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Nine 500-mm-wide, 110-mm-thick A533B Class I wide plates were tested at +70°C (158°F). Three crack types were used: (1) semi-elliptical, (2) surface notched, and (3) through-thickness center cracked. Various notch depths were employed. The progress of the stable propagating ductile tear resulting in the specimen from the use of the relatively stiff wide-plate rig was marked periodically using an unloading technique.
Estimates of the crack propagation resistance JR-curves for these tests were made and compared to resistance curves obtained from small scale laboratory bend specimens.
The crack morphology exhibited by the surface notched wide-plate specimens, which propagate in the through-thickness direction, was essentially normal ductile rupture in contrast to the through-thickness crack, which showed mostly shear rupture.
Semi-elliptical notched specimens initially behaved in a similar fashion to the surface notched, and after penetration of the plate thickness, continuing propagation behaved as a center cracked plate.
Derivations of a simple estimation formula for the JR-curves for the surface notched and semi-elliptical geometries have been made. Using these formulas, comparisons of all tests with the crack propagating in the L-T and L-S orientations were made.
The results of large-scale tension and large- and small-scale bend tests indicate that laboratory tests give reasonable lower bound estimates of the more structurally relevant tension situation in the L-T orientation where full-plate-thickness bend specimens are employed.
In the L-S orientation much more restrictive thickness requirements are necessary to achieve conservative estimates from laboratory bend tests and as an initial guideline the requirement B > 25(JR/σY) is suggested for surface notched geometries although this may not be restrictive enough for very ductile materials.
ductile fracture, fracture toughness, steels, elasto-plastic analysis, crack initiation, crack propagation, geometry, shape, fracture (materials)
Senior research engineer, The Welding Institute, Abington Hall, Abington, Cambridge