報告書番号

T99017

タイトル（和文）

ガスタービン動翼材Inconel738LCの高温強度評価法の開発 -第４報：温度変動繰返し変形条件下への非弾性構成式の拡張-

タイトル（英文）

Development of high temperature strength evaluation method for Inconel738LC (4th report: Extension of inelastic constitutive equations to anisothermal conditions)

概要 （図表や脚注は「報告書全文」に掲載しております）

本研究ではガスタービン動翼材・Ni基超合金IN738LCの温度変動下における非弾性変形挙動について検討した。IN738LCを用いて450～950℃で等温および温度変動下の変形特性試験を行った結果、温度変動繰返し変形条件下において、繰返し変形に伴い高温側の応力が低下し低温側の応力が増大するという通常の金属材料では見られない特異な非弾性挙動が観察された。実験結果に基づく考察から高温側でのみ背応力の静的回復項が作用すると仮定し、既研究で等温条件に対して提案した非弾性構成式を温度変動条件下へと拡張した。拡張非弾性構成式を用いてIN738LC の様々な非弾性挙動について数値シミュレーションを行った結果、等温下の各非弾性挙動はもちろん、温度変動繰返し変形についても妥当な精度で記述できることが確認された。

概要 （英文）

A series of deformation tests was conducted on Ni-based superalloy IN738LC under isothermal and anisothermal conditions between 450℃ and 950℃. Under the isothermal conditions, the material shows no rate/time-dependency below 700℃, while there is distinct rate/time-dependency above 800℃. Anomalous inelastic behavior was observed under the anisothermal conditions; with an increase of cycles, stress at higher temperatures becomes smaller in absolute value, and stress at lower temperatures becomes larger under both In-Phase and Out-of-Phase conditions. This inelastic behavior is quite difficult to describe adequately by conventional constitutive models. Based on the experimental results, the previously proposed viscoplastic constitutive model for IN738LC at 850℃ was extended to the anisothermal conditions. In the constitutive model, evolution of internal variable Y, which was incorporated in a dynamic recovery term of a back stress in order to represent anisotropic deformation resistance, was assumed to be active under the higher temperatures and negligible under the lower temperatures. With material constants determined from the isothermal data, the extended constitutive model was applied to the anisothermal cyclic loading as well as monotonic tension, stress relaxation, creep and cyclic loading under the isothermal conditions. It was demonstrated that the present constitutive model was successful in describing the inelastic behavior of the material adequately, including the "anomalous inelastic behavior" observed under the anisothermal conditions.

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