SYMPOSIA PAPER Published: 01 January 1988
STP24484S

Application of Small Specimen Crack Growth Data to Engineering Components at High Temperature: A Review

Source

This review considers the standard low-cycle fatigue (LCF) specimen, the area of the component it represents, the empirical crack growth relations measured on that specimen, and their ranges of validity. It also presents some recent observations on the effects of crack shape, strain rate, weld material, notches, and aging upon cyclic propagation rates at high temperature.

In applying LCF growth results to estimate crack behavior in service, size effects must be considered. From crack growth tests at constant plastic strain on LCF specimens of differing width, it is shown in both cases that the cracks accelerated, then decelerated after a critical depth which occurred sooner in the smaller specimens. Accompanying variations in the shape of the hysteresis loop and crack closure effects (all of which have implications for service loading) are also reported.

Beyond a certain depth in the specimen, crack growth is no longer describable by the bulk plastic strain, so other parameters (cyclic J integral and equivalent stress intensity) are compared and their ranges of validity discussed.

The survey next considers a constant-load test where, despite equal tension and compression ranges, ratchetting of the specimen occurred, leading to quite different conditions for crack closure. The crack growth data nevertheless agree with LCF data when the correct stress range is taken into account.

Finally, a high temperature lifetime assessment route is briefly described, where the user is permitted to enter a permissible defect path which utilizes many of the experimental short crack data mentioned in this review.

Author Information

Skelton, RP
Technology Planning & Research Division, Central Electricity Generating Board, Central Electricity Research Laboratories, Leatherhead, Surrey, England
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Details
Developed by Committee: E08
Pages: 209–235
DOI: 10.1520/STP24484S
ISBN-EB: 978-0-8031-5035-5
ISBN-13: 978-0-8031-0944-5