GB/T 228-2002规定了用直接法和移位法测定断后伸长率, 直接法测得的断后伸长率随断口所在的位置而变化, 不具备唯一性；移位法弥补了直接法的不足, 但是比较麻烦。笔者提出了一种测定断后伸长率的新方法——解析法。该方法利用断口两侧伸长变形的对称性, 在试样断裂后较长的一半中, 已经包含了试样伸长的全部信息的特征, 虚拟一个拉伸试样；这个虚拟试样断口两侧的伸长变形是对称的, 继而利用GB/T 17600-1998中的断后伸长率换算公式计算得到所要求的断后伸长率。解析法得到的断后伸长率测定结果优于直接法和移位法, 特别适用于对材料断后伸长率研究的工作。

It is specified to use direct measuring method and position transferring method for the measurement of percentage elongation after fracture in GB/T 228-2002. The value of elongation measured by direct measuring method would vary from the location of the broken, and it was not characterized as the only one. Although position transferring method was a remedy for the above method, it was very complicated. The analytical method was proposed to take use of symmetry of elongation deformation from both sides of the broken, and based on the character of which the elongation deformation from the half of the longer part after breaking had covered all the information of elongation, and tensile specimen was invented of which the elongation deformation from both sides of the broken was symmetric. Then the required elongation would be calculated by the way of conversion formula of elongation of GB/T 17600-1998. The result from the analytical method was better than that of the direct measuring method and position transferring method. The analytical method was specially applied to research of percentage elongation after fracture of material.