SYMPOSIA PAPER Published: 01 January 1976
STP33378S

Prediction of Fatigue Crack Growth under Irregular Loading

Source

Fatigue crack growth under irregular loading is calculated from constant-amplitude test data. The results of such calculations are compared with measurements of crack growth in modified compact tension specimens made of two commonly used structural steels and subjected to three different irregular load histories, each applied at several load levels.

Two crack growth rate relations are utilized: I, the Forman relation, and II, a relation based on an effective stress intensity range concept. The Forman relation is used with two different methods of “counting” load ranges, that is, crack growth is calculated: (a) for all rising tensile load ranges as they occur in the load history and (b) for the load history condensed by a method which forms overall ranges and includes only the top decile of all rising tensile ranges. Crack growth rate Relation II is used only with counting Method a. The three resulting prediction methods are designated Ia, Ib, and II. Methods Ia and Ib disregard sequence effects, while Method II includes them.

Predictions of crack growth using Methods Ia and Ib agree with average test lives to within a factor of two in nearly all cases, with the exception of those instances where large compressive loads cause gross yielding and accelerated growth. Predictions based on Method II are superior to those for Ia and Ib when such gross yielding occurs and are comparably good for the other cases investigated here.

Author Information

Nelson, DV
General Electric Co., Sunnyvale, Calif.
Fuchs, HO
Stanford University, Stanford, Calif.
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Details
Developed by Committee: E08
Pages: 267–286
DOI: 10.1520/STP33378S
ISBN-EB: 978-0-8031-4672-3
ISBN-13: 978-0-8031-0344-3