Observations of interfacial damage in the fiber bridged zone of a titanium matrix composite
- Univ. of Dayton Research Inst., OH (United States)
This paper presents the results of both nondestructive and destructive evaluations performed after a fatigue crack growth test run under out-of-phase thermomechanical fatigue (TMF) conditions. Post test evaluation indicates that the damage along the fiber-matrix interface in the fiber bridged zone in the TMF specimen is of much greater scale than the slip region predicted by the shear lag models in their current form. To evaluate the environmental attack on the fiber-matrix interfacial region, a thermomechanical fatigue crack growth test was performed on a single edge notch specimen with clamped ends (15). The specimen was a 4-ply, unidirectional, fiber reinforced titanium with a fiber volume fraction [approx] 36 %. The matrix material was Ti-15Mo-3Nb-3Al-0.2Si (wt %), and the reinforcing fibers were silicon carbide, SCS-6. During the test, the specimen developed two matrix cracks from the corners of the diamond-saw notch. The cracks then propagated perpendicular to the fiber and load direction. Crack length was monitored using electric potential drop (EDP) over the life of the specimen. The crack length was also verified through periodic optical measurements of the surface cracks. The crack growth rate increased initially as the matrix cracks grew away from the notch. As the matrix cracks continued across the specimen the crack growth rate began to decrease. This type of behavior in composite crack growth is indicative of a developing fiber bridged zone in the wake of the matrix crack. Since the bridging zone continued to develop across the entire matrix crack region, the crack growth rate further diminished to a point that only small crack extensions (0.1 mm) occurred over long periods (6 days). Upon reaching this slow growth rate, the test was terminated prior to fracture after the specimen was subjected to 14,612 thermomechanical cycles over a period of 36 days.
- OSTI ID:
- 5985382
- Journal Information:
- Scripta Metallurgica et Materialia; (United States), Journal Name: Scripta Metallurgica et Materialia; (United States) Vol. 29:6; ISSN SCRMEX; ISSN 0956-716X
- Country of Publication:
- United States
- Language:
- English
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