高导无氧铜杆的冲击拉伸断裂系列实验以及基于样本体积单元的分析

采用Hopkinson装置和一种基于一级气体炮的高速冲击拉伸断裂装置,研究了无刻槽高导无氧铜(OFHC)杆在一系列冲击拉伸速度下的断裂。当冲击拉伸速度大于40m/s时,断裂位置总在冲击拉伸端附近,此速度被确定为OFHC的实验临界冲击拉伸速度。一种受单轴冲击拉伸荷载的、中心含椭球空穴的样本体积单元被用于数值模拟所含空穴的增长与失稳的过程。OFHC的J-C与Z-A 本构关系用于描述基体材料的动态响应。讨论了空穴失稳条件并提出以空穴形状演化为判据,比较了空穴失稳时的样本体积单元平均径向应变与无刻槽杆的冲击断裂应变。也用这种样本体积单元模型分析了OFHC的实验临界冲击拉伸速度。

Fracture tests of OFHC bars under impact tension and analysis based on a representative volume element

Unnotched oxygen-free high conductive(OFHC) bars were tested at different tensile velocities on a tension Hopkinson bar and a novel facility for high-speed tensile tests based on a one-stage gas gun system.And the impact velocity corresponding to the fracture at the impact end was determined as the experimental critical impact velocity in tension of OFHC.A representative volume element(RVE) was modeled by a circular cylinder containing an ellipsoid void at its center and the RVE was dynamically loaded by an axial velocity at its top.The entire process was numerically simulated from the void growth to void instability in the RVE for OFHC which obeyed the J-C or Z-A constitutive relation.The conditions of dynamic void instability were discussed and a criterion based on void shape evolution was presented.The average radial strains of the RVE in void instability were compared with the experimental localized fracture strains of the unnotched OFHC bars under uniaxial impact tension.The experimental critical impact velocity in tension of OFHC was also analyzed by using the RVE model.