Abstract
In evaluating the margin against fracture under various loadings, resistance against initiation and propagation of fracture needs to be evaluated. Elastic-plastic finite element analysis is a powerful tool for such assessment but prediction of plastic strain and stress state in structures needs stress-strain relations to be implemented in the analysis. For avoiding the necessity of testing and processing the data each time, true stress-strain relations whose constants can be determined from fundamental properties such as yield or proof stress, tensile strength, rupture elongation and reduction of area were developed based on the results of uniaxial tensile tests on many kinds of alloys used in nuclear power plants. Tensile tests were also conducted for notched round bar and grooved plate specimens made from four representative materials at various temperatures below creep regime. Conventional large strain elastic-plastic analyses were performed on these specimens to clarify the needs of introduction of the effect of damage on deformation in addition to a failure criterion. Then the calculation of damage based on equivalent plastic strain rate and stress triaxiality factor was introduced to be used for the prediction of failure and gradual decrease of deformation resistance. It was found, although the predictions became more realistic, that behavior of some of the specimens could not be predicted well when the effects of stress triaxiality factor were calibrated based on the analyses of other types of specimens, suggesting the necessity of introducing other parameter which will be addressed in a companion paper.
