Strain energy release ratio

being known as thermodynamics generalized force

was applied to describe fatigue damage course of orthotropy materials.From the definition of strain energy release ratio

a triaxiality factor for single crystal superalloy that contains three elastic constants was defined.Not only may the triaxiality factor show the multiaxial complex stress states as well as the coupling effect of the tensile and torsional stress in orthotropy material while the applied loading deflects from the principal axes directions of material coordinate system.It is a prolongation for triaxiality factor of isotropy material.By using the triaxiality factor to modify strain range as a failure parameter and introducing a cyclic characteristic parameter for damage force to take account of alternately changed characteristic of cyclic loading

a low cycle fatigue damage model for single crystal superalloy was proposed.The low cycle fatigue test data correlation to DD3 and CMSX-2 single crystal superalloy with the parameter by using multivariate linear regression analysis is good and the all test data fall into the factor of 2.0 and 2.5 scatter band respectively.