yieldstyrke

Yieldstyrke, or yield strength, is the stress level at which a material begins to deform plastically and will no longer return to its original shape when the load is removed. It is a key material property used in engineering design to ensure components remain within the elastic, recoverable range under service loads.

In practice, many metals show a distinct yield point on a stress–strain curve, sometimes with an upper yield point followed by a lower yield point as plastic deformation begins. For metals without a clearly defined yield point, the 0.2% offset yield strength is used. This value represents the stress corresponding to 0.2 percent permanent (plastic) strain and provides a standardized way to specify yield strength.

Yield strength is typically determined from a uniaxial tensile test on a representative specimen. The result is reported in units of force per area, usually megapascals (MPa) or ksi. It is related to, but distinct from, other properties such as tensile strength (ultimate tensile strength) and elongation at break. Design often focuses on keeping service stresses below yield strength to avoid permanent deformation.

The yield strength of a material is influenced by composition, microstructure, and temperature. Grain size, work hardening, phase distribution, and heat treatment can raise or lower yield strength. Temperature, strain rate, and loading conditions also affect it. In polycrystalline metals, yield behavior is frequently analyzed using yield criteria such as Von Mises or Tresca.

Common examples vary widely: mild steel may have yield strengths around 250–400 MPa, while high-strength alloys can exceed 1000 MPa. Yield strength thus serves as a fundamental parameter for ensuring safety and performance in structural and mechanical components.