An Advanced Sine-Hyperbolic Creep-Damage Model Incorporating Threshold Strength

Abstract

This study aims at improving the classic sine-hyperbolic (Sinh) creep-damage model to predict minimum-creep-strain-rate (MCSR), rupture, damage, and creep deformation. The Sinh model employs a continuum-damage-mechanics-based framework to model secondary and tertiary creep regimes. In Sinh, the creep strain and damage rate equations exhibit an implicit threshold stress that arises during numerical optimization. Herein, the Sinh model is modified to include an explicit threshold strength as a material property and the tensile strength. Threshold strength is defined as the lower limit for creep activation at a given temperature. Stresses are applied below the threshold, resulting in infinite life. The advanced Sinh offers several advantages including a physical significance of stress ratios where the onset of creep is defined by threshold strength, a closed-form solution where the rate equations remain finite at any combination of stress and temperature, and adaptability in finite element analysis where the solution space remains numerically stable. Experimental creep data of 304 SS at multiple isotherms are gathered from prior literature. The advanced Sinh is calibrated to the MCSR and SR data of 304 SS. The calibration of threshold strength follows a standard procedure from literature and is observed to be realistic for stainless steel at elevated temperatures. The MCSR and SR predictions illustrate the Sigmoidal bend and demonstrate zero creep rate and infinite life at or below threshold strength. The creep deformation and damage predictions exhibit agreement with experimental data. The advanced Sinh is validated by employing finite element simulation to ensure the applicability of the model across a range of applications. The advanced Sinh improved creep response prediction and added physical realism to the model's framework.