Volume 5, Issue 3 (March 2008)
Crack Arrest Testing Using Small Wide Plate SE(T) Specimens
A greatly scaled-down version of the wide plate crack arrest test has been developed to characterize the crack arrest performance of a high strength, low alloy (HSLA) steel alloy in the upper region of the ductile-brittle transition. The specimen is a single-edge notched, 152 mm wide by 19 mm thick by 910 mm long plate subjected to a strong thermal gradient and a tensile loading. The thermal gradient is required to arrest the crack at temperatures high in the transition region, close to the expected service temperature for crack arrest applications in surface ships. Strain gages are placed along the crack path to obtain crack position and crack velocity data, and this data, along with the applied loading is combined in a “generation mode” analysis using finite element analysis to obtain a dynamic analysis of the crack arrest event. A prior investigation demonstrated the feasibility of the technique and this investigation was devised to obtain a larger dataset of crack arrest toughness values of an HSLA-100 steel plate to better characterize the upper transition crack arrest performance of this alloy. Brittle crack initiation, significant cleavage crack propagation, and subsequent crack arrest was achieved in all eight of the tests conducted in this investigation. The cleavage cracks were observed to propagate at nearly constant velocity, typically in the range of 350–400 m/s before arresting abruptly. A crack arrest master curve approach was used to characterize the fracture toughness and a crack arrest reference temperature, TKIA=−136°C was determined for the HSLA-100 plate. This corresponded to a shift in the crack initiation reference temperature of +36°C. The shift in reference temperature was much less than that observed for low Ni steel alloys.