查看更多>>摘要：An underwater directional acoustic emitter is conceived with a highly anisotropic lattice material,whose acoustic charac-teristics manifest strong dependence on the orientation of the lattice material's principal axis.Exploiting these features,a cylindrical structure made of such anisotropic lattice material is engineered to possess distinct impedance values in different directions,thereby facilitating wave emission along the principal axis while inducing reflection in other directions.Notably,through numerical simulations,it is demonstrated that the emission direction can be effectively manipulated by adjusting the principal axis orientation,concurrently enhancing the emitted power.In contrast to previous directional acoustic struc-tures,the compact emitter presented in this study can get rid of the size-wavelength constraint,enabling effective control of low-frequency waves.
查看更多>>摘要：Texture is inevitably introduced during the manufacturing of most NiTi shape memory alloys(SMAs),and the textured nanocrystalline NiTi has been extensively employed in engineering.However,the effect of texture,and the joint effect of grain size(GS)and texture on the functional properties of NiTi SMAs and the corresponding microscopic mechanisms have not been clearly understood yet.In this work,based on the phase field method,the effect of texture on the GS-dependent functional properties of NiTi SMAs,including super-elasticity(SE),one-way shape memory effect(OWSME),and stress-assisted two-way shape memory effect(SATWSME),is investigated,and the corresponding microscopic mechanisms are revealed.Moreover,the samples with discrete geometrical gradients and/or texture gradients are designed to achieve graded functional properties.The simulation results indicate that the dependence of functional properties on texture is due to the effect of crystallographic orientation on martensite transformation and reorientation,which can lead to different inelastic strains.In the designed samples with texture gradients,the stress-strain responses of sheets with various textures are different,allowing for the coordination of overall deformation of the sample by combining such sheets,with varying inelastic deformation degrees.Thus,the overall response of the sample differs from that without texture gradient,leading to the achievement of graded functional properties.The simulation results and new findings in this work contribute to a deeper understanding of the effects of texture,GS,and their interaction on the functional properties of SMAs,and provide valuable reference for the design and development of SMA-based devices with desired functional properties.
查看更多>>摘要：Under the framework of the small deformation crystal plasticity theory,a crystal plastic cyclic constitutive model for body-centered cubic(BCC)cyclic softening polycrystalline metals is established.The constitutive model introduces the isotropic softening rule that includes two different mechanisms:namely softening under monotonic deformation and softening under cyclic deformation on each slip system.Meanwhile,a modified Armstrong-Frederick nonlinear kinematic hardening rule is adopted.The appropriate explicit scale transition rule is selected to extend the single crystal constitutive model to the polycrystalline constitutive model.Then the model is used to predict the uniaxial and multiaxial ratcheting deformation of BCC axle steel EA4T to verify the rationality of the proposed model.The simulation results indicate that the newly established crystal plasticity model can not only describe the cyclic softening characteristics of BCC axle steel EA4T well,but also reasonably describe the evolution laws of uniaxial ratcheting and nonproportional multiaxial ratcheting deformation.Moreover,the established crystal plastic cyclic constitutive model can reasonably predict the ratcheting behavior of BCC single crystal as well.
查看更多>>摘要：This paper investigates the steady-state thermoelastic problem of a circular nanohole embedded in an infinitely large elastic plane subjected to a uniform far-field heat flux.A lowly conductive surface model is used to account for the effects of surface phonon scattering,while the complete Gurtin-Murdoch model is utilized to characterize the effects of surface tension and surface elasticity.The closed-form solution to the temperature and stress field surrounding the hole is derived in the context of complex variable methods.Several numerical examples are presented to analyze the influence of surface effects on thermal stress fields.It is shown that surface effects induce notable increases in normal and shear stresses around the hole.Specifically,all three stress components(hoop,normal,and shear)in the vicinity of the hole exhibit substantial augmentation with increasing surface tension and surface modulus.In particular,it is found that the presence of surface effects amplifies the variation in stress gradients and intensifies stress concentration around the hole.
查看更多>>摘要：Auxetic metamaterials,which exhibit the negative Poisson's ratio(NPR)effect,have found wide applications in many engineering fields.However,their high porosity inevitably weakens their bearing capacity and impact resistance.To improve the energy absorption efficiency of auxetic honeycombs,a novel vertex-based hierarchical star-shaped honeycomb(VSH)is designed by replacing each vertex in the classical star-shaped honeycomb(SSH)with a newly added self-similar sub-cell.An analytical model is built to investigate the Young's modulus of VSH,which shows good agreement with experimental results and numerical simulations.The in-plane dynamic crushing behaviors of VSH at three different crushing velocities are investigated,and empirical formulas for the densification strain and plateau stress are deduced.Numerical results reveal more stable deformation modes for VSH,attributed to the addition of self-similar star-shaped sub-cells.Moreover,compared with SSH under the same relative densities,VSH exhibits better specific energy absorption and higher plateau stresses.Therefore,VSH is verified to be a better candidate for energy absorption while maintaining the auxetic effect.This study is expected to provide a new design strategy for auxetic honeycombs.
查看更多>>摘要：The integration of additive manufacturing and topology optimization makes it possible to fabricate complex configurations,especially for microscale structures,which can guarantee the realization of high-performance structural designs.However,topology results often contain microstructures(several multicellular scales)similar to the characteristic length of local macrostructures,leading to errors in structural performance analysis based on classical theories.Therefore,it is necessary to consider the size effect in topology optimization.In this paper,we establish a novel topology optimization model utilizing the integral nonlocal theory to account for the size effect.The approach consists of an integral constitutive model that incor-porates a kernel function,enabling the description of stress at a specific point in relation to strain in a distant field.Topology optimization structures based on nonlocal theory are presented for some benchmark examples,and the results are compared with those based on classical medium theory.The material layout exhibits significant differences between the two approaches,highlighting the necessity of topology optimization based on nonlocal theory and the effectiveness of the proposed method.
查看更多>>摘要：Piezoelectric semiconductors(PSs),such as ZnO and GaN,known as the third-generation semiconductors,have promising applications in electronic and optoelectronic devices due to the coexistence and interaction of piezoelectricity and semicon-ductor properties.Theoretical modeling of PS structures under external loads,such as thermal and mechanical loads,plays a crucial role in the design of PS devices.In this work,we propose a nonlinear fully coupling theoretical model and investi-gate the multi-field coupling behaviors of PS structures and PN junctions under thermal and mechanical loads,considering physical and geometric nonlinearities.The electromechanical and semiconducting behaviors of a PS rod-like structure with flexural deformations under different combinations of temperature changes and mechanical loads are evaluated.The tuning effect of temperature changes and mechanical loads on multi-field coupling behaviors of PSs is revealed.The current-voltage characteristics of PS PN junctions are studied under different combinations of temperature changes and mechanical loads.The obtained results are helpful for the development of novel PS devices.
查看更多>>摘要：Single-phase concentrated solid solution alloys(SP-CSAs),including high-entropy alloys,have received extensive attention due to their excellent irradiation resistance.In this work,displacement cascade simulations are conducted using the molecular dynamics method to study the evolution of defects in Ni-based SP-CSAs.Compared with pure Ni,the NiCr,NiCo,and NiCu alloys exhibit a larger number of Frankel pairs(FPs)in the thermal peak stage,but a smaller number of surviving FPs.However,the NiFe alloy displays the opposite phenomenon.To explain these different observations for NiFe and other alloys,the formation energy and migration energy of interstitials/vacancies are calculated.In the NiFe alloy,both the formation energy and migration energy barrier are higher.On the other hand,in NiCr and other alloys,the formation energy of interstitials/vacancies is lower,as is the migration energy barrier of interstitials.The energy analysis agrees well with previous observations.The present work provides new insights into the mechanism behind the irradiation resistance of binary Ni-based SP-CSAs.
查看更多>>摘要：Most existing treatments for origami-folding simulations have focused on regular-shaped configurations.This article aims to introduce a general strategy for simulating and analyzing the deformation process of irregular shapes by means of compu-tational capabilities nowadays.To better simulate origami deformation with folding orders,the concept of plane follow-up is introduced to achieve automated computer simulation of complex folding patterns,thereby avoiding intersection and pen-etration between planes.Based on the evaluation criteria such as the lowest storage energy with tightening and the fastest pace from tightening to unfolding,the optimal crease distribution patterns for four irregular('N'-,'T'-,'O'-,and'P'-shaped)origami configurations are then presented under five candidates.When the dimensions of the origami are fixed,it is discovered that simpler folding patterns lead to faster deformation of the origami configuration.When the folding complexity is fixed,higher strain energy results in more rapid origami expansion.
查看更多>>摘要：In this work,a new methodology is presented to mainly solve the fluid-solid interaction(FSI)equation.This methodology combines the advantages of the Newmark precise integral method(NPIM)and the dual neural network(DNN)method.The NPIM is employed to modify the exponential matrix and loading vector based on the DNN integral method.This involves incorporating the basic assumption of the Newmark-β method into the dynamic equation and eliminating the acceleration term from the dynamic equilibrium equation.As a result,the equation is reduced to a first-order linear equation system.Subsequently,the PIM is applied to integrate the system step by step within the NPIM.The DNN method is adopted to solve the inhomogeneous term through fitting the integrand and the original function with a pair of neural networks,and the integral term is solved using the Newton-Leibniz formula.Numerical examples demonstrate that the proposed methodology significantly improves computing efficiency and provides sufficient precision compared to the DNN method.This is particularly evident when analyzing large-scale structures under blast loading conditions.
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