帽型试样动态绝热剪切破坏演化分析

STUDY OF EVOLUTION OF ADIABATIC SHEAR FAILURE IN HAT-SHAPED SPECIMEN UNDER DYNAMIC LOADING

利用分离式霍普金森压杆加载Ta2钛合金扁平闭合帽形受迫剪切试样,结合数字图像相关法和"冻结"试样的微观金相观察,研究剪切区剪切应变的演化、绝热剪切带形成条件等.结果显示:受迫剪切试样在动态加载过程,剪切区剪切应变不断集中,形成绝热剪切带,裂纹沿绝热剪切带发展;随加载率提高,绝热剪切起始临界应变减小;进一步利用数字图像相关法DIC场应变分析及金相微观观测对比,利用卸载回复特性对绝热剪切带起始临界条件进行了讨论,计算的绝热剪切带起始时温升仅为86℃.材料软化可能不是绝热剪切带起始的控制条件,相反是由于绝热剪切带形成造成的应变高度集中发展导致温度急剧升高.

By digital image correlation method（DIC）and microscopic metallurgical observation of‘freezing＇samples,this paper experimentally studies the initiation and propagation of adiabatic shear localization of Ta2 titanium alloy in a closed flat hat-shaped specimen struck by split Hopkinson pressure bars.The results show that the width of shear zone in hat-shaped specimen is continually narrow-down until the formation of adiabatic shear band,and the crack will propagate along this band from the end to the center of shear zone.It is also shown that the critical shear strain of adiabatic shear band initiation increases with increasing loading rate.Furthermore,the results of DIC show that the initiation of adiabatic shear localization can be taken as the time when the elastic strain of element located near the plastic shear zone begins to rebound according to the stress unloading theory.The evolution of heat in shear zone converted by plastic work shows that the temperature of initiation is only 86℃,this result means that the thermal softening of material may not be the key condition of initiation of adiabatic shear localization,however,the sharp increase of temperature is the result of high-plastic-strain in adiabatic shear band.