Establishment of fatigue crack propagation law without stress intensity factor as parameter

2021 Fiscal Year Final Research Report

• Project/Area Number: 20K21048
• Research Category: Grant-in-Aid for Challenging Research (Exploratory)
• Allocation Type: Multi-year Fund
• Review Section: Medium-sized Section 24:Aerospace engineering, marine and maritime engineering, and related fields
• Research Institution: Kyushu University
• Principal Investigator: Gotoh Koji 九州大学, 工学研究院, 教授 (60274487)
• Project Period (FY): 2020-07-30 – 2022-03-31
• Keywords: 疲労 / 疲労亀裂伝播則 / 両振り塑性仕事 / 応力拡大係数 / 構造・材料

Outline of Final Research Achievements

The aim of this study was to develop a method to estimate fatigue crack growth history without using the stress intensity factor as a parameter. The results obtained are as follows.
(1) The cyclic plastic zone dimensions near the crack tip during fatigue crack propagation tests were measured by digital image correlation, and the relationship between these dimensions and fatigue crack propagation rate was investigated. The establishment of a fatigue crack propagation law with cyclic plastic work near the crack tip as a parameter was also confirmed.(2) The propagation law obtained in (1) was implemented in an elasto-plastic FE analysis to enable fatigue crack propagation simulation with the aid of utilising a remeshing process.(3) To improve the accuracy of crack growth history estimation by FE analysis, a stress-strain relationship was measured that is applicable to cyclic loading and high strain concentration conditions near the crack tip.

Free Research Field

船舶海洋工学

Academic Significance and Societal Importance of the Research Achievements

疲労亀裂伝播則は応力拡大係数範囲をパラメータとするParis則が提案されて以降，これの改善によってのみ発展したが，本研究の成果は破壊力学パラメータを不要とする疲労亀裂伝播則の可能性を示唆しており，学術面における独自性が極めて大きい．また，亀裂進展に伴う破壊力学パラメータの計算を不要し，通常の構造設計段階において得られる情報のみで疲労亀裂成長を評価できるため，社会インフラの疲労強度評価を簡潔かつ高精度に実施可能となり，社会的意義も大きい．