SYMPOSIA PAPER Published: 01 January 1988

Fatigue Damage Accumulation During Cycles of Nonproportional Straining


Nonproportional biaxial fatigue tests were performed using cruciform-shaped specimens of AISI 316 stainless steel at room temperature, in order to study the effect of nonproportional straining on crack growth rate. While the fluctuating stress applied perpendicular to the crack was common to all the tests, including the uniaxial test, the stress parallel to the crack was applied for only half the former period and only on either the raising or the downward part of the cycle.

The crack growth rate of the specimen subjected to uniaxial loading was more than five times faster than the growth rate of the cracks in the biaxial specimen, which is contrary to the reduced endurance observed for nonproportional loading of 1% chromium-molybdenumvanadium steel in tension-torsion.

Transmission electron microscopy observations of regions next to the fracture surface showed a very different dislocation substructure relating to uniaxial and biaxial loading. The degree of strain hardening in both conditions was estimated by employing dislocation models suitable for each case. If a “slipping off” mechanism for crack propagation is adopted, then the difference in crack growth rate experienced by the biaxial specimens can be explained by considering the magnitude of the strength of the slipband in each case.

Author Information

de los Rios, ER
University of Sheffield, Sheffield, U.K.
Brown, MW
University of Sheffield, Sheffield, U.K.
Miller, KJ
University of Sheffield, Sheffield, U.K.
Pei, HX
Academia Sinica in Shenyang, China
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Developed by Committee: E08
Pages: 194–213
DOI: 10.1520/STP23217S
ISBN-EB: 978-0-8031-5034-8
ISBN-13: 978-0-8031-0925-4