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Volume 15, Issue 3 (September 1993)
Application of Fiber Bridging Models to Fatigue Crack Growth in Unidirectional Titanium Matrix Composites
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Several fiber bridging models were reviewed and applied in this research to study the matrix fatigue crack growth behavior in center notched 8 SCS-6/Ti-15-3 and 4 SCS-6/Ti-6AI-4V titanium matrix composites (TMCs). Observations revealed that fatigue damage consisted primarily of matrix cracks and fiber-matrix interfacial failure in the unidirectional TMC. Fiber-matrix interface failure included fracture of the brittle reaction zone and cracking between the two carbon-rich fiber coatings. Intact fibers in the wake of the matrix cracks reduce the stress intensity factor range. Thus, an applied stress intensity factor range () is inappropriate to characterize matrix crack growth behavior. Fiber bridging models were used to determine the matrix stress intensity factor range in the unidirectional TMC. In these models, the fibers in the wake of the crack are idealized as a closure pressure. An unknown constant frictional shear stress is assumed to act along the debond or slip length of the bridging fibers. In this study, the frictional shear stress was used as a curve fitting parameter to available data (crack growth data, crack opening displacement (COD) data, and debond length data). Large variations in the frictional shear stress required to fit the experimental data indicate that the fiber bridging models in their present form lack predictive capabilities. However, these models provide an efficient and relatively simple engineering method for conducting parametric studies of the matrix crack growth behavior based on constituent properties.
Resident research associate, National Research Council, NASA Langley Research Center, Hampton, VA
Senior scientist, NASA Langley Research Center, Hampton, VA
Stock #: CTR10376J
Title Application of Fiber Bridging Models to Fatigue Crack Growth in Unidirectional Titanium Matrix Composites