Study on Mechanism of Bending Ftigue Breakage and Strengthening Method of Gear Teeth

Research Project

Project/Area Number	06650176
Research Category	Grant-in-Aid for General Scientific Research (C)
Allocation Type	Single-year Grants
Research Field	設計工学・機械要素・トライボロジー
Research Institution	Tottori University
Principal Investigator	ODA Satoshi Faculty of Eng., Tottori Univ., Professor, 工学部, 教授 (50032016)
Co-Investigator(Kenkyū-buntansha)	MIYACHIKA Kouitsu Faculty of Eng., Tottori Univ., Assoc.Prof., 工学部, 助教授 (30157664) KOIDE Takao Faculty of Eng., Tottori Univ., Assoc.Prof., 工学部, 助教授 (60127446)
Project Period (FY)	1994 – 1995
Project Status	Completed (Fiscal Year 1995)
Budget Amount *help	¥1,900,000 (Direct Cost: ¥1,900,000) Fiscal Year 1995: ¥400,000 (Direct Cost: ¥400,000) Fiscal Year 1994: ¥1,500,000 (Direct Cost: ¥1,500,000)
Keywords	Gear / Fatigue Strength / Sintered Metal / Shot-Peening / Ion-Nitriding / Tufftriding / Load Variation / Miner's Hypothesis / 調質 / 焼結温度 / 密度 / 浸炭焼入れ / ずぶ焼入れ
Research Abstract	Bending fatigue tests (pulsator tests) for shot-peened sintered metal gears were carried out, and the effect of shot-peening on the bending fatigue strength of sintered metal gears was determined. The tooth profile changes of gears due to ion-nitriding, tufftriding and case-hardening were examined, and the deformations of gears due to these strengthening methods were determined. The bending fatigue tests for ion-nitrided gears with different case depths under uniform cyclic loading conditions were carried out, and the bending fatigue strength of ion-nitrided gears was determined. Furthermore, the bending fatigue characteristics of the ion-nitrided gears under two-step loading conditions was discussed on the basis of Miner's hypothesis. The main results obtained from this investigation are summarized as follows. 1. The surface hardnesses of case-hardened sintered metal gears increase by applying shot-peening, but the case depths of these gears do not change depending on shot-peening. The surface hardnesses do not change with the carbon content (in the range of C0.3-0.5%), but the core hardnesses increase with the carbon content. 2. The bending fatigue strengths of case-hardened sintered metal gears become 20-40% larger by applying shot-peening. 3. The tooth profile changes of gears due to ion-nitriding and tufftriding are almost equal and fairly small, but those due to case-hardening are fairly large. 4. The bending fatigue limits of S45C and SACM645 ion-nitrided gears become maximums for ion- nitriding time 34 and 17 hours, respectively, and are about 40 and 80% larger than the normalized gears. The bending fatigue limits of S45C gears become about 30% larger by tufftriding. 5. The bending fatigue breakage of ion-nitrided gears occurs by the propagation of some of small cracks which initiate at the compound layr.