熱応力緩和構造モデル(1)供試体熱過渡強度試験; 第4報,非弾性と強度評価

Creep fatigue test of thermal strees mitigation structure model (1) Under thermal transient loadings; (4) Inelastic analysis and damage evaluation

田中 信之*

not registered

本報では非弾性解析を実施する事により弾性解析結果に基づくクリープ疲労強度評価手法の精度向上を図るとともに、非弾性解析を応力、歪挙動の予測に留めずに、強度評価にまで適用する手法確立のための研究の一環として、繰返し熱過渡荷重を受ける構造物のクリープ疲労強度の評価を非弾性解析結果を用いて実施した結果について報告する。評価対象は構造物強度確性試験施設(略称TTS)で熱過渡試験を実施し、クリープ疲労強度データの得られている熱応力緩和構造モデル(1)供試体であり、まず解析手法に関連して、塑性に関する構成則に異なる歪速度での応力-ひずみ関係を使用することにより、弾塑性解析における応力-歪挙動に及ぼす歪速度の影響を検討した。また解析モデル化の過程で構造不連続部、溶接継手部等の詳細形状モデル化、母材部・溶金部に対する異なる材料特性のモデル化を含めた広範な弾性及び弾塑性クリープ解析を行ない、さらに、これらの解析結果に基づいて、設計基準の有する安全裕度を取り除いた正味ベースのクリープ疲労損傷評価を実施した。上記解析及び評価の結果、下記の知見が得られた。1. 定常繰返し応力ひずみヒステリシス曲線の2直線近似式を弾塑性構成則として用いる場合、熱過渡試験条件に対応するひずみ速度110の-6乗/sec条件では従来使用されてきた110の-3乗/sec条件に対し歪範囲、クリープ疲労損傷として大きな値を与える。この傾向は形状不連続部で大きく現われる。

This report describes the inelastic analysis and creep-fatigue damage evalution of the thermal Stress Mitigation Structure Model (1).The model was subjected to severe cyclic thermal transient loadings between 250C and 620C by using Thermal Transient Test Facility for Structures(TTS). Heat transfer analyses using the measured temperature data and both elastic and inelastic thermal stress analyses were carried out by using detailed structure models and cyclic stress-strain curves obtained from two kinds of strain rate conditions as the constitutive stress-strain relationship. As for analyses of weldments, metallurgically discontinuous modeling as well as homogeneous modeling were investigated. Analysis results were utilized mainly for two objectives. 0ne was to advance the present creep-fatigue damage evaluation method (TTSDS) based on elastic analysis results. And the other was to present the prospect of damage evaluation method based on inelastic analysis. Main discussions and results are summarized as follows. (1)Basically the shape of elastically evaluated creep-fatigue damage distributions along the structure surfaces were almost the same as the ones evaluated inelastically for almost all portions of the model except for geometrically discontinuous portions such as weldment edges. And both evaluations demonstrated a good agreement with the crack distribution on the structure surfaces. (2)But more precise analysis showed that creep-fatigue damage based on elastic analysis gave non-conservative value when strain concentration factor (K in TTSDS) of 1.2 was uniformly assigned. Adequate value of K was evaluated up to 1.8 at certain weldment edges. (3)Bi-linear approximation of cyclic stress-strain curve at the condition of 110 l/s strain rate, corresponding to thermal transient test, gave larger strain range and larger creep-fatigue damage than the ones at the condition of 110 l/s ...