非弾性解析による設計法の研究(1)-評価フローの検討-

Study on structural design method by inelastic analysis(1); Investigation of design procedure

笠原 直人; 安藤 昌教

kasahara, Naoto; Ando, Masanori

高速増殖炉機器は材料のクリープ変形が生じる高温域で運転されるため非弾性設計が不可欠であり、合理的な設計を実現するために「非弾性解析による設計」の積極的な採用が期待されている。非弾性解析の主たる難しさは解析解が構成式等の解析法に依存することにある。本研究では、荷重の性質が構成式依存性に及ぼす影響を調査し、ラチェットひずみの構成式依存性は1次応力と弾性追従係数増大に伴い大きくなるが1次応力には比較的鈍感であることを明らかにした。また、構成式を系統的に変化させた場合の非弾性解析解の影響を調査し、構造物には構成式に鈍感な弾性追従特性が存在し、応力緩和曲線で記述されることを明らかにした。これらの結果に基づき、古典的構成式によるクリープ解析から、構成式に鈍感な弾性追従特性と1次応力を評価し、その結果に基づき保守的な解を与える構成式を選定した後に詳細非弾性解析を実施する設計アプローチを提案した。

Application of 'design by inelastic analysis' is expected to the rational structural design of fast reactor components where creep deformations occur due to elevated temperature operations. A main difficulty of the inelastic analysis method is a dependency of its solution to analysis methods such as constitutive equations. This study revealed that a dependency of ratchet strains on constitutive equations increases when an elastic follow-up factor or a primary stress enhances. It was also clarified that dependencies of strain ranges and fatigue damages on constitutive equations increase when an elastic follow-up factor increases, but they are rather insensitive to a primaly stress. Furthermore, it became evident. from the systematic investigations of dependencies on constitutive equations, that structures have elastic follow-up characteristics described by relaxation locus, which is insensitive to constitutive equations. Based on the above results, the authors have proposed an inelastic design approach. The first step of the approach is the evaluation of elastic follow-up characteristics and primary stresses by creep analyses with classical constitutive equations. The next step is the selection of constitutive equations that give conservative solutions under certain elastic follow-up characteristics and primary stresses. The third step is the detailed inelastic analyses with selected constitutive equations.