基于位错密度的Fe-22Mn-0.6C型TWIP钢物理本构模型研究

A PHYSICAL CONSTITUTIVE MODEL FOR Fe-22Mn-0.6C TWIP STEEL BASED ON DISLOCATION DENSITY

基于位错密度及孪晶体积分数的演化,建立了Fe-22Mn-0.6C孪晶诱导塑性(TWIP)钢滑移和孪生的塑性物理本构模型,该模型考虑了孪晶内的滑移对整体塑性变形的贡献及孪晶区和基体区Taylor因子的差异,采用基体滑移、孪晶区孪生和滑移的加权求和描述微区塑性变形.考虑应变速率对热激活应力的影响,进一步建立了应变速率与屈服应力之间的关系.采用Euler法对该模型进行数值计算,将计算结果与实验结果进行对比,其平均相对误差值只有0.84%,相对于不考虑孪晶区滑移的模型和考虑孪晶区滑移但未考虑Taylor因子差异的模型,平均误差分别降低1.1%和2.9%.分析了孪晶与滑移机制的相互作用及对宏观变形的影响,结果表明,孪生速率与滑移速率之间负相关,孪生速率增大滑移速率减小;孪生趋于饱和时,孪生速率降低而滑移速率迅速增加;应变速率增加屈服应力增大,而对应变硬化率无显著影响.

Based on the evolution of dislocation density and volume fraction of twins, a physically based con- stitutive model of Fe-22Mn-0.6C twinning induced plasticity （TWlP） steel has been developed. By taking the influ- ence of slip inside twins on the plastic deformation and the difference of the average Taylor factors between the twinned regions and matrix regions into account, the plastic strain at the representative element was presented as the weighted sum of matrix slip, twinning and slip in twinned regions in this model. A linear function between yield stress and strain rate with natural logarithm was established by considering the effect of strain rate on thermally activated stress. And then, The Euler method was adopted and the parameters of this model were obtained in order to describe as accurately as the experimental results. The results from the model are in good agreement with the experimental results and the average relative error is only 0.84%. Compared with the model free of slip and the model free of the difference of Taylor factor at twinned regions, the average relative error is reduced 1.1% and 2.9%, respectively. The interaction between two twins and the sliding mechanism and its impact on the macro-de- formation were investigated. The results show that there is a negative correlation between gliding rate and twinning rate and slip rate decreases with the increase of twinning rate. When the twins become saturated, the twin rate decreases rapidly, being opposite to the slip rate. The yield stress increases and the rate of strain hardening remains approximately unchanged with the increase of strain rate.