Effects of fiber bridging and fiber fracture on fatigue cracking in a titanium-matrix composite
- Purdue Univ., West Lafayette, IN (United States). School of Mechanical Engineering
Continuous-fiber titanium-matrix composites (TMCs) are being considered for a number of aerospace structures where high specific strength and stiffness are required at elevated temperatures. Potential applications include advanced gas turbine components and hypersonic aircraft structures. To design lightweight, damage-tolerant TMC structures, an understanding of fatigue crack propagation in TMCs is necessary. Here, constant amplitude fatigue tests were performed on [0]{sub 4} and [0/90]{sub s}SCS-6/TIMETAL 21S titanium-matrix composite specimens to study fiber bridging of matrix fatigue cracks. Crack length was monitored throughout the tests, and displacements near the crack surface were measured periodically by placing an Elber gage (1.5-mm gage length point extensometer) across the crack at a number of positions. Specimens were removed prior to failure and mechanically polished to the first layer of fibers and the extent of fiber bridging observed. While some cracks were fully bridged, other cracks contained broken fibers among the intact, bridging fibers. A model has been developed to study the mechanics of a cracked unidirectional composite with any combination of intact and broken fibers in the wake of the matrix crack. Displacements near the crack surface predicted by the model agree with the Elber gage measurements for cracks that were fully bridged. Predictions were also performed for bridged cracks with discrete fiber breaks in the crack wake based on the geometry observed after polishing with good correlation between the predictions and the experimental measurements.
- OSTI ID:
- 566497
- Report Number(s):
- CONF-950569--
- Country of Publication:
- United States
- Language:
- English
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