说明：  用于计算材料的粘弹塑性变形行为的Umat子程序，参考书籍为《非线性本构关系在ABAQUS中的实现》第八章
(Umat subroutine for calculating viscoelastic plastic deformation behavior of materials, the reference book is chapter 8 of "realization of nonlinear constitutive relation in ABAQUS")