The Application of Elastic-Plastic Fracture Mechanics Parameters in Fracture Safe Design.

摘要

The report summarizes some of the methods currently used for assessing the fracture toughness of materials under elastic-plastic conditions. The main parameters considered are (1) plane strain fracture toughness, (2) equivalent energy, (3) contour integral (J),and (4) crack opening displacement (COD). Gross strain crack tolerance and stress concentration are also discussed. Of these parameters,the contour integral and the crack opening displacement have most potential for future development. COD and J are shown to be equivalent;however,at the present stage of development the COD concept has several advantages over the J concept. The development of the COD concept and the method for analyzing tests on model pressure vessels with 6in. thick walls are described. A comparison with other methods showed that although the COD analysis gives conservative estimates of the flaw size to cause failure,further work is necessary to predict vessel burst conditions when failure is preceded by extensive plasticity and ductile tearing. A simple nomogram to determine COD levels to ensure leak before break conditions is also developed.