应变速率对零件加工过程材料性能影响分析

Influence Analysis of the Strain Rate on the Material Properties During the Parts Processing

汽车零件加工过程并非绝对的静态过程,而是在较低变形速率的加工过程,应变速率对整个过程中性能变化具有重要影响。针对汽车零件常用的低合金高强钢HC340LA材料成形过程中应变速率对性能影响进行分析,同时模拟零件成形时不同的冲压速率,选取HC340LA进行8个准静态低应变速率拉伸性能测试,获取不同应变速率下材料的力学性能变化和加工硬化变化,同时基于Johnson-Cook模型获取材料的应变速率敏感性因数;将应变速率的影响嵌入到有限元仿真分析模型中,获取材料的成形极限FLD图,并与试验结果和经验公式结果进行对比。结果可知:应变速率对材料的强度和塑形都有影响,随着应变速率增大先降低后增大;应变速率对屈强比和平均n值影响很小几乎可以忽略;材料应变速率敏感性参数C值为0.017,应变速率敏感性较大;在准静态的应变速率范围内,应变速率对HC340LA的加工硬化影响能力较弱;嵌入应变率影响因素后,有限元结果与试验结果一致性较好,应变特征点误差小于3%;经验公式与试验结果在胀形变形区差别较大,应变特征点误差较大。为指导实际设计生产提供参考依据。

The machining process of auto parts is not an absolute static process,but a machining process with a lower deformation rate. The strain rate has an important influence on the performance change of the entire process. According to the influence analysis of strain rate on the properties of the high strength low alloy steel HC340L which commonly used in automotive parts during the forming process,and different stamping rates during part forming were simulated,HC340LA was selected for 8 quasi-static low strain rate tensile properties test to obtain the mechanical properties change and hardening change of materials under different strain rates. The strain rate sensitivity factor of the material was obtained based on the Johnson-Cook model. The influence of strain rate was embedded in the finite element simulation analysis model to obtain the FLD diagram of the material forming limit,and compared with the experimental results and empirical formula results. The results show that:the strain rate has an effect on the strength and shape of the material. It decreases first and then increases as the strain rate increases. The strain rate has little effect on the yield ratio and the average n value. The material strain rate sensitivity is negligible. The parameter C value is 0.017,and the strain rate sensitivity is large. In the quasi-static strain rate range,the strain rate has weak influence on the processing hardening of HC340LA. After embedding the influence factors of strain rate,the finite element results are in good agreement with the experimental results,and the strain characteristic point error is less than 3%;the empirical formula and the experimental results are different in the bulging deformation zone,and the strain characteristic point error is large. It provides a reference for guiding the actual design and production.