ISSN: 1945-7553
CODEN: JTEVAB
Published Online: 2 August 2011
Page Count: 18

The Effect of Large Scale Plastic Deformation on Fatigue Crack Length Measurement with the Potential Drop Method

Ljustell, P.
Dept. of Solid Mechanics, KTH Engineering Sciences, Royal Institute of Technology,

(Received 4 November 2010; accepted 16 June 2011)

Abstract

A combined experimental and numerical investigation was conducted on the effects of plastic deformation and material resistance on the relationship between the potential difference and crack size, denoted calibration curve, or equation. The stainless steel 316L was used at room temperature for investigating the limitations of the calibration curve. The nominal calibration equation, obtained from the undeformed geometry, can be used for fatigue crack length measurements at large plastic deformation. However, the reference potential must, for reliable crack length measurements, be measured at the deformed state and later adjusted at every major change of (plastic) deformation. The major part of the change in reference potential was attributed to the geometry change and only a minor part to the resistivity change. The scatter in the potential drop measured crack length, measured on a cycle by cycle basis, was about 30 times smaller here compared to the compliance measured crack length. Also, in situ potential drop sampling was possible, i.e., the test did not need to be stopped for crack length measurements.

Keywords:
potential drop, crack length measurement, fatigue crack growth, large scale yielding, LCF

Paper ID: JTE103532
DOI: 10.1520/JTE103532
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