CRACK-ARREST FRACTURE-TOUGHNESS TESTING OF NAVAL CONSTRUCTION STEELS

A program was undertaken to apply the ASTM E 1221 test method to two s ubmarine steels exhibiting high ratios of toughness to yield stress. T he objective was to measure the capacities of these steels and represe ntative shipyard welds to arrest fast running cracks. Although the met hod is not a measure of dynamic toughness, it was considered to be a p rocedure capable of comparing the crack arresting abilities of these s teels. The work has shown that it is possible to follow ASTM E 1221 an d obtain valid crack arrest fracture toughness results for materials w ith 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, howev er, have a high level of unreliability, necessitating a large number o f tests and extensive re-testing to obtain valid results. Test tempera tures below -60 degrees C were required to obtain run-arrest events, a nd as such could not easily be related to material qualification proce dures such as explosion bulge testing or to submarine operating temper atures.