Crack closure is held to be responsible for very low fatigue crack growth rates in many alloys such as Al-Li 2090 T8E41, and early crack face contact during unloading or prolonged contact during loading seems to reduce the driving “force” for crack extension. High resolution x-ray computed tomography (i.e., microtomography) allows one to image the entire volumes of samples and to quantify opening as a function of applied load over the entire crack surface. Crack closure results are reported for a fatigue crack grown under load ratio R=0.1 in a compact tension sample of Al-Li 2090 T8E41; the crack was free to choose its path unconstrained by side-grooves which are normally used to suppress crack deflection. The inter-relationship between crack path, crack face contact and applied load level are discussed.
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The US portion of this research was supported by the US Office of Naval Research through grants N00014-94-1-0306, -94-1-0726 and -97-1-0557 and the UK portion through EPSRC Grant GR/J25628. We thank R. Brown of MPRL and M.A. Langøy for their help with fatigue crack propagation and J.D. Haase, D.J. Ryan and A. Guvenilir for help with computers.
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Morano, R., Stock, S., Davis, G. et al. X-Ray Microtomography of Fatigue Crack Closure as a Function of Applied Load in Al-Li 2090 T8E41 Samples. MRS Online Proceedings Library 591, 56–60 (1999). https://doi.org/10.1557/PROC-591-31