以屈服接近度分段函数表示的非线性流变模型的程序实现

基于三轴流变试验提出的非线性黏弹塑性流变模型存在蠕变门槛值、长期强度和非线性黏塑性体等组件。这种复杂的流变模型在进行程序实现时存在着诸多问题，比如一维的蠕变门槛值和长期强度推广至三维时难于表达、非线性黏塑性部分难于处理等问题。通过引入屈服接近度参数作为蠕变方程分段函数的判别准则，解决了三维情况下蠕变门槛值和长期强度的表达问题；详细推导了黏塑性部分的表达形式，并给出了三维中心差分形式，实现了流变模型在FLAC3D中的二次开发。通过算例验证了程序开发的正确性，对流变模型进行参数辨识，拟合曲线与试验曲线吻合较好，表明了所建模型的正确性与合理性。

Program implementation of nonlinear rheological model based on yield approach index piecewise function

Based on triaxial rheological experiment, a nonlinear visco-elastoplastic rheological model is proposed which has creep threshold value, long-term strength, nonlinear viscoplastic body and other components. There are many problems in programming of this complex rheological model, for example, one-dimensional creep threshold value and long-term strength are difficult to express when extended to three-dimensional, and it was difficult to deal with nonlinear viscoplastic part. The yield approach index parameter is used as identification criterions of the creep equation piecewise function, the problems which the creep threshold value and long-term strength in three-dimension are difficult to express, are solved. The expression of viscoplastic part is derived detailedly; and three-dimensional central difference form is given, therefore, the secondary development of this rheological model for FLAC3D is achieved. A case study is given to verify correctness of program compiling. The rheological parameters are identified, the fitting curves are in good agreement with the experimental curves, so as to indicate that the model is correct and reasonable.