Simple Data Analytics Approach Coupled with Larson–Miller Parameter Analysis for Improved Prediction of Creep Rupture Life

Changho Lee,Taejoo Lee,Yoon Suk Choi 대한금속·재료학회 2023 METALS AND MATERIALS International Vol.29 No.11

Machine learning of the creep rupture life dataset, which consists of test temperatures, stresses and rupture lives, receivedless attention in the community due to numerous physics-based and empirical models already available for the prediction ofthe creep rupture life, and a limited number (typically about 10 to 40) of available creep rupture life data points consideredto be too small to be trained for the reliable prediction. A simple data analytics approach was developed for the quick andreliable assessment of the creep rupture life. The proposed approach involves linear regression as a major algorithm and thefour features [two generic features (temperature (T) and stress (σ)) and two physics-informed features (ln σ and −1/T)], andexhibited superior creep rupture life predictions (validated by the 41 creep datasets of ferritic Cr steels) without any violationof creep phenomenology and data overfitting. In particular, the proposed approach was extremely useful to assess thefidelity of the Laron–Miller relation for a given creep rupture life dataset and to find an optimum Larson–Miller constantthat minimizes a deviation from the ideal Larson–Miller relation. An analytical model was also developed based on curvefitting of Larson–Miller parameters calibrated by the optimum Larson–Miller constant. The proposed analytical model gaveadditional improvement in creep rupture life prediction, particularly for creep datasets, of which creep rupture lives wereslightly less predicted by the data analytics approach. The two proposed models provided a synergistic effect in creep rupturelife prediction when interactively used.

An Empirical Approach to Analyze Creep Rupture Behavior of P91 Steel

Muhammad Junaid Aslam,Cemil Hakan Gur 한국재료학회 2021 한국재료학회지 Vol.31 No.5

P91 steel has been a highly researched material because of its applicability for high-temperature applications. Considerable efforts have been made to produce experimental creep data and develop models for creep life prediction. As creep tests are expensive and difficult to conduct, it is vital to develop authenticated empirical methods from experimental results that can be utilized for better understanding of creep behavior and can be incorporated into computational models for reliable prediction of creep life. In this research, a series of creep rupture tests are performed on the P91 specimens within a stress range of 155 MPa to 200 MPa and temperature range of 640 oC (913 K) to 675 oC (948 K). The microstructure, hardness, and fracture surfaces of the specimens are investigated. To analyze the results of the creep rupture tests at a macro level, a parameter called creep work density is derived. Then, the relationships between various creep parameters such as strain, strain rate, time to rupture, creep damage tolerance factor, and creep work density are investigated, and various empirical equations are obtained.

Normalized Coffin-Manson Plot in Terms of a New Life Function Based on Stress Relaxation under Creep-Fatigue Conditions

Jeong, Chang Yeol,Nam, Soo Woo,Lim, Jong Dae 대한금속재료학회 2003 METALS AND MATERIALS International Vol.9 No.2

A new life prediction function based on a model formulated in terms of stress relaxation during hold time under creep-fatigue conditions is proposed. From the idea that reduction in fatigue life with hold is due to the creep effect of stress relaxation that results in additional energy dissipation in the hysteresis loop, it is suggested that the relaxed stress range may be a creep-fatigue damage function. Creep-fatigue data from the present and other investigators are used to check the validity of the proposed life prediction equation. It is shown that the data satisfy the applicability of the life relation model. Accordingly, using this life prediction model, one may realize that all the Coffin-Manson plots at various levels of hold time in strain-controlled creep-fatigue tests can be normalized to make one straight line.

증기발생기 전열관용 Alloy 690 소재의 크리프 특성에 미치는 탄화물 형성의 영향

김형규,홍석민,김종민,김민철,이영국 대한금속·재료학회 2023 대한금속·재료학회지 Vol.61 No.4

The creep properties of Alloy 690, used as a steam generator tube material in nuclear power plants,were evaluated at 650oC, 750oC, and 850oC. The parameters of creep life prediction models were derived usingthe Larson-Miller (LM), Manson-Haferd (MH), and Orr-Sherby-Dorn (OSD) models, to use as mechanicalproperties under a virtual severe accident condition like station black out (SBO). The yield strength (YS) andcreep property of Alloy 690 were compared with those of Alloy 600, and the effects of the precipitation behaviorof Cr carbides on creep properties were analyzed. The YS of Alloy 600 decreased rapidly above the temperatureof 750oC, but the YS of Alloy 690 decreased linearly up to the temperature of 850oC because of the formationof M23C6 carbides. The creep stress exponent (n) of Alloy 690 was between 5 and 6, and this indicated thatdislocation creep was the major creep mechanism at the test temperatures. The results of creep tests werewell matched with the LM, MH, and OSD models for Alloy 690, and there were no significant differences inaccuracy between the models. The stress-rupture test results of Alloy 600 and Alloy 690 using the LM modelshowed that the decrease in creep strength with rupture time of Alloy 690 was steeper than that of Alloy 600at high temperatures. This indicated that Alloy 690 was more susceptible to creep degradation under longtermcreep conditions. The precipitation of Cr carbides in Alloy 690 increased YS, benefitting creep propertiesfor short-term creep. However, the Cr carbides coarsened significantly under loading conditions at hightemperature, and this deteriorated the creep properties for long-term creep.

초고온 가스로용 Alloy 617의 크리프 수명예측 신뢰성 평가

김우곤 ( Woo Gon Kim ),박재영 ( Jae Young Park ),김선진 ( Seon Jin Kim ),홍성덕 ( Sung Deok Hong ),김용완 ( Yong Wan Kim ) 대한금속재료학회(구 대한금속학회) 2012 대한금속·재료학회지 Vol.50 No.10

This paper evaluates the reliability of creep rupture life under service conditions of Alloy 617, which is considered as one of the candidate materials for use in a very high temperature reactor (VHTR) system. A Z-parameter, which represents the deviation of creep rupture data from the master curve, was used for the reliability analysis of the creep rupture data of Alloy 617. A Service-condition Creep Rupture Interference (SCRI) model, which can consider both the scattering of the creep rupture data and the fluctuations of temperature and stress under any service conditions, was also used for evaluating the reliability of creep rupture life. The statistical analysis showed that the scattering of creep rupture data based on Z-parameter was supported by normal distribution. The values of reliability decreased rapidly with increasing amplitudes of temperature and stress fluctuations. The results established that the reliability decreased with an increasing service time.

Life Prediction of IN738LC Considering Creep Damage under Low Cycle Fatigue

이정민,위성욱,윤정한,송현우,김용석,구재민,석창성 한국정밀공학회 2018 International Journal of Precision Engineering and Vol.5 No.2

As growing attention on greenhouse gas reduction, developing an eco-friendly power generation system of power plants and enhancing its efficiency has been actively researched. In order to increase the efficiency, the operating temperature has been raised, and hence the application of Ni-base super-alloy has increased to a core component of the power generation system like a turbine blade, a rotor and a boiler. Especially, turbine blades are exposed to high-temperature and high-pressure, and they bear mechanical loads due to the centrifugal force of the high-speed rotation. Thus, the durability of the blade material should be tested under high temperature conditions. In high temperature LCF tests, damage occurs in specimens because of creep. Hence, the aim of this study is to estimate the life of LCF precisely by considering the creep damage in specimens generated during the LCF test. We conducted the LCF tests to propose a new life prediction method considering the fatigue and creep damage. Finally, this study demonstrates the reliability of the prediction method by comparing the predicted life with the actual fatigue life. Through this, we expect to predict the fatigue life more accurately by predicting the fatigue life under different fatigue strain frequencies considering the creep damage.

A new creep model and its application in the evaluation of creep properties of a titanium alloy at 500 °C

Wenming Ye,Xuteng Hu,Yingdong Song 대한기계학회 2020 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.34 No.6

Creep is one of the important failure mechanisms of structures operating in high-temperature environments, so accurately assessing the creep properties of materials is essential to structural design and analysis. However, most of the creep researches, there is no uniform method to accurately describe the creep deformation and life. On the basis of previous studies, this paper replaceed the nominal stress in the traditional creep model with the normalized stress of tensile strength and obtains a new constitutive model capable of describing the whole process of creep. It is also applied to the evaluation of creep properties of TC11 titanium alloy at 500 °C. The parameters of different creep constitutive models are obtained by fitting experimental data, including θ-projection model, Batsoulas model, CDM model and proposed model. The advantages and disadvantages of different models are also analysed. In addition, the improvement of the new constitutive model is also discussed.

Influence of data size on the reliability assessment of creep life of grade 91 steel

김우곤,박재영,B. K. Choudhary,김선진,김민환,장진성 대한기계학회 2014 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.28 No.11

Influence of data size on a reliability assessment of the long-term creep life of Grade 91 steel was investigated for two different sets oflarge body of creep-rupture data comprising 690 (Set-1) and 1072 (Set-2) data points. The Z-parameter on the Larson-Miller parameter ofcreep rupture data supported a normal distribution well. Based on the normal distribution, the reliability of the predicted creep life for thetwo data sets was assessed to obtain variations in reliability owing to fluctuations in the service conditions and the dispersion of the creepdata using a service condition-creep rupture property interference (SCRI) model. A large number of random variables for Z-parameterwere generated using Monte-Carlo simulation. A reliability assessment for the two data sizes under specific service conditions has beencomparatively demonstrated. It was found that the size of the creep-rupture data influenced the reliability of the creep life prediction.

입계 cavitation 손상기구에 기초하는 오스테나이트계 스테인리스강의 크리프-피로 수명예측법과 입계 탄화물 특성 변화에 의한 수명 향상에 관한 연구

洪鉉郁,南壽祐,尹暎喆,洪鎭完 대한금속재료학회 2002 대한금속·재료학회지 Vol.40 No.4

It is understood that grain boundary cavitation is one of the detrimental processes for the degradation of austenitic stainless steels that reduces the creep-fatigue life at high temperatures. A new damage function based on a model for the creep-fatigue life prediction in terms of nucleation and growth of grain boundary cavities is proposed for austenitic stainless steel. This damage function is a combination of the fatigue and creep terms related to the cavitational damage (cavity nucleation and growth) in the life prediction equation and is found to be generally applicable to all the materials in which failure is controlled by the grain boundary cavitational damage. The cavity nucleation factor, P', which is introduced in the creep-fatigue life model, is found to be closely related with the characteristics of grain boundary carbides acting as cavity nucleation sites. The modification of carbide characteristics through grain boundary serration is successfully made by the special heat treatment so that the modified carbides are favorable for cavitation resistance, resulting in a lowered P' value of material. It is observed that the creep-fatigue life is remarkably improved by the modification of carbide characteristics through grain boundary serration.

응력 및 온도 변화시 무기력계수를 이용한 크리프-피로 수명설계

박정은(Jung Eun Park),양성모(Sung Mo Yang),한재희(Jae Hee Han),유효선(Hyo Sun Yu) 대한기계학회 2011 大韓機械學會論文集A Vol.35 No.2

발전설비 및 자동차의 엔진에서 고온과 응력이 발생하므로 안전을 위하여 제품을 생산하기 전에 재료의 수명설계가 필요하다. 본 연구에서는 온도, 응력, 파단 시간으로 이루어진 무기력계수를 이용하여 수명설계를 수식화하였다. 통합수명식을 이용하여 SP-Creep 시험 데이터와 계산된 데이터를 비교하였다. SP-Creep 시험은 X20CrMoV121강의 파단시간을 획득하기 위하여 수행하였고 수명설계식을 통해 하중, 온도, 하중-온도가 작용하는 3가지 경우를 고려하였다. 첫째로, 무기력계수는 SP-Creep 시험에서 획득한 파단응력과 시간에 의해 계산하였다. 두 번째로, 온도 조건을 주어 수명을 예상하였다. 세 번째로, 부재는 피로와 크리프가 동시에 작용할 때 커플링 효과 때문에 더 열악한 상태에 놓이게 된다. 수명은 커플링 효과 때문에 현저하게 감소하는 것으로 나타났다. High temperature and stress are encounted in power plants and vehicle engines. Therefore, determination of the creep-fatigue life of a material is necessary prior to fabricating equipments. In this study, life design was determined on the basis of the lethargy coefficient for different temperatures, stress and rupture times. SP-Creep test data was compared with computed data. The SP-Creep test was performed to obtain the rupture time for X20CrMoV121 steel. The integration life equation was considered for three cases with various load, temperature and load-temperature. First, the lethargy coefficient was calculated by using the obtained rupture stress and the rupture time that were determined by carrying out the SP-Creep test. Next, life was predicted on the basis of the temperature condition. Finally, it was observed that life decreases considerably due to the coupling effect that results when fatigue and creep occur simultaneously.