Fracture Behavior of a Fiber-Reinforced Titanium Matrix Composite with Open and Filled Holes at Room and Elevated Temperatures

Abstract

A study was conducted to experimentally investigate the fracture behavior of a titanium-based metal matrix composite (MMC), SCS-9/β21s, with open and filled holes subjected to static tensile load. This study was conducted with unidirectional, crossply, and quasi-isotropic laminates. Unnotched and notched coupons having specimen width to hole diameter ratio of six were tested at room temperature, 482°C, and 650°C. Pins of materials 7075-T6 and Mar-m-246 were employed for filled hole tests. Tests were also conducted on unnotched off-axis and angle-ply laminates to obtain experimental data for the shear strength and the shear modulus of the laminae. Material integrity, residual stresses, interfacial failures, failure progression, and notch sensitivity of the tested MMC were addressed. The molybdenum ribbon was found to have a significant impact on the damage initiation and integrity of the MMC. The release of residual stresses and interfacial failures gave rise to a bilinear stress strain curve in laminates with off-axis plies. Final laminate response was governed by nonlinear behavior caused by debonding and failure of 0° fibers in conjunction with plasticity in the matrix material. All fracture surfaces exhibited ductile fracture due to tensile overload. Matrix cracking occurred at loads higher than 80% of the failure strength in the 650°C tension specimens. Matrix cracking did not occur at the other temperatures. Laminates displayed notch sensitivity at room temperature and 482°C. At 650°C the laminates displayed much less notch sensitivity; or, the laminates were much less sensitive to the existence of the hole. The insertion of pins into open holes had negligible effect on the stiffness, strength, and failure progression of the laminates at room and elevated temperatures.