Evaluation of effective stress around Mode II crack tips under rolling contact fatigue

• Project/Area Number: 19K14875
• Research Category: Grant-in-Aid for Early-Career Scientists
• Allocation Type: Multi-year Fund
• Review Section: Basic Section 18040:Machine elements and tribology-related
• Research Institution: University of Toyama
• Principal Investigator: Mizobe Koshiro 富山大学, 学術研究部工学系, 准教授 (70727718)
• Project Period (FY): 2019-04-01 – 2021-03-31
• Project Status: Completed (Fiscal Year 2020)
• Budget Amount: ¥4,160,000 (Direct Cost: ¥3,200,000、Indirect Cost: ¥960,000); Fiscal Year 2020: ¥910,000 (Direct Cost: ¥700,000、Indirect Cost: ¥210,000); Fiscal Year 2019: ¥3,250,000 (Direct Cost: ¥2,500,000、Indirect Cost: ¥750,000)
• Keywords: 転がり疲労 / 介在物 / き裂 / 炉ー高周波併用加熱 / 炉-高周波併用加熱法 / 非金属介在物 / き裂進展下限界 / 二重硬化層 / モードⅡ / 下限界応力拡大係数幅

Outline of Research at the Start

軸受はもはや統計的に発生する破壊を許さず、定期検査による寿命保証の時代に入りつつある。寿命保障には内部せん断き裂進展下限界(ΔKⅡth)が重要な設計基準となるが、材料内部の停留き裂を観察できないことがボトルネックとなり、ΔKⅡthの直接測定ができなかった。そこで申請者が開発した炉―高周波併用加熱法により二重の材料硬化層を作成し、研究室が特許を持つ転がり疲労試験機を用いて、き裂の全数観察を行う。この組合せにより、転がり疲労下で発生した内部き裂を二重硬化層の間に誘導し、そのうち停留き裂を観察し、解析によりせん断応力を求め、ΔKⅡthを測定することを目的とする。

Outline of Final Research Achievements

In order to evaluate a driving force of the crack propagation under rolling contact fatigue using high-carbon high-chromium steels, we observed the fatigue cracks from non-metallic inclusions. We prepared the shaft which was furnace and induction quenched (FIH method) and performed one-point rolling contact fatigue. Through this FIH method, this specimen had a subsurface soft area of 0.5 mm from the surface. After the rolling contact fatigue tests, we found many fatigue cracks from the non-metallic inclusions. There were various lengths and depths of cracks and the cracks in the soft area were longer than those in other areas. This indicates that we successfully control crack initiation and propagation under rolling contact fatigue in FIH specimens.

Academic Significance and Societal Importance of the Research Achievements

風力発電機などに使用される大型軸受では、近年20年の実用寿命保証が求められており、軸受メーカーは超長期間、莫大な補償に備える事となってしまっている。このような超長期全数保証の根拠を確率的な現象に求めてしまっては、あまりに経済的な損失が大きい。本研究で得られた成果は破壊力学のき裂停留パラメータに注目したものであり、将来的に軸受の全数寿命保障に対する設計指針を確立することにつながる。

Research Products

• [Journal Article] Image Evaluation of Distribution of Carbide Particles in Repeatedly Quenched (Two and Three Times) JIS-SUJ2 Steels (2021)
  • Author(s): Mizobe Koshiro、Matsueda Takahiro、Miyabe Yoshinobu、Kida Katsuyuki
  • Journal Title: Solid State Phenomena Volume: 315 Pages: 66-71
  • DOI: 10.4028/www.scientific.net/ssp.315.66
  • Peer Reviewed
• [Journal Article] Observation of Crack Originating from Non-Metallic Inclusions in Furnace-Induction Heated SUJ2 Steel under One-Point Rolling Contact Fatigue at High Contact Pressure (2021)
  • Author(s): Koshiro Mizobe, Yuto Nakamura, Yuki Yano, Takahiro Matsueda and Katsuyuki Kida
  • Journal Title: Materials Science Forum (in press) Volume: 1033 Pages: 3-7
  • Peer Reviewed
• [Presentation] Effect of surface hardening methods (IH and FIH) on the various types of rolling contact fatigue (ball-shaft and ball-plate) (2020)
  • Author(s): Koshiro Mizobe
  • Organizer: 2020 the 8th International Conference on Mechanical Engineering, Materials Science and Civil Engineering (ICMEMSCE2020)
  • Int'l Joint Research / Invited
• [Presentation] Fracture behavior of repeatedly induction-heated shafts on various types fatigue situation (rotating bending, rolling contact and reciprocating motion) (2020)
  • Author(s): Koshiro Mizobe
  • Organizer: 2020 8th International Conference on Metallurgy Technology and Materials (ICMTM2020)
  • Int'l Joint Research / Invited
• [Presentation] 鋼の回繰返し焼入れした高炭素クロム軸転曲げ疲労試験から観察された疲労起点介在物と材料組織 (2019)
  • Author(s): 溝部浩志郎、木田勝之
  • Organizer: 日本鉄鋼協会第178回秋季講演大会 機械構造用鋼表面硬化部材の疲労損傷Ⅱシンポジウム