结构钢中绝热剪切带形成与扩展的光学观测与数值模拟

绝热剪切带(Adiabatic Shear Band,ASB)是许多金属材料在冲击载荷作用下发生破坏的主要原因之一,它是近年来冲击动力学和损伤力学研究的前沿和热点。相关的理论研究主要针对一维剪切条件,分析应力、应变、剪切速度、材料热物理和力学性能、初始缺陷大小之间的关系,得到一个由多个物理量组合而成的量来判别材料出现剪切带的难易。ASB的实验主要利用Hopkinson压杆、扭杆、压剪炮等加载技术,研究钛合金、钨合金、高强结构钢等材料的剪切带特征,包括局部温度和变形分布、剪切带出现的阈值等。但是,对剪切带演化过程的在位观察及其动态实时演化的研究还较少见,妨碍了人们对由于剪切局部化而导致的材料破坏机理的深入认识。针对45钢,在Hopkinson压杆上,开展了不同冲击加载条件下剪切带演化过程的在位观察及可视化研究。利用自行设计的高分辨力的光学观测系统和基于数字相关理论的图像处理软件,捕捉了单一试样在冲击加载条件下ASB逐渐形成和扩展的过程。同时,利用LS-DYNA商业程序对试样的冲击压缩过程进行了数值模拟,所得主要结果与实验观测基本一致。

Optical Observation and Numerical Simulation on the Evolution of Adiabatic Shear Band in Structural Steel

Adiabatic shear band (ASB) may cause damages and failures of many metal materials under impact loading, which is a key issue in the research of damage mechanism. The theoretical study is mainly focused on the relationship among the strain, stress, speed of shear and the initial flaw size in one-dimension shear conditions, which is used to determine the possibility of the generation of ASB. By experimental investigations, the features of ASB of titanium alloy, tungsten alloy and high-strength structural steel, including deformation fields, local temperature and the threshold value for ASB generating, can be detected. However, since there is little study on the real-time and in situ measurements on the evolution process of ASB, the failure details according to the shear-localization are still unknown. In this paper, the real-time observations and visualizations on the evaluation of ASB in 45 steel under different impact conditions in SHPB are presented. The generating and evaluating processes in a single sample are detected and analyzed by a self-design optical system and the self-designed software, which is based on Digital Correlation method with high resolution. At the same time, the numerical simulations and micro-observations by SEM are obtained by LS-DYNA and the simulation results are in good agreement with the experimental ones.