Strain rate sensitivity of epoxy resin in tensile and shear loading

The mechanical response of E-862 and PR-520 resins is investigated in tensile and shear loadings. At both types of loading the resins are tested at strain rates of about 5 X 10(-5), 2, and 450-700 s(-1). In addition, dynamic shear modulus tests are carried out at various frequencies and temperatures, and tensile stress relaxation tests are conducted at room temperature. The results show that the toughened PR-520 resin can carry higher stresses than the untoughened E-862 resin. Strain rate has a significant effect on the response of both resins. In shear, both resins show a ductile response with maximum stress that is increasing with strain rate. In tension, a ductile response is observed at low strain rate (similar to 5 X 10(-5) s(-1)), and brittle response is observed at the medium and high strain rates (2 and 700 s(-1)). The hydrostatic component of the stress in the tensile tests causes premature failure in the E-862 resin. Localized deformation develops in the PR-520 resin when loaded in shear. An internal state variable constitutive model is proposed for modeling the response of the resins. The model includes a state variable that accounts for the effect of the hydrostatic component of the stress on the deformation.