Assessing the capability of the Wilshire equations in predicting uniaxial creep curves: An application to Waspaloy

Materials at High Temperatures

2022

Self Cite

In this paper, a new constitutive model is presented that combines the Wilshire equations with a modified Kachanov-Rabotnov continuum damage mechanics (CDM) to enable the prediction of uniaxial creep curves that contain both a primary and tertiary stage.Another advantage of this approach is that the Wilshire equations have been shown to accurately extrapolate the operational failure times and minimum creep rates from very shortterm tests. This approach also removes the need to estimate the Wilshire time to strain equation at numerous different strains. A simple but multi-step procedure is also introduced for estimating the unknown parameters of this model. When applied to Waspaloy data, the model was shown to represent the shape of the experimental creep curves reasonably well 9especially at low and high strains) and provides reasonable creep curve predictionswith percentages errors averaging around 4-5%.

Section: Estimationmentioning

confidence: 99%

“…Most recently, Evans and Williams [15] have incorporated Artificial Neural Network technology (ANN) into the Wilshire methodology as a solution. However, the resulting model has no closed form expression and is quite cumbersome to implement.…”

Section: Introductionmentioning

confidence: 99%

Incorporating the Wilshire equations for time to failure and the minimum creep rate into a continuum damage mechanics for the creep strain of Waspaloy

Materials at High Temperatures

2022

Self Cite

“…First, the creep behavior of Waspaloy has been shown to be dependent on applied condition with two distinct regions corresponding to the stresses above and below r Y (the yield stress). [20,21] This change in creep behavior is due to differing mechanisms of creep at different applied conditions. Whittaker et al [21] highlighted the dominance of diffusive climb at stresses below r Y with dislocation-dislocation interaction in the form of forest hardening limiting creep rates at higher stresses.…”

Section: Equivalent Uniaxial Stress For a Given Spc Forcementioning

confidence: 99%

“…[20,21] This change in creep behavior is due to differing mechanisms of creep at different applied conditions. Whittaker et al [21] highlighted the dominance of diffusive climb at stresses below r Y with dislocation-dislocation interaction in the form of forest hardening limiting creep rates at higher stresses. Birosca et al [22] showed that geometrically necessary dislocation (GND) densities are higher at the grain boundaries in Waspaloy samples crept below r Y , whereas GND densities were more uniformly spread through grains in samples crept above r Y .…”

Section: Equivalent Uniaxial Stress For a Given Spc Forcementioning

confidence: 99%

An Investigation into the Correlation of Small Punch and Uniaxial Creep Data for Waspaloy

Williams

Harrison

2021

Metall Mater Trans A

Within the aerospace sector, the understanding and prediction of creep strains for materials used in high-temperature applications, such as Nickel-based super alloys, is imperative. Small punch testing offers the potential for understanding creep behavior using much less material than conventional uniaxial testing but in contrast to uniaxial creep tests, the stress in small punch creep (SPC) tests is multiaxial. SPC testing can be a valuable tool for validating models of creep deformation, but the key to unlocking its full capability is through the accurate correlation of the creep material properties measured through both techniques. As such, the focus of this paper is to correlate the creep behavior of Waspaloy obtained through conventional uniaxial testing to that obtained via small punch creep testing. Recently, and for low chrome steels, this has been achieved through use of the ksp method, but there are good reasons for believing this technique will not work so well for Nickel-based super alloys. This paper shows this to be the case for Waspaloy and proposes some alternative methods of correlation based on combining the Monkman–Grant relation and the Wilshire equations for both uniaxial and small punch creep. It was found that this latter approach enabled the accurate conversion of SPC minimum displacement rates to equivalent uniaxial minimum creep rates which, when combined with the Wilshire equations, enabled SPC test loads to be converted into equivalent uniaxial stresses (and visa versa) with levels of accuracy that were significantly reduced when compared to using the ksp method. Further, the random error associated with these conversions were dramatically increased.

“…Recent literature has shown that failure times and minimum creep rates can be predicted reliably from accelerated test data, with the scope to further explore the ability to predict time to strains [4][5][6][7][8][9][10][11][12]. Evans and Williams [13] have modified the existing Wilshire equations so that entire creep curves can be predicted using accelerated tests at a range of conditions, and analysed the interpolated and/or extrapolated creep curves using modern statistical techniques. Given the importance of strain for developing new aeroengine materials, the aim of this paper is to build on this work by exploring the suitability of this modified Wilshire equation in predicting the times to various strains for the Nickel-based superalloy RR1000.…”

Section: Introductionmentioning

confidence: 99%

Modification of the Wilshire strain equation: An application to RR1000

Williams

Materials Science and Technology

Williams

et al. 2021

Being able to accurately predict creep strain as a function of time is important both in preventing aeroengine blades rubbing against their outer casings, but also in being able to convert small punch test data into equivalent uniaxial test results using finite element models. Modern studies have found success in applying the Wilshire equations to uniaxial creep test results. The capability of the Wilshire equation to interpolate creep curves was assessed using uniaxial creep tests carried out on RR1000. In this paper, an artificial neural network (ANN) was used to modify the Wilshire equation for the time taken to reach various strains so that the parameters of the Wilshire equation could be interpolated as a function of strain. The model was then evaluated using statistics on predictive accuracy, which showed that the model was capable of predicting the shape and scale of the creep curves with high accuracy. These modifications also revealed that the activation energy is dependent upon the average internal stress and thus strain.