钢材应变硬化与应变率效应的试验

Experimental Study on Strain Hardening and Strain Rate Effect of Q420 Steel

摘要:

利用INSTRON拉伸试验机和Zwick/Roell HTM5020型高速拉伸试验机对Q420钢材开展了不同应变率下（0.001~288 s-1）的单轴拉伸试验，研究应变率效应对钢材力学性能的影响.试验结果表明，Q420钢为应变率敏感型材料，其硬化特征随应变率的提高而变化.采用ANSYS中LSDYNA模块对静力和动力拉伸试验进行仿真模拟，通过逆向反推的方式获得了Q420钢颈缩后的真实应力应变曲线.仿真结果显示，Q420钢材的真实应力应变关系随着应变率的提高，从幂次型的Ludwik准则向指数型的Voce准则转化.为得到更优的动本构模型，在H/VR本构模型中引入新的应变率准则，以CowperSymonds模型中的钢材动力放大系数代替H/VR本构模型中的线性Wagoner应变率准则.结果显示，修正H/VR本构模型很好地吻合了试验数据，准确反映了大应变状态下的应变硬化特征和应变率对应变硬化的影响.

关键词:应变率; 应变硬化; 本构模型; Q420

Abstract:

Uniaxial tensile tests of Q420 steel at different strain rates (0.001288 s-1) were carried out to study strain rate effect on mechanical properties by INSTRON and Zwick/Roell HTM5020 testing machine. The experimental results show that Q420 steel is sensitive to strain rates, with strain hardening characteristic changing along strain rates. Finite element (FE) modeling of these tensile tests is developed to reversely extrapolate the true stressstrain relationship of Q420 steel beyond necking, using LSDYNA of ANSYS. The simulation results show that the true stressstrain relationships of Q420 steel transform from powerlaw Ludwik model to exponential Voce model with the increasing strain rate. To get a fine dynamic constitutive model, a modified H/VR model is established by introducing a new strain rate sensitivity function into the H/VR constitutive model, where Wagoner rate law is replaced by the dynamic increase factor of the CowperSymonds model. The results show that the modified H/V–R model fits the experimental data well and captures strain hardening at high strain accurately as well as the variation of strain hardening with strain rate.

Key words:strain rate; strain hardening; constitutive model; Q420