As pointed out by Casey and Naghdi~([2]),the introduced internal variables,such as plastic strain and back stress in plasticity should be defined,at least theoretically,so that the theory can be testable.

• Casey和Naghd i(1992)指出,塑性本构理论中引入的量如塑性应变和背应力张量等至少在理论上必须有明确的定义,从而使理论可进行实验验证。