Substantiative research on the repeating contact model for the formation mechanism of granular region in subsurface fracture

2022 Fiscal Year Final Research Report

• Project/Area Number: 19H02034
• Research Category: Grant-in-Aid for Scientific Research (B)
• Allocation Type: Single-year Grants
• Section: 一般
• Review Section: Basic Section 18010:Mechanics of materials and materials-related
• Research Institution: National Institute for Materials Science
• Principal Investigator: OGUMA Hiroyuki 国立研究開発法人物質・材料研究機構, 構造材料研究拠点, 主幹研究員 (80515122)
• Co-Investigator(Kenkyū-buntansha): 吉中 奎貴 国立研究開発法人物質・材料研究機構, 構造材料研究拠点, 主任研究員 (00825341)
• Project Period (FY): 2019-04-01 – 2023-03-31
• Keywords: 超高サイクル疲労 / 内部起点型破壊 / 真空環境 / 組織微細化 / 凝着 / 粒状領域 / 高強度金属材料

Outline of Final Research Achievements

In the very high cycle fatigue of titanium alloys, a peculiar region with a granular aspect forms on the fracture surface of the subsurface fracture. The formation mechanism of this granular region was investigated, focusing on the environment to which the fatigue crack is exposed and the mechanical conditions. Model experiments using spherical specimens, along with detailed observations and analysis, revealed that repeated surface contact and separation in a vacuum caused the formation of asperities. Moreover, it was found that microstructural refinement and adhesion were the dominant phenomena. Based on the experimental results, a new model for the formation mechanism of the granular region is proposed. This model can explain the characteristics of the granular region and the properties of a subsurface fracture, which occurs at lower stress levels and has a longer life compared to a surface fracture.

Free Research Field

材料強度学

Academic Significance and Societal Importance of the Research Achievements

超高サイクル疲労における内部疲労き裂の進展機構について、材料の種類に依存しないモデルを示したことにより、高強度金属材料に関して統一的な疲労強度・寿命の評価と予測手法を確立できることが示唆される。そして、破壊機構の詳細が明らかになることにより、超高サイクル域における高強度化や長寿命化ならびにバラツキを小さくするための材料設計や構造設計の指針を出すことが可能になると思われる。本研究の成果が、高強度金属材料を適用する機械構造物の高信頼性化へと繋がることが期待される。