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Study on Fatigue Crack Initiation and Propagation Process of Ship Structural Materials by Computational Mechanics Approach

计算力学方法研究船舶结构材料疲劳裂纹萌生和扩展过程

基本信息

批准号：
14550859
负责人：
OSAWA Naoki
金额：
$ 2.24万
依托单位：
Osaka University
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (C)
财政年份：
2002
资助国家：
日本
起止时间：
2002 至 2004
项目状态：
已结题

来源：
https://kaken.nii.ac.jp/en/grant/KAKENHI-PROJECT-14550859/
关键词：
fatigue finite element method cyclic plasticity crystal plasticity dual phase steel fatigue crack ship structural material き裂計算力学高張力鋼ボロノイ分割

项目摘要

The relationship between the fatigue crack initiation and propagation behaviors and the microscopic nature of dual-phases ship structural steels with superior fatigue strength, which were developed recently, are investigated by computational mechanics approach in order to acquire knowledge conducive to the additional improvement of the fatigue strength of these materials. The crystalline plasticity theory is employed in this study because the mezoscopic mechanical properties and geometrical aspects (shape, size, arrangement of grains, etc.) of hard and soft phases can be incorporated in the calculation models. As results, followings are found ;(1)An automated preprocessing software system which can generate FE-meshes of cracked polycrystalline media with desired grain size and shape is developed.(2)The increase in the hardness of the hard phase leads to the decrease in the microscopic fatigue crack initiation parameter (FP) of the hard phase under low stress amplitude conditions while … More such effect vanishes under medium and high stress amplitude conditions. This means that an improvement in the fatigue crack initiation and propagation properties can be expected under small stress amplitude conditions, when the hardness of the hard phase increases.(3)The deformation behavior in the vicinity of the crack tip in a soft phase grain changes from mode I to mode II when the crack tip comes near the boundary of the hard phase. This means that the decrease in the propagation rate and the detour of the fatigue crack path can be expected at the boundary of the soft and hard phases.(4)The crack opening stress increases and the crack opening displacement decreases when the swiftness of cyclic softening is large. This means that the driving form of fatigue crack propagation is supposed to be weakened for the materials which show cyclic softening.(5)When a fatigue crack propagates in a narrow soft phase channel, both the crack opening stress and the crack opening displacement are not affected by the channel width This means that a fatigue crack slips through a hard phase when there exists a very narrow interstice in it. Less

本文采用计算力学方法研究了近年来新开发的具有优异疲劳强度的双相船舶结构钢的疲劳裂纹萌生和扩展行为与微观性质之间的关系，以期为进一步提高这类材料的疲劳强度提供理论依据。由于软、硬相的宏观力学性能和几何方面（形状、尺寸、晶粒排列等）可以纳入计算模型，因此本研究采用了晶体塑性理论。结果发现：(1)开发了一种能够生成具有理想晶粒尺寸和形状的裂纹多晶介质有限元网格的自动化预处理软件系统。(2)在低应力幅值条件下，硬相硬度的提高导致硬相微观疲劳裂纹萌生参数（FP）的降低，而在中、高应力幅值条件下，这种影响基本消失。这意味着在小应力幅条件下，当硬相硬度增加时，疲劳裂纹的萌生和扩展性能可以得到改善。(3)当裂纹尖端靠近硬相晶界时，软相晶粒中裂纹尖端附近的变形行为由I型转变为II型。这意味着在软、硬两相的交界处，疲劳裂纹扩展速率的减小和路径的迂回是可以预期的。(4)当循环软化速度较大时，裂缝张开应力增大，裂缝张开位移减小。这意味着对于表现出循环软化的材料，疲劳裂纹扩展的驱动形式应该被削弱。(5)当疲劳裂纹在狭窄的软相通道中扩展时，裂纹张开应力和裂纹张开位移都不受通道宽度的影响，这意味着当存在很窄的间隙时，疲劳裂纹穿过硬相。少