Fatigue Crack Growth Thresholds of Deflected Mixed-Mode Cracks in PWA1484

[+] Author and Article Information
K. S. Chan, J. Feiger, Y.-D. Lee

Southwest Research Institute®, San Antonio, TX 78238

R. John

Air Force Research Laboratory, Materials and Manufacturing Directorate (AFRL/MLLMN), Wright-Patterson AFB, Dayton, OH 45433

S. J. Hudak

Southwest Research Institute, San Antonio, TX 78238

J. Eng. Mater. Technol 127(1), 2-7 (Feb 22, 2005) (6 pages) doi:10.1115/1.1836765 History: Received January 01, 2003; Revised September 14, 2004; Online February 22, 2005
Copyright © 2005 by ASME
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Fatigue crack path of [111]/[011̄] oriented PWA1484 during Mode I loading and mixed Mode I and II loading at a 45 deg phase angle. Mode I fatigue occurred on the (111) plane. The mixed-mode crack propagated self-similarly on (111) under mixed Mode I and II initially, but it subsequently deflected on a TPNC plane
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FRANC2D/L KI and KII solutions obtained using the actual path for Specimen SC-16-90 tested under pure Mode II loading
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A summary of da/dN data vs ΔKI or ΔKeq for 〈001〉/〈011〉 oriented PWA1484 (SC-5) tested under Mode I or mixed Mode I and II loading at ϕ=45 deg
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A comparison of da/dN curves for pure Mode I cracks (SC-5, SC-6, SC-7, and SC-8) against local Mode I deflection cracks (SC-9 and SC-11) with the same 〈001〉/〈110〉 crack orientation
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A comparison of da/dN curves for pure Mode I cracks, a Mode II self-similar crack, and local Mode I deflected cracks with the approximately same 〈111〉/〈112̄〉 crack orientation
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Fitting of P&W threshold model to FCG threshold data of PWA1484 for the 〈001〉/〈010〉 orientation. The angle β corresponds to the crack deflection angle or the secondary orientation
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Fitting of the P&W threshold model to FCG threshold data of PWA1484 for the 〈001〉/〈110〉 orientation
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FCG data of a Mode I TPNC crack compared against that of a Mode II crystallographic (111) crack in 〈111〉/〈011̄〉 oriented PWA1484. At ΔKI>ΔKt, the crystallographic (111) crack propagates at a high FCG rate than a TPNC crack at identical ΔKeq values. The reverse is true for ΔKI<ΔKt
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Calculated and measured crack deflection angles as a function of 90-ϕ, when ϕ=arctan(ΔKII/ΔKI) is the mode-mixity phase angle. Deviation of experimental data from the MTS criterion is caused by orientation dependence in the Mode I threshold. The current model treats threshold anisotropy, which is fitted to the experiment. The calculation shows how a small threshold anisotropy can cause a relatively large deviation in the crack deflection angle




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