Theoretical analysis of the effect of branched-cracks on the creep crack growth of advanced heat-resistant materials based on finite element method using a penalty function

The Nickel based directionally solidified superalloy has been developed as a gas turbine blade material for high electrical efficiency power plant. Turbine blades are faced with the centrifugal stress from the high-speed rotation under high temperature creep conditions. In the present study, in order to clarify the effect of an oblique crack on the resistant of creep deformation and crack growth, analyses of elastic-plastic creep FEM using a penalty function were conducted. The model of analysis used is a plate with double edge V notches and the type of elements used for analysis is 6-nodes isoparametric elements. Two type models for crack extension were considered such as straight-cracking and an oblique crack. The method of a crack extension is based on the increment application of inverse reaction and release of penalty function at the release nodes. On the basis of the elastic-plastic-creep FEM analysis using a penalty function, it was found that creep crack growth behavior and deformation were characterized by the toughening effects induced by the constitution law of stress-strain rate for creep deformation and crack branch such as an oblique crack. The crack growth behavior derived by this analysis were found to be in good agreement with the corresponding experimental characteristics.