一种考虑静水压力和偏应力共同作用的相变临界准则

A CRITICAL CRITERION FOR PHASE TRANSFORMATION CONSIDERING BOTH HYDROSTATIC PRESSURE AND DEVIATORIC STRESS EFFECTS

同时考虑静水压力和偏应力的影响,分别建立了“应力诱发”和“形变诱发”相变的临界准则.准则在主应力空间中给出的相变临界曲面呈现明显的拉压不对称性.在弹性阶段,偏应力对相变总是起促进作用.塑性屈服后,偏应力通过塑性功产生的温升影响相变临界面,从而对高温相到低温相转变起阻碍作用,反之起促进作用.静水压力对相变可能起促进作用,也可能起阻碍作用,取决于相变时材料的体积是膨胀还是收缩.建立的相变临界准则对准静态加载条件下的Fe20%Ni0.5%C合金和Fe30%Ni合金和一维应变冲击条件下的Fe32%Ni0.035%C合金中的γα相变进行了拟合和预测,预测与实验结果有较好的吻合.在主应力空间中柱形屈服面可能与锥形相变临界面相交,从而在一定条件下将发生“形变诱发”相变和“应力诱发”相变间的转变,这一推论有待实验的验证.

Taking the hydrostatic pressure together with the deviatoric stress into consideration, the critical criterions of phase transformation have been established for “stress induced” and “strain induced” phase transitions. The critical surface of the criterion in the principal stress space demonstrates asymmetric property to tension and compression. The deviatoric stress always promotes the phase transformation at elastic state. If the material yields, the deviatoric stress will affect the critical surface via the temperature increase caused by the plastic work. It retards the transformation from high temperature phase to low temperature phase but assists the reverse transformation. The hydrostatic pressure may assist or oppose the phase transformation depending on the volume change of the phase transformation. Using the criterion established. We fitted and predicted the γ α transformation in Fe 20%Ni 0.5%C, Fe 30%Ni alloys under quasi static condition and Fe 32%Ni 0.035%C alloy under shock loading. The prediction is in good agreement with the experimental data. Because the cylindrical yield surface may intersect with the conic critical surface of phase transition in the principal stress space, a “strain induced” phase transition will become a “stress induced” phase transition at certain condition. This prediction needs to be verified experimentally.