高导无氧铜动态本构关系对于单轴冲击拉伸下空穴增长和失稳的影响

Effect of Dynamic Constitutive Relations on Void Growth and Instability for OFHC Copper Subjected to Uniaxial Impact Tension

对于高导无氧铜提出一种动态计算的空穴单元模型,由SHBP试验等得到的典型动态本构关系,用于描述空穴间基体的本构行为。此样本材料体积为一圆柱体,其中心包含一个椭球空穴,单元顶部施以轴向常速度加载。在不同应变率下,给出了采用J-C或Z-A本构关系的高导无氧铜中空穴增长到失稳的整个过程。文中讨论了空穴动态失稳的条件,并提出以空穴形状演化为判据。此判据导出与光滑杆冲击拉伸断裂应变一致的结果。计算结果显示,用J-C本构关系得出的空穴失稳早于用Z-A本构关系得出的空穴失稳,计算得出的空穴形状演化与准静态半经验公式估算的空穴形状演化在空穴增长一定阶段基本一致,然而,随着空穴失稳的发生,半经验公式不能预测空穴的动态失稳。

A dynamically computational void cell model was presented for oxygen-free high-conductive(OFHC) copper.The typical dynamic constitutive relations obtained from SHPB tests are used to describe the constitutive behavior of matrix material OFHC copper between neighboring voids.The representative material volume was modeled by a circular cylinder which has an ellipsoid void in its center and dynamically loaded at a constant axial velocity at the top of the cell.The computed entire process from the void growth to void instability in OFHC copper with J-C or Z-A constitutive relation was shown at different average strain rates.The conditions of dynamic void instability were discussed,and a criterion based on void shape evolution was presented.The criterion was used to derive the fracture strains consistent with the experimental results of unnotched bars subjected to impact tension.It is concluded that the void instability computed with J-C constitutive relation occurs earlier than that with Z-A constitutive relation.It seems that our computed void shape evolution is coincident with the void growth predicted by the available semi-empirical relation.However,with the development of void instability,the semi-empirical relation could not predict the dynamic evolution of void.