# Test and Measurement World

## Test and Measurement World Terminology Section

One Stop For Your Test and Measurement Need

## stress vs strain | difference between stress and strain

This page compares stress vs strain and mentions difference between stress and strain.

Introduction: A metal bar is shown in the figure-1. Let us understand tension and compression in the metal bar.
Tension: A bar of metal is subjected to a force (T) which will elongate its dimension along the long axis (e.g. in axial direction).

Compression:It is the force which acts in opposite direction and shortens the length. ### Stress

• It is the force per unit area.
• It is expressed by following equation. σa = T/A (N/m2)
• It is also expressed in units of Pascal or Pa. • Stress is internal resistance to external force.

### Strain

• The fractional change in the length is known as strain.
• It is expressed by following equation. εa = dL/L (µm/m)
• Stress is displacement and deformation due to external force.

➤Stress is linearly related to strain for elastic materials. -εa = σa/Ey = (T/A)/Ey ,
➤Where, Ey = constant, T = External Force, A = Cross area Hooke's law:
The law states that within the limit of elasticity, the stress induced (σ) in the solid due to some external force (F) is always in proportion with the strain (ε). The figure-2 depicts relationship between stress and strain.
➤ σ ∝ ε
➤ σ = E* ε
➤ E = σ/ε
Where, E = Young's modulus or proportionality limit.