Experimental Verification of Fatigue Strength Properties under Non-proportional Multiaxial Variable Loading and Improvement of Fatigue Strength Evaluation Method

2020 Fiscal Year Final Research Report

• Project/Area Number: 18K03854
• Research Category: Grant-in-Aid for Scientific Research (C)
• Allocation Type: Multi-year Fund
• Section: 一般
• Review Section: Basic Section 18010:Mechanics of materials and materials-related
• Research Institution: Ritsumeikan University
• Principal Investigator: Itoh Takamoto 立命館大学, 理工学部, 教授 (40242581)
• Co-Investigator(Kenkyū-buntansha): 小川 文男 立命館大学, 理工学部, 助教 (00424812) ; 坂根 政男 立命館大学, 総合科学技術研究機構, 上席研究員 (20111130)
• Project Period (FY): 2018-04-01 – 2021-03-31
• Keywords: 金属疲労 / 材料強度 / 寿命評価 / 多軸負荷

Outline of Final Research Achievements

A fatigue life evaluation program for non-proportional multiaxial variable loading has been developed. The IS method proposed by the principal investigators is used to evaluate the stress or strain, and the waveform is divided by the Rain-flow method after converting the multiaxial load to uniaxial load. The IS method is used to convert a multiaxial load into a uniaxial load, and then the waveform is divided by the Rrain-flow method. When dividing the waveform based on the Rainflow method, if data noise is included, the noise is treated as a maximum and/or a minimum value, and the waveform cannot be divided properly. Therefore, in order to remove the noise, a numerical algorithm that performs the 7-point approximation method was added to the program. A improved program for fatigue life evaluation was developed by solving nonlinear equations related to stress or strain using the Newton method.

Free Research Field

材料力学

Academic Significance and Societal Importance of the Research Achievements

非比例多軸変動負荷における疲労寿命の評価については実質に即し、実用的かつ高度な知識を有しない技術者でも運用できるソフトウェアは開発されていない。本研究では多軸疲労の解析において実績のあるIS法にレインフロー法による波形分割、ノイズ除去の概念を組み込んだ方法を提案した。非比例ひずみ範囲あるいは応力範囲をCoffin-Manson則と比較して、非線形方程式を解くことで疲労寿命を求めるとともに、変動負荷の影響を解析できる。現時点では、概念と基礎的なプログラムを開発した段階であるが、このような簡便で取り扱いが容易な非比例多軸変動負荷の解析手法は他では提案されておらず、工学的に重要であると考えられる。