Crack arrest fracture toughness testing of naval construction steels

A program was undertaken to apply the ASTM E 1221 test method to two submarine steels exhibiting high ratios of toughness to yield stress. The objective was to measure the capacities of these steels and representative shipyard welds to arrest fast running cracks. Although the method is not a measure of dynamic toughness, it was considered to be a procedure capable of comparing the crack arresting abilities of these steels. The work has shown that it is possible to follow ASTM E 1221 and obtain valid crack arrest fracture toughness results for materials with room temperature K-Jc as high as 240 MPa root m and a yield stress of 690 MPa using specimens of 50-mm thickness. The process did, however, have a high level of unreliability, necessitating a large number of tests and extensive re-testing to obtain valid results. Test temperatures below -60 degrees C were required to obtain run-arrest events, and as such could not easily be related to material qualification procedures such as explosion bulge testing or to submarine operating temperatures.