Mixed Mode I and II Fully Plastic Crack Growth from Simulated Weld Defects.
MASSACHUSETTS INST OF TECH CAMBRIDGE DEPT OF MECHANICAL ENGINEERING
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In symmetric specimens, the crack advances into the relatively undamaged region between two plastic shear zones. A crack near a weld or shoulder, loaded into the plastic range, may have only a single shear band, along which the crack grows in prestrained and damaged material with less ductility than the usual symmetrical configurations. A crack ductility can be defined as the minimum displacement per unit crack growth. A low crack ductility requires higher stiffness of the surrounding structure for fracture-stable design. Tests of six alloys showed that, for the low hardening alloys, the crack ductility in the asymmetric case is less than a third of the symmetric. In the higher hardening alloys the crack ductility in the asymmetric case is smaller by a factor of 1.2 at most. A noteworthy result is the presence of a Mode I opening component even with asymmetry, as is shown by the far field displacement vector being more than 45 deg from the transverse direction. The crack direction is less than 45 deg, indicating the effect of triaxiality on cracking. Finally, a logarithmic tensile singularity in the mean stress was found for rigid-plastic flow past a growing crack of finite angle with rigid flanks under combined shear and tension. The tensile singularity predicts yielding of the crack flanks.
- Fabrication Metallurgy