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| 1 | A modified θ projection model for constant load creep curves-I.Introduction of the model显示文摘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. | Chao Fu Yadong Chen Xiaofei Yuan Sammy Tin Stoichko Antonov Koichi Yagi Qiang Feng | 2019 | Journal of Materials Science & Technology2019，35，1： | 4 |
| 2 | A modified θ projection model for constant load creep curves-Ⅱ.Application of creep life prediction显示文摘To minimize the deviation of the predicted creep curves obtained under constant load conditions by the original θ projection model, a new modified version that can be expressed by ε = θ_1(1-e^(-θ2t)) +θ3 (e^(θ_4e^θ5^εt)-1), was derived and experimentally validated in our last study. In the present study, the predictive capability of the modified θ projection model was investigated by comparing the simulated and experimentally determined creep curves of K465 and DZ125 superalloys over a range of temperatures and stresses. Furthermore, the linear relationship between creep temperature and initial stress was extended to the 5-parameter model. The results indicated that the modified model could be used as a creep life prediction method, as it described the creep curve shape and resulted in predictions that fall within a specified error interval. Meanwhile, this modified model provides a more accurate way of describing creep curves under constant load conditions. The limitations and future direction of the modified model were also discussed. In addition, this modified θ projection model shows great potential for the evaluation and assessment of the service safety of structural materials used in components governed by creep deformation. | Chao Fu Yadong Chen Xiaofei Yuan Sammy Tin Stoichko Antonov Koichi Yagi Qiang Feng | 2019 | Journal of Materials Science & Technology2019，35，4： | 1 |
| 3 | Hot deformation characteristics of a polycrystalline γ–γ′–δ ternary eutectic Ni-base superalloy显示文摘 | Martin Detrois Randolph C. Helmink Sammy Tin | 2013 | Materials Science & Engineering A2013，，： | 1 |
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