Stress–strain curve

curve which represents the deformation caused by a force

A stress-strain curve is a graph that is used to describe the relationship between stress and strain of a specific material; with stress being captured on the y-axis and the strain on the x-axis. Stress is the amount of force needed to change the material's shape: in this case, to make it longer. Strain is a measurement of how much the shape changes.

Stress-strain curve By Nicoguaro - Own work, CC BY 4.0,

This graph is usually made by testing a material with a tensile test. The test consists of a force, of varying amount, is used to pull the sample apart at a constant rate until it breaks. This graph is used to show important characteristics of a material such as the yield strength, ultimate strength, fracture point, strain hardening, necking and Young's modulus.

  • Yield strength - point after which permanent, un-fixable damage occurs (think of overstretching a rubber band and now it's larger than it was originally)
  • Ultimate strength - strongest recorded measurement of the material a.k.a maximum stress
  • Fracture point - point at which the material breaks
  • Strain hardening - area where the material becomes stronger, but is undergoing permanent, un-fixable damage
  • Necking - area where the material is past it's ultimate strength and now the material is becoming smaller in area at the location where it breaks
  • Young's modulus - the slope of the stress-strain curve before the yield strength point, used to describe "plastic" deformation a.k.a. damage to the material that can be completely reversed (think of stretching a rubber band and returning it back to place and it's back to it's original size)