超弹性NiTi合金率相关相变图案演化模拟

基于超弹性NiTi合金薄板在不同温度下的拉伸实验结果,采用三段线性弹塑性本构模型,通过热物理常数等效法考虑相变潜热对温升的影响,利用有限元软件ABAQUS对相变图案演化进行模拟,揭示相变图案演化的率相关性机理。模拟结果表明:超弹性NiTi合金在拉伸过程中发生应力诱发马氏体相变,宏观表现为局部相变带的萌生、扩展与合并;由于相变潜热的释放,相变带的萌生伴随着局部温升,温升的峰值与加载应变率密切相关;局部相变带与加载方向成一定夹角,角度为50°~65°;随着加载速率增加,试样从等温向绝热状态转变,相变应力与局部温升随之增加,相变更容易在低温区域萌生,导致相变带数量不断增加;模拟的超弹性NiTi合金在不同应变率下的相变图案及温度场演化与实验结果吻合较好,为阐明该合金的相变局部化演变过程提供了参考。

Simulation on rate-dependent transformation pattern evolution of super-elastic NiTi alloy

Based on thin plate tensile tests of super-elastic NiTi alloy at different temperatures,a trilinear elasto-plastic constitutive model was adopted and the effect of latent heat of phase transformation on the temperature rise was considered through an equivalent method of thermo-physical constants.The transformation pattern evolutions were simulated by finite element software ABAQUS,and the rate-dependent mechanisms were also revealed.The simulated results show that the stress-induced martensitic transformation occurs under tensile loading,which macroscopically exhibits as the initiation,propagation and merging of local transformation bands;due to the release of latent heat,the initiation of transformation bands is accompanied by local temperature rise,and peak temperature rise is closely related to the loading strain rate;the local transformation bands are at a certain angle to the loading direction,which is about 50°-65°;with the increase of loading rate,the sample is changed from the isothermal state to the adiabatic one,the transformation stress and local temperature rise increase then.Therefore,the transformation tends to occur in the low temperature region,which results in an increasing number of transformation bands.The simulated transformation patterns and temperature field evolutions of super-elastic NiTi alloy at different strain rates are in good agreement with the corresponding experimental results,which provide a reference for clarifying the evolution of transformation localization of the alloy.