THE MICROMECHANICS OF FATIGUE CRACK-GROWTH AT 25-DEGREES-C IN TI-6AL-4V REINFORCED WITH SCS-6 FIBERS

Micromechanics parameters for fatigue cracks growing perpendicular to fibers were measured for the center-notched specimen geometry. Fiber displacements, measured through small port holes in the matrix made by electropolishing, were used to determine fiber stresses, which ranged from 1.1 to 4 GPa. Crack opening displacements at maximum load and residual crack opening displacements at minimum load were measured. Matrix was removed along the crack flanks after completion of the tests to reveal the extent and nature of the fiber damage. Analyses were made of these parameters, and it was found possible to link the extent of fiber debonding to residual COD and the shear stress for fiber sliding to COD. Measured experimental parameters were used to compute crack growth rates using a well-known fracture mechanics model for fiber bridging tailored to these experiments.