Special Section on Digital Photoelasticity: Advancements and Applications

Experimental evaluation of plasticity-induced crack shielding from isochromatic data

[+] Author Affiliations
Jose M. Vasco-Olmo, Francisco A. Díaz

Universidad de Jaén, Escuela Politécnica Superior de Jaén, Departamento de Ingeniería Mecánica y Minera, Campus Las Lagunillas, Jaén, 23071, Spain

Opt. Eng. 54(8), 081203 (Feb 26, 2015). doi:10.1117/1.OE.54.8.081203
History: Received October 28, 2014; Accepted January 12, 2015
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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.

© 2015 Society of Photo-Optical Instrumentation Engineers

Citation

Jose M. Vasco-Olmo and Francisco A. Díaz
"Experimental evaluation of plasticity-induced crack shielding from isochromatic data", Opt. Eng. 54(8), 081203 (Feb 26, 2015). ; http://dx.doi.org/10.1117/1.OE.54.8.081203


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