| Comprehensive tests and analysis of fracture toughness of quenched and self tempered (QST) steels (A913) and the ordinary carbon and high strength low-alloy steels commonly specified for highway bridges (A572 and A588) were performed throughout the range of service temperatures, thicknesses, initial crack lengths, and loading rates.; Two new methodologies to directly estimate the crack length, J and CTOD parameters, as well as J and CTOD-R curves from the test data load and displacement only are proposed. The first method can be used for the analysis of both static and dynamic load rate test data without the need of the final data triplet consisting of the load, displacement, and final measured crack length; hence the test can be run up to specimen fracture without the intervention of a stop block to arrest the final crack. The second method, however, needs final measured crack length for calibration but does not require iteration; hence it is much simpler than the normalization method.; A ductility factor definition based on without crack extension curve is also proposed, to provide a qualitative measure from fracture mechanic point of view of the rotation capacity before instability. This factor describes the state of plastic deformation and is highly dependence of specimen geometry and temperature, therefore, it can provide a qualitative measure whether the material can be used for LRFD plastic design practice at the service temperature. |
