NOTCH-SENSITIVITY AND SHEAR BANDS IN BRITTLE-MATRIX COMPOSITES

Matrix cracking, fiber breaking and interface sliding cause nonlinear deformation in fiber-reinforced brittle matrix composites. When a notc hed sample is loaded in tension, the nonlinear deformation usually loc alizes around the notch, spreads the stress in the ligament more evenl y, and thereby leads to a higher fracture load. We simulate the interp lay of two deformation mechanisms: a tensile band ahead of, and shear bands perpendicular to, a notch. The shear deformation evens out the s tress distribution in the tensile band, and the strength of the tensil e band sets the extent of the shear deformation. Each band is simulate d by a traction-deformation law. The work of fracture is computed from a small-scale inelastic problem, and the fracture loads of notched sa mples from a large-scale inelastic problem. Several important conclusi ons emerge from the simulation. First, weak shear bands can substantia lly increase the work of fracture. Second, the fracture loads of notch ed samples are well correlated with the unnotched strength, work of fr acture and notch size, by a formula independent of the shear band desc ription. The results of the simulation are used to explain the availab le experimental data and to suggest an evaluation procedure for notch- sensitivity.