Effect of orientation of two-dimensional filler on dynamic mechanical properties of cured epoxy resin



Dynamic mechanical properties of cured epoxy resin filled with mica flake, as two-dimensional filler, were investigated over the temperature range from room temperature to 200°C. Two series of composite specimens were examined. One is series RM, containing ill-oriented mica flakes, and another is RMB, containing mica flakes oriented in the direction parallel to the specimen surface. Both tensile and shear moduli for RMB series were determined by dynamic mechanical experiments. The tensile modulus for RMB series was always higher than that for RM series over the whole temperature range. The shear modulus for RMB series was low, compared with that of the tensile modulus in the rubbery state. The behavior of the modulus reinforcement, observed both in the glassy and rubbery states, was compared with recently proposed theories of Wu and Padawer and Beecher. In the glassy state, the tensile modulus of RM series follows Wu's theory, while that of the RMB series agrees with Padawer and Beecher's theory. In the rubbery state, the tensile modulus of each series cannot be well explained by either theory. It was proposed that the tensile stress applied to the specimen was converted to shear stress in a thin resinous layer sandwiched by two mica flakes. The modulus behavior of the RMB series can be fully explained by this model.