Failure Characteristics of SCS-6/Ti-24Al-11Nb Composite with a Circular Hole atRoom and Elevated Temperatures

摘要

Off-axis loading of eight ply, unidirectional specimens with and without acircular hole determined the ultimate tensile strength of SCS-6/Ti-24Al-11Nb composite at temperatures of 25 degrees C and 650 degrees C and fiber orientations of 0 degrees, 15 degrees, 45 degrees. Longitudinal moduli of the tested orientations compared closely to the rule of mixtures calculated values, and strengths compared closely to those predicted by the Tsai-Wu failure theory. The small diameter hole does not act as a stress concentrator, but merely reduces the material's strength in proportion to area loss. This result differs from those predicted by linear finite element analysis and orthotropic stress concentration theory. Radiography, used to detect damage prior to failure, showed no fiber breakage nor matrix cracking. Microscopic examination of the fracture surfaces indicates a weak fiber/matrix interface bond at both room and elevated temperatures. Brittle fracture of fibers and matrix with little fiber pull out occurs at room temperature, while brittle fiber fracture and ductile matrix fracture with greater fiber pull out occurs at elevated temperatures.