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Wide plates of A572 Grade 50 steel were tested in four-point bending. The plate thickness was 50 mm. The plates were surface cracked, with two different aspect ratios. The test temperature was varied through the transition range. Critical crack-tip opening displacement (CTOD) was measured by scanning electron microscopy (SEM). CTOD at fracture compared well with data from standard bend bar tests for the same materials. Applied strains were measured using three different methods. For low aspect ratios, the measure of applied strain was a major source of uncertainty in the application of the CTOD design curve. Safe predictions from standard bend bar data could be made only if lower-bound CTOD values were assumed. For larger aspect ratios, the design curve was overconservative due to an underestimation of CTOD for a given applied strain. Scatter in CTOD data was due primarily to manganese sulfide stringers which caused delamination at the crack tip under conditions of ductile crack initiation.
mechanical properties, fracture test, wide-plate test, temperature transition, crack-tip opening displacement, elastic-plastic fracture, fracture properties, manganese sulfide inclusions, hot-rolled structural steel, fracture design
Professor, The Norwegian Institute of Technology, Trondheim,
Assistant professor, University of Florida, Gainesville, FL
Physicist, National Bureau of Standards, Boulder, CO