Fracture mechanics and fractography of fatigue and creep fracture under service conditions.

使用条件下疲劳和蠕变断裂的断裂力学和断口分析。

• 批准号: 60550058
• 负责人: KOTERAZAWA Ryoichi
• 金额: $ 1.15万
• 依托单位: University of Tsukuba
• 依托单位国家: 日本
• 项目类别: Grant-in-Aid for General Scientific Research (C)
• 财政年份: 1985
• 资助国家: 日本
• 起止时间: 1985 至 1986
• 项目状态: 已结题
• 来源: https://kaken.nii.ac.jp/grant/KAKENHI-PROJECT-60550058/
• 关键词: Fatigue; Creep; Fracture mechanics; Fractography; Variable stress

Fatigue and creep crack propagation studies were carried out under variable stress conditions where overstresses of a very small number of cycles(1--2cycles) or of very short time( <about> 10sec) were applied intermittently between understress below the threshold of a large number of cycles (more than <10^5> cycles) or of long time( <about> 10hr).In the case of fatigue crack propagation at room temperature, Propagation rates were accelerated significantly (more than one hundred times in some cases) by such variable stresses as compared with the case of steady cyclic stresses both in air and in inert gas(nitrogen) environment. When magnitude of the understress is low, the acceleration was less in air than in nitrogen gas. This is shown to be a result of crack closure due to oxidation of fracture surface by means of Auger electron spectroscopy.In the case of creep crack propagation at elevated temperature, the acceleration by variable stresses was considerably less in thick plate specimens than in thin plate specimens, indicating an important effect of the deformation in thickness direction on the acceleration.In the case of creep-fatigue crack propagation under alternating stresses at elevated temperature, it was shown that the crack propagation is correleted well in terms of <DELTA> J both in air and in vacuum. The propagation rates in vacuum were slightly less than those in air due to absence of oxidation.

疲劳和蠕变裂纹扩展研究是在变应力条件下进行的，在低于大量循环阈值（超过<10^5>循环）或长时间（<约> 10hr）的欠应力之间间歇性施加极少量循环（1- 2循环）或极短时间（<约>0sec）的过应力。在室温下疲劳裂纹扩展的情况下，与空气和惰性气体（氮气）环境下的稳定循环应力相比，这种变应力的扩展速度明显加快（在某些情况下超过100倍）。当欠应力强度较小时，空气中的加速度小于氮气中的加速度。通过俄歇电子能谱分析表明，这是由于断口表面氧化导致裂纹闭合的结果。在高温蠕变裂纹扩展情况下，变应力加速度在厚板试样中明显小于薄板试样，说明厚度方向的变形对加速度有重要影响。在高温交变应力下蠕变疲劳裂纹扩展的情况下，在空气和真空中，裂纹扩展与<DELTA> J有很好的相关性。由于没有氧化，真空中的繁殖速率略低于空气中的繁殖速率。

项目成果

Takayoshi Nosho, Ryoichi Koterazawa and Toshikazu Murakami: "Fatigue and creep crack propagation under variable stresses" Proc. of the 4th Symposium on Fractography, Society of Materials Science, Japan. 46-50 (1986)

Takayoshi Nosho、Ryoichi Koterazawa 和 Toshikazu Murakami：“可变应力下的疲劳和蠕变裂纹扩展”Proc。

納所孝至,小寺沢良一,村上寿一: 日本材料学会第5回フラクトグラフィシンポジゥム前刷集. 46-50 (1986)

Takashi Noso、Ryoichi Koterasawa、Juichi Murakami：日本材料科学学会第五届断裂学研讨会预印本集，46-50 (1986)。

Takayoshi Nosho and Ryoichi Koterazawa: "Low cycle fatigue crack propagation and fractography of a SUS304 steel at elevated temperature" Proc. of the 24th Symposium on Strength of Materials at High Temperatures. 112-116 (1986)

Takayoshi Nosho 和 Ryoichi Koterazawa：“SUS304 钢在高温下的低周疲劳裂纹扩展和断口分析”Proc。

納所孝至,小寺沢良一: 日本材料学会第24回高温強度シンポジウム前刷集. 112-116 (1986)

Takashi Nosho，Ryoichi Koterasawa：日本材料科学学会第 24 届高温强度研讨会预印本集 112-116 (1986)。