Three standards for engineering yield strength

Yield strength, that is, the stress when the material begins to produce macroscopic plastic deformation, generally has the following three standards in engineering:
1. Yield strength The standard is to specify that a certain residual deformation occurs. For example, the stress of 0.2% residual deformation is usually used as the yield strength, and the symbol is Rp0.2.
2. Proportional limit: Stresses that conform to the linear relationship on the stress-strain curve are often expressed internationally. When σp exceeds σp, it is believed that the material begins to yield.
2. Elastic limit: After loading the sample, unloading it. The material can fully elastically restore stress. Rel is usually expressed internationally. When the stress exceeds Rel, the material is considered to begin to yield.