Thickness debit effect on cyclic creep damage evolution in Inconel 718 superalloy: experimental investigation, theoretical modeling and numerical implementation

Cyclic creep damage presents a critical threat to the structural reliability of thin-walled components operating under high-temperature conditions. In this study, stress-controlled cyclic creep tests were performed on Inconel 718 specimens with varying thicknesses to investigate the thickness debit effect (TDE) on damage evolution at 650 °C. Fractographic analyses revealed the dominant damage mechanisms under both monotonic and cyclic creep conditions. A theoretical framework was developed to model cavity nucleation and growth, accounting for cavity closure induced by cyclic loading and the enhanced plastic deformation associated with TDE. The proposed model captures the deformation response and predicts fatigue life within a factor of 1.5. Supported by robust numerical implementation, the framework provides mechanistic insight into cyclic creep cavity evolution, offering guidance for the design and assessment of thin-walled high-temperature structures.