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Optical Engineering

Experimental evaluation of plasticity-induced crack shielding from isochromatic data
Author(s): Jose M. Vasco-Olmo; Francisco A. Díaz
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Paper Abstract

The plasticity-induced crack shielding effect is evaluated during fatigue crack growth using transmission photoelasticity. The proposed methodology is based on the evaluation of the stress intensity factors calculated from the analysis of the isochromatic fringe patterns observed at the vicinity of a crack tip. Four different mathematical models describing the crack tip stress fields (namely models based on Westergaard’s, Williams’s, and Muskhelishvili’s equations and a new model called Christopher–James–Patterson) have been employed. Thus, a comparative study to evaluate which of the models is more suitable for fatigue crack shielding evaluation has been performed. A set of fatigue experiments on polycarbonate middle-tension specimens at different R-ratios have been conducted. Experimental results reveal the presence of plasticity-induced crack shielding on growing fatigue cracks for specimens tested at a low R-ratio. In addition, a retardation effect on the fatigue growth rate has been observed due to the shielding effect induced by the plasticity generated both at the crack tip and along the crack flanks. All these results highlight the enormous potential of transmission photoelasticity for the evaluation of plasticity-induced crack shielding on growing fatigue cracks.

Paper Details

Date Published: 26 February 2015
PDF: 12 pages
Opt. Eng. 54(8) 081203 doi: 10.1117/1.OE.54.8.081203
Published in: Optical Engineering Volume 54, Issue 8
Show Author Affiliations
Jose M. Vasco-Olmo, Univ. de Jaén (Spain)
Francisco A. Díaz, Universidad de Jaén (Spain)


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