SYMPOSIA PAPER Published: 01 January 1976
STP33369S

A Model for Fatigue Crack Growth Delay Under Two-Level Block Loads

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After reviewing previous attempts to quantify delay, a composite stress intensity parameter, (Kℓmax/Khmax) ∙ ΔK; proposed to correlate the number of delay cycles in simple two-level variable-load amplitude tests for various combinations of stress levels. Its application is restricted in the present investigation to room temperature tests in an air environment. Delay (cycles) is defined herein as the period of apparent zero crack growth after the overload, and the stress intensity factors, Kℓmax and Khmax refer to the stress intensities accompanying the lower and higher load levels, respectively. It is hypothesized on the basis of experimental observations that material under different two-level block loading sequences, but having equal values of the parameter, will experience the same delay.

Good correlations for data on aluminum alloys, titanium alloys, and carbon steel taken from the work of several investigators are obtained using the parameter. An empirical model relating the delay to a power function of the parameter is suggested. Limitations of the model are pointed out and discussed. The engineering significances of the parameter with respect to the determination of crack propagation life and crack arrest conditions are discussed.

Author Information

Adetifa, OA
University of Waterloo, Waterloo, Ontario, Canada
Gowda, CVB
Westinghouse Corp., Madison, Pa.
Topper, TH
University of Waterloo, Waterloo, Ontario, Canada
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Developed by Committee: E08
Pages: 142–156
DOI: 10.1520/STP33369S
ISBN-EB: 978-0-8031-4672-3
ISBN-13: 978-0-8031-0344-3