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Observations of subcritical crack initiation and growth processes by scanning acoustic microscope

扫描声学显微镜观察亚临界裂纹萌生和扩展过程

基本信息

批准号：
63550085
负责人：
OGURA Keiji
金额：
$ 1.34万
依托单位：
Osaka University
依托单位国家：
日本
项目类别：
Grant-in-Aid for General Scientific Research (C)
财政年份：
1988
资助国家：
日本
起止时间：
1988 至 1989
项目状态：
已结题

来源：
https://kaken.nii.ac.jp/grant/KAKENHI-PROJECT-63550085/
关键词：
Scanning Acoustic Microscope Fatigue Slip bands Surface cracks Initial stage of crack growth 初期き裂進展

项目摘要

Scanning acoustic microscope (SAM) was used to investigate the the crack initiation and propagation processes in the subcritical crack growth problems such as fatigue, stress corrosion and creep. The main interest was put on examining when and how the slip bands grow into the microcracks in fatigue. The materials selected in this study were pure copper, pure nickel and type 304 stainless steel. Fatigue tests were conducted and interrupted in a certain stage. The samples were provided for the observations by SAM and an optical microscope. The results are summarized as follows.1. The fine fatigue slip bands were able to observe when a frequency of ultrasonics was selected beyond 600MHz in the SAM observation. Subsurface informations, on the other hand, were able to obtain only when the lower frequency less than 40OMHz was used in the observations. The slip bands and cracks in the SAM image were visible best in intensity in the pure nickel samples.2. A clear difference was often observed in the SAM images in the certain two slip bands in which no differences were found in the optical microscopic images. This was found to be due to the differences in the subsurface situation and in the surface topography of the two slip bands.3. An interference fringes were observed around the initiated cracks, These fringes, however, were not observed for any slip bands. The transitional process from a slip band to a crack was unfortunately not examined in this study.4. The depth and the inclined angle of the initiated cracks were estimated quantitatively by the analyses of a V(z) curve and an interference fringe.

利用扫描声学显微镜（SAM）研究了疲劳、应力腐蚀和蠕变等亚临界裂纹扩展问题中裂纹的萌生和扩展过程。主要研究滑移带在疲劳过程中何时以及如何扩展成微裂纹。本研究选用的材料为纯铜、纯镍和304型不锈钢。进行疲劳试验，并在一定阶段中断。提供样品用于SAM和光学显微镜的观察。研究结果如下：1.当超声频率超过600MHz时，SAM观察中能够观察到精细的疲劳滑移带。另一方面，只有在观测中使用低于400MHz的较低频率时才能获得地下信息。SAM图像中的滑移带和裂纹在纯镍样品中的强度最好.在光学显微镜图像中没有发现差异的某些两个滑移带中，在SAM图像中经常观察到明显的差异。这被认为是由于两个滑移带的亚表面情况和表面形貌的差异。在初始裂纹周围观察到干涉条纹，而在滑移带周围没有观察到干涉条纹。不幸的是，从滑移带到裂纹的过渡过程在本研究中没有研究。通过对V（z）曲线和干涉条纹的分析，定量地估算了裂纹的深度和裂纹的倾角。