Influence of current density on nano-Al_2O_3/Ni+Co bionic gradient composite coatings by electrodeposition

Metal and nano-ceramic nanocomposite coatings were prepared on the gray cast iron surface by the electrodeposition method. The Ni-Co was used as the metal matrix,and nano-Al2O3 was chosen as the second-phase particulates. To avoid poor inter-face bonding and stress distribution,the gradient structure of biology materials was found as the model and therefore the gradient composite coating was prepared. The morphology of the composite coatings was flatter and the microstructure was denser than that of pure Ni-Co coatings. The composite coatings were prepared by different current densities,and the 2-D and 3-D morphologies of the surface coatings were observed. The result indicated that the 2-D structure became rougher and the 3-D surface density of apices became less when the current density was increased. The content of nanoparticulates reached a maximum value at the current density of 40mA·cm^-2,at the same time the properties including microhardness and wear-resistance were analyzed. The microhardness reached a maximum value and the wear volume was also less at the current density of 40mA·cm^-2. The reason was that nano-Al2O3 particles caused dispersive strengthening and grain refining.

A Selective‑Response Hypersensitive Bio‑Inspired Strain Sensor Enabled by Hysteresis Effect and Parallel Through‑Slits Structures

Flexible strain sensors are promising in sensing minuscule mechanical signals,and thereby widely used in various advanced fields.However,the effective integration of hypersensitivity and highly selective response into one flexible strain sensor remains a huge challenge.Herein,inspired by the hysteresis strategy of the scorpion slit receptor,a bio-inspired flexible strain sensor(BFSS)with parallel through-slit arrays is designed and fabricated.Specifically,BFSS consists of conductive monolayer graphene and viscoelastic styrene–isoprene–styrene block copolymer.Under the synergistic effect of the bio-inspired slit structures and flexible viscoelastic materials,BFSS can achieve both hypersensitivity and highly selective frequency response.Remarkably,the BFSS exhibits a high gage factor of 657.36,and a precise identification of vibration frequencies at a resolution of 0.2 Hz through undergoing different morphological changes to high-frequency vibration and low-frequency vibration.Moreover,the BFSS possesses a wide frequency detection range(103 Hz)and stable durability(1000 cycles).It can sense and recognize vibration signals with different characteristics,including the frequency,amplitude,and waveform.This work,which turns the hysteresis effect into a"treasure,"can provide new design ideas for sensors for potential applications including human–computer interaction and health monitoring of mechanical equipment.

Laser-based bionic manufacturing

Over millions of years of natural evolution,organisms have developed nearly perfect structures and functions.The self-fabrication of organisms serves as a valuable source of inspiration for designing the next-generation of structural materials,and is driving the future paradigm shift of modern materials science and engineering.However,the complex structures and multifunctional integrated optimization of organisms far exceed the capability of artificial design and fabrication technology,and new manufacturing methods are urgently needed to achieve efficient reproduction of biological functions.As one of the most valuable advanced manufacturing technologies of the 21st century,laser processing technology provides an efficient solution to the critical challenges of bionic manufacturing.This review outlines the processing principles,manufacturing strategies,potential applications,challenges,and future development outlook of laser processing in bionic manufacturing domains.Three primary manufacturing strategies for laser-based bionic manufacturing are elucidated:subtractive manufacturing,equivalent manufacturing,and additive manufacturing.The progress and trends in bionic subtractive manufacturing applied to micro/nano structural surfaces,bionic equivalent manufacturing for surface strengthening,and bionic additive manufacturing aiming to achieve bionic spatial structures,are reported.Finally,the key problems faced by laser-based bionic manufacturing,its limitations,and the development trends of its existing technologies are discussed.

Superhydrophobicity of Bionic Alumina Surfaces Fabricated by Hard Anodizing

Bionic alumina samples were fabricated on convex dome type aluminum alloy substrate using hard anodizing technique. The convex domes on the bionic sample were fabricated by compression molding under a compressive stress of 92.5 MPa. The water contact angles of the as-anodized bionic samples were measured using a contact angle meter （JC2000A） with the 3μL water drop at room temperature. The measurement of the wetting property showed that the water contact angle of the unmodi- fied as-anodized bionic alumina samples increases from 90° to 137° with the anodizing time. The increase in water contract angle with anodizing time arises from the gradual formation of hierarchical structure or composite structure. The structure is composed of the micro-scaled alumina columns and pores. The height of columns and the depth of pores depend on the ano- dizing time. The water contact angle increases significantly from 96° to 152° when the samples were modified with self-assembled monolayer of octadecanethiol （ODT）, showing a change in the wettability from hydrophobicity to su- per-hydrophobicity. This improvement in the wetting property chemical modification. is attributed to the decrease in the surface energy caused by the

Kinematics of Terrestrial Locomotion in Mole Cricket Gryllotalpa orientalis

The fore leg of mole cricket （Orthoptera： Glyllotalpidae） has developed into claw for digging and excavating. As the result of having a well-suited body and appendages for living underground, mole cricket still needs to manoeuvre on land in some cases with some kinds of gait. In this paper, the three-dimensional kinematics information of mole cricket in terrestrial walking was recorded by using a high speed 3D video recording system. The mode and the gait of the terrestrial walking mole cricket were investigated by analyzing the kinematics parameters, and the kinematics coupling disciplines of each limb and body were discussed. The results show that the locomotion gait of mole cricket in terrestrial walking belongs to a distinctive alternating tripod gait. We also found that the fore legs of a mole cricket are not as effective as that of common hexapod insects, its middle legs and body joints act more effective in walking and turning which compensate the function of fore legs. The terrestrial lo-comotion of mole cricket is the result of biological coupling of three pairs of legs, the distinctive alternating tripod gait and the trunk locomotion.

4D printing of PLA/PCL shape memory composites with controllable sequential deformation

Shape memory polymers(SMPs)are a promising class of materials for biomedical applications due to their favorable mechanical properties,fast response,and good biocompatibility.However,it is difficult to achieve controllable sequential shape change for most SMPs due to their high deformation temperature and the simplex deformation process.Herein,shape memory composites based on polylactic acid(PLA)matrix and semi-crystalline linear polymer polycaprolactone(PCL)are fabricated using 4D printing technology.Compared with pure PLA,with the rise of PCL content,the 4D-printed PLA/PCL composites show decreased glass transition temperature(Tg)from 67.2 to 55.2°C.Through the precise control of the deformation condition,controllable sequential deformation with an outstanding shape memory effect can be achieved for the PLA/PCL shape memory composites.The response time of shape recovery is less than 1.2 s,and the shape fixation/recov-ery rates are above 92%.In order to simulate sequential petal opening and sequential drug releasing effects,a double-layer bionic flower and a drug release device,respectively,are presented by assembling PLA/PCL samples with different PLA/PCL ratios.The results indicate the potential applications of 4D-printed PLA/PCL composites in the field of bio-inspired robotics and biomedical devices.

Overdischarge-induced evolution of Cu dendrites and degradation of mechanical properties in lithium-ion batteries

The degradation of mechanical properties of overdischarge battery materials manifests as a significant effect on the energy density,safety,and cycle life of the batteries.However,establishing the correlation between depth of overdischarge and mechanical properties is still a significant challenge.Studying the correlation between depth of overdischarge and mechanical properties is of great significance to improving the energy density and the ability to resist abuse of the batteries.In this paper,the mechanical properties of the battery materials during the whole process of overdischarge from discharge to complete failure were studied.The effects of depth of overdischarge on the elastic modulus and hardness of the cathode of the battery,the tensile strength and the thermal shrinkage rate of the separator,and the performance of binder were investigated.The precipitation of Cu dendrites on the separator and cathode after dissolution of anode copper foil is a key factor affecting the performance of battery materials.The Cu dendrites attached to the cathode penetrate the separator,causing irreversible damage to the coating and base film of the separator,which leads to a sharp decline in the tensile strength,thermal shrinkage rate and other properties of the separator.In addition,the Cu dendrites wrapping the cathode active particles reduce the adhesion of the active particles binder.Meanwhile,the active particles are damaged,resulting in a significant decrease in the elastic modulus and hardness of the cathode.

Bioinspired soft actuators with highly ordered skeletal muscle structures

Mammals such as humans develop skeletal muscles composed of muscle fibers and connective tissue,which have mechanical properties that enable power output with three-dimensional motion when activated.Artificial muscle-like actuators developed to date,such as the McKibben artificial muscle,often focus sole contractile elements and have rarely addressed the contribution of flexible connective tissue that forms an integral part of the structure and morphology of biological muscle.Herein,we present a class of pneumatic muscle-like actuators,termed highly mimetic skeletal muscle(HimiSK)actuator,that consist of parallelly arranged contractile units in a flexible matrix inspired by ultrasonic measurements on skeletal muscle.The contractile units act as a muscle fiber to produce active shortening force,and the flexible matrix functions as connective tissue to generate passive deformation.The application of positive pressure to the contractile units can produce a linear contraction and force.In this actuator,we assign different flexible materials as contractile units and a flexible matrix,thus forming five mold actuators.These actuators feature three-dimensional motion on activation and present both intrinsic force-velocity and force-length characteristics that closely resebmle those of a biological muscle.High output and tetanic force produced by harder contractile units improve the maximum output force by up to about 41.3%and the tetanic force by up to about 168%.Moreover,high displacement and velocity can be generated by a softer flexible matrix,with the improvement of maximum displacement up to about 33.3%and velocity up to about 73%.The results demonstrate that contractile units play a crucial role in force generation,while the flexible matrix has a significant impact on force transmission and deformation;the final force,velocity,displacement,and three-dimensional motion results from the interplay of contractile units,fluid and flexible matrix.Our approach introduces a model of the presented HimiSK actuators to better understand the mechanical behaviors,force generation,and transmission in bioinspired soft actuators,and highlights the importance of using flexible connective tissue to form a structure and configuration similar to that of skeletal muscle,which has potential usefulness in the design of effective artificial muscle.

Progress in Bio‑inspired Anti‑solid Particle Erosion Materials:Learning from Nature but Going beyond Nature

Solid particle erosion is a common phenomenon in engineering fields,such as manufacturing,energy,military and aviation.However,with the rising industrial requirements,the development of anti-solid particle erosion materials remains a great challenge.After billions of years of evolution,several natural materials exhibit unique and exceptional solid particle erosion resistance.These materials achieved the same excellent solid particle erosion resistance performance through diversified strategies.This resistance arises from their micro/nanoscale surface structure and interface material properties,which provide inspiration for novel multiple solutions to solid particle erosion.Here,this review first summarizes the recent significant process in the research of natural anti-solid particle erosion materials and their general design principles.According to these principles,several erosion-resistant structures are available.Combined with advanced micro/nanomanufacturing technologies,several artificial anti-solid particle erosion materials have been obtained.Then,the potential applications of anti-solid particle erosion materials are prospected.Finally,the remaining challenges and promising breakthroughs regarding anti-solid particle erosion materials are briefly discussed.

Biological coupling anti-wear properties of three typical molluscan shells—Scapharca subcrenata, Rapana venosa and Acanthochiton rubrolineatus

Molluscan shells are fascinating examples of highly ordered hierarchical structure and complex organic-inorganic biocomposite material. However, their anti-wear properties were rarely studied especially in the perspective of biological coupling. So in the current study three typical shells, Scapharca subcrenata, Rapana venosa and Acanthochiton rubrolineatus, were selected as coupling models to further study their anti-wear properties. Stereomicroscope and scanning electron microscopic observations showed that all these three shells had specific surface morphologies and complicated section microstructures. Importantly, a special structure, pore canal tubules, was discovered in the shells of Scapharca subcrenata and Acanthochiton rubrolineatus, which probably contributed most to their anti-wear properties. X-ray diffraction and micro-Vikers hardness tester were further adopted to analyze the phase compositions and micro-hardness of the shells. The measured results demonstrated that aragonite was the most extensive phase present in the shell, and possesed a relatively high micro-hardness. In this paper, the shells were described in details in morphology, structure and material with emphasis on the relationship with anti-wear property. The study revealed that the selected seashells possess distinct anti-wear properties by complicated mechanisms involving the integrated functions of multiple biological coupling elements, and this would provide inspiration to the design of new bionic wear resistance components.

Effects of Bionic Units in Different Scales on the Wear Behavior of Bionic Impregnated Diamond Bits

Based on anti-wear theory of soil animals, the samples of impregnated diamond bit with bionic self-regenerated non-smooth surface were designed and fabricated. Such a bionic surface was characterized by concave-shape units of different scales that continuously maintained their shape and function during the whole working process. Abrasion tests were carried out to investigate the performance of samples. Results showed that the bionic samples exhibit excellent wear resistance and drilling performance under the action of bionic self-regenerated units, especially those with units of 2 mm - 3 mm diameter. The par- ticle-trapping mechanism coming from the self-regenerated concaves and the lubricating mechanism coming from the con- tinuously self-supplying of solid lubricant are important reasons for reducing or even avoiding the severe abrasions. The im- proved drilling performance of bionic samples derives from, on the one hand, the back edge of bionic unit that contributes to exposing new diamond and supplying additional shear stresses to increase the cutting ability, on the other hand, the enhanced load per unit area due to the decreased contact area at the frictional interface. The relationship between the wear behavior and the scale of bionic unit was revealed. The unit of smaller scale on the bionic samples can enhance the shear stress level. Further reducing the scale to a contain extent will diminish the wear resistance of sample. While increasing the scale can lead to the poor lubricating effect.

Tribological performance of microstructured surfaces with different wettability from superhydrophilic to superhydrophobic

The anti-friction function of superwetting surfaces with superhydrophobicity has been demonstrated.However,the influence regularity of wettability to tribological performance,and the underlying mechanism are still unclear.Here,two kinds of microstructured surfaces with different wettability are fabricated on the substrate of steel by controlling surface chemical compositions.The water contact angles on these surfaces range from 0°to 151°.The ball-plate tribological tests are performed under water lubrication.The results show that the tribological performance is closely related to surface wettability.The friction coefficient increases with the increase of contact angles when the surfaces are hydrophilic rather than superhydrophilic.In contrast,the friction coefficient on the hydrophobic surfaces decreases with the increase of contact angles.Furthermore,the best anti-friction capability is obtained on the superhydrophobic surfaces,and the anti-friction mechanism is elucidated.The lowest friction coefficient was 0.12 under the load of 10 N.This work provides strong evidence of an association between tribological property and wettability,which may inspire the fabrication and application of special wetting surfaces in friction control.

Graphene Oxide-Induced Substantial Strengthening of High-Entropy Alloy Revealed by Micropillar Compression and Molecular Dynamics Simulation

Plastic deformation mechanisms at micro/nanoscale of graphene oxide-reinforced high-entropy alloy composites(HEA/GO)remain unclear.In this study,small-scale mechanical behaviors were evaluated for HEA/GO composites with 0.0 wt.%,0.3 wt.%,0.6 wt.%,and 1.0wt.%GO,consisting of compression testing on micropillar and molecular dynamics(MD)simulations on nanopillars.The experimental results uncovered that the composites exhibited a higher yield strength and flow stress compared with pure HEA micropillar,resulting from the GO reinforcement and grain refinement strengthening.This was also confirmed by the MD simulations of pure HEA and HEA/GO composite nanopillars.The immobile<100>interstitial dislocations also participated in the plastic deformation of composites,in contrast to pure HEA counterpart where only mobile 1/2<111>perfect dislocations dominated deformation,leading to a higher yield strength for composite.Meanwhile,the MD simulations also revealed that the flow stress of composite nanopillar was significantly improved due to GO sheet effectively impeded dislocation movement.Furthermore,the mechanical properties of HEA/1.0 wt.%GO composite showed a slight reduction compared with HEA/0.6 wt.%GO composite.This correlated with the compositional segregation of Cr carbide and aggregation of GO sheets,indicative of lower work hardening rate in stress-strain curves of micropilar compression.

Graphene enables equiatomic FeNiCrCoCu high-entropy alloy with improved TWIP and TRIP effects under shock compression

Graphene(Gr)reinforced high-entropy alloy(HEA)matrix composites are expected as potential candidates for next-generation structural applications in light of outstanding mechanical properties.A deep comprehension of the underlying deformation mechanisms under extreme shock loading is of paramount importance,however,remains lacking due to experimentally technical limitations in existence.In the present study,by means of nonequilibrium molecular dynamics simulations,dynamic deformation behaviors and corresponding mechanisms in equiatomic FeNiCrCoCu HEA/Gr composite systems were investigated in terms of various shock velocities.The resistance to dislocation propagation imparted by Gr was corroborated to encourage the elevated local stress level by increasing the likelihood of dislocation interplays,which facilitated the onset of twins and hexagonal close-packed(HCP)martensite laths.Meanwhile,the advent of Gr was demonstrated to endow the HEA with an additional twinning pathway that induced a structural conversion from HCP to parent face-centered cubic(FCC)inside HCP martensite laths,different from the classical one that necessitated undergoing the intermediate procedure of extrinsic stacking fault(ESF)evolution.More than that,by virtue of an increase in flow stress,the transformation-induced plasticity(TRIP)effect was validated to be additionally evoked as the predominant strain accommodation mechanism at higher strains on the one hand,but which only assisted plasticity in pure systems,and on the other hand,can also act as an auxiliary regulation mode together with the twinning-induced plasticity(TWIP)effect under intermediate strains,but with enhanced contributions relative to pure systems.One may expect that TRIP and TWIP effects promoted by introducing Gr would considerably inspire a synergistic effect between strength and ductility,contributing to the exceptional shock-resistant performance of FeNiCrCoCu HEAs under extreme regimes.

Amorphization transformation in high-entropy alloy FeNiCrCoCu under shock compression

High-entropy alloys(HEAs)possess immense potential for structural applications due to their excellent mechanical properties.Deeply understanding underlying deformation mechanisms under extreme regimes is crucial but still limited,due to the restrictions of existing experimental techniques.In the present study,dynamic deformation behaviors in equiatomic FeNiCrCoCu HEAs were investigated in terms of various shock velocities through nonequilibrium molecular dynamics simulations.The amorphous atoms by amorphization transformation were corroborated to be conducive to dislocation nucleation and propagation.Also,the dominant plasticity pattern was confirmed to be taken over by amorphization under higher velocities,while dislocation slips merely prevailed for lower shock ones.More importantly,for a shock velocity of 1.4 km/s,multi-level deformation modes appearing in deformation,first amorphization and then a combination of amorphization and dislocation slip,was demonstrated to substantially contribute to the shock wave attenuation.These interesting findings provide important implications for the dynamic deformation behaviors and corresponding mechanisms of the FeNiCrCoCu HEA system.

Role of Multi-scale Hierarchical Structures in Regulating Wetting State and Wetting Properties of Structured Surfaces

Amplifying the intrinsic wettability of substrate material by changing the solid/liquid contact area is considered to be the main mechanism for controlling the wettability of rough or structured surfaces.Through theoretical analysis and experimental exploration,we have found that in addition to this wettability structure amplification effect,the surface structure also simultaneously controls surface wettability by regulating the wetting state via changing the threshold Young angles of the Cassie-Baxter and Wenzel wetting regions.This wetting state regulation effect provides us with an alternative strategy to overcome the inherent limitation in surface chemistry by tailoring surface structure.The wetting state regulation effect created by multi-scale hierarchical structures is quite significant and plays is a crucial role in promoting the superhydrophobicity,superhydrophilicity and the transition between these two extreme wetting properties,as well as stabilizing the Cassie-Baxter superhydrophobic state on the fabricated lotus-like hierarchically structured Cu surface and the natural lotus leaf.

Design,Testing and Control of a Magnetorheological Damper for Knee Prostheses

This study aims to develop a magnetorheological(MR)damper for semi-active knee prostheses to restore the walking ability of transfemoral amputees.The core dimensions of the MR damper were determined via theoretical magnetic field calculations,and the theoretical relationship between current and joint torque was derived through electromagnetic simulation.Then,a physical prototype of the semi-active prosthetic knee equipped with the MR damper was manufactured.Based on the data obtained from angle sensor,pressure sensor(loadcell),and inertial measurement unit(IMU)on the prosthesis,a matching control algorithm is developed.The joint torque of the MR damper can be adaptively adjusted according to the walking speed of the amputee,allowing the amputee to realize a natural gait.The effectiveness of the control program was verified by the ADAMS and MATLAB co-simulation.The results of the test and simulation show that the MR damper can provide sufficient torque needed for normal human activities.

Design of bionic water jet thruster with double-chamber driven by electromagnetic force

In response to the limitations of the single-chamber water jet thruster used in underwater vehicles mimicked by natural cephalopods,a novel approach involving a double-chamber water jet thruster has been proposed.This thruster utilizes electromagnetic force to manipulate the diaphragm,thereby altering the volume of the upper and lower chambers to achieve water jet propulsion.Experimental investigations were conducted to determine the tensile length-force characteristics of the diaphragm made of Agileus30.Subsequently,key parameters of essential propulsion components,such as solenoid coils,electromagnets,and currents,were established based on the tensile length-force curve,and the propulsion capabilities of the system were evaluated through theoretical analysis.Theoretical assessments indicate that the system does not produce reverse thrust regardless of whether the coil moves up or down.Further experimental results demonstrate that the maximum peak propulsion force generated by the dual-chamber water jet thruster within a 3-s cycle is 0.253N.

Particle Erosion Resistance of Bionic Samples Inspired from Skin Structure of Desert Lizard, Laudakin stoliczkana

In order to improve the particle erosion resistance of engineering surfaces, this paper proposed a bionic sample which is inspired from the skin structure of desert lizard, Laudakin stoliczkana. The bionic sample consists of a hard shell （aluminum） and a soft core （silicone rubber） which form a two-layer composite structure. The sand blast tests indicated that the bionic sample has better particle erosion resistance. In steady erosion period, the weight loss per unit time of the bionic sample is about 10% smaller than the contrast sample. The anti-erosion mechanism of the bionic sample was studied by single particle impact test. The results show that, after the impact, the kinetic energy of the particle is reduced by 56.5% on the bionic sample which is higher than that on the contrast sample （31.2%）. That means the bionic sample can partly convert the kinetic energy of the particle into the deformation energy of the silicone rubber layer, thus the erosion is reduced.

The Sound Suppression Characteristics of Wing Feather of Owl （Bubo bubo）

Many species of owls are able to fly noiselessly, and their wing feathers play an important role for the silent flight. In this paper, we studied the sound suppression mechanism of the eagle owl （Bubo bubo） by Stereo Microscope （SM）, Scanning Electron Microscopy （SEM） and Laser Scanning Confocal Microscope （LSCM）. To investigate the effects of special charac- teristics of wing feather on owl silent flight, the acoustic properties, including the sound absorption coefficient and flight noise, were compared between the eagle owl and common buzzard （Buteo buteo）. The results show that the eagle owl generates lower noise than common buzzard during flight, and its wing feather has better sound absorption properties. The leading edge serration and trailing edge fringe can improve the pressure fluctuation of turbulence boundary, and suppress the generation of vortex sound. The elongated distal barbules form a multi-layer grid porous structure which also has an effect on sound absorption. This research not only can give the inspiration for solving the aerodynamic noise of aircraft and engineering machine, but also can provide a new idea for the design of low-noise devices.