Shear Modulus of Epoxy Resin Under Compression

The matrix shear modulus of a unidirectionally fiber-reinforced composite material is one of the factors affecting its compressive shear mode fracture and it depends on the compressive stress.

In order to investigate the effect of compressive stress on the shear modulus, a special form of test specimen was designed such that compressive and torsional loads could be applied simultaneously. Test specimens were molded from epoxy resin for structural use.

Under every constant compressive load, specimens were subjected to torsional moment, and the corresponding strains were measured from which shear strains were calculated. Then the shear modulus was obtained as a function of compressive stress.

It was found that the shear modulus of epoxy resin decreased with increasing compressive stress in the range beyond the proportional limit, and the order of magnitude of its reduction was found.