Development of two-dimensional strain mapping technique around a fatigue crack using the pulsed neutron Bragg-edge transmission imaging and neutron diffraction

2021 Fiscal Year Final Research Report

• Project/Area Number: 20K20106
• Research Category: Grant-in-Aid for Early-Career Scientists
• Allocation Type: Multi-year Fund
• Review Section: Basic Section 80040:Quantum beam science-related
• Research Institution: Japan Atomic Energy Agency
• Principal Investigator: SU Yuhua 国立研究開発法人日本原子力研究開発機構, 原子力科学研究部門 J－PARCセンター, 技術副主幹 (20644264)
• Project Period (FY): 2020-04-01 – 2022-03-31
• Keywords: 疲労 / 中性子ブラッグエッジイメージング / 中性子回折 / 残留ひずみ / ステンレス鋼

Outline of Final Research Achievements

Fatigue damage is known as one of the major concerns in maintaining the integrity of large-scale engineering components. The nonlinear strain/stress distribution around a fatigue crack tip has a great impact to understand the fatigue and crack growth behavior of engineering component. This research is devoted to develop the fatigue evaluation technique by a combination of two neutron methods: Bragg-edge transmission imaging and diffraction.Two-dimensional maps of inhomogeneous residual strain and microstructure for the compact tension samples, which had been under different fatigue loading conditions, were determined by Bragg-edge spectral analysis. The obtained Bragg-edge imaging results were quantitatively compared with those determined by diffraction. The obtained original information of the strain and crystalline structure state inside the bulk gives a greater understanding on crack tip elastic and plastic strain evolution mechanisms in engineering materials.

Free Research Field

金属材料

Academic Significance and Societal Importance of the Research Achievements

これまでの研究では、実工業製品における高周波焼入歯車の結晶組織構造・残留ひずみが評価できた。その一方で、構造材料における事故の 8 割を占めているのが疲労破壊であり、材料の疲労き裂発生及び進展挙動の理解は実用上の最重要課題であった。疲労き裂の進展特性の定量評価技術を開発するために、中性子ブラッグエッジイメージング法及び中性子回折法を用いて、繰り返し負荷によるひずみの進展の計測が可能となった。中性回折法によって疲労き裂先端近傍の残留応力分布が測定できた。また、相応力解析において疲労き裂周辺の残留応力分布は、材料の相違によって異なることが確認された。