Search

This study discusses the brittle fracture controlling parameter for the steel components under mixed mode loading with focusing on the Weibull stress concept proposed as an original Beremin model. The Weibull stress based on the original Beremin model, which is calculated by integrating a maximum principal stress over the fracture process zone around crack-tip, is widely demonstrated to be a fracture cntrolling parameter independent of crack-tip plastic constraint for 3PB specimen under mode I loading. Critical Weibull stress obtained by 3PB test founds to be different from that obtained by 4PS specimen under mixed mode loading. The reason why the Weibull stress can not be a unified fracture controlling parameter is interpreted from the crack-tip stress fields that shows the different principal stress ratio between the specimens subjected to mode I and mixed mode loading conditions. A new fracture model considering stress components other than maximum principal stress is necessary to propose a fracture controlling parameter independent of plastic constraint and loading mode mixture.

The small specimen tensile test is commonly used as the basic test to evaluate the irradiation effect on the strength of fusion structural materials after irradiation, and a lot of attempts were made to qualify the data obtained by small size specimen, but the specific attention on the evaluation of strain were not satisfactory given. This study therefore aims to propose a novel non-contact strain measurement technique, based on digital image correlation (DIC) method, for reduced-activation ferritic/martensitic (RAFM) steel, e.g., F82H, as the leading candidate structural material of fusion in-vessel components in Japan. A flat rectangular miniature specimen, e.g., SS-J3 type, was adopted to evaluate non-irradiated and neutron-irradiated tensile properties. In the proposed DIC, very tiny surface machining flaws were recognized by the DIC computation program and utilized to set several pairs of the gauge end points with a fixed gauge length. In case of the room-temperature test, it was clearly demonstrated that this procedure could provide more precise and reliable data compared with the previous approach of the single-scan measurement under floated gauge length. Superior linearity was achieved and recognized DIC points of concern were traceable during the entire period of the test. By applying this technique, superior high-dose stability of elastic properties of F82H was first demonstrated.

核融合ブランケット用構造材料である低放射化フェライト鋼の研究開発のためには，微小試験片試験技術を用いた照射効果の評価が不可欠となる．しかし，微小試験片を用いた評価結果は，サイズ効果等によって標準試験法の評価結果とズレが生じる場合があり，その結果をそのまま設計に適用できないことが懸念される．本研究では，核融合ブランケットを構造設計する際に不可欠な低放射化フェライト鋼F82Hの引張特性について，標準試験片と微小試験片による評価結果の比較検討を行う．, 日本原子力学会 2018年秋の大会