Numerical analysis of the reinforcement effect of a strain gage applied to a soft material

Abstract The reinforcement effect of a strain gage bonded to a low modulus material is described by a simple equation that relates the assigned, calibrated gage factor, the actual gage factor at which the strain indicator may be set to record the actual strain in the test piece outside of the neighborhood of the gage site, and a certain parameter that depends on the physical and geometrical properties of the strain gage and the specimen. It is found that the interaction effects due to reinforcement by the strain gage can be reduced substantially by increasing the length or by decreasing the thickness of the gage, whereas decreasing the thickness of the adhesive layer has but little positive effect. It is shown that appreciable error may be introduced into the data if the reinforcement effect of a strain gage bonded to a soft material is neglected in experimental stress analysis studies.