高速冲击载荷下AM80镁合金的力学本构及仿真模拟

Mechanical constitutive equation and simulation of AM80 magnesium alloy under high speed impact load

采用霍普金森压杆技术对固溶态AM80镁合金进行大应变率范围下的高速冲击实验,应变速率分别为700、1100、2150、2750和3650 s^(-1)。结果表明:实验用AM80镁合金的流变应力随应变速率的增加而增加,表现出明显的正应变率敏感性;当载荷由准静态转为动态时,合金的流变应力显著增加。基于不同应变率下的应力—应变曲线确定实验用镁合金的Johnson-Cook(J-C)本构方程。采用ABAQUS有限元软件对合金的SHPB实验进行了数值模拟,根据模拟得到的入射波、反射波和透射波形计算得到各应变速率下的应力—应变曲线,并与实验及J-C本构拟合的应力—应变响应进行对比。结果表明:即使在本构拟合所选应变速率范围外,仿真分析结果也与实验及本构拟合结果基本吻合;但在较高应变时,由于本构未考虑温升效应,使得拟合结果与实验结果的差异较低应变时明显要大。

High speed impact experiments of a solution treated AM80 magnesium alloy were carried out with a large strain rate range based on split Hopkinson pressure bar （SHPB） technique, the applied strain rates were 700, 1100, 2150, 2750 and 3650 s-1, respectively. The results show that the flow stress of the studied AM80 magnesium alloy increase with increasing strain rate, demonstrating visible positive strain rate sensitivity. In addition, the flow stress increases significantly when the applied load transfers from quasi-static to dynamic. A Johnson-Cook dynamic constitutive equation is obtained by fitting the experimental stress-strain curves under various strain rates. The SHPB dynamic compressions of the material were simulated by using ABAQUS software with the fitted Johnson-Cook constitutive parameters. Calculated incident, reflected and transmitted waves were correlated with the stress-strain response of the solution treated AM80 samples using two-wave analytical method. The stress-strain curves at different strain rates obtained in the simulations were compared with the experimental and fitting stress-strain responses. The results show that the numerical simulation results and fitting results based on the Johnson-Cook strain-rate dependent constitutive model for the studied Mg alloy are basically in agreement with the experimental results, even the strain rate without in the range for constitutive fitting. Furthermore, an obviously large difference is detected at high strains as compared with that at low strains due to the neglect of local temperature rise under high strain rate loading.