Investigation of Plastic Zone Development in Dynamic Tear Test Specimens
Defence Research Establishment Atlantic Halifax, N.S. Canada
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This paper presents on-going investigations on plastic zone development in dynamic tear DT type three-point bend specimens used to measure the fracture toughness of marine structural materials. The purpose of the study is to use finite element technology to provide an understanding of the plastic zone development, to determine the upper limit of temperature relative to full size transition curves where elastic plastic fracture becomes invalid. In earlier studies, the authors utilized 2-D finite element models to compute the ratio of crack tip blunting stretch zone to plastic zone size radius that is used to determine the elastic-plastic fracture toughness. Those studies established the feasibility, as well as limitations, of 2-D finite element modeling for computing the plastic zone development in DT specimens. In the present study we present efforts geared towards improving the 2-D modeling, as well as investigations into the use of 3-D models to provide estimates of the shear lip size. The ABAQUS finite element software was used to model the elastic-plastic behavior of the specimens. The DT specimen was made of 350WT steel and the crack was induced by pressing the notch, followed by fatigue cracking at a limit load level of 40 of the specimen limit load. The specimen was loaded until fixed amounts of permanent deformation were recorded.