A modified θ projection model for constant load creep curves-I.Introduction of the model

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英文篇名：A modified θ projection model for constant load creep curves-I.Introduction of the model 作者：Chao ; Fu ; Yadong ; Chen ; Xiaofei ; Yuan ; Sammy ; Tin ; Stoichko ; Antonov ; Koichi ; Yagi ; Qiang ; Feng 英文作者：Chao Fu;Yadong Chen;Xiaofei Yuan;Sammy Tin;Stoichko Antonov;Koichi Yagi;Qiang Feng;Beijing Advanced Innovation Center for Material Genome Engineering, State Key Laboratory for Advanced Metals and Materials, University of Science and Technology Beijing;Department of Mechanical, Materials, & Aerospace Engineering, Illinois Institute of Technology;National Center for Materials Service Safety, University of Science and Technology Beijing; 英文关键词：Superalloy;;Creep;;Life prediction;;Modified θ projection model;;Constant load creep 中文刊名：CLKJ 英文刊名：材料科学技术(英文版) 机构：Beijing Advanced Innovation Center for Material Genome Engineering, State Key Laboratory for Advanced Metals and Materials, University of Science and Technology Beijing;Department of Mechanical, Materials, & Aerospace Engineering, Illinois Institute of Technology;National Center for Materials Service Safety, University of Science and Technology Beijing; 出版日期：2019-01-15 出版单位：Journal of Materials Science & Technology 年：2019 期：v.35 基金：the National Key Research and Development Program of China(Grant No.2017YFB0702902);; the National Natural Science Foundation of China(Grant Nos.51631008and 51771019);; the National High Technology Research Program of China(Grant No.2012AA03A513);; the 111 Project(No.B170003) 语种：英文; 页：CLKJ201901030 页数：8 CN：01 ISSN：21-1315/TG 分类号：225-232

摘要

Estimating long-term creep deformation and life of materials is an effective way to ensure the service safety and to reduce the cost of long-term integrity evaluation of high temperature structural materials.Since the 1980 s, the θ projection model has been widely used for predicting creep lives due to its ability to capture the characteristic transitions observed in creep curves obtained under constant true stress conditions. However, the creep rupture behavior under constant load or engineering stress conditions cannot be simulated accurately using this model because of the different stress states. In this paper, creep curves obtained under constant load conditions were analyzed using a modified θ projection model by considering the increase in true stress with creep deformation during the creep tests. This model is expressed as ε = θ_1(1-e~(-θ_2t)) + θ3 e~(θ_4e~θ5~εt)-1, and was validated using the creep curves of K465 and DZ125 superalloys tested at a range of temperatures and engineering stresses. Moreover, it was shown that the predictive capability of the modified θ projection model was significantly improved over the original one, as it reduces the prediction uncertainty from a range of 10% to 20% to below 5%. Meanwhile,it was shown that the model can be reasonably used for predicting constant stress creep conditions, when appropriate parameters are used. The prediction performance of the modified model will be discussed in another paper. The results of this study show great potential for the evaluation and assessment of the service safety of structural materials used in applications where designs are limited by creep deformation.
        Estimating long-term creep deformation and life of materials is an effective way to ensure the service safety and to reduce the cost of long-term integrity evaluation of high temperature structural materials.Since the 1980 s, the θ projection model has been widely used for predicting creep lives due to its ability to capture the characteristic transitions observed in creep curves obtained under constant true stress conditions. However, the creep rupture behavior under constant load or engineering stress conditions cannot be simulated accurately using this model because of the different stress states. In this paper, creep curves obtained under constant load conditions were analyzed using a modified θ projection model by considering the increase in true stress with creep deformation during the creep tests. This model is expressed as ε = θ_1(1-e~(-θ_2t)) + θ3 e~(θ_4e~θ5~εt)-1, and was validated using the creep curves of K465 and DZ125 superalloys tested at a range of temperatures and engineering stresses. Moreover, it was shown that the predictive capability of the modified θ projection model was significantly improved over the original one, as it reduces the prediction uncertainty from a range of 10% to 20% to below 5%. Meanwhile,it was shown that the model can be reasonably used for predicting constant stress creep conditions, when appropriate parameters are used. The prediction performance of the modified model will be discussed in another paper. The results of this study show great potential for the evaluation and assessment of the service safety of structural materials used in applications where designs are limited by creep deformation.

引文

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