報告書番号

Q05009

タイトル（和文）

多軸応力下におけるNi基一方向凝固超合金の構成式の開発

タイトル（英文）

Development of constitutive equations for nickel-based directionally solidified superalloy under multiaxial stress condition

概要 （図表や脚注は「報告書全文」に掲載しております）

本研究では、1,300℃級GT材料である一方向凝固（DS）超合金の多軸クリープ変形挙動を実験により明らかにすると共に、単軸・多軸応力下における異方性を適切に評価できる構成モデルを開発した。870℃において軸ねじり多軸クリープ変形試験を行ったところ、同一のミーゼス相当応力に対して引張応力とせん断応力の比が1：1の場合にクリープ速度は最も低い値を示した。既報の構成モデルを本試験結果に適用したところ、せん断応力が支配的な場合にクリープ変形を過大評価する傾向があり、その精度は不十分であることが分かった。結晶塑性解析結果に基づき、非弾性ひずみが２成分の和よりなる構成モデルを開発した。計算結果と実験データを比較したところ、本モデルは単軸応力下の各種変形（高速/低速単調引張、応力緩和、クリープ）、および、多軸応力下のクリープ変形を妥当な精度で評価できることが確認された。

概要 （英文）

Multiaxial creep tests using tension-torsion tubular specimens were conducted on Ni based directionally solidified (DS) superalloy at 870℃, where an axis of the specimen is in agreement with a grain growth direction of the material. The DS superalloy exhibited anisotropic creep behavior, and creep deformation resistance of the material was the lowest when ratio of tensile stress to shear stress is equal to unity under constant von Mises stress conditions. A viscoplastic constitutive model proposed in authors’ previous work on the DS superalloy was applied to the test results to examine its validity under the multiaxial stress conditions. The calculation results showed that an accuracy of the prediction of the creep deformation is not sufficient, especially, under shear stress conditions. Crystal plasticity analysis was conducted in order to investigate creep deformation mechanism at length scale of the crystal grain. Comparison of the analytical and the experimental results indicated that octahedral and cubic slip systems are active under the creep conditions. Anisotropic deformation property due to each slip system was suggested for the DS material, using the crystal plasticity model with simplified assumptions. On the basis of the analysis, new viscoplastic constitutive model was developed for the DS superalloy. A feature of the model was that inelastic strain is divided into two strain tensors, which are correspond to the octahedral and cubic slip systems. Calculations using the constitutive model were carried out for monotonic tension, relaxation under uniaxial condition, and creep under uniaxial and multiaxial stress condition to evaluate its capability for predicting the deformation of the material. It was demonstrated that the constitutive model could adequately describe the anisotropic behavior under uniaxial and multiaxial stress conditions with a set of material parameters.

報告者

キーワード