腐蚀坑诱发疲劳的概率研究

Benjamin Starr, Serge L. Shishkin, C. Sahay, Suhash Ghosh
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引用次数: 0

摘要

腐蚀疲劳是导致飞机和涡轮部件过早失效的主要损伤机制,特别是在海洋环境中。已经看到,与干燥空气中的疲劳强度相比,即使是相对温和的腐蚀性大气也会大大降低许多结构的疲劳强度。这一过程开始于由于腐蚀坑引起的表面退化,腐蚀坑成为疲劳起始点和零件加载时的初始损伤。表面凹坑的微观组织和形貌是裂纹萌生的关键。假定裂纹起源于狭窄的“微坑”的尖角和底部。根据这些凹坑的密度和微观组织分布,对裂纹萌生过程进行了统计表征。在表面损伤起爆分析的基础上,引入了由坑尺寸和最高曲率组成的新的形态特征,并通过引入的形态特征的分布证明了这些特征是有效的点蚀疲劳度量指标。这些特性的分布是由实测数据估计出来的。在不同的坑形分布和曲率下,评价了不同热处理铝2024试样的点蚀形貌的影响。试样寿命的统计分布是使用“最薄弱环节”方法来估计的,即通过计算表面任何地方至少产生一个裂纹的概率。本文详细介绍了裂纹起裂的统计模型、腐蚀参数估计的方法以及统计建模的代表性数值实例。在Zygo ZeGage三维轮廓仪上对表面凹坑特征进行了无损测量。ZeGage使用相干扫描干涉测量(CSI)技术,该技术使用光的波长来定义其高精度。精心校准的CSI分析器可以测量更大范围的表面质量,并具有亚纳米精度的可重复结果。高放大倍率(20倍,50倍,100倍)镜头增加了测量更光滑表面的通用性。采用分割方法进行大面积扫描。所选镜头的大视场和自动快速扫描允许在拼接这些单独的片段后获得相当小的数据文件。
本文章由计算机程序翻译,如有差异,请以英文原文为准。
Probabilistic Study of Corrosion Pit-Induced Fatigue
Corrosion fatigue is the major damage mechanism responsible for the premature failure of the aircrafts and turbine parts, especially in the marine environment. It has been seen that even relatively mild corrosive atmospheres can reduce the fatigue strength of many structures considerably as compared to their fatigue strength in dry air. The process starts with the surface degradation due to the corrosion pits, that become fatigue initiation sites and the initial damage when the part is loaded. Microstructure and morphology of the surface pits is critical for the crack initiation. It is assumed that the cracks are initiated at the sharp corners and bottoms of the narrow “micropits”. The paper provides a statistical characterization of the crack initiation process based on these pits’ density and microstructure distribution. Based on the surface damage initiation analysis, new morphological characteristics combining the pit size and highest curvature are introduced and have shown to be the efficient metrics for pitting fatigue with the distribution of introduced morphological characteristics. The distribution of these characteristics is estimated from the measured data. Effects of pitting morphology are evaluated for various heat-treated Aluminum 2024 specimens, with varying distribution of pit shapes and curvatures. The statistical distribution of specimen life is estimated using the “weakest link” approach, that is, by computing the probability that at least one crack is initiated anywhere on the surface. The paper contains a detailed description of crack initiation’s statistical model, methodology of corrosion parameter estimation and representative numerical examples of statistical modeling. The surface pit characterization has been nondestructively measured on a Zygo ZeGage 3D profiler. The ZeGage uses a Coherence Scanning Interferometry (CSI) technique which uses the wavelength of light to define its high precision. A carefully calibrated CSI profiler can measure a larger range of surface qualities with repeatable results in sub-nanometer precision. High magnification (20x, 50x, 100x) lenses increase the versatility in measuring even smoother surfaces. Large area scanning was done using a segmentation approach. A large field of view of the selected lens and automated rapid scanning allowed for reasonably smaller data files obtained after stitching these individual segments.
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