The effect of processing conditions on the compressive and shear strength of 2-D carbon-carbon laminates

Abstract

An experimental study was performed to determine the effect of processing conditions on the failure mechanisms and strength of 2-D carbon-carbon laminates under uniaxial compression and shear loading. Specifically, the mechanical properties are related to the size and density of material discontinuities which, in turn, depend upon the numbers of matrix impregnation and carbonization cycles, and subsequent heat treatments. Five samples with different numbers of carbonization and heat-treatment cycles were considered; all had the same 8 harness-fiber-weave architecture and 0 °0 ° layup. Compressive strengths ranging from 130 to 270 MPa were obtained. All samples failed through the formation of a diagonal shear fault across the laminate which, on the local scale, consisted of bundle kinks (at crimps) interspersed with interply delaminations. Failure mechanisms under both interlaminar and in-plane shear loading were also determined for all the samples by using a direct shear setup. Interlaminar shear strengths (ILSS) ranged from 5 to 8 MPa, and in-plane shear strengths were in the range of 15 to 28 MPa. The failure under ILSS loading was through the formation of a planar shear fault following the crimp boundaries, whereas under in-plane shear, the failure was through interply delaminations on sample faces normal to the plies.