Comparison of J-integral from single specimen SE(T) tests on API-5L X100 line pipe steel

摘要

The clamped single-edge notched tension (SE(T)) specimen has seenincreased use as a single-specimen testing scheme to determine tearingresistance curves in high strength steel pipe. The SE(T) specimen withappropriate notch geometry is a low-constraint specimen designed toreduce conservatism in the toughness measurement when compared toother toughness testing methods. The J-integral is robust and simple tocalculate from data obtained by the use of several direct experimentalmeasurements. This study employed a wide variety of instrumentation onAPI 5L X100 SE(T) specimens with fixed test parameters for directcomparison. This paper presents the details of the instrumentation anddetermination of the J-integral used in developing resistance curves. Theresults of this study show that directly measuring strain gradients canyield commensurate results to other non-codified methods currentlyunder development for evaluating J-resistance curves in pipeline steels.Such experimental comparisons are needed to assure that the analysismethods used in both test-method development and in structural analysisaccurately simulate the actual material behavior. Because the highfracture toughness of modern pipeline steels allows the development ofextensive strain fields before significant tearing, practical strain gradientmeasurement techniques with local strain capacity up to 20 % will beneeded to more accurately quantify the comparison between calculationsand experiment. To the authors’ knowledge this direct comparison hasnever been conducted and published by use of independentinstrumentation on the same specimens.