Curve Fitting for Damage Evolution through Regression Analysis for the Kachanov–Rabotnov Model to the Norton–Bailey Creep Law of SS-316 Material

Abstract

In a number of circumstances, the Kachanov–Rabotnov isotropic creep damage constitutive model has been utilized to assess the creep deformation of high-temperature components. Secondary creep behavior is usually studied using analytical methods, whereas tertiary creep damage constants are determined by the combination of experiments and numerical optimization. To obtain the tertiary creep damage constants, these methods necessitate extensive computational effort and time to determine the tertiary creep damage constants. In this study, a curve-fitting technique was proposed for applying the Kachanov–Rabotnov model into the built-in Norton–Bailey model in Abaqus. It extrapolates the creep behaviour by fitting the Kachanov–Rabotnov model to the limited creep data obtained from the Omega-Norton–Bailey regression model and then simulates beyond the available data points. Through the Omega creep model, several creep strain rates for SS-316 were calculated using API-579/ASME FFS-1 standards. These are dependent on the type of the material, the flow stress, and the temperature. In the present work, FEA creep assessment was carried out on the SS-316 dog bone specimen, which was used as a material coupon to forecast time-dependent permanent plastic deformation as well as creep behavior at elevated temperatures and under uniform stress. The model was validated with the help of published experimental creep test data, and data optimization for sensitivity study was conducted by applying response surface methodology (RSM) and ANOVA techniques. The results showed that the specimen underwent secondary creep deformation for most of the analysis period. Hence, the method is useful in predicting the complete creep behavior of the material and in generating a creep curve.

Correlation Analysis of Established Creep Failure Models through Computational Modelling for SS-304 Material

“…The symbol λ represents a material constant that can be calculated directly from the available experimental data for this case. The ideal value for p was suggested here to be 3/2 units less than the value of λ. Appropriately, the creep strain rate of the sin-h model is given by Equation (22). In this scenario, it is possible to derive the material constant (λ) directly from experimental data.…”

“…According to this theory, p should be 3/2 units less than the actual number. Equation (22) represents the sin-h model's creep strain rate [33].…”

“…The curve-fitting for varying loads and temperatures could then be accomplished by comparing the generic power-law regression equation to the NB power-law [22]. For the analysis example, the extrapolation assumed that the existing trend in the material's behavior would continue along with time.…”

“…An acceptability criterion for the prediction plot was a coefficient of determination R 2 value of 0.9803, which was significantly higher than the criterion set by the ASME FFS-1/API-579 standards for this plot. To assess the effects of material degradation at the tertiary stage of creep for the SS-304 material, the tertiary creep damage constant (ω) was derived in the regression equations [22].…”

“…It is significant to understand the limitations of creep failure models by analytically computing them in the FE package Abaqus [2]. The curve-fitting approach for damage evolution is one of the methods proposed to undo the shortcomings of the models by tracking a material's creep deformation behavior in the tertiary creep regime [22]. The difficulty in determining the creep parameters required for FE analysis for any material while implementing creep models may be overcome by regression analysis [23].…”