Page 180 - Biaxial Multiaxial Fatigue and Fracture

BiaxiallMultiaxial Fatigue and Fracture
Andrea Carpinteri, Manuel de Freitas and Andrea Spagnoli (Eds.)
Published by Elsevier Science Ltd. and ESIS. 165

SEQUENCED AXIAL AND TORSIONAL CUMULATIVE FATIGUE:
LOW AMPLITUDE FOLLOWED BY HIGH AMPLITUDE LOADING

Peter BONACUSE
US Army Research Laboratory,
NASA Glenn Research Center,
Brook Park, OH, USA
and
Sreeramesh WLURI
Ohio Aerospace Institute,
NASA Glenn Research Center,
Brook Park, OH, USA

ABSTRACT
The experiments described herein were performed to determine whether damage imposed by
axial loading interacts with damage imposed by torsional loading, This paper is a follow on to
a study [ 11 that investigated effects of load-type sequencing on the cumulative fatigue behavior
of a cobalt base superalloy, Haynes 188, at 538°C. Both the current and the previous study
were used to test the applicability of cumulative fatigue damage models to conditions where
damage is imposed by different loading modes. In the previous study, axial and torsional two
load level cumulative fatigue experiments were conducted, in varied combinations, with the
low-cycle fatigue (high amplitude loading) applied first. In present study, the low amplitude
fatigue loading was applied initially. As in the previous study, four sequences (axial/axial,
torsion/torsion, axial/torsion, and torsion/axial) of two load level cumulative fatigue
experiments were performed. The amount of fatigue damage contributed by each of the
imposed loads was estimated by both the Palmgren-Miner linear damage rule (LDR) and the
non-linear, damage curve approach (DCA). Life predictions for the various cumulative loading
combinations are compared with experimental results. Unlike the previous study where the
DCA proved markedly superior, no clear advantage can be discerned for either of the
cumulative fatigue damage models for the loading sequences performed. In addition, the cyclic
deformation behavior under the various combinations of loading is presented.

KEYWORDS

Multiaxial, cumulative fatigue, axial loading, torsional loading, tubular specimens.