ISSN: 1945-7553
CODEN: JTEVAB
Page Count: 14

Fatigue Crack Propagation Threshold: What Is It and How Is It Measured?

Marci, G
Institute for Materials Research, DLR-German Aerospace Research Establishment, Cologne,

(Received 5 February 1997; accepted 7 November 1997)

Abstract

The present understanding of a “fatigue crack propagation threshold” implies a nonpropagation condition of a fatigue crack and in addition some property usable for design (similar to the “fatigue strength” in Wöhler-type fatigue). The first task is the definition of a nonpropagation condition, to be denoted as ΔK_th. In the next step, a “property usable for FCP design” is defined which is a nonpropagation condition characterized as the largest amplitude ΔK which does not produce fatigue crack propagation rates larger than 10⁻⁷ mm/cycle under any cyclic loading condition. The parameter so defined is termed the threshold and denoted as ΔK_T. Every ΔK_T is a nonpropagation condition, but not every nonpropagation is a threshold value ΔK_T. The existence of such a parameter ΔK_T has to be proven by special, extensive tests, which are presented with the respective results. Once the proof related to ΔK_T has been furnished, measurement of ΔK_T is done by the simplest technique available. Nonpropagation conditions ΔK_T and threshold ΔK_T data for Al- and Ti-alloys are presented. Furthermore, test procedures and specimen preparations are outlined.

Keywords:
fatigue crack propagation threshold ΔKT, nonpropagation condition ΔKth, material property

Paper ID: JTE11995J
DOI: 10.1520/JTE11995J
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