An Appraisal of Two Simplified Inelastic Methods of the ASME Code

In this work, two simplified inelastic analysis rules existing in the ASME Boiler and Pressure Vessel Code have been appraised. The first rule is intended as a correction for plasticity due to Poisson’s ratio effects. Based on a number of analytical and experimental evaluations, it is shown that the variable Poisson’s ratio approach helps bring the simplified elastic analyses in line with inelastic analysis findings. This is carried out by multiplying the elastically calculated stresses (that are based on an assumed Poisson’s ratio of 0.3) by the factor K_ν to reflect changes in the Poisson’s ratio associated with local plastic deformation. The second rule makes use of a fatigue enhancement factor, K_e which is employed when the linearized elastically calculated stress ranges exceed twice the material yield strength, thus necessitating inelastic evaluations. An analytical approach based on local strain method, as well as the expressions used in the Japanese MITI code has been used for comparison. A number of practical situations have been cited to illustrate the application of these rules.