Abstract Improved formulae for estimating crack tip opening displacement (CTOD) from test records of compact tension (C(T)) specimens are developed. Two-dimensional, plane strain, finite element analyses of 1T C(T) specimens are made for normalized crack depths, a/W, of 0.40–0.70 using Ramberg–Osgood material behavior with strain hardening coefficients n=5, 10, and 20. Finite element predictions of J, CTOD, crack mouth opening displacement (CMOD) and load are used to obtain proportionality constants relating the area under the load–CMODpl curve to Jpl, and J to CTOD in terms of a/W and n. Improvements in CTOD estimates of 25% over existing estimation methods are obtained. Correction factors for displacements measured on the specimen front face instead of the load line are also examined.
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