Fracture Micromechanics of Intermetallic and Ceramic Matrix Continuous Fiber Composites
1991
Davidson, D. L.
Micromechanics parameters for fatigue cracks growing perpendicular to fibers were 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 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 debonding, estimated at 245 MPa, to COD. Measured experimental parameters were used to compute crack growth rates using a wall known fracture mechanics model for fiber bridging tailored to these experiments. The potential for microstructural manipulation to yield further increases in fatigue crack growth resistance for the metals and alloys currently being used in gas turbine construction is small. Studies of fatigue crack growth through aluminum, titanium and superalloys have shown that there are many similarities in the mechanisms of crack growth and the crack tip micromechanics for these materials. Conversely, composite materials reinforced with continuous strong fibers offer the promise of drastic increases in fatigue crack growth resistance.
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