Final answer:
The yield strength of a material is the point where its behavior changes from elastic to plastic, marking the onset of permanent deformation.
Step-by-step explanation:
The point at which a metal's behavior changes from elastic to plastic, which is the onset of permanent deformation, is referred to as the material's yield strength. When the stress applied on a material exceeds this point, the material no longer returns to its original shape upon the removal of the applied force, indicating it has undergone plastic deformation. Young's modulus is a measure of the stiffness of a solid material and defines the relationship between stress (force per unit area) and strain (proportional deformation) in a material in the linear (elastic) regime. Although Young's modulus relates to elasticity, it is not the value at which the transition from elastic to plastic behavior occurs. The elastic limit is the maximum stress that a material can withstand without permanent deformation, but it is the yield strength that specifically marks the transition from elastic to plastic.