Fatigue crack growth through |
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Authors: | D L Davidson J B Campbell |
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Affiliation: | (1) Southwest Research Institute, 78228 San Antonio, TX;(2) Southwest Research Institute, 78228 San Antonio, TX |
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Abstract: | Fatigue cracks were grown at 25 °C and 800 °C in a titanium aluminide alloy heat-treated to give a γ+ α
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lamellar microstructure. These lamellae, having widths of =0.5 to 2 μm, were in colonies approximately 1.2 mm across. Crack
growth was observed and photographed under high resolution conditions using a loading and heating cyclic stage for the scanning
electron microscope. Stereoimaging was used to measure displacements around crack tips, from which crack opening displacements
and strains were derived. Cracks were found to grow about 10 times faster at 25 °C than at 800 °C, and the threshold stress
intensity for fatigue crack growth was lower at 25 °C. Strain to fracture the lamellae was determined as ≈0.08, while fatigue
crack tips could sustain up to 0.3 strain at 25 °C and 0.5 strain at 800 °C. The lamellar micro- structure was found to have
a strong influence on crack tip behavior. |
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Keywords: | |
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