脆性材料SHPB试验中实现近似恒应变率加载必要性的研究

Study on the Necessity of Achieving Nearly Constant Strain-Rate Loading in Split Hopkinson Pressure Bar Tests for Brittle Materials

基于分离式霍普金森压杆(SHPB)试验的数值模拟,对脆性材料SHPB试验中是否需要实现近似恒应变率加载的必要性进行了研究。结果表明在脆性材料的SHPB试验中,即使整形入射应力波在反射应力波中产生了一个近似平台,脆性材料试样中仍旧存在显著的由惯性产生的径向围压,说明在SHPB试验中实现了由反射应力波中的近似平台所表征的近似恒应变率加载也不能表示SHPB试样中的应变率为近似恒定。因此,在脆性材料SHPB试验中应用波形整形技术并不能改变转折应变率表征SHPB试样中应力状态转变的特性。无论是否采用了波形整形技术,应用脆性材料SHPB试验结果时都应考虑惯性引起的径向围压的影响。

Split Hopkinson pressure bar（SHPB） technique has been frequently used to measure the compressive stress-strain relation of brittle materials at high strain-rates.A lot of study is performed on how to achieve nearly constant strain-rate loading condition in SHPB brittle material specimens during the effective loading period by employing techniques like pulse-shapers.This paper appraises the necessity of achieving nearly constant strain-rate loading in SHPB tests of brittle samples based on numerical simulations of SHPB tests.It is found that the inertia-induced lateral confinement of brittle material specimens is still significant even the shaped incident stress pulse can generate a nearly flat plateau in the reflected pulse in SHPB tests.It implies that the achievement of nearly constant strain-rates represented by nearly flat plateaus in the reflected pulse in SHPB tests may not give true nearly constant strain-rates in SHPB brittle material specimens.It is concluded that the application of techniques like pulse-shapers in SHPB tests on brittle materials may not change the nature of the observed transition strain-rate,which represents the transition of the stress state.Therefore,the inertia-induced lateral confinement effect needs to be considered in the interpretation of any SHPB results for brittle materials even though techniques such as pulse-shapers are used.