主要区别-屈服强度与抗拉强度

在材料工程中，屈服强度和抗拉强度是两个可以用来表征材料的特性。屈服强度和抗拉强度之间的主要区别在于屈服强度是材料永久变形时的最小应力，而抗拉强度则描述了材料在断裂前能够承受的最大应力。

材料的应力应变特性

When a solid material is not experiencing any external forces, all the molecules that make up the material are vibrating about their equilibrium positi***. This is the lowest-energy configuration for the molecules, and if they are moved away from their equilibrium positi*** the molecules would attempt to get back to their equilibrium positi***. Technically, stress is a measurement of these intermolecular forces. If the material is not under acceleration, then the intermolecular forces should be balanced by the external forces acting on the material. Therefore, we can get an indication of stress by measuring the external forces acting on the object. The stress ( ) on an object is given by the external force on the object divided by the cross-sectional area of the sample of a material.

When an object is under stress, it undergoes deformation. Strain is a measurement that gives the change in length of an object divided by the original length. Strain is usually given the symbol  . If we subject a sample of material to different levels of stress, measure corresponding strains and then produce a graph of stress vs. strain, then we obtain what is called a stress-strain curve, which is characteristic curve for a given material. The graph below shows the stress-strain curve for a typical ductile material such as steel:

Stress – strain curve for a ductile material

什么是屈服强度(yield strength)？

当材料上的应力缓慢增加时，可以看到应变在开始时按比例增加。如果消除了对材料产生应力的力，那么材料就会恢复到原来的形状。当一种材料能够做到这一点时，我们就说这种材料是有弹性的（比如橡皮筋）。如果材料上的应力不断增加，那么材料最终会达到一个点，当材料变得如此变形时，即使变形力被消除，材料也无法恢复其原始形状。材料停止弹***的应力称为屈服强度。当材料不能恢复到原来的形状时，我们说材料是塑料的。

什么是抗拉强度(tensile strength)？

假设你不断增加材料上的力超过屈服强度。材料不断变形，最终分子间的作用力无法抵抗外力，材料就会断裂。材料在断裂前能承受的最大应力称为抗拉强度或极限强度。

当你看上面的应力-应变曲线时，应力似乎随着材料的不断拉长而减小。这是因为用于绘制这些图表的应力和应变的定义没有考虑到在材料上施加力时发生的区域变化。相反，这里假设面积保持不变。这种不考虑区域变化的应力定义称为工程应力。如果考虑到面积的变化，则应力-应变曲线表明，随着材料不断伸长，应力也随之增加。将该区域的连续变化考虑在内的应力定义称为真应力。

屈服强度(yield strength)和抗拉强度(tensile strength)的区别

定义：

屈服强度是导致材料失去弹性的应力。

抗拉强度是材料在断裂前能承受的最大应力。