Local Crack-Tip Strain Concept for Fatigue Crack Initiation and Propagation

[+] Author and Article Information
Heihachi Shimada, Yasubumi Furuya

Department of Metal Processing and Mechanical Metallurgy, Tohoku University, Sendai 980, Japan

J. Eng. Mater. Technol 109(2), 101-106 (Apr 01, 1987) (6 pages) doi:10.1115/1.3225947 History: Received April 29, 1985; Online September 15, 2009


The existence of the unified local strain field where we can substantially combine the two fatigue stages, crack initiation and propagation, was experimentally confirmed. Using the fine-grid-method, the changes of local notch-root or crack-tip strain and these histories were investigated until the small elemental block of material was broken by crack initiation and propagation. It became clear that the crack-tip strain behavior and its fracture process showed the similarity with local strain damage accumulation on crack initiation process. Especially, when the local strain history in the “elemental size, ρ*” adjacent to the crack-tip was taken into account, very good agreement of two stages could be obtained, ρ* depended on the kind of material. Based on this result, we have proposed a new idea termed “local crack-tip strain concept” that has the possibility for more simple, one parameter approach for future fatigue life analysis. It qualitatively differs from the currently used macroscopic, two parameters approach by combining the gross-strain (Δεtotal ) fatigue life curve and fracture mechanics parameter (ΔK).

Copyright © 1987 by ASME
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