A modified θ projection model for constant load creep curves-I.Introduction of the model
来源期刊：JOURNAL OF MATERIALS SCIENCE TECHNOLOG2019年第1期
论文作者：Chao Fu Yadong Chen Xiaofei Yuan Sammy Tin Stoichko Antonov Koichi Yagi Qiang Feng
文章页码：223 - 230
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 = θ1(1-e-θ2t) + θ3 eθ4eθ5εt-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.
Chao Fu1，Yadong Chen1，Xiaofei Yuan1，Sammy Tin2，Stoichko Antonov1，Koichi Yagi3，Qiang Feng1
1. Beijing Advanced Innovation Center for Material Genome Engineering, State Key Laboratory for Advanced Metals and Materials, University of Science and Technology Beijing2. Department of Mechanical, Materials, & Aerospace Engineering, Illinois Institute of Technology3. National Center for Materials Service Safety, University of Science and Technology Beijing
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 = θ1(1-e-θ2t) + θ3 eθ4eθ5εt-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.
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