Shear Band Characterization of Mixed Mode I and II Fully Plastic Crack Growth.
MASSACHUSETTS INST OF TECH CAMBRIDGE DEPT OF MECHANICAL ENGINEERING
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Fully plastic crack growth in singly grooved tensile specimens is characterized locally by the directions and amounts of fracture and slip on various planes. The model relates macroscopic quantities, including the crack growth ductility, defined as the axial displacement per unit ligament reduction, which is of practical importance in determining the stiffness of the surrounding structure that is needed to prevent unstable fracture. Applied to six different structural alloys with strain hardening exponents from 0.1 to 0.2, the model gave crack growth ductilities within 10 for the symmetrical configurations, where the value ranged from 0.25 to 0.4, and were unrelated to the strain hardening exponent. For the asymmetrical configurations that occur near welds or shoulders, the crack growth ductility for the low hardening materials drops to 0.07 to 0.11. The predicted values were uniformly high by a factor of two, providing a good relative ranking of the alloys. Other macroscopic correlations were generally within 10. Thus this slip plane model of fully plastic crack growth provides a useful correlation between macroscopic measurements made on the specimens after fracture, and the important loss of crack growth ductility that occurs in asymmetric configurations with materials with low strain hardening.
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