Shear strain is a strain that acts parallel to the face of a material that it is acting on. Normal strain acts perpendicular to the face of that it is acting on. There are two ways to interpret shear strain: the average shear strain and the engineering shear strain. The variable used to denote average shear strain is ε while γ denotes engineering shear strain.

Consider an infinitesimal rectangle in the xy plane subject to shear strain. The rectangle becomes a parallelogram where α is the displacement from the y axis in the x direction and δ is the displacement from the x axis in the y direction. The average shear strain is

ε_xy = 0.5(α+δ) = ε_yx

Definition of engineering shear strain:

γ = ε_xy+ε_yx = 2ε_xy

γ = α+δ = θ-β

θ is the angle before deformation and β is the angle at that same point after deformation. Therefore γ describes the total deformation. Although, strain is dimensionless, it is usually stated as in./in. or some similar sign convention.

See also

• Shear modulus
• Moiré pattern (the Moiré effect can be used to measure strain)