---
term: "Stress–Strain Curve"
category: "material-testing"
shortDefinition: "The graph of stress versus strain in a tensile or compression test; engineering curves use original area A0, while true curves use instantaneous area and reveal continued hardening after necking."
formula: "σeng = F/A0 ,  εeng = ΔL/L0"
relatedStandards: ["ISO 6892-1","ASTM E8"]
url: "https://vectorbtc.com.tr/resources/glossary/stress-strain-curve/"
---

A **stress–strain curve** is the fundamental record of how a material resists deformation from elastic loading through yielding, strain hardening, necking, and fracture. The **engineering curve**—force divided by **original area**—is convenient for specification testing and drops after UTS when necking reduces load despite rising true stress in the neck.

The initial **linear elastic** segment yields **Young’s modulus** and proportional limit. **Yielding** marks the onset of measurable plasticity; proof strengths like **Rp0.2** operationalize yield for gradual-yielding materials. The **strain-hardening** region shows increasing flow stress as dislocation density rises.

**Necking** begins when the strain-hardening rate can no longer compensate for area loss under constant engineering stress definitions. **Toughness** (energy to fracture) is the area under the engineering curve up to fracture when plotted in stress–strain space with appropriate units.

Digital acquisition at adequate sampling rate captures **serrations** (Portevin–Le Chatelier) in some alloys and helps detect **instrumentation anomalies** such as slip or resonance.