What is the maximum stress that a material can endure while maintaining a direct proportionality between stress and strain called?

Explanation

The proportional limit refers to the highest stress level at which stress and strain remain directly proportional. Beyond this point, the material no longer follows Hooke's Law. The elastic limit is the maximum stress before permanent deformation, the yield strength is where plastic deformation begins, and the modulus of elasticity is the ratio of stress to strain within the elastic range.