FRACTURE-BEHAVIOR OF A FIBER-REINFORCED TITANIUM MATRIX COMPOSITE WITH OPEN AND FILLED HOLES AT ROOM AND ELEVATED-TEMPERATURES

A study was conducted to experimentally investigate the fracture behav ior of a titanium-based metal matrix composite (MMC), SCS-9/beta21s, w ith open and filled holes subjected to static tensile load. This study was conducted with unidirectional, cross-ply, and quasi-isotropic lam inates. Unnotched and notched coupons having specimen width to hole di ameter ratio of six were tested at room temperature, 482-degrees-C, an d 650-degrees-C. Pins of materials 7075-T6 and Mar-m-246 were employed for filled hole tests. Tests were also conducted on unnotched off-axi s and angle-ply laminates to obtain experimental data for the shear st rength and the shear modulus of the laminae. Material integrity, resid ual stresses, interfacial failures, failure progression, and notch sen sitivity of the tested MMC were addressed. The molybdenum ribbon was f ound to have a significant impact on the damage initiation and integri ty of the MMC. The release of residual stresses and interfacial failur es gave rise to a bilinear stress strain curve in laminates with off-a xis plies. Final laminate response was governed by nonlinear behavior caused by debonding and failure of 0-degrees fibers in conjunction wit h plasticity in the matrix material. All fracture surfaces exhibited d uctile fracture due to tensile overload. Matrix cracking occurred at l oads higher than 80% of the failure strength in the 650-degrees-C tens ion specimens. Matrix cracking did not occur at the other temperatures . Laminates displayed notch sensitivity at room temperature and 482-de grees-C. At 650-degrees-C the laminates displayed much less notch sens itivity; or, the laminates were much less sensitive to the existence o f the hole. The insertion of pins into open holes had negligible effec t on the stiffness, strength, and failure progression of the laminates at room and elevated temperatures.