SYMPOSIA PAPER Published: 01 January 1985
STP36244S

Fatigue Behavior of Cyclically Softening and Hardening Steels Under Multiaxial Elastic-Plastic Deformation

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To investigate the fatigue behavior of cyclically softening and hardening steels under multiaxial elastic-plastic strains, axial strain, and shear strain controlled fatigue tests under constant amplitude loading were carried out. S-N curves under axial strain and torsional pure shear as well as under combined axial strain and shear, in and out of phase, were obtained for the cyclically softening high-strength steel 30Cr-Ni-Mo 8 (similar to AISI Type 4340) and the cyclically hardening stainless steel X 10Cr-Ni-Ti 18 9 (AISI Type 321) in the region of low-cycle fatigue.

For both steels, used for vessels, pipings, shafts, etc., the fatigue life to crack initiation (crack depth a < 1 mm) is reduced by an out-of-phase (δ = 90°) loading of the specimens in comparison to in-phase loading.

The decrease of fatigue life under out-of-phase strains is caused by the changing direction of principal strains resulting in an interaction of the deformations in all directions on the surface. This interaction is taken into account by the arithmetic mean value of shear amplitudes acting in all interference planes of the surface. The equivalent strain is then calculated according to the octahedral shear strain hypothesis. Using this equivalent strain and the S-N curve for uniaxial strain, the fatigue life under combined strain is predicted. For the multiaxial strain evaluation it is important to know if the local strains and shears are deformation or load controlled.

Author Information

Sonsino, CM
Stress Analysis and Strength Evaluation Department, Fraunhofer-Institut für Betriebsfestigkeit (LBF), Darmstadt, Federal Republic of Germany
Grubisic, V
Stress Analysis and Strength Evaluation Department, Fraunhofer-Institut für Betriebsfestigkeit (LBF), Darmstadt, Federal Republic of Germany
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Details
Developed by Committee: E08
Pages: 586–605
DOI: 10.1520/STP36244S
ISBN-EB: 978-0-8031-4921-2
ISBN-13: 978-0-8031-0444-0