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A database derived from tests on specimens with a large range of ligament (b) and thickness (B) dimensions was systematically analyzed to evaluate constraint loss and statistical size effects on cleavage fracture toughness. The objectives were to: (1) decouple size effects related to constraint loss, mediated by b and B, from those arising from statistical effects, primarily associated with B; and, (2) develop procedures to transfer toughness data to different conditions of constraint and B. The toughness database for a Shoreham pressure vessel steel plate, tested at a common set of conditions, was described in a companion paper. Quantification of constraint loss was based on an independently calibrated 3D finite-element critical stress-area, σ ∗ - [ K J m / K J c ] , model. The measured toughness data, KJm, were first adjusted using computed [ K J m / K J c ] constraint loss factors to the corresponding values for small scale yielding conditions, K J c = K J m / [ K J m / K J c ] . The KJc were then statistically adjusted to a KJr for a reference Br = 25.4 mm. The B adjustment was based on a critically stressed volume criterion, modified to account for a minimum toughness, Kmin, consistent with modest modifications of the ASTM E 1921 Standard procedure. The combined σ ∗ - [ K J m / K J c ] - K min adjustment procedure was applied to the Shoreham b − B database, producing a homogeneous population of KJr data, generally within the expected scatter. The analysis suggests that: (1) there may be a maximum B beyond which statistical size effects diminish, and (2) constraint loss in the three-point bend specimens begins at a relatively low deformation level. A corresponding analysis, based on a Weibull stress, σ w - [ K J m / K J c ] - K min , adjustment procedure, yielded similar, but somewhat less satisfactory, results. The optimized adjustment procedure was also applied to other KJm data for the Shoreham plate from this study, as well as a large database taken from the literature. The population of 489KJr data points, covering an enormous range of specimen sizes, geometries and test temperatures, was found to be consistent with the same master curve T0 = −84 °C derived from the b − B database. Thus, calibrated micromechanical models can be used to treat size and geometry effects on KJm, facilitating using small specimens and data transfer to predict the fracture limits of structures. |
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