应力脉冲对CCCD-SHPB试验系统测试结果影响的数值分析

NUMERICAL ANALYSIS OF EFFECT OF STRESS IMPULSE ON TESTING RESULT FOR CCCD-SHPB DYNAMIC FRACTURE TEST SYSTEM

3维动态有限元分析结果表明,脉冲上升沿时间、幅值及试件直径对CCCD-SHPB(central cracked circular disk-split Hopkinson pressure bar)动态断裂试验系统的试验结果有较大影响,改变脉冲上升沿时间或脉冲幅值可以得到不同加载速率下材料的动态断裂韧度。进一步计算结果表明,在动态加载的初期阶段,由于试件两边载荷不平衡,导致CCCD-SHPB动态断裂试验系统中存在与试件尺寸相关的特征时间ΔT,且ΔT近似等于应力波在试件中来回往返两次的时间;动态断裂试验时,试件从加载至断裂的时间应大于特征时间ΔT,否则试验结果不可靠。

3-D dynamic finite element method analysis confirms that the rise time and stress level of the stress impulse as well as the specimen diameter have a significant effect on the testing result of CCCD-SHPB（central cracked circular disk-split Hopkinson pressure bar）dynamic fracture test system, and the dynamic fracture toughness under different loading rates can be achieved by changing the rise time and stress level of the stress impulse. Due to the unbalance of loads on two sides of specimen at the early stages of dynamic loading, a characteristic time △ T, which is dependent on specimen size, is introduced. Its value is approximately equal to the time of which stress wave travels back and forth in the specimen for two times. It is necessary that the time of which specimen is loaded till fracture must be greater than A T when the dynamic fracture test is conducted.