MULTIAXIAL LOW-CYCLE FATIGUE DAMAGE EVALUATION USING AC POTENTIAL METHOD FOR ALLOY 738LC SUPERALLOY

This paper studies tension/torsion multiaxial low-cycle fatigue lives and creep-fatigue damage evaluation for Alloy 738LC superalloy. Tensio n/torsion creep-fatigue tests were carried our using hollow cylinder s pecimens and multiaxial creep-fatigue lives were obtained. The Mises' equivalent strain correlated the multiaxial low cycle fatigue lives wi thin a factor of two scatter band. An a.c. potential method is develop ed to detect the creep-fatigue damage associated with crack nucleation and extension. A.c. potentials at high frequencies accurately detect the creep-fatigue damage from the early stage of life while those at l ow frequencies detect that in the final stage of life. A.c. potentials at high frequencies detect the crack density, defined as the total cr ack length per unit area, and maximum crack length more sensitively th an those at low frequencies.