The International Union of Laboratories and Experts in Construction Materials(简称为RILEM)提供的应力-应变曲线实测方法中,有几个关键参数:the strain hardening point "εst",the uniform strain "εuni",the ultimate strain "εu",the strain hardening modulus Est,是怎么定义的,有没有国外同行或做过类似工作的同盟,请画一个曲线图示意一下。