Development of fatigue design method of small-sized structures based on controlled nano-crystalline microstructure

2017 Fiscal Year Final Research Report

• Project/Area Number: 15H03896
• Research Category: Grant-in-Aid for Scientific Research (B)
• Allocation Type: Single-year Grants
• Section: 一般
• Research Field: Materials/Mechanics of materials
• Research Institution: Nagoya Industrial Science Research Institute (2016-2017); Meijo University (2015)
• Principal Investigator: Tanaka Keisuke 公益財団法人名古屋産業科学研究所, 研究部, 上席研究員 (80026244)
• Co-Investigator(Kenkyū-buntansha): 來海 博央 名城大学, 理工学部, 教授 (30324453) ; 清水 憲一 名城大学, 理工学部, 准教授 (50294434)
• Project Period (FY): 2015-04-01 – 2018-03-31
• Keywords: 機械材料・材料力学 / 疲労 / 破壊力学 / 薄膜 / ナノ結晶 / き裂進展 / 結晶粒径依存性 / 微小構造体

Outline of Final Research Achievements

The effect of notches on the fatigue strength reduction was studied using two types of nickel thin films were produced by electrodeposition: ultra-fine grained film (UFG) with the grain size of 384 nm and nano-crystalline grained film (NCG) with that of 17 nm. Micro-sized notches introduced by FIB. The fatigue strength decreased with increasing depth of micro-notches. NCG had much higher strength than UFG compared at the same notch depth. The fatigue limit was controlled by crack initiation. A fictitious crack model successfully predicted the reduction of the fatigue limit due to micro-notches. The characteristic crack length of NCG was much smaller than that of UFG. Macro-notched specimens produced by the UV-LIGA process also follow the fatigue strength reduction predicted by the fictitious crack model. Micro-mechanisms of fatigue crack initiation and propagation on nanocrystalline thin films were examined based on SEM and EBSD observations.

Free Research Field

材料強度学