Evaluation of Flow and Fracture Propensity of Notched Steel Plates by Means of a Photoelastic Model

摘要

The factors affecting brittle strength are examined, with an emphasis on the concept of notch-constraint by which normally ductile metals, such as steel, can be induced to fracture in a brittle manner. Experimental brittle fracture studies are reviewed with an emphasis on tests of notched and welded wide-plates, for which representative data are discussed. A model of the vicinity of the Wells notch used in the wide-plate tests was designed and fabricated out of epoxy material into birefringence was 'frozen.' The use of three-dimensional photoelasticity to examine the stresses in this model, which was loaded so as to simulate the wide-plate specimen, allowed detailed investigation of the stresses in the immediate notch vicinity. On the basis of the stresses found to exist in the Wells notch, three fracture initiation mode possibilities are postulated: (a) a shear mode, initiating at the notch-tip, leading to ductile fracture, (b) shear fracture, initiating at the notch-tip, converging into a cleavage fracture as the region of high triaxiality becomes involved in the fracture process, and (c) cleavage fracture initiating in the region of high triaxiality away from the notch-tip.