Round-robin Analysis of Standard Data Sets for Fracture Toughness Evaluation in ASTM E1820

Abstract A set of standard data sets from typical fracture toughness tests was used in an analytical round-robin to determine whether the proposed data sets were suitable for use as adjuncts to ASTM E1820-09, “Standard Test Method for the Measurement of Fracture Toughness.” Four laboratories participated in the round-robin and submitted analyses of all of the data sets. The results showed good agreement among the laboratories on the individual J-integral calculations and crack size estimates. However, small differences in the estimated crack extension during the tests led to large uncertainty in the calculated fracture toughness of up to 20 % of the mean value of the fracture toughness from all of the laboratories for the data set. A synthesized test record that eliminated the nonlinear behavior commonly observed in unloading compliance test records was developed and distributed to the participants. There was excellent agreement among the results from all participants for the synthesized data set. The standard data sets were determined to be suitable for validating analysis programs for calculating fracture toughness in accordance with ASTM E1820. The uncertainty in the calculated fracture toughness could be reduced by prescribing in the test method exactly which data points in an unload are to be used for estimating the crack length, rather than letting the user decide which data points to include.