---
term: "Yield Strength"
category: "material-testing"
shortDefinition: "The stress at which a material begins to deform plastically under monotonic loading; metals are often reported as Rp0.2 using the 0.2% plastic strain offset on the engineering stress–strain curve."
formula: "Rp0.2 from σ at εp = 0.2%"
relatedStandards: ["ISO 6892-1","ASTM E8"]
url: "https://vectorbtc.com.tr/resources/glossary/yield-strength/"
---

**Yield strength** separates **elastic** deformation (recoverable on unloading) from **plastic** flow (permanent strain). In low-carbon steels, a distinct **upper and lower yield point** may appear due to dislocation unlocking (Lüders bands); other alloys show gradual yielding without a sharp knee.

When a sharp yield is absent, international standards specify **proof strength** such as **Rp0.2**: a line parallel to the elastic portion, offset by **0.2% plastic strain**, intersects the curve to define the proof stress. Rp0.1 and other offsets are used for spring steels or aerospace alloys requiring tighter elastic limits.

Accurate yield reporting requires **extensometry** aligned with the gauge section, correction for machine compliance at low strains, and controlled strain rates because many metals are strain-rate sensitive. Misalignment or grip slippage exaggerates apparent yielding.

Yield strength governs **elastic design limits** for static components, but designers must also check buckling, fatigue, and creep depending on service temperature and load history. For anisotropic sheet metals, tensile yield may differ with rolling direction; multiple orientations should be tested.