界面效应对纳米多孔材料宏观弹塑性力学性能的影响

Effects of interface effects on the macroscopic elastoplastic properties of nanoporous materials

当多孔材料的孔洞为纳米尺度时,基体/孔洞的界面效应会对这种材料的弹塑性力学性能产生较大影响.本文通过理论分析将描述界面效应的传统数学界面模型等效为具有一定厚度的界面相模型,并基于ABAQUS的UMAT子程序开发了界面相材料模型.以此为基础,采用有限元数值模拟的方法,研究了孔隙率、孔径尺寸及界面残余应力对纳米多孔金属材料宏观弹塑性拉伸-压缩性能的影响.结果表明,孔径尺寸和界面残余应力一定时,孔隙率增大引起有效弹性模量和屈服强度减小;若孔隙率与界面残余应力保持不变,孔径尺寸增大会引起有效屈服强度和流动应力增大;界面残余应力会导致纳米多孔金属拉伸-压缩曲线存在明显的不对称现象;由于界面相的负刚度效应,当纳米多孔金属变形到一定程度时呈现出软化现象,即宏观应力随变形增加而减小.

For the porous materials with nanoscale voids,the interface effect between the solid matrix and the void has a great influence on the macroscopic elastoplastic properties of such material.Through the theoretical analysis,this work treated the typical mathematical interfacial model describing the interface effects as the interfacial phase model with a certain thickness,and developed a material model of the interfacial phase model using the UMAT subroutine of ABAQUS software.On this basis,the finite element numerical method is employed to study the effects of porosity,pore size and interfacial residual stress on the macroscopic elastoplastic tensile and compressive mechanical properties of nanoporous metals.The results show that the increasing porosity causes the effective elastic modulus and the yield strength to decrease in magnitudes when the pore size and the interfacial residual stress keep constant.the increasing pore size leads to the increase of the effective yield strength and the flow stress when the porosity and the interface residual stress are constant.The interfacial residual stress induces the asymmetry of the tension-compression curves of the nanoporous metal, and due to the negative stiffness of the interfacial phase, the nanoporous metal exhibits the stress softening phenomenon. That is the macroscopic stress decreases as the deformation increases when the material deforms to a certain degree.