YIELD-BEFORE-BREAK FRACTURE-MECHANICS ANALYSIS OF HIGH-STRENGTH STEELPRESSURE-VESSELS

Case study examples of fracture mechanics testing and analysis of Ni-C r-Mo high-strength steel cannon tubes are presented. The testing and a nalysis include the situation of significant plastic deformation accom panying fracture, which often occurs when high pressure is applied to high-toughness steel pressure vessels. The analysis is based on a comp arison of the size of the Irwin crack-tip plastic zone with the remain ing ligament of the tube in the area of the critical fatigue crack whi ch causes final failure. The results of the study show that the type o f final failure can be predicted-as either a relatively safe, yield-be fore-break failure or a less safe running-crack type of failure-for a variety of material, configuration, and loading conditions.