Effects of radiation-induced cross-linking of mechanical properties of boron--epoxy composites

The paper attempts to correlate the increase in elastic modulus and strength of epoxy matrix systems due to radiation exposure with the prediction of micromechanical theories which suggest that filament-controlled strengths should increase with increase in matrix modulus. Matrix strength and modulus were determined as a function of gamma-ray doses from four-point bending of specimens with fibers aligned perpendicular to the beam axis. Bond strengths were obtained from short-beam shear tests, and filament-controlled strengths and moduli were obtained from three-point bending of specimens with fibers aligned along the beam axis. It is shown that transverse flexural strength and modulus increase with increasing gamma dose until the apparent maximum cross-linking is obtained and then decrease thereafter. In contrast with the micromechanical theories, the longitudinal flexural strength and modulus are unchanged in the region of gamma dose in which matrix properties are enhanced but begin to increase at higher doses where matrix properties are significantly degraded. Thus, any functional relationship between matrix-controlled and filament-controlled properties is found in the matrix-degradation region at high exposure doses and is an inverse relationship