Test for the deep:magnetic loading characterization of elastomers under extreme hydrostatic pressures

Soft robot incarnates its unique advantages in deep-sea exploration,but grapples with high hydrostatic pressure’s unpredictable impact on its mechanical performances.In our previous work,a self-powered soft robot showed excellent work performance in the Mariana Trench at a depth of 11000 m,yet experienced notable degradation in deforming capability.Here,we propose a magnetic loading method for characterizing elastomer’s mechanical properties under extremely high hydrostatic pressure of up to 120 MPa.This method facilitates remote loading and enables in-situ observation,so that the dimensions and deformation at high hydrostatic pressure are obtained and used for calculations.The results reveal that the Young’s modulus of Polydimethylsiloxane(PDMS)monotonously increases with pressure.It is found that the relative increase in Young’s modulus is determined by its initial value,which is 8% for an initial Young’s modulus of 2200 kPa and 38% for 660 kPa.The relation between initial Young’s modulus and relevant increase can be fitted by an exponential function.The bulk modulus of PDMS is about 1.4 GPa at 20℃ and is barely affected by hydrostatic pressure.The method can quantify alterations in the mechanical properties of elastomers induced by hydrostatic pressure,and provide guidance for the design of soft robots which serve in extreme pressure environment.

Unraveling the reaction reversibility and structure stability of nickel sulfide anodes for lithium ion batteries

The electrochemical performance of lithium-ion batteries,i.e.specific capacity and cyclability,is primarily determined by chemical reversibility and structural stability of the electrodes in cycling.Here we have investigated the fundamental reaction behaviors of nickel sulfide(NixSy)as lithium-ion battery anodes by in-situ TEM.We find that Ni_(3)S_(2)is the electrochemically stable phase,which appears in the first cycle of the NixSyanode.From the second cycle,conversion between Ni_(3)S_(2)and Li_(2)S/Ni is the dominant electrochemical reaction.In lithiation,the NixSynanoparticles evolve into a mixture of Ni nanocrystals embedded in Li_(2)S matrix,which form a porous structure upon full lithiation,and with the recrystallization of the Ni_(3)S_(2)phase in delithiation,a compact and interconnected network is built.Structural stability in cycles is susceptible to particle size and substrate restraint.Carbon substrate can certainly improve the tolerance for size-dependent pulverization of NixSynanoparticles.When NixSynanoparticle exceeds the critical size value,the morphology of the particle is no longer well maintained even under the constraints of the carbon substrate.This work deepens the understanding of electrochemical reaction behavior of conversiontype materials and helps to rational design of high-energy density battery anodes.

X-Mechanics——An endless frontier

In contrast to the conventional wisdom that mechanics is a relatively mature subject, the new manifestation of mechanics in an extended or crossed form is unfolding. Mechanics is now powering all subjects, from physical sciences, life sciences to social sciences. We name this new phase for the development of mechanics X-Mechanics. The present article outlines the contents of X-Mechanics from four aspects: cross media, cross scales, cross compliances, and cross cyber/physical spaces. X-Mechanics constitutes an endless frontier of science and technology.

Research progress on advanced rail materials for electromagnetic railgun technology

Electromagnetic railgun attracts more and more attention due to its advantage in speed,cost,and obscurity.It is found that the rail should withstand huge mechanical and thermal shocks during the launching operation.The forms of rail failure are accompanied by gouge,grooving,transition,and arc ablation,etc.The service life of the rail has become a bottleneck restricting the development of electromagnetic railgun technology.A series of researches are carried out to solve rail failure,including analysing the failure mechanism and using various advanced rail materials.This paper provides a comprehensive review of rail materials,including material composition,preparation,microstructure,and properties.We begin from a short background of the requirement of the rail material.Then a detailed investigation of rail materials is described,and the performances of those materials are introduced.Finally,further development prospect of rail material is discussed.

Effect of interfacial stiffness on the stretchability of metal/elastomer bilayers under in-plane biaxial tension

Flexible electronic devices are often subjected to large and repeated deformation,so that their functional components such as metal interconnects need to sustain strains up to tens of percent,which is far beyond the intrinsic deformability of metal materials(~1%).To meet the stringent requirements of flexible electronics,metal/elastomer bilayers,a stretchable structure that consists of a metal film adhered to a stretchable elastomer substrate,have been developed to improve the stretch capability of metal interconnects.Previous studies have predicted that the metal/elastomer bilayers are much more stretchable than freestanding metal films.However,these investigations usually assume perfect bonding between the metal and elastomer layers.In this work,the effect of the metal/elastomer interface with a finite interfacial stiffness on the stretchability of bilayer structures is analyzed.The results show that the assumption of perfect interface(with infinite interfacial stiffness)may lead to an overestimation of the stretchability of bilayer structures.It is also demonstrated that increased adhesion between the metal and elastomer layers can enhance the stretchability of the metal layer.

Molding of polyether ether ketone(PEEK)and its composites:a review

Over the last half-century,polyether ether ketone(PEEK)has emerged as a widely adopted thermoplastic polymer,primarily due to its lower density,exceptional mechanical properties,high-temperature and chemical resistance,and biocompatibility.PEEK and its composites have found extensive applications across various fields,including machinery,aerospace,military equipment,electronics,and biomedicine,positioning themselves as promising substitutes for traditional metal structures.Nevertheless,achieving optimal performance and functional molding of PEEK and its composites presents a formidable challenge,given their inherent characteristics,such as semi-crystallinity,high melting temperature,heightened viscosity,low dielectric coefficient,and hydrophobic properties.In this paper,we present a comprehensive review of the molding methods and processes of PEEK and its composites,including extrusion molding,hot compression molding,injection molding,and 3D printing.We also introduce typical innovative applications within the fields of mechanics,electricity,and biomedicine while elucidating methodologies that leverage the distinctive advantages of PEEK and its composites.Additionally,we summarize research findings related to manipulating the properties of PEEK and its composites through the optimization of machine parameters,process variables,and material structural adjustments.Finally,we contemplate the prevailing development trends and outline prospective avenues for further research in the advancement and molding of PEEK and its composites.

Decohesion of graphene from a uniaxially-stretched substrate:Failure analysis of a frictional adhesive interface

Composite structures consisting of two-dimensional(2D)materials deposited on elastic substrates have a wide range of potential applications in flexible electronics.For such devices,robust 2D film/substrate interfacial adhesion is essential for their reliable performance when subjected to external thermal and mechanical loads.To better understand the strength and failure behavior of the 2D film/substrate interfaces,two types of graphene/polymer samples with distinct interfacial adhesion properties are fabricated and tested by uniaxially stretching the substrates.Depending on the interfacial adhesion,two drastically different debonding rates are observed,i.e.,rapid snap-through debonding and more progressive crack propagation.Motivated by the experimental observation,we propose an improved shear-lag model with a trapezoidal-shaped cohesive zone to derive an analytical solution for the decohesion behavior.The theoretical model reveals that the decohesion behavior of the frictional adhesive interface is governed by three dimensionless parameters.Particularly,the dimensionless length of the film essentially determines the decohesion rate;while the other two parameters affect the critical substrate strain to initiate debonding.By fitting the experimental data with the theoretical model,the intrinsic adhesion properties of the two samples are obtained with physically meaningful values.This work offers an analytical solution to describing the decohesion behavior of general thin film/substrate systems with a frictional adhesive interface,which is beneficial for characterizing and optimizing the mechanical properties of various thin film/polymer devices.

A learning-based control pipeline for generic motor skills for quadruped robots

Performing diverse motor skills with a universal controller has been a longstanding challenge for legged robots.While motion imitation-based reinforcement learning(RL)has shown remarkable performance in reproducing designed motor skills,the trained controller is only suitable for one specific type of motion.Motion synthesis has been well developed to generate a variety of different motions for character animation,but those motions only contain kinematic information and cannot be used for control.In this study,we introduce a control pipeline combining motion synthesis and motion imitation-based RL for generic motor skills.We design an animation state machine to synthesize motion from various sources and feed the generated kinematic reference trajectory to the RL controller as part of the input.With the proposed method,we show that a single policy is able to learn various motor skills simultaneously.Further,we notice the ability of the policy to uncover the correlations lurking behind the reference motions to improve control performance.We analyze this ability based on the predictability of the reference trajectory and use the quantified measurements to optimize the design of the controller.To demonstrate the effectiveness of our method,we deploy the trained policy on hardware and,with a single control policy,the quadruped robot can perform various learned skills,including automatic gait transitions,high kick,and forward jump.

Multi-Material magnetic field-assisted additive manufacturing system for flexible actuators with programmable magnetic arrangements

Manufacturing flexible magnetic-driven actuators with complex structures and magnetic arrangements to achieve diverse functionalities is becoming a popular trend.Among various manufacturing technologies,magnetic-assisted digital light processing(DLP)stands out because it enables precise manufacturing of macro-scale structures and micro-scale distributions with the assistance of an external magnetic field.Current research on manufacturing magnetic flexible actuators mostly employs single materials,which limits the magnetic driving performance to some extent.Based on these characterizations,we propose a multi-material magnetic field-assisted DLP technology to produce flexible actuators with an accuracy of 200μm.The flexible actuators are printed using two materials with different mechanical and magnetic properties.Considering the interface connectivity of multi-material printing,the effect of interfaces on mechanical properties is also explored.Experimental results indicate good chemical affinity between the two materials we selected.The overlap or connection length of the interface moderately improves the tensile strength of multi-material structures.In addition,we investigate the influence of the volume fraction of the magnetic part on deformation.Simulation and experimental results indicate that increasing the volume ratio(20%to 50%)of the magnetic structure can enhance the responsiveness of the actuator(more than 50%).Finally,we successfully manufacture two multi-material flexible actuators with specific magnetic arrangements:a multi-legged crawling robot and a flexible gripper capable of crawling and grasping actions.These results confirm that this method will pave the way for further research on the precise fabrication of magnetic flexible actuators with diverse functionalities.

Inhibition of Heterogeneous Nucleation in Water by Hydrogel Coating

Heterogeneous nucleation plays a critical role in the phase transition of water,which can cause damage in various systems.Here,we report that heterogeneous nucleation can be inhibited by utilizing hydrogel coatings to isolate solid surfaces and water.Hydrogels,which contain over 90%water when fully swelled,exhibit a high degree of similarity to water.Due to this similarity,there is a great energy barrier for heterogeneous nucleation along the water-hydrogel interface.Additionally,hydrogel coatings,which possess polymer networks,exhibit higher fracture energy and more robust adhesion to solid surfaces compared to water.This high fracture and adhesion energy acts as a deterrent for fracture nucleation within the hydrogel or along the hydrogel-solid interface.With a hydrogel layer approximately 100μm thick,the boiling temperature of water under atmospheric pressure can be raised from 100 to 108℃.Notably,hydrogel coatings also result in remarkable reductions in cavitation pressure on multiple solid surfaces.We have demonstrated the efficacy of hydrogel coatings in preventing damages resulting from acceleration-induced cavitation.Hydrogel coatings have the potential to alter the energy landscape of heterogeneous nucleation on the water-solid interface,making them an exciting avenue for innovation in heat transfer and fluidic systems.

Granular Ionogel Particle Inks for 3D Printed Tough and Stretchable Ionotronics

Ionogels have garnered great attention as promising soft conducting materials for the fabrication of flexible energy storage devices,soft actuators,and ionotronics.However,the leakage of the ionic liquids,weak mechanical strength,and poor manufacturability have greatly limited their reliability and applications.Here,we propose a new ionogel synthesis strategy by utilizing granular zwitterionic microparticles to stabilize ionic liquids.The ionic liquids swell the microparticles and physically crosslink microparticles via either electronic interaction or hydrogen bonding.Further introducing a photocurable acrylic monomer enables the fabrication of double-network(DN)ionogels with high stretchability(>600%)and ultrahigh toughness(fracture energy>10 kJ/m^(2)).The synthesized ionogels exhibit a wide working temperature of−60 to 90℃.By tuning the crosslinking density of microparticles and physical crosslinking strength of ionogels,we synthesize DN ionogel inks and print them into three-dimensional(3D)motifs.Several ionogelbased ionotronics are 3D printed as demonstrations,including strain gauges,humidity sensors,and ionic skins made of capacitive touch sensor arrays.Via covalently linking ionogels with silicone elastomers,we integrate the ionogel sensors onto pneumatic soft actuators and demonstrate their capacities in sensing large deformation.As our last demonstration,multimaterial direct ink writing is harnessed to fabricate highly stretchable and durable alternating-current electroluminescent devices with arbitrary structures.Our printable granular ionogel ink represents a versatile platform for the future manufacturing of ionotronics.

A molecular dynamics study on mechanical performance and deformation mechanisms in nanotwinned NiCo-based alloys with nano-precipitates under high temperatures

Molecular dynamics simulations are performed to investigate the mechanical behavior of nanotwinned NiCo-based alloys containing coherent L12 nano-precipitates at different temperatures,as well as the interactions between the dislocations and nano-precipitates within the nanotwins.The simulation results demonstrate that both the yield stress and flow stress in the nanotwinned NiCo-based alloys with nano-precipitates decrease as the temperature rises,because the higher temperatures lead to the generation of more defects during yielding and lower dislocation density during plastic deformation.Moreover,the coherent L12 phase exhibits excellent thermal stability,which enables the hinderance of dislocation motion at elevated temperatures via the wrapping and cutting mechanisms of dislocations.The synergistic effect of nanotwins and nano-precipitates results in more significant strengthening behavior in the nanotwinned NiCo-based alloys under high temperatures.In addition,the high-temperature mechanical behavior of nanotwinned NiCo-based alloys with nano-precipitates is sensitive to the size and volume fraction of the microstructures.These findings could be helpful for the design of nanotwins and nano-precipitates to improve the high-temperature mechanical properties of NiCo-based alloys.

Enhanced plastic deformation capacity in hexagonal-close-packed medium entropy alloys via facilitating cross slip

Alloys with a hexagonal close-packed(HCP)lattice often suffer from intrinsic brittleness due to their in-sufficient number of slip systems,which limits their practical uses.In this paper,nevertheless,we show that remarkably tensile ductility in HCP Hf-Zr-Ti medium entropy alloys(MEAs)was achieved,particu-larly in the MEAs with a higher content of Hf.Both first-principles calculation and experimental analyses reveal that addition of Hf increases basal I2 stacking fault energy and decreases prismatic stacking fault energy in these HCP MEAs,which promotes the source of pyramidal dislocations due to the facilitated cross slips of basal dislocations and eventually give rise to the observed large tensile ductility.Our current findings not only shed new insights into understanding deformation of HCP alloys,but also provide a basis for controlling alloying effects for developing novel HCP complex alloys with optimized properties.

Atomistic simulations of martensitic transformation processes for metastable FeMnCoCr high-entropy alloy

Non-equiatomic FeMnCoCr high-entropy alloy(HEA),which exhibits a great potential to break the strength-ductility trade-off relationship,has drawn abundant attention from researchers in experiments.However,atomic simulations of such excellent alloys are limited due to the lack of proper interatomic potentials.In this work,the complete martensitic transformation of nonequiatomic HEA is reproduced via atomic simulations with a novel interatomic potential under EAM framework.The physical parameters of interatomic potential agree well with experimental measurements and first-principles calculations.According to the atomic simulation results of poly-crystalline under tension and compression,two basic transition models of TRIP-DP-HEA for martensitic transformation are revealed,i.e.,the overlapping of intrinsic stacking faults or the growth of hcp laminates simultaneously.Moreover,the pathway for martensitic transformation is elucidated with the gliding of Shockley partial dislocations of 1/6<112>burgers vectors.

Mechanical Properties and Deformation Mechanisms of Metallic Glasses Under Hydrostatic Pressure

Metallic glasses(MGs)are promising structural materials with high strength,large elastic strain limit and enhanced wear resistance.On the way to tune the mechanical performance of MGs,numerous efforts have been devoted to investigating the effect of hydrostatic pressure(σh)on the mechanical properties and deformation mechanisms of MGs.The application of sufficiently large magnitudes ofσh to MGs has been considered a feasible way to improve strength and delocalize plastic deformation in MGs.In this paper,we review recent studies on pressure-dependent thermodynamic properties,mechanical strength and hardness,as well as elevated ductility of MGs due to the pressure-induced change of deformation and failure mechanisms.Observations of intriguing mechanical behaviors of MGs,and the corresponding theoretical modeling and atomistic understanding of plastic deformation in MGs under pure hydrostatic pressure and more general stress states are discussed.These findings not only deepen the understanding of pressure-dependent mechanical behaviors of MGs,but also point out the potential of tuning mechanical behaviors of MGs through stress engineering.

高压热处理调节FeP金属玻璃空化行为

脆性金属玻璃的空化现象可追溯其本征的高原子密度涨落.有目的地调节金属玻璃内部结构以抑制其空化行为一直是被关注的问题.本文通过分子动力学模拟研究了高压热处理对脆性Fe_(80)P_(20)金属玻璃空化行为的影响.高压热处理可诱导Fe_(80)P_(20)金属玻璃发生年轻化,有效抑制空化的发生.伴随压力和温度的增加,Fe_(80)P_(20)金属玻璃的空间异质性逐渐减小,同时磷原子的分布变得相对均匀.分析表明,高压热处理可诱导Fe_(80)P_(20)金属玻璃局部原子结构从“类液态”转变为“类固态”,致使空化需要更大的外加应力诱发.上述结果为理解金属玻璃的空间异质性和空化行为之间的关联规律提供了新的思路.

纳米尺度砷化硼的超大拉伸弹性

砷化硼(BAs)是一种具有超高热导率的半导体,未来集成到功能器件会不可避免地承受外部应力,因此对BAs弹性和强度的研究非常紧迫.在这项工作中,我们从BAs单晶中制备了长度为1–3μm,宽度为100–300 nm的BAs纳米桥,并沿着[100],[101]和[111]取向进行了原位单轴拉伸试验.试验结果表明,BAs单晶纳米桥的拉伸弹性具有明显的取向依赖性,其中[100]取向纳米桥的拉伸应变高达9%,相应拉伸强度高达34.8 GPa.另外,我们从理论上探讨了拉伸应变对BAs电子结构和热输运的影响.结果表明,随着应变的增加,BAs的带隙会减小,晶格热导率显著降低.其中,若沿[111]方向发生12%的拉伸应变,BAs将由间接带隙转变为直接带隙半导体;而在相同应变量下,沿[100]方向的拉伸应变对BAs热导率的影响要显著低于[101]和[111]方向.这些发现为BAs的能带调控和热管理提供了重要的启示,如在实际器件中可通过“应变工程”实现BAs电和热的调控.

Effects of Sc on the vacancy and solute behaviours in aluminium

Element Sc is a promising candidate for optimizing the high-temperature mechanical properties of Al alloys.In this study,the Sc-solute,Al_(3) Sc-vacancy and Al_(3) Sc-solute interactions in aluminium are inves-tigated extensively by using first-principles calculations.The correlation between the various interaction energies and the solute atomic size,and the Sc-solute compound formation energy has been evaluated.A negative correlation between the first nearest neighbour Sc-solute binding energies and the lowest Sc-solute compound formation energies has been identified,while the second nearest neighbour Sc-solute binding energies increase monotonically with the solute atomic size.Al_(3) Sc precipitates can bind vacancy strongly at the specific atomic site,but their relatively low number density limits their influence on va-cancy behaviours during the ageing period shortly after quenching.Compared to the atomic size,the trend for solute segregating at the interface between Al_(3) Sc precipitate and Al bulk is more strongly re-lated to the Sc-solute binding energy.The calculated results can clarify the available experimental obser-vations for Al-Sc,Al-Cu,Al-Mg-Si and Al-Zn-Mg-Cu alloys,and it is hoped to guide the design of high-performance Al alloys.

Evolution of precipitate and precipitate/matrix interface in Al-Zn-Mg-Cu(-Ag)alloys

Evolution of precipitate and precipitate/matrix interface in artificially aged Al-Zn-Mg-Cu(-Ag)alloys has been systematically studied.In the early stage of ageing,Ag,as a fast diffuser,can promote the formation of solute pairs and small clusters.Solute clusters are further demonstrated to be able to act as precursors forη’precipitates by in-situ STEM heating.With prolonged ageing time,the precipitate/matrix interface evolves from the Zn-dominated interface between early-stageη’and Al matrix to the Zn and Mg co-segregatedη’/Al andη_(2)/Al interfaces.Theη’/Al interfacial layers are shown to precede the formation ofη’,while theη_(2)/Al interfaces are found to be closely related to the thickening process ofη_(2)and the involved particular atomic movements are specified.Experimental observations and DFT calculations re-veal that forη’andη_(2),Ag can dissolve into the precipitate as well as locate at the precipitate/matrix interface without showing preference.For Cu,its dissolution in the precipitate and segregation on the interface mainly occur forη_(2)rather thanη’.The incorporation of Ag and Cu does not change the defined precipitate structure.

Natural overlaying behaviors push the limit of planar cyclic deformation performance in few-layer MoS_(2) nanosheets

As a typical two-dimensional(2D)transition metal dichalcogenides(TMDCs)material with nonzero band gap,MoS_(2)has a wide range of potential applications as building blocks in the field of nanoelectronics.The stability and reliability of the corresponding nanoelectronic devices depend critically on the mechanical performance and cyclic reliability of 2D MoS_(2).Although an in situ technique has been used to analyze the mechanical properties of 2D materials,the cyclic mechanical behavior,that is,fatigue,remains a major challenge in the practical application of the devices.This study was aimed at analyzing the planar cyclic performance and deformation behavior of three-layer MoS_(2)nanosheets(NSs)using an in situ transmission electron microscopy(TEM)variable-amplitude uniaxial low-frequency and cyclic loading-unloading tensile acceleration test.We also elucidated the strengthening effect of the natural overlaying affix fragments(other external NSs)or wrinkle folds(internal folds from the NS itself)on cycling performances and service life of MoS_(2)NSs by delaying the whole process of fatigue crack initiation,propagation,and fracture.The results have been confirmed by molecular dynamics(MDs)simulations.The overlaying enhancement effect effectively ensures the long-term reliability and stability of nanoelectronic devices made of few-layer 2D materials.