Tests and Interpretation of Mixed Mode I and II Fully Plastic Fracture from Simulated Weld Defects.
MASSACHUSETTS INST OF TECH CAMBRIDGE DEPT OF MECHANICAL ENGINEERING
Pagination or Media Count:
Most fracture tests use symmetric specimens, with the crack advancing into the relatively undamaged region between two plastic zones. A crack near a weld or shoulder, loaded into the plastic range, may have only a single shear band, however, along which the crack grows into prestrained and damaged material with less ductility than the usual symmetric configurations. Tests on six alloys show that the crack growth ductility, defined as the minimum displacement per unit ligament reduction, is less in the asymmetric case than in the symmetric one by a factor of 3 for low hardening alloys with strain hardening exponents n 0.1. This means that with low-hardening typically high strength alloys, the surrounding structure must be 3 times stiffer for fracture stable design. For higher hardening alloys n 0.23 the crack growth ductility is less in the asymmetric case by a factor of at most 1.2. The crack initiation ductility here approximately the crack tip displacement CTD is relatively unaffected by asymmetry, but it cannot always be relied on for ductility, e.g. in low cycle fatigue. Therefore tests such as these on crack growth ductility are needed for help in design and maintenance of structures.
- Metallurgy and Metallography
- Couplers, Fasteners and Joints