. Typically, the lubrication film thickness is in the range of a few microns and the characteristic time for vapor bubble generation and collapse is about one millisecond, respectively. The authors have developed a Journal Bearing Model Experiment, which is designed according to similarity laws providing fully similar flow conditions to real journal flows while offering ideal access to the flow by means of optical measurement equipment. Compared with other methods, e.g., pulsed laser, electrical discharge, tube arrest, applied to produce vapor bubbles, the work on hand applies a dynamic variation of the minimum film thickness to produce suction cavitation, which proves the applicability of this novel approach to study vapor cavitation in fluid films similar to lubricant flows. The results are obtained by means of digital high-speed photography of vapor bubbles from inception to implosion triggered by the dynamic variation of the minimum film thickness of a narrow gap flow. Moreover, the results are set in relation to a general overview of cavitation processes.

In this paper, an experiment is carried out to acquire the dynamic mechanical properties of a simulated sandstone tunnel by a dual DIC system. The sandstone tunnel is simulated by large sandstone with a prefabricated hole in the center. The speckle size required by DIC system was evaluated, and the results showed that for large specimens a marker pen could be used to spot speckles and make sure that the diameters of speckle points in an image should be ranged from three to five pixels. The dual DIC system is composed of a low-speed camera and a high-speed camera. The low-speed camera is used to record the speckle patterns of the sandstone in one side during the whole process of compression load, and the high-speed camera is placed in the other side to record speckle patterns for 11.5 seconds before and after failure. It is realized that monitoring whole process of deformation and instantaneous failure in two directions is required. Measurement results are effectively analyzed. The results are shown as follows: At the initial stage of loading the sandstone is in an elastic stage without macroscopic cracks. With the increase in compression load the sandstone has several small stress releases and several obvious macroscopic cracks. In the final stage of loading, the distribution of normal stress and shear stress are almost the same, and cracks are subjected to the coupling effect of normal stress and shear stress. The two ends of the prefabricated hole perpendicular to the applied load direction are prone to cracks parallel to the applied load direction.

Engineered cardiac tissues (ECTs) derived from human induced pluripotentstem cells (hiPSCs) are viable alternatives for cardiac repair, patient-specificdisease modeling, and drug discovery. However, the immature state of ECTslimits their clinical utility. The microenvironment fabricated using 3D scaffoldscan affect cell fate, and is crucial for the maturation of ECTs. Herein, theauthors demonstrate an electric-field-driven (EFD) printed 3D highly orderedmicrostructure with cell feature size to promote the maturation of ECTs. Thesimulation and experimental results demonstrate that the EFD jet microscale3D printing overcomes the jet repulsion without any prior requirements forboth conductive and insulating substrates. Furthermore, the 3D highlyordered microstructures with a fiber diameter of 10–20μmandspacingof60–80μm have been fabricated by maintaining a vertical jet, achieving thelargest ratio of fiber diameter/spacing of 0.29. The hiPSCs-derivedcardiomyocytes formed ordered ECTs with their sarcomere growth along thefiber and developed synchronous functional ECTs inside the 3D-printedscaffold with matured calcium handling compared to the 2D coverslip.Therefore, the EFD jet 3D microscale printing process facilitates thefabrication of scaffolds providing a suitable microenvironment to promote thematuration of ECTs, thereby showing great potential for cardiac tissueengineering.

Nanoscale aluminium (nAl)-based composites find important applications in propellant, explosives and pyrotechnics, and the improved combustion efficiency is always desirable but challenging. A core-shell nAl@CuO composite with improved combustion performance was prepared by means of a biological interfacial layer, which is inspired by the fast polymerization and strong adhesion of juglone and tannic acid in walnut peel juice. It is found that interfacial layer contains phenolic hydroxyl and amino groups, which could interact with nAl and introduce the growth of CuO crystal, respectively. Obtained nAl@CuO shows higher stability but 1.2 times more heat release than that of the mechanically mixed nAl/CuO. In addition, nAl@CuO also has 5 times faster burning rate than the mechanically mixed one. It is believed that interfacial layer hindered the direct contact of reactants but improved mass transport/diffusion efficiency in nAl@CuO. Thus, Al based composites with higher stability and superior combustion efficiency could be obtained by this interfacial layer.

The rotating detonation combustor (RDC) has received remarkable attention in the aerospace community. In this work, an experimental RDC model supplied by liquid kerosene and oxygen-enriched air is established. A parametric survey is performed with different injection throats, outlet restrictions, and equivalence ratios to analyze the rotating detonation wave propagation modes comprehensively. Dynamic pressure transducers and a high-speed camera are both employed to identify wave modes synchronously. Overall, the propagation modes are found to be highly dependent on the injection throat and combustor outlet restriction. With a large injection to annulus area ratio of 0.3, a single-wave mode is characterized when no restriction is added at the combustor outlet. Reducing the outlet area leads to a decrease in the wave frequency and a narrower steady rotating detonation propagation regime. The propagation stability of the rotating detonation is strengthened when the injection to annulus area ratio decreases to 0.2. A dual-wave collision mode and a four-wave collision mode are observed, depending on the outlet restriction. A preliminary stable RDC operation range correlated with outlet to injection throat area ratio and equivalence ratio is achieved. Furthermore, an interval value of the outlet to injection throat area ratio is proposed to reach the potential positive total pressure gain. These findings should serve as the reference for RDC configuration design in air-breathing and gas-turbine propulsion systems.

The understanding and experimentation of abrasive wear mechanisms at high speeds is still poorly investigated in literature. This is mainly due to a lack of suitable, well-instrumented test rigs for fundamental, single abrasive wear events. Standard scratch tests, which are often utilized for studies of abrasion phenomena, operate in the low-speed range up to some mm/s, while applications suffering from abrasive wear often operate at speeds exceeding 1 m/s (e.g., rolling, grinding, machining). Numerical approaches, especially particle-based methods, allow the simulation of such fast deformation processes, but rely on hardening models that require a precise knowledge of material parameters. Thus, the Johnson-Cook material model was parametrized using data from high-speed compression tests of pure aluminum. A series of scratch tests with increasing depths were then simulated using the particle- based Material Point Method (MPM). Experimentation was done on a pendulum scratch test rig equipped with a Rockwell C diamond cone. By adjusting the balance point of the swing arm of ~1 m length, a velocity of 6.8 m/s was achieved at its tip as measured with a high-speed camera. Scratches of several depths were performed, and their force signals acquired. Post-test analyses comprised topography measurements and EBSD on cross-sections of the scratches to investigate the microstructural changes due to the high-speed wear event. Scratch topographies and abrasive mechanisms compared favorably between experiment and simulation for the aluminum. The extent of strain hardening was significantly reduced compared to low-speed experiments. The calibration of the high-speed force sensor was successful and now allows the investigation of new alloys and determination of material parameters under high-speed abrasive conditions.

In the present effort, impact of bullets fired at high speeds on a stationary target was used as a high strain-rate plastic deformation method to generate Functionally Graded Materials (FGMs). The bullet-shaped Aluminum alloy Al5052 specimens impacted the UHMWPE target at different projectile velocities ranging from 100 m/s to 750 m/s, to study the effect of the impact speed. Moreover, few of the projectiles impacted along the longitudinal axis whereas the remaining projectiles impacted with an obliquity to investigate the effect of leading-edge shape. The metallography of the projectile specimens fired at 750 m/s shows grain refinement from 70 ± 3μm at the rear/ un-deformed point to 10 ± 1μm at the front/ severely deformed point which is in the impact zone. Similar but of less magnitude variations were observed at other impact speeds also. The hardness variation was 45% (70 ± 3 HV at the rear surface to 102 ± 2 HV at the front face) at 750 m/s. Moreover, least variation in hardness and grain size was observed for projectile impacted at lowest velocity tested (100 m/s). Further, functionality in hardness and grain refinement was seen in graded direction due to shape of the projectile specimens, impact velocity, and target material. Depending upon the impact angles, axisymmetric (impacted normal to the longitudinal axis) or unsymmetrical (impacted at an angle) variation of grain refinement and hardness was observed.

The presence of metal vapor influences arc stability in both arc and hybrid welding. It is assumed that the composition of the metal vapor, and therefore the substrate material composition, plays an important role due to the different ionization energies of the material elements. In this study, a special setup is used to investigate the influence of metal vapor on the behavior of a vertically oriented arc generated between two equal electrodes by a separate laser-induced vapor generation using a transversally oriented laser beam welding process with additional support materials beside the process zone of the arc. Several aluminum alloys, steel materials, and titanium alloys are used as vapor-producing support materials.

The experiments show that the arc voltage increased under the presence of metal vapor, which implies a decrease in arc stability, leading partially to an extinction of the arc. The influence of the ionization energy is evaluated by calculating the average ionization energy for each material composition. In the case of inducing metal vapor into the arc zone, a smaller ionization energy and a lower amount of alloying elements of the support material result in a lower arc voltage increase and, therefore, higher arc stability. A higher effect on the arc stability when using elements with a smaller ionization energy for the second electron than the first argon electron is not measurable.

Hardwood species are becoming increasingly important with the growing need for a diversity of forests that have recently been facing global temperature changes or conifer pests. This further leads to the growth of its potential as a building material that may originate from sustainable production. As hardwoods need to be properly processed, the article deals with the disintegration of European beech. The influence of wood grain direction, uncut chip thickness and cutting speed on the cutting force magnitudes was experimentally investigated using the device with a rotating arm of approximately 4 m in diameter. Then, the disintegration process was modelled using the finite element method in Abaqus/Explicit. The developed material model consisting of orthotropic elasticity and plasticity with rate-independent and rate-dependent tensile–compressive failure asymmetry was implemented through the user subroutine, while the crack initiation and propagation were realized using the element deletion technique. The computationally predicted average values of cutting forces and chip shapes were, except for a few tests, in good agreement with the experiments. It means that the model may be used for further investigation, such as the influence of tool wear.

Introduction of nanophases into the interface between fibers and matrix in fiber-reinforced polymer composites can form multiscale composites with significantly improved interfacial bonding. The nanophases of various geometric shapes (e.g., nanotubes, nanoparticles, or nanosheets) show quite different reinforcing efficiency. To elucidate the underlying mechanisms of this discrepancy, a multiscale mechanical model is proposed to establish the relation between the geometric shape of nanophases at nano-/micro-scale and the transverse tensile strength of composites at macro-scale. Three typical carbon-based nanophases are chosen for comparison, i.e., fibrous carbon nanotubes (CNTs), granular buckminsterfullerene (BF) nanoparticles, and lamellar graphene oxide (GO) nanosheets. The study indicates that high aspect ratio nanotubes have the superior enhancing effect as individual, but the advantage could be counteracted by the relatively low distribution density in the interfacial region due to their geometric features. The two factors need to be carefully balanced to achieve the desired ultimate performance of multiscale composites.

Depositing drops on a solid surface without entrapping bubbles is desirable for many spray coating and printing applications. Tian et al. [J. Fluid Mech. 946, A21 (2022)] reported that an electric field can be applied to eliminate air bubble entrapments for neutral drops. Herein we provide a complete physical picture of the entire process of a drop impacting onto the solid surface under an external electric field. The electrohydrodynamic behavior during the drop impact is divided into three stages: the deformation of the drop in the electric field prior to contact, the initial contact of the drop with the substrate, and the rich postcontact phenomena including spreading, receding, jetting, and fragmentation. The results show that under the increasingly stronger electric fields, the modest drop oscillation transforms into a vertically stretched spindle. As the drop approaches the substrate, the electric stress at the south pole increases rapidly, which sharpens the bottom surface into a conical shape. The cone angle is determined by both the impact velocity and the electric field strength. After the contact, the surface electric stress tends to pull the drop upward, breaking up the drop, forming several jetting modes, and reducing the maximum spreading radius. The various drop deposition modes are summarized in a phase diagram, which sheds light on identifying appropriate electric fields for high-quality drop depositions without air bubble entrapments or jettings.

A single-winged maple seed (samara) is dispersed laterally by a crosswind in contrast to simply descending straight down (zero dispersion) in quiescent air. This article presents the general kinematic response of a particular type of samaras (Acer buergerianum) in stable autorotation to the disturbance of a concentrated crosswind (simulated via slot jet) with the crosswind strength varied distinctively from weak to strong. A relatively weak crosswind slower than the tip velocity of the stably autorotating samara causes only damped undulations of its descent trajectory. In contrast, we demonstrate that the samara exhibits a bi-modal response when disturbed by a relatively strong crosswind (velocity greater than samara tip velocity). The strong crosswind enables the samara either to float laterally with the crosswind or drop-out through the crosswind with the switching of its rotational direction. Regardless of crosswind strength, stable autorotation is re-established after the samara leaves the crosswind zone, albeit accompanied by large-scale undulations in its descent trajectory. More importantly, before landing, the samara regains its original terminal descent velocity achieved in quiescent air.

Injectable granular gels consisting of densely packed microgels serving as scaffolding biomaterial have recently shown great potential for applications in tissue regeneration, which allow administration via minimally invasive surgery, on-target cargo delivery, and high efficiency in nutrient/waste exchange. However, limitations such as insufficient mechanical strength, structural integrity, and uncontrollable differentiation of the encapsulated cells in the scaffolds hamper their further applications in the biomedical field. Herein, we developed a new class of granular gels via bottom-up assembly of cell-laden microgels via photo-triggered imine-crosslinking (PIC) chemistry based on the microfluidic technique. The particulate nature of the granular gels rendered them with shear-thinning and self-healing behavior, thereby functioning as an injectable and adaptable cellularized scaffold for bone tissue regeneration. Specifically, single cell-laden, monodisperse microgels composed of methacrylate- and o-nitrobenzene-functionalized hyaluronic acid and gelatin were prepared using a high-throughput microfluidic technique with a production rate up to 3.7 × 108 microgels/hr, wherein the PIC chemistry alleviated the oxygen inhibition on free-radical polymerization and facilitated enhanced fabrication accuracy, accelerated gelation rate, and improved network strength. Further in vitro and in vivo studies demonstrated that the microgels can serve as carriers to support the activity of the encapsulated mesenchymal stem cells; these cell-laden microgels can also be used as cellularized bone fillers to induce the regeneration of bone tissues as evidenced by the in vivo experiment using the rat femoral condyle defect model. In general, these results represent a significant step toward the precise fabrication of engineered tissue mimics with single-cell resolution and high cell-density and can potentially offer a powerful tool for the design and applications of a next generation of tissue engineering strategy.

The emergence of tetrahydroborate (BH4–)/cyanoborohydride (BH3CN–) anion-based ionic liquid fuels in combination with high test peroxide (>90%H2O2, HTP) oxidizers has accelerated the greening of bipropellants. However, most BH4– and BH3CN– anion-based ionic liquids are sensitive to water, making it difficult to store them. Here, novel difunctional promoters are designed for hypergolic ignition of BH4–/BH3CN– anion-free ionic liquids with 90%H2O2. The transition metal in anions of promoters is expected to catalyze the exothermic decomposition of H2O2, and the substituted borohydride in cations of promoters acts as the ignition source. These novel difunctional promoters show good solubility in commercially available 1-allyl-3-methylimidazolium dicyanamide and 1-butyl-3-methylimidazolium dicyanamide ionic liquid fuels, and the composite fuels exhibit high density, acceptable viscosity, and high thermostability. The addition of difunctional promoters ensures the smooth hypergolic ignition of BH4–/BH3CN– anion-free ionic liquid fuels with a minimum ignition delay time of 34.0 ms, and no apparent microexplosion and secondary combustion are observed during the ignition process. With the increase in the amount of the promoter, density specific impulses of the composite fuels improve gradually. This work provides a platform strategy for designing promoters by synergy of cations and anions and makes efforts to seek green bipropellants.

We carried out experimental and numerical investigations on the axisymmetric spreading evolution of dynamic spin coating with a single drop of ethanol. The results show that the dynamic spreading process consists of two stages: inertial spreading stage and centrifugal thinning stage. These two stages are connected by a transient state in between characterized by the minimum contact line moving velocity. The Weber number determines the spreading in the first stage, similar to the case of the impact of a drop on a static substrate. The rotational Bond number has a marginal effect on the inertia spreading and the radius at the transient state. In the centrifugal thinning stage, the rotational Bond number dominates the flow while the effect of the Weber number is negligible.

3-D braided composite three-way circular tubes are integrated seamless connected tubes used for high strength connecting joints. We developed a novel braiding method of ‘yarn-added, yarn realigned’ to prepare three-way tubular preforms. Low-velocity impact compressions (LVIC) along axial direction were conducted to find effects of branch length and braiding layers on impact damage with drop-weight tester, high-speed camera, Micro-CT and digital image correlation (DIC). It was found that the three-way braided tubes have uniform structure both at the branches and joint regions. There is shear band induced by the weakened interface appeared after the peak load and formed within 60 μs under impact. The ultimate strength was positively correlated with the impact energy and braiding layers, while negatively correlated with the branch tube length. The test results showed that the branch length affected the position of stress concentration, and the influence of braiding layers on the LVIC behaviors is more significant than that of the branch length.

Revealing mechanical behaviors of three-dimensional five-directional (3D5d) braided composites at different strain rates is a key point to its durability design and structural optimization. Here we report compressive responses, surface deformations and failure behaviors of aged 3D5d braided composites under different strain rates with digital image correlation (DIC) technique, X-ray micro-computed (micro-CT) tomography and finite element analysis (FEA). The compressive rigidity, peak stress, maximum strain, energy absorption, surface strain and damages exhibit strain rate strengthening effects and ageing weakening behaviors. The strain concentration zone transfers from X-shaped to transverse V-shaped at the square cross-section with the increasing of strain rate. Moreover, ageing effect does not change the internal shear mode, while it changes the near-surface crack distribution along axial direction and crack propagation path under impact loading. The failure modes show strain rate correlation. The FEA results reveal the failure mechanisms of the aged 3D5d braided composites under different strain rates.

Anisotropic mechanical behaviors are the most prominent feature of 3D braided composites compared with homogeneous materials. This study reports anisotropic low-velocity impact behaviors of 3D braided carbon fiber/epoxy composites along in-plane (IP) and out-of-plane (OP) directions after thermo-oxidative ageing. The stress–strain responses, local strain and damage evolution were obtained. The stress distribution of each yarn and the interface damage propagation were analyzed with numerical analysis method. The retention rate of peak stress of 94.4% and elastic modulus of 91.45% along OP direction are greater than those along IP direction, which are 76.21% and 71.27% respectively. It reveals that the OP direction loading has a better performance on resistance ageing degradation than that in IP loading, and the stiffness degradation is more sensitive. There are X-shape shear damages along OP direction, and interior damages in surrounding area and yarn path along IP direction. Furthermore, the tight braided structure contributed to resisting degradation of mechanical properties along IP direction.

Achieving accurate and efficient target deposition of pesticide droplets is the principal factor in minimizing environmental risk. For hydrophobic surfaces, adding tank-mix adjuvants containing surfactants to modulate interfacial behavior is warranted, which lacks common laws to guide practical applications directly. Machine learning is developing rapidly and makes many data-based decisions in various industrial processes. Hence, according to machine learning-based analysis of fundamental physical quantities, proposing quantitative sustainability metrics to improve interface behavior is essential. Comparing the interfacial behavior of five adjuvants, the common denominator is that droplets in the Wenzel state with higher adhesion tension and lower contact angles can generate the pinning force that causes energy dissipation, reduces pesticide losses, and weakens environmental pollution. Simultaneously, the interfacial behavior of pesticide droplets including adjuvants on citrus leaves is verified, while the phytotoxicity experiment under high temperature and the laboratory bioassay are carried out. The results show that the eco-friendly alkyl polyglycoside (APG) as the glycosidic surfactant has nontarget biosafety and better mite control, which can be exploited as a commercial tank-mix adjuvant for promotion. This study provides a new insight into guiding adjuvants added to pesticides on account of quantitative sustainability metrics, which has important implications for food safety and agricultural green development.

Following a previously published paper in studying stone-skipping processes, detailed experimental figures are revealed in this paper. A mathematical model is also provided to explain the observed phenomena and measured data. The model separates the skipping process into several stages. It emphasizes, in particular, a hitting stage and a sliding stage, and also includes capillary-gravity wave resistance in its formulation. During these two stages, scale analysis is applied first to evaluate the relative importance among various forces acting on the stone. After reasonable simplification, a numerical algorithm is established to depict motion of the stone starting from its first hit of water to final sink. The total number of skips under specified initial throwing conditions can be predicted accordingly. The agreement between the analytical and experimental results indicates the applicability of the proposed model.

Functional textiles with superhydrophobicity and high adhesion to water, called parahydrophobic, are attracting increasing attention from industry and academia. The hierarchical (micronanoscale) surface patterns in nature provide an excellent reference for the manufacture of parahydrophobic functional textiles. However, the replication of the complex parahydrophobic micronanostructures in nature exceeds the ability of traditional manufacturing strategies, which makes it difficult to accurately manufacture controllable nanostructures on yarn and textiles. Herein, a two-photon femtosecond laser direct writing strategy with nanoscale process capability was utilized to accurately construct the functional parahydrophobic yarn with a diameter of 900 μm. Inspired by rose petals, the parahydrophobic yarn is composed of a hollow round tube, regularly arranged micropapillae (the diameter is 109 μm), and nanofolds (the distance is 800 nm) on papillae. The bionic yarn exhibited a superior parahydrophobic behavior, where the liquid droplet not only was firmly adhered to the bionic yarn at an inverted angle (180°) but also presented as spherical on the yarn (the maximum water contact angle is 159°). The fabric woven by the bionic yarn also exhibited liquid droplet-catching ability even when tilted vertically or turned upside down. Based on the excellent parahydrophobic function of bionic yarn, we demonstrated a glove that has very wide application potential in the fields of water droplet-based transportation, manipulation, microreactors, microextractors, etc.

In this paper, the puncture resistance of carbon fiber reinforced polymer (CFRP) with different thicknesses under various puncture energy was studied by in-situ observation. The puncture failure process of CFRP was analyzed using a high-speed camera and thin-film pressure sensor in terms of damage image and local pressure change. The experimental results show that the puncture threshold load (PTL) representing material penetration is usually located at the initial loss position of material stiffness. The penetration load can be divided into linear growth and delamination failure zones. Image localization was used to mark the puncture feature points on the puncture force–displacement curve to help characterize the puncture failure process. The theoretical equations of puncture force and displacement before material penetration are proposed and verified by introducing yield stress and friction force, and the correlation between the material thickness and the puncture resistance was proved. In addition, the failure modes and fracture morphology of CFRP after puncture are analyzed and summarized. After puncture impact, fiber fracture, pull out and slip deformation under the action of tensile force and cutting force, and matrix fracture and peel damage. The increase of impact energy leads to a broader range of impact damage but does not change the failure modes.

The stability of droplet transfer plays an important role in the weld formation and spatters suppression during the laser-MIG hybrid welding. However, a debate exists on whether increased laser power improves or suppresses the droplet transfer. In this study, the role of laser heat source was investigated in a wide range of laser power. The transfer frequency was firstly improved by increasing laser power, and then it was decreased once the laser power proceeded a critical value. The variation of droplet transfer frequency was determined by the competition between electromagnetic force and metal vapor reaction force. With increasing laser power, the arc conductivity was better and the arc current was improved, leading to increase of the electromagnetic force. As a result, the droplet transfer was promoted and the deposition rate of wire metal was increased. However, rapid increase of metal vapor reaction force was obtained when the laser power exceeded the critical value, producing a greater resistance on droplet transfer. Furthermore, the critical value of laser power was mainly determined by the characteristics of laser source, materials, laser focusing distance and laser-arc distance. This work will provide more guidance on matching processing parameters of the laser-MIG hybrid welding to improve weld formation and suppress spatters by stabilizing the droplet transfer.

Spinal cord injury (SCI) frequently results in motor, sensory and autonomic dysfunction for which there is currently no cure. Recent preclinical and clinical research has led to promising advances in treatment; however, therapeutics indicating promise in rodents have not translated successfully in human trials, likely due, in part, to gross anatomical and physiological differences between the species. Therefore, large animal models of SCI may facilitate the study of secondary injury processes that are influenced by scale, and assist the translation of potential therapeutic interventions. The aim of this study was to characterize two severities of thoracic contusion SCI in female domestic pigs, measuring motor function and spinal cord lesion characteristics, over two weeks post-SCI. A custom instrumented weight drop injury device was used to release a 50 g impactor from 10 cm (n=3) or 20 cm (n=7) onto the exposed dura, to induce a contusion at the T10 thoracic spinal level. Hind limb motor function was assessed at 8 and 13 days post-SCI using a 10-point scale. Volume and extent of lesion-associated signal hyperintensity in T2-weighted magnetic resonance (MR) images was assessed at 3, 7 and 14 days post-injury. Animals were transcardially perfused at 14 days post-SCI and spinal cord tissue was harvested for histological analysis. Bowel function was retained in all animals and transient urinary retention occurred in two animals after catheter removal. All animals displayed hind limb motor deficits. Animals in the 10 cm group demonstrated some stepping and weight bearing and scored a median 2-3 points higher on the 10-point motor function scale at 8 and 13 days post-SCI, than the 20 cm group. Histological lesion volume was 20 % greater, and 30 % less white matter was spared, in the 20 cm group than in the 10 cm group. The MR signal hyperintensity in the 20 cm injury group had a median cranial-caudal extent approximately 1.5 times greater than the 10 cm injury group at all three time points, and median volumes 1.8, 2.5 and 4.5 times greater at day 3, 7 and 14 post-injury, respectively. Regional differences in axonal injury were observed between groups, with amyloid precursor protein immunoreactivity greatest in the 20 cm group in spinal cord sections adjacent the injury epicenter. This study demonstrated graded injuries in a domestic pig strain, with outcome measures comparable to miniature pig models of contusion SCI. The model provides a vehicle for the study of SCI and potential treatments, particularly where miniature pig strains are not available and/or where small animal models are not appropriate for the research question.

Memristor-based in- memory computing paradigm is a promising path for edge detection in image preprocessing on end devices that reduces the computational pressure on data centers. However, the implementation of the well-performing Canny operator for edge detection faces challenges in terms of computational time and area overhead when mapped to memristor arrays. In this work, we proposed an efficient memristive one-step implementation of a fast-Canny operator. Exploiting the associative property of multiplication, the conventional Canny operator consisting of Gaussian and Sobel operators is converted into a fast-Canny operator and mapped to an array of nine parallel memristors. Then, the output currents are the final pixels of the edge image. To verify the feasibility of the method, successful edge detection with high accuracy (OIS = 0.73) is achieved in device-aware simulation under device variation (<50%) and image noise ( σ = 6%). Additionally, the implementation of the fast-Canny operator on memristor arrays can reduce the processing time by half and save the area of buffer compared to the prior two-convolution Canny operation. Our work suggests that the memristive fast-Canny operator could be a promising and efficient hardware solution for edge detection at the network edge.

Background
The wettability of the target surfaces affects the wetting and deposition of pesticides on them. The properties of leaf surfaces change after infestation by Tetranychus urticae Koch. Studying the surface wettability of T. urticae and the changes in leaf wettability after infestation is important to guide the use of acaricides.

Results
The body surface of T. urticae is an ellipsoidal crown covered with dense cuticle striations and hairs arranged in different directions, which makes the surface of T. urticae rough and hydrophobic. The abaxial surfaces of the leaves are rougher and more hydrophobic than the adaxial surfaces. After infestation by T. urticae, the faded spots were sunken on the adaxial surface and raised on the abaxial surface, where they had formed new wide peaks and valleys. The adaxial surface became obviously rougher and more hydrophobic, while the roughness of the abaxial surface became slightly larger, and the change in hydrophobicity was not obvious. The contact angles of the studied commercial acaricide on these surfaces were greater than 65° and were affected by the infestation. Reducing the surface tension can allow for better wetting of these surfaces and eliminate changes in leaf wettability.

Wire and arc additive manufacturing (WAAM) is a novel technique for fabricating large and complex components applied in the manufacturing industry. In this study, a low-carbon high-strength steel component deposited by WAAM for use in ship building was obtained. Its microstructure and mechanical properties as well as fracture mechanisms were investigated. The results showed that the microstructure consisted of an equiaxed zone, columnar zone, and inter-layer zone, while the phases formed in different parts of the deposited component were different due to various thermal cycles and cooling rates. The microhardness of the bottom and top varied from 290 HV to 260 HV, caused by temperature gradients and an inhomogeneous microstructure. Additionally, the tensile properties in transversal and longitudinal orientations show anisotropy characteristics, which was further investigated using a digital image correlation (DIC) method. This experimental fact indicated that the longitudinal tensile property has an inferior performance and tends to cause stress concentrations in the inter-layer areas due to the inclusion of more inter-layer zones. Furthermore, electron backscattered diffraction (EBSD) was applied to analyze the difference in Taylor factor between the inter-layer area and deposited area. The standard deviation of the Taylor factor in the inter-layer area was determined to be 0.907, which was larger than that in the deposited area (0.865), indicating nonuniform deformation and local stress concentration occurred in inter-layer area. Finally, as observed from the fracture morphology on the fractured surface of the sample, anisotropy was also approved by the comparison of the transversal and longitudinal tensile specimens

There is a scarcity of available data on boiling process in vertically oriented tube bundles in accessible sources. Lack of systematic studies is limiting further expansion of this highly efficient process of heat transfer into heat recovery field. In this paper boiling process of three triangular pitched and vertically oriented tubes has been studied in ethanol at 78 °C. The main focus of this work was to study the effect of tube spacings on heat transfer coefficient (HTC) and bubbles behavior (bubble departure diameter in particular) that were visualised with the help of a high speed camera. Experiments were performed in a wide range of tube spacings (from 10.75 to 0.25 mm) and heat flux densities (from 3 to 70 kW/m2).

By developing a thermo-mechanical coupled model, we quantitatively analyzed the effect of thermo-oxidative ageing on the temperature, thermal strain and thermal stress histories of braided composites during high-speed impact. We also considered temperature dependence of elastic modulus during impact in this model. The proposed model was first applied to the unaged composites, then the results were compared to the impact responses captured by the split Hopkinson bar and the high-speed camera. The comparisons of the experimental and numerical results show that the proposed model could capture the adiabatic temperature rise, stress-strain responses and failure process of braided composites during high-speed impact. The validated model was subsequently employed to thermo-oxidative aged composites. Results show that the temperature rise, thermal strain and thermal stress all depend on the mechanical properties of resin, and they decreased with the increase of ageing temperature since the performance of resin is compromised by thermo-oxidation ageing. The change of resin performance after ageing leads to the change in the temperature rise during impact, so the stiffness of composites will decrease in varying degrees after ageing.

Debris flows are common geological hazards in mountainous regions worldwide. The scale of debris flows can be significantly enhanced by basal erosion and bank collapse in the transportation process, resulting in an increase in casualties and property losses. However, the mechanisms of this growth are largely unclear. Here, we conduct a series of experiments to investigate the erosion of two different bed sediments (coarse-grained and widely graded) by released flows with three different densities and two different volumes. The erosion mechanisms of bed sediments are revealed by comparing detailed sensor data for flow level, pore pressure and total normal stress. A flow nose develops on the coarse-grained bed sediment, resulting in a high flow depth and low velocity, while a tabular flow develops on the widely graded bed sediment, leading to a low flow depth and high velocity. The mean erosion rates of the coarse-grained bed sediment are generally higher than those of the widely graded bed sediment due to significant pore pressure developed in coarse-grained bed sediment. The feedback effect of bed sediment on the erosion process strongly influences the flow depth and velocity, which in turn affects the mean erosion rate of bed sediment. The interaction between the overlying flow and sediment bed controls the erosion pattern: coarse-grained bed sediment is eroded by a layer of mass movement whereas widely graded bed sediment is progressively scoured. The interaction between debris flow and bed sediment during erosion is principally attributed to pore-pressure transmission.

The metal transfer behaviour of slant feature of thin-walls fabricated by cold metal transfer (CMT) process in step-over deposition mode was observed by high speed camera. A slanted short circuiting transfer (SSCT) was generated during deposition and then analysed by asymmetrical magnetic and force model, complicating metal transfer behaviour in comparison with conventional deposition process. The SSCT allowed the droplet to transfer obliquely into the molten pool on previous layer, owing to the pushing force generated by unevenly distributed electromagnetic field in asymmetrical deposition model. The surface tension between wire and liquid metal is the most important force that retarded droplet transfer. The retraction force and electromagnetic force are the main forces to promote droplet transition. The positive forces that promote droplet transfer process can be arranged as Fem > Fr > Fg. The wall width was mainly affected by wire feed speed and the inclined angle can be significantly increased with increasing step-over distance.

The macroscopic mechanical behaviors generally correlate with nanomechanical properties, especially elastic modulus. This paper presents the thermo-oxidative ageing effects on nanoscale elastic modulus and impact failure mechanism of 3D braided composites at micro and macro levels using PeakForce Quantitative Nano-Mechanics (PF-QNM) and digital image correlation (DIC) technologies. The values of nanoscale elastic modulus of near-fiber resin pocket were about three times than that of global modulus in neat resin under low-velocity impact compression (LVIC) loading. However, the modulus retention rates were consistent which was ∼88% after ageing for 16 days at 180 °C. The decline of them has provided a direct evidence for resin degradation after ageing. In addition, the in-plane impact failure mechanism of braided composites mainly contained five modes, i.e., matrix cracking, interface cracking, matrix fracture and peeling off, fiber buckling and slipping, and fiber breakage. Thermo-oxidative ageing only changed the crack propagation path but not the damage modes.

The stability of droplet transfer plays an important role in the weld formation and spatters suppression during the laser-MIG hybrid welding. However, a debate exists on whether increased laser power improves or suppresses the droplet transfer. In this study, the role of laser heat source was investigated in a wide range of laser power. The droplet transfer was firstly improved by increasing laser power, and then it was suppressed once the laser power proceeded a critical value. The variation of droplet transfer frequency was determined by the competition between electromagnetic force and metal vapor reaction force. With increasing laser power, the arc conductivity was better and the arc current was improved, leading to increase of the electromagnetic force. As a result, the droplet transfer was promoted and the deposition rate of wire metal was increased. However, rapid increase of metal vapor reaction force was obtained when the laser power exceeded the critical value, producing a greater resistance on droplet transfer. Furthermore, the critical value of laser power was mainly determined by the characteristics of laser source, materials and laser-arc distance. This work will provide more guidance on matching processing parameters of the laser-MIG hybrid welding to improve weld formation and suppress spatters by stabilizing the droplet transfer.

This work presents experimental studies with numerical modeling, aiming at the development of guidelines for shaping aluminum alloy AA6111-T4, t = 1.5 mm thick, with the use of a shear-slitting operation. During the experimental tests, parametric analyses were conducted for the selected material thickness. For the purposes of the material deformation’s analysis, a vision system based on the digital image correlation (DiC) method was used. Numerical models were developed with the use of finite element analysis (FEA) and the mesh-free method: smoothed particle hydrodynamics (SPH), which were used to analyze the residual stress and strain in the cutting zone at different process conditions. The results indicate a significant effect of the horizontal clearance between knives on the width of the deformation zone on sheet cut edge. Together with the clearance value increase, the deformation zone increases. The highest burrs on the cut edge were obtained, when the slitting speed was set to v = 17 m/min, and clearance to hc = 6%t. A strong influence was observed of the horizontal clearance value at high slitting speeds on burr unshapeliness. The most favorable conditions were obtained for v = 32 m/min, hc = 0.062 mm, and rake angle of upper knife for α = 30°. For this configuration, a smooth sheared edge with minimal burr height was obtained.

Previous methods for the investigation of high-speed cutting processes for bio-based materials failed since essential principles for the investigation of dynamic processes have not been taken into account. The novel self-developed device, based on the principle of a rotor arm, enables a detailed analysis of cutting processes. The rotor arm has a diameter of 4 m, enabling precise analysis of cutting processes. The device enables analysis of speeds up to 100 m/s of the more or less linear cutting process. Stiffness of the set-up, the natural frequency of the system, and a series of cuts per test may cause a convoluted signal demanding dynamic calibration of the measurement chain. The newly developed device enables the conduction of single cuts per examination at relatively high speed. Thus, the influence of the previous cut is eliminated. Previous research has not provided a possibility to study linear cutting processes at the mentioned velocity. The accuracy of the device was proven within various examinations. A correction based on real chip thickness measurement was applied. Finally cutting of beech, using a wide set of parameters, was examined. The cutting forces of the beech sample increased linearly with chip thickness. Nevertheless, the influence of velocity showed non-linear progression. The smallest force was observed at 20 m/s. From this cutting speed, force always increased when velocity was changed.

In this work, a design concept of bioinspired functional surfaces is proposed for lubricant control at surfaces and interfaces subjected to external thermal gradients. Inspired by the conical structures of cactus and the motion configuration of Centipedes, a bioinspired surface of wedged-groove with an oriented capillary pattern is constructed. The effect of geometrical parameters on the directional lubricant manipulation capacity and sliding anisotropy is discussed. It is found that by regulating the orientation of the capillary pattern, a controllable lubricant self-transport capacity can be achieved for varying conditions from surfaces to interfaces, with or without thermal gradients. The lubricant self-transport process is captured, and the mechanism is revealed. The design philosophy of the proposed bioinspired functional surface is believed to have potential applications for lubricant control in modern machinery and complex liquid control in lab-on-a-chip and microfluidics devices.

The collisional interaction process between bubbles and particles is considered to play an important role in flotation. This paper aims to investigate the effect of particle hydrophobicity on the bubble-particle collision and subsequent interaction process. Four types of bubble-particle interaction behaviors were observed, namely the non-collision, the collision but without attachment, the attachment with jump-in after collision, and the attachment without jump-in after collision. The ‘jump-in’ event was interpreted as the rupture of the water film, providing the formation and growth of a ‘three-phase contact line’ (TPCL). The mildly hydrophobic particle could attach to the bubble surface without the rupture of the water film, whereas the highly hydrophobic particle had the higher collision and attachment probability. The significant effect of particle hydrophobicity was found in the observed particle trajectories and velocities. The distance between the bubble and the particle of weakly hydrophobicity and mildly hydrophobicity remained almost constant in the particle sliding process on the bubble surface. However, the highly hydrophobic particle was observed to jump in instantaneously after a short interaction time. Influenced by hydrodynamic drag, the maximum sliding velocity of any particles near the bubble’s equatorial plane was higher than the particle terminal velocity, and highly hydrophobic particle had a higher difference. The analysis of the individual force components of particle provides valuable insights into the kinematic properties of particle as it slides. The hydrodynamic drag coefficient decreased with an increase in the particle contact angle, implying the highly hydrophobic particle had a smaller hydrodynamic drag. Additionally, the reaction force was introduced for the first time to satisfy the radial force balance relationship, and explanations were proposed in terms of its source.

Droplet rebound from hydrophobic leaves is a major factor influencing pesticide utilization. The use of a surfactant is a major strategy to reduce droplet rebound, promoting pesticide deposition on hydrophobic agricultural plant leaves. However, most surfactants known to regulate droplet rebound are either anionic or cationic. In this study, ethoxylated propoxylated 2-ethyl-1-haxanol (EH 6) was identified as a nonionic surfactant that inhibits droplet rebound while promoting the complete spreading of the droplet on hydrophobic leaves. Compared with the widely reported nonionic surfactant Tween 20, EH 6 performs better at concentrations above 0.3%. This phenomenon can be attributed to the rapid migration of EH 6 from the bulk to the newly generated interface, significantly reducing the surface tension. We introduce a simple and effective strategy that can be used to enhance droplet deposition on hydrophobic plant surfaces, which may offer future economic and environmental benefits.

This study used a nickel-based filler metal to fabricate a surfacing layer on a low-carbon steel substrate by a hybrid welding process with a rotating laser and arc. The surfacing layer's weld formation was studied using optical microscopic observation (OM). The microstructure of the layers was studied by using the scanning electron microscope (SEM), energy dispersive spectrum (EDS) and X-ray diffraction (XRD). The arc, metal transfer, molten pool flow behaviors, and U–I characteristics during hybrid laser arc welding (HLAW) were analyzed using the arc analyzer and high-speed camera. The results show that a rotating laser improves the weld formation of gas metal arc welding (GMAW). The microstructure of the two surfacing layers consists of dendritic γ phase and a small amount of Laves and NbC phases. The high dilution rate of the HLAW surfacing layer results in relatively more Laves and fewer NbC phases. The arc length of HLAW is dynamically deflected with the rotation of the laser, which expands the arc action and heating area of the molten pool. The droplet transfer mode changed from globular transfer dominant in GMAW to the projected transfer dominant in HLAW. The location where the droplet transfer into the molten pool is dynamic changed, forming a multi-point impact on the molten pool. Combined with the deflected arc with the laser rotating laser, the HLAW has a broad and deep molten pool. Understanding the metal transfer behavior of Ni-based alloys in rotating laser-induced arc hybrid surfacing is of great significance for improving surfacing forming.

The unsteady powder mass flowrate of the available feeding systems and the bad control of the areas being eroded have been often noticed in the abrasive air jet machining process. In addition to the delivery of dry powder, the powder can be evenly mixed with liquid to form a slurry, and then sent to the mixing chamber of an air jet machine; i.e., multiphase jet machining (MJM) was proposed in this paper. The method whereby using the viscous water to suspend the abrasives was found to enhance the stability of powder mass flowrate, thereby decreasing the fluctuation in the machining depth. Whereafter, five types of liquid-based slurries were prepared and their effects on the jet erosion zone were investigated. It was found that the control of the erosion zone was improved to varying degrees when the abrasives were transported into the air jet by viscous liquid as the carrier fluid due to the two roles: reducing the occurrence of third and/or second particle impacts; inducing a viscous boundary layer that could reduce the negative effect of the divergence of jet beam and particle rebounding. In particular, the use of an oil-based slurry could completely eliminate the unwanted frosted zone around the machined features. CFD simulations were used to understand the mechanisms causing these effects. Overall, it is shown that the abrasive air jets can be designed to have a good resolution, so it is feasible to mill or polish surface without the need for a mask to define the edges.

Direct writing technology is a promising approach for the preparation of reactive materials. The polymer binder provides a mechanically stable, processable and shapeable energetic structure for composites. Herein, Direct-writing energetic inks consisting of nitrocellulose (NC) and VitonF2311 as well as nanothermite were developed. Firstly, Fourier transform infrared spectroscopy (FT-IR) was used to analyze the intermolecular hydrogen bonds in the hybrid polymers, and the stability of the network structure was characterized by rheometer, and the mechanical properties of binders were also tested. The results show the best binder formulation is 20 wt% NC and 80 wt% F2311. The elongation at break of the binder is 600.94%, and the elastic modulus is 8.29 MPa. NC provides high tensile strength for the hybrid binder; F2311 provides high fracture tensile rate for the hybrid binder, and as a high-energy initiator, pre-ignition reaction occurs when the temperature reaches 350 °C. Then the as-prepared inks not only has excellent rheological properties so that it can be loaded with 90 wt% nanothermite, but also possess a homodisperse for components and good combustion performance. The average flame temperature is about 2400 K at atmospheric pressure.

Current techniques for the generation of cell-laden microgels are limited by numerous challenges, including poorly uncontrolled batch-to-batch variations, processes that are both labor- and time-consuming, the high expense of devices and reagents, and low production rates; this hampers the translation of laboratory findings to clinical applications. To address these challenges, we develop a droplet-based microfluidic strategy based on metastable droplet-templating and microchannel integration for the substantial large-scale production of single cell-laden alginate microgels. Specifically, we present a continuous processing method for microgel generation by introducing amphiphilic perfluoronated alcohols to obtain metastable emulsion droplets as sacrificial templates. In addition, to adapt to the metastable emulsion system, integrated microfluidic chips containing 80 drop-maker units are designed and optimized based on the computational fluid dynamics simulation. This strategy allows single cell encapsulation in microgels at a maximum production rate of 10 ml hr-1 of cell suspension while retaining cell viability and functionality. These results represent a significant advance toward using cell-laden microgels for clinical-relevant applications, including cell therapy, tissue regeneration and 3D bioprinting.

Surfaces designed to reduce the contact time of impacting droplets are potentially of great importance for fundamental science and technological applications, for example, anti-icing, self-cleaning and heating transfer applications. Previous studies have shown that the contact time can be reduced via introducing one or several crossing macroscale wires on superhydrophobic surfaces (SHSs). However, the impacts that strike far from the wires (off-center impacts) have contact times that are equal to those obtained on SHSs. Here we demonstrate that this problem can be largely solved by using macro anisotropic SHSs (macro-aniso-SHSs)—in which the wires are parallel and macroscaled. The droplet contact time depends on the spacing between the macrostripes and is remarkably reduced by 40–50% when the spacing is comparable to the droplet size. Obvious differences in the contact time are not observed for impacts that are centered on the stripe and in the groove. The impacts centered in the groove produce new hydrodynamics that are characterized by extended spreading, easy break up and bouncing in a flying-eagle configuration. The study discusses the underlying mechanisms of the impact processes. Moreover, the effect of parallel wires on the contact time is discussed by comparing the droplet impact data for grooved rice leaves and non-grooved cabbage leaves. The enhanced drop mobility associated with the macro-aniso-SHSs should be very useful in many industrial applications.

Interface debonding between fiber reinforced polymers (FPR) and substrates is the principal failure mode for FRP-reinforced structure. To understand the bond–slip relationship at FRP-to-brick interfaces under dynamic loading, the influences of the dynamic enhancement of material performance on the bond–slip curve were studied. Single-lap shear tests under two different loading rates were performed, and the slip distribution curves at different loading stages were fitted to derive the bond–slip relationship. Then a numerical model considering the strain rate effects on materials was built and verified with test results. Further, the influences of brick strength, FRP stiffness and slip rate on the bond–slip relationship were investigated numerically. The research results show that FRP stiffness mainly influences the shape of the bond–slip curve, while brick strength mainly influences the amplitude of the bond–slip curve. The variations of the bond–slip relationship under dynamic loading, i.e., under different slip rates, are mainly caused by the dynamic enhancement of brick strength, and also by the dynamic enhancement of FRP stiffness, especially within a specific slip rate range. The proposed empirical formula considering dynamic FRP stiffness and dynamic brick strength can be used to predict the bond–slip relationship at the FRP-to-brick interface under dynamic loading

This paper reports the damage mechanisms of 3-D carbon fiber/epoxy braided composite under multiple impact compressions along out-plane direction. The multiple compression tests were conducted on a split Hopkinson pressure bar (SHPB) apparatus. The compressive deformations and damages were photographed with high speed camera and compared with those from finite element analyses (FEA). We found that the initial compressive damages are fiber/resin interface damage and resin fragmentation. Then the braided preform was in a severe shear damage which accompanied with further damages of interface and resin under the followed impact compressions. The energy absorptions by the reinforcement and epoxy resin at the multiple impacts were decomposed. The braided composite has the highest energy absorption capability at the first impact. The yarn orientation in braided preform leads to non-uniform stress and strain distribution. This non-uniformity easily induced the local damage and furthermore the catastrophic failure under the multiple compressions.