Shear testing involves an applied force or load that acts in a direction parallel to the plane in which the load is applied. Shear loads act differently than, say, tensile or compressive loads that act normal or perpendicular to the axis of loading. Direct shear and torsional shear are important forces used to determine shear properties. Direct or torsional loading depends on the forces a material is expected to be subjected to during service.
Before testing, the specimen is accurately measured using proper instruments and the gauge length is marked. Proper precautions should be taken to centre the specimen in the machine or fixture. The grippers are tightened to insure against slippage, yet not so tight as to cause deformations which would affect test results.
Relationship of shear stress to shear strain:
τ = Gγ, where: γ = tgθ = Δy/Δz0
G is Shear Modulus (Units: N/m2)
For isotropic material:
E = 2G (1+ν) ν G ˜ 0.4 E