对于层裂强度传统测定方法有效性的讨论

基于Gathers的工作,对试件靶背部贴有低阻抗材料的平面冲击波致层裂试验,导出了传统方法测定层裂强度的一般方程,在无低阻抗材料且作声学近似的条件下,即为Novikov的测定层裂强度的方程。研究指出,传统方法确定的层裂强度测定方程仅仅可能对采用瞬时层裂准则得到的数值模拟的层裂信号有效。数值模拟表明,层裂面上的由损伤演化引起的应力松弛严重影响层裂片中的应力剖面,因而影响靶板自由面速度历史或靶板-低阻抗材料界面应力历史。研究揭示,传统方法导出的估算层裂强度方程由于没有计及应力松弛,对于实测的靶板自由面速度历史或靶板-低阻抗材料界面应力历史并非有效。

ON THE VALIDITY OF THE TRADITIONAL METHODOLOGY OF SPALL STRENGTH MEASUREMENT

Based on Gathers work,general equations for traditional measurement of the spall strength are given for the planar spall experiment with a low impedance buffer placed behind the target.In the case of no buffer,the equations become the expression given by Novikov within the acoustic approach.It is indicated that the spall strength equations determined by the traditional methodology are valid only for the numerically simulated ‘pullback’ by a local instantaneous critical stress criterion.Numerical simulations show that the propagation of wave profile in the spall scab is affected seriously by the stress relaxation due to the damage evolution on the spall plane.Therefore,the free surface velocity profile of target or the stress profile of the interface between target and low impedance buffer depends strongly on the damage evolution on the spall plane.It is revealed that the traditional determination of spall strength without taking into account the stress relaxation is invalid measure of the spall strength.