ひずみ制御引張試験のデータによる乗算型の粘塑性モデルの同定

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タイトル別名
  • IDENTIFICATION OF MULTIPLICATIVE VISCOPLASTICITY MODEL BY THE DATA OF STRAIN-CONTROLLED TENSILE TEST
  • ひずみ制御引張試験のデータによる乗算型の粘塑性モデルの同定 : 構造用鋼材の高温時の時間依存性挙動に関する研究(その1)
  • ヒズミ セイギョ ヒッパリ シケン ノ データ ニ ヨル ジョウザンガタ ノ ネンソセイ モデル ノ ドウテイ : コウゾウヨウ コウザイ ノ コウオンジ ノ ジカン イソンセイ キョドウ ニ カンスル ケンキュウ(ソノ 1)
  • Study on time-dependent behavior of structural steel at elevated temperatures Part 1
  • 構造用鋼材の高温時の時間依存性挙動に関する研究　その１

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 The success of simulating the collapsing behavior of steel columns under fire conditions depends on how accurately time-dependent mechanical properties of structural steels can be predicted at elevated temperatures and high stress levels. In the field of fire resistant design of steel buildings, high-temperature creep behavior is not often included in constitutive relationships, but has a significant influence on the fire response of the structures. In this paper, the multiplicative viscoplasticity model was selected for time-dependent mechanical model of structural steel at elevated temperatures, and the material constants of the model were identified by using the stress-strain curves of tensile tests at two different tensile speeds at elevated temperatures.<br> All experimental results have been obtained using specimens of SM490 steel that were made in Ref. 7. Uniaxial tensile test of SM490 under temperature (350, 400, 500, 550, 600, 700°C) and tensile speeds (1.0 and 0.05 mm/min), corresponding to the strain rates of about 1.5 %/minute (FAST tests) and 0.08 %/minute (SLOW tests) respectively, were carried out. The experimental results showed that the flow stresses of SM490 were both temperature and strain rate dependent. Due to the rate dependency at high temperature, the ultimate stresses of FAST tests were higher than those of SLOW tests at 500~700°C<br> A multiplicative viscoplasticicity model was selected to represent the uniaxial monotonic behavior of SM490 steel, and the set of material constants of the model was identified by the results of uniaxial tensile tests. The fitting parameters were determined with a nonlinear least squares optimization method through a Gauss-Newton iterative procedure. Comparing the material constants of strain-rate sensitivity in reference 9 with those derived from the mechanical model in this study, the strain-rate sensitivity between them was almost the same.<br> By integrating the viscoplasticity model under constant stress condition, the Norton-Bailey creep law can be explicitly obtained. Therefore, we can simulate the actual creep curves by the creep model, which was derived from the viscoplasticity model, and we were able to evaluate the validation of the mechanical model for estimation of actual creep response behavior. Correlations between measured and predicted creep strains for SM490 steel at elevated temperatures were obtained and a relatively good correspondence was found. Especially, the simulated creep curves at the highest applied stress level corresponded with the actual creep responses, and the predicted creep curves at low strain levels gave a little variation. This relation could depend on the fact that the stress response levels of the tensile tests were higher than those of actual creep experiments in reference 7.<br> From the comparison of creep responses, it appears that one can predict the creep response of structural steels reasonably well from strain controlled tensile data. This is clearly useful considering that the strain controlled tensile tests can be accomplished rapidly compared with a set of creep tests.<br> In summary, the following results were obtained:<br> 1) The effect of strain rates on the stress-strain curves of tensile tests was expressed reasonably well with the use of the multiplicative viscoplasticity model. Comparing the strain-rate sensitivity in reference 9 with those derived from the mechanical model, the material constants of strain-rate sensitivity between them were evaluated and found to be almost the same.<br> 2) In the case of creep tests at over 500°C and highest stress level, the creep model derived from the multiplicative viscoplasticity model approximated to the experimental result of creep tests reasonably well. Finally, the accuracy of creep model at relatively low stress levels did not obtain satisfactory results.

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