Shear fracture of C/C composites with variable stacking sequence

Cross-ply laminated carbon-carbon composites with changing ply ratio of 0 degrees and 90 degrees were fractured under shear using several test methods. In these tests, special attention was placed on the understanding of the damage mechanisms. The +/- 45 degrees off-axis shear test yielded the most precise shear stress-strain relation and was recommended to measure the shear modulus G(12). On thhe other hand, for shear strength measurement, the Iosipescu test was superior. The non-linearity in the shear stress-strain curve was found to be solely due to matrix cracking, while the peak shear stress was determined by fibre failure. In order to measure the shear strength by the Iosipescu test, two fracture planes normal and parallel to the loading axes have to be considered. The shear strength increased linearly with fibre volume fraction normal to the corresponding plane. The overall highest shear strength was obtained for the (0/90)(n) laminate. (C) 2001 Elsevier Science Ltd. All rights reserved.