What is the stress at which a test specimen exhibits a specific amount of plastic strain?

Yield strength is defined as the stress level at which a material begins to deform plastically. Beyond this point, the specimen will show a permanent deformation, meaning that if the stress is removed, the material will not return to its original shape. This is critical in engineering and materials science, as it helps to delineate the transition from purely elastic behavior, where stress and strain are proportional, to plastic behavior, where the material undergoes irreversible deformation.

Understanding yield strength is essential for designing structures and components that must withstand loads without permanent deformation. It ensures that materials are used within their limits and provides an indication of how much stress a material can endure before it begins to deform in a way that cannot be recovered. The other terms mentioned—tensile strength, shear strength, and compressive strength—refer to different types of stress limits but are not specifically related to the onset of plasticity in the same way that yield strength is.