很多结构设计中我们需要确保在施加应力的条件下只会发生弹性形变。某一个结构或者组件在经历了塑性变形或者说形状发生了永久性的变化之后可能就无法满足其应用的功能要求。屈服发生的点可以通过应力-应变曲线最初开始偏离线性关系的位置来确定，该点我们有时候称之为弹性极限。然而该点的精确位置较难测定。直线与应力-应变曲线弯向塑性变形区间的交点所对应的应力被定义为屈服强度。
In many structural designs, we need to ensure that only elastic deformation occurs under the condition of applied stress. A structure or component may not be able to meet the functional requirements of its application after it undergoes plastic deformation or permanent shape changes. The point at which yield occurs can be determined by the position where the stress-strain curve initially begins to deviate from the linear relationship, which we sometimes call the elastic limit. However, the precise location of this point is difficult to determine. The stress corresponding to the intersection of the straight line and the bending plastic deformation section of the stress-strain curve is defined as the yield strength.
对于具有非线性弹性区间的材料来说，不可能使用应变截距的方法，通常将产生某特定程度应变所需的应力定义为屈服强度。弹性-塑性转变十分明显而且出现非常突然，我们称这种想象为屈服点现象。在上屈服点处，塑性形变由工程应力的明显下降开始。形变在某上下范围浮动的应力值之内持续发生，我们称该应力为下屈服点。接下来应力随着应变的增加而升高。对于具有这种效应的金属来说，其屈服强度被认为是与下屈服点相关的平均应力值，因为该应力比较明显且对测试过程的敏感性较低。因此对于这些材料来说，我们没有必要使用应变截距的方法。
For materials with nonlinear elastic intervals, it is impossible to use the method of strain intercept. The stress required to produce a certain degree of strain is usually defined as yield strength. The elastic plastic transition is very obvious and very sudden. We call this imagination a yield point phenomenon. At the upper yield point, the plastic deformation begins with a marked decrease in engineering stress. Deformation occurs continuously under a certain range of stresses, and we call this stress the lower yield point. The stress increases with the increase of strain. For metals with this effect, the yield strength is considered to be the average stress associated with the lower yield point, because the stress is obvious and the sensitivity to the test process is low. Therefore, it is not necessary for us to use strain intercept method for these materials.