Theyield strength of a material is defined as the stress which induces a predetermined amount of permanent deformation in the material. It is thelowest stress from which permanent deformation can be achieved in a material. At this point (Point 3 as shown in Figure 1) the strain begins to increase very rapidly without any corresponding increase in stress.
I like to share this Theoretical Yield Formula with you all through my article.
Diagram showing yield strength:
Description of yield strength
Notall materials have an obvious yield point. For this reason, yield strength is often defined by an offset method as shown in Figure 1. Sucha yield strength corresponds to a definite or stated amount of permanent set, usually 0.2 or 0.5 percent of the original gauge length (indicated as ‘D’ in Figure 1 for 0.2 percent) although 0.001, 0.1, and 0.5 percent are sometimes used.