SYMPOSIA PAPER Published: 01 January 1988

Comparison of Methods for Measuring Fatigue Crack Closure in a Thick Specimen


The objective of this paper is to compare fatigue crack closure loads obtained by various crack opening displacement methods. Crack closure loads are obtained by three different techniques: optical interferometry, backface strain measurements, and crack mouth opening displacement (CMOD) gage measurements. Optical interferometry gives complete through-the-thickness variation of crack closure, while backface strain and CMOD measurements provide an average (bulk) crack opening load for the entire specimen thickness. The present paper focuses on comparing the bulk specimen measurements of crack opening load with point measurements obtained at various points along the crack front from the interferometry method. It was observed that the closure loads obtained from backface strain measurements agree well with the CMOD closure values, although the interferometric crack opening loads are higher than either compliance techniques.

Author Information

Ray, SK
Boeing Aircraft Company, Renton, WA
Grandt, AF
Boeing Aircraft Company, Renton, WA
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Developed by Committee: E08
Pages: 197–213
DOI: 10.1520/STP27209S
ISBN-EB: 978-0-8031-5052-2
ISBN-13: 978-0-8031-0996-4