What is the greatest stress a material can withstand without a permanent elongation occurring upon complete unloading of the specimen?

The greatest stress a material can withstand without experiencing permanent elongation when unloaded is referred to as the elastic limit. This is a critical concept in materials science and engineering, as it indicates the maximum amount of stress that a material can endure while still returning to its original shape and dimensions after the load is removed. When the applied stress remains below this threshold, the material behaves elastically, meaning that any deformation is fully reversible.

This is distinct from other stress points such as the yield stress, which marks the point at which permanent deformation begins, and the ultimate stress, where a material reaches its maximum strength before failure. The proportional limit, on the other hand, is related to the linear relationship between stress and strain but does not necessarily indicate the onset of irreversible deformation. Understanding the elastic limit is essential in designing structures and components to ensure they perform safely within their operational limits.