18CrNiMo7-6合金钢J-C损伤模型失效参数研究

Investigation on Failure Parameters of J-C Damage Model of 18CrNiMo7-6 Alloy Steel

针对高速冲击、机械成型加工等数值模拟中广泛应用的Johnson-Cook(J-C)损伤模型失效参数求取问题,对18CrNiMo7-6合金钢材料开展了3个系列的力学实验。通过缺口试样准静态拉伸实验和有限元模拟,确定了既考虑空间分布效应,又考虑应变累积效应的应力三轴度的计算方法。结果表明:失效应变随应力三轴度的增大而减小;通过10^(-3)、10、10^(3)s^(-1)应变率下的拉伸实验与霍普金森拉杆(SHTB)冲击实验,发现随着应变率的增大,材料屈服强度有所增加,表明了材料有明显的应变率强化效应,并且失效应变随着应变率的增大而增大;在25、200、300、400℃的拉伸实验中发现随着温度的升高,材料屈服强度逐渐降低,但材料的抗拉强度在300℃时要高于200℃下的结果,并且随着温度的升高失效应变逐渐减小。根据上述实验结果拟合得到了J-C损伤模型失效参数,从拟合优度可以看出拟合所得参数的可靠性。最后通过Taylor冲击实验与有限元模拟进行验证,结果表明,当冲击速度为430 m/s时,实验与仿真得到的冲击试样均发生了破坏,并且有限元模拟得到的试样破坏形态与实验结果最大误差为6.3%,结果吻合良好,验证了所选用的J-C损伤模型的合理性以及实验所得参数的有效性。

In this study,three series of mechanical tests were carried out on 18CrNiMo7-6 alloy steel materials to determine the damage parameters of the Johnson-Cook(J-C)damage model,which could be widely used in numerical simulations such as high-speed impact and mechanical forming.Through the quasi-static tensile test and finite element simulation of notched specimens,the calculation method of stress triaxiality considering both spatial distribution effect and strain accumulation effect was determined.The results showed that the failure strain decreased with the increase of stress triaxiality.Through the tensile test at 10^(-3) s^(-1),10 s^(-1) and 10^(3)s^(-1) strain rates and the impact test of SHTB,it was found that the yield strength of the material increased with the increase of strain rate,indicating that the material had obvious strain rate strengthening effect,and the failure strain increased with the increase of strain rate.In the tensile tests at 25℃,200℃,300℃and 400℃,it was found that the yield strength of the material decreased gradually with the increase of temperature,but the tensile strength of the material at 300℃was higher than that at 200℃,and the failure strain decreased gradually with the increase of temperature.According to the above experimental results,the parameters of J-C damage model were fitted,and the reliability of the fitted parameters could be seen from the goodness of fit.Finally,experimental results and finite element results of Taylor test were compared.The results showed that when the impact speed was 430 m/s,the impact samples obtained from the experiment and simulation were damaged,and the maximum error between the failure mode of the samples obtained by finite element simulation and the experimental results was 6.3%.The rationality of the J-C damage model selected in this study and the effectiveness of the experimental parameters were verified.