Fatigue crack propagation under various kind of loading

各种载荷下的疲劳裂纹扩展

• 批准号: 06555302
• 负责人: TOYOSADA Masahiro
• 金额: $ 8.19万
• 依托单位: KYUSHU UNIVERSITY
• 依托单位国家: 日本
• 项目类别: Grant-in-Aid for Scientific Research (A)
• 财政年份: 1994
• 资助国家: 日本
• 起止时间: 1994 至 1996
• 项目状态: 已结题
• 来源: https://kaken.nii.ac.jp/grant/KAKENHI-PROJECT-06555302/
• 关键词: crack opening and closure; random load; DELTAKAPPA_<RP>; plastic zone size received fatigue damage; inherent stress; cohesive force model; 二段二重ブロック荷重; 過小荷重による疲労き裂の加速現象; シミュレーションモデル; 表面き裂の合体成長; 等価分布応力; 遅延減速現象; 疲労き裂の停留条件; 表面き裂のK値; バネモデル

A Simulation model of fatigue crack opening and closing phenomena is introduced by developing Dugdale model.It is confirmed that the simulated RPG load (Re-tensile plastic zone Generated load) is in good agreement with experimental one.It becomes clear that a delayd retardation effect on fatigue crack propagation just after decreased maximum load can be also quantitatively assessed by effective stress intensity factor range DELTAKAPPA_<RP> corresponding to the period in which the re-tensile plastic zone appears, and stopping condition of a fatigue crack propagation is that DELTAKAPPA_<RP>*0.It is also confirmed from the model that plastic zone size omega received fatigue damage is proportional to a two power of DELTAKAPPA_<RP>. It is reported that a fatigue crack propagation curve in residual stress distribution field and under "storm model" loading with changing mean load can be quantitatively assessed by using omega. However a problem occures in case of receiving very large spike load, which is assessed to unsafe side.In the early stage of fatigue initiation, small surface cracks emanate and repeat coalescence one after another. Therefore aspect ratio of each surface crack has a large scatter. However the aspect ratio of a flctitious representative surface crack of which K value at the deepest point is the same as an increased K value due to interference effect of vicinity surface cracks and the depth is the same of the same of the deepest surface crack among surface cracks changes to be linear to the depth before the completion of coalesence. Moreover the method of a surface crack to be modeled into two dimensional problem by series springs model is also introduced.

通过对Dugdale模型的改进，建立了疲劳裂纹张开和闭合现象的模拟模型，证实了模拟的RPG载荷（Re-tensile plastic zone Generated load）与实验结果吻合较好，同时还表明，最大载荷降低后对疲劳裂纹扩展的延迟效应也可以用再拉伸塑性区出现的有效应力强度因子范围Δ KAPPA_来定量评价<RP>，疲劳裂纹扩展的终止条件为Δ KAPPA_<RP>* 0。从模型中还证实了塑性区尺寸Ω与Δ KAPPA_的2次方成正比<RP>。本文介绍了用Ω函数定量评估在变平均载荷的“风暴模型”载荷作用下，残余应力场中的疲劳裂纹扩展曲线。但在承受很大的峰值载荷时会出现问题，被评估为不安全。在疲劳萌生的早期阶段，表面小裂纹会萌生并一个接一个地重复合并。因此，每个表面裂纹的纵横比具有较大的分散性。然而，最深点处的K值与由于邻近表面裂纹的干涉效应而增加的K值相同并且表面裂纹中的最深表面裂纹的深度与最深表面裂纹的深度相同的代表性表面裂纹的纵横比在合并完成之前改变为与深度成线性。此外，还介绍了用串联弹簧模型将表面裂纹问题模拟成二维问题的方法。

项目成果

豊貞 雅宏 他3名: "ΔK_<RP>の物理的意味と構造物の疲労寿命推定法" 日本造船学会論文集. 第180号. 539-547 (1996)

Masahiro Toyosada 等 3 人：“ΔK_<RP> 的物理意义和结构的疲劳寿命估计方法”日本造船学会会刊第 180. 539-547 号（1996 年）。

豊貞雅宏・丹羽敏男: "RPG荷重のシミュレーション" 日本造船学会論文集. 176. 427-438 (1994)

Masahiro Toyosada 和 Toshio Niwa：“RPG 负载的模拟”日本造船学会汇刊 176. 427-438 (1994)。

Masahiro Toyosada et.al.: "Phhsical meaning of DELTAKAPPA_<RP> and fatigue crack propagation in the residual stress distribution field" International Journal of Fatigue. (in publishing).

Masahiro Toyosada 等人：“DELTAKAPPA_<RP> 的物理意义和残余应力分布场中的疲劳裂纹扩展”国际疲劳杂志。

Masahiro Toyosada and Toshio Niwa: "Simulation of RPG load" Jour.of the Soc.of Naval Architects of Japan. Vol.176. 427-438 (1994)

Masahiro Toyosada 和 Toshio Niwa：“RPG 负载模拟”Jour.of the Soc.of Naval Architects of Japan。

Masahiro Toyosada Toshio Niwa koji Gotoh: "Approximate Solution of K Value for a Surface Crack due to two Dimensional Problem by Series Springs Model" Jour.of the Soc.of Naval Architects of Japan. Vol.178. 535-543 (1995)

Masahiro Toyosada Toshio Niwa koji Gotoh：“基于串联弹簧模型的二维问题导致的表面裂纹 K 值的近似解”日本造船学会杂志。