Strain (Mechanical Design)

Strain is a measure of the deformation of a material relative to its original size when subjected to an external force. It quantifies how much a material stretches, compresses, or distorts under stress. Strain is a dimensionless quantity, as it represents a ratio of change in length to original length. The general formula for strain is:

strain = change in length / original length or ε = ΔL / L₀,

where ε (epsilon) is the strain, ΔL is the change in length, and L₀ is the original length of the material before deformation.

Strain is classified into two main types: elastic strain and plastic strain.

  • Elastic strain occurs when deformation is temporary and the material returns to its original shape upon removal of the applied force. This follows Hooke’s Law, which states that within the elastic limit, strain is proportional to stress (σ = E × ε), where E is the modulus of elasticity.
  • Plastic strain occurs when the material is permanently deformed after exceeding its yield point. In this case, even when the force is removed, the material does not return to its original dimensions.