Supposition of the Interior Originating Fatigue Fracture Mechanism of Titanium Alloy Based on the Surface Small Crack Growth Properties in High Vacuum

基于高真空表面细裂纹扩展特性的钛合金内部起源疲劳断裂机制的假设

• 批准号: 12650066
• 负责人: NAKAMURA Takashi
• 金额: $ 2.37万
• 依托单位: HOKKAIDO UNIVERSITY
• 依托单位国家: 日本
• 项目类别: Grant-in-Aid for Scientific Research (C)
• 财政年份: 2000
• 资助国家: 日本
• 起止时间: 2000 至 2001
• 项目状态: 已结题
• 来源: https://kaken.nii.ac.jp/grant/KAKENHI-PROJECT-12650066/
• 关键词: Interior Originating Fracture; Surface Originating Fracture; Very High Cycle Fatigue; Fatigue Limit; High Vacuum; Ti-6A1-4V; Small Crack; Fractography; Ti-6A1-4V

Recently, some researchers reported that fatigue fracture in Ti alloy occurred from interior of the material in very high cycle over 10^7-10^8. The reason of this phenomenon has not been clarified. This study focused on the environment of the material where crack surface is not exposed to ambient air, and carried out fatigue experiments in high vacuum using specimens with small artificial defect. We investigated the mechanism of interior fatigue fracture by comparing crack propagation processes in air, vacuum and inside environment of the material. As a result, the following were obtained :1. A high vacuum environment improved the fatigue life drastically.2. The threshold of crack propagation was determined by the initiation of the crack in air whereas by the arrest of the crack in vacuum. The latter phenomenon coincided with the dominant factor of fatigue limit of interior fracture.3. Transitional stress intensity factor from stage 2a to stage 2b process decreased in high vacuum as compared with in air. This could be explained by the decrease of the local yield stress at crack tip. The longer fatigue life in high vacuum was considered to result from the lower efficiency of the adsorbed film, which facilitated the plastic deformation at crack tip.4. The tendency of longer fatigue life of interior originating fracture coincided with that in high vacuum. However, fatigue life in high vacuum was much longer than interior fracture. Fracture surfaces of interior fracture were more similar to those of surface fracture in high vacuum than in air, but they did not completely correspond to those in high vacuum. It seemed that the interior environment of material was not equal to high vacuum, and that the amount of gaseous molecule which affected crack propagation, was larger in the interior of the material than in high vacuum.

最近，有研究者报道，在10^7-10^8的超高循环下，钛合金的疲劳断裂发生在材料内部。这种现象的原因还没有弄清楚。本研究针对裂纹面不暴露于大气环境下的材料环境，采用人工小缺陷试件进行高真空下的疲劳试验。通过比较裂纹在空气、真空和材料内部环境中的扩展过程，探讨了材料内部疲劳断裂的机理。结果表明：1.高真空环境显著提高了疲劳寿命.裂纹扩展的门槛值由空气中裂纹的萌生决定，而由真空中裂纹的止裂决定。后一种现象与内构件疲劳极限的主导因素相吻合.与空气中相比，高真空中从2a阶段到2b阶段的过渡应力强度因子降低。这可以用裂纹尖端局部屈服应力的降低来解释。高真空条件下疲劳寿命的延长是由于低真空吸附膜的吸附效率降低，有利于裂纹尖端的塑性变形.内源断裂的疲劳寿命增长趋势与高真空下的趋势一致。高真空下的疲劳寿命远大于内部断裂。在高真空条件下，内部断口的断口形貌与表面断口的形貌相似，但与空气中的断口形貌不完全对应。材料的内部环境似乎并不等于高真空，材料内部影响裂纹扩展的气体分子量比高真空中大。

项目成果

Takashi NAKAMURA, Hiroyuki OGUMA, Toru NOGUCHI: "Gigacycle Fatigue Properties of Ti-6A1-4V under Uniaxial Tension"Proceedings of the 8th International Fatigue Congress, FATIGUE '02, (June, 2002, @Stockholm, Sweden). (decided to be issued).

Takashi NAKAMURA、Hiroyuki OGUMA、Toru NOGUCHI：“单轴张力下 Ti-6A1-4V 的千兆循环疲劳特性”第八届国际疲劳大会论文集，FATIGUE 02，（2002 年 6 月，@斯德哥尔摩，瑞典）。

小熊博幸, 中村 孝, 杉野淳一, 野口 徹: "Ti-6A1-4V合金の高サイクル疲労特性と応力比の相関"日本機械学会材料力学部門講演会公演論文集. No.01-16. 247-248 (2001)

Hiroyuki Oguma、Takashi Nakamura、Junichi Sugino、Toru Noguchi：“Ti-6A1-4V 合金的高周疲劳特性与应力比的相关性”日本机械工程学会材料力学系论文集 No.01-16。 247-248（2001）

小熊博幸, 中村 孝, 野口 徹: "Ti-6Al-4V合金の疲労寿命分布特性と破壊形態"材料. 50巻・10号. 1074-1079 (2001)

Hiroyuki Oguma、Takashi Nakamura、Toru Noguchi：“Ti-6Al-4V 合金的疲劳寿命分布特征和断裂形貌”材料，第 50 卷，第 1074-1079 期。

小熊博幸, 中村 孝, 野口 徹: "Ti-6A1-4V合金の疲労寿命分布特性と破壊形態"材料. 50巻・10号. 1074-1079 (2001)

Hiroyuki Oguma、Takashi Nakamura、Toru Noguchi：“Ti-6A1-4V 合金的疲劳寿命分布特征和断裂形貌”材料，第 50 卷，第 1074-1079 期。

Hiroyuki OGUMA, Takashi NAKAMURA, Toru NOGUCHI: "Fatigue Life Distribution and Fracture Types of T1-6A1-4V Alloy"Journal of the Society of Material Science Japan. Vol. 50, No. 10. 1074-1079 (2001)

Hiroyuki OGUMA、Takashi NAKAMURA、Toru NOGUCHI：《T1-6A1-4V 合金的疲劳寿命分布和断裂类型》日本材料学会杂志。