Study On Mechanical Properties Of Nanoporous-Metal Ligaments Under Tension And Bending

Nano-porous metal materials have great potential applications in the fields of new electrodes,molecular sieves and catalysis due to a series of excellent and novel physical,chemical and mechanical properties brought by their ultra-high surface area.In recent years,with the gradual improvement of preparation technology,nanoporous metal materials have shown broad application prospects,especially in the field of new energy.The fine microstructure and significant size effect also put forward new requirements for mechanical research.For example,with a series of refined functional devices such as nanoporous metal intelligent filters and actuators,in order to meet engineering applications,it is necessary to strictly control the prediction accuracy of deformation under external load.Surface effect must be considered in the analysis of mechanical properties of nano-porous metal materials,because it is an important factor affecting the mechanical properties of nanomaterials.Based on the Gurtin-Murdoch surface elasticity theory,Euler-Bernoulli beam theory and Timoshenko beam theory,the influences of surface effect and shear deformation on the effective elastic modulus,Poisson’s ratio and bending behavior of nano-ligaments were studied.The size dependence of surface effects and the effects of relative density and shear deformation on effective elastic modulus and mean critical stress of nanoporous metal materials were analyzed by two-dimensional honeycomb and three-dimensional Gibson-Ashby open-cell foam models.Firstly,nano-porous copper was prepared by dealloying method,and the formation of nanoporous metal ligaments was studied.The results showed that the morphology of ligaments was affected by the atomic proportion in the alloy precursor,the concentration of corrosive liquid and the corrosion time.Excessive corrosion would seriously deform the original morphology of ligaments,passivating and forming polyhedral structure,which may affect the mechanical properties of materials.Secondly,the nanowire was used as the model to study the nanowire metal ligament.The results showed that the effective elastic modulus,Poisson’s ratio,bending deflection and critical pressure of the nanowire ligament were mainly controlled by the surface residual stress,and were not sensitive to the surface elasticity.The surface residual stress causes hardening effect between beam and cantilever beam.The softening effect of the ligament beam caused by shear deformation is significant when the length-diameter ratio is small.Finally,the single-cell model was analyzed based on the research results of the nanoligament.The analysis shows that the effective elastic modulus and the mean critical pressure of the nano-porous metal materials increase with the increase of the relative density,and the shear deformation reduces the effective elastic modulus and the mean critical pressure.The influence degree of surface effect on effective elastic modulus and mean critical stress of nanoporous metal materials is negatively correlated with section size and relative density,in which surface elasticity has obvious effect on low relative density materials and surface residual stress has obvious effect on high relative density materials.The effect of surface effect on the effective elastic modulus and the mean critical stress is enhanced or weakened,which mainly depends on the surface elasticity.