材料断裂表面微观三维形貌扫描白光干涉表征关键问题研究

The measurement and quantitative analysis of fracture surface three-dimensional microtopography have important values for understanding the initiation and propagation of crack process, thereby obtain increasing attention. In this study we use scanning white-light interferometry (SWLI) for the characterization of fracture, but for it's large height variation, non-homogeneous and weak reflection of the fracture surface，the detected interferometric signals will seriously degrade and, in most cases, submerge in noise, which consequently cause large recontruction error. Therefore, this project is designed to investigate how to further enhance the interference signal, effectively reduce the noise and increase the signal-to-noise improvement ratio, and study on the mechanism of the interferometry degradation due to large depth ambiguity and surface phase distortion, and analyze their influences on the measurement, explore the method for the restoration of interferometry signals and processing of outliers data so as to reduce the measurement error; In combination with the microscopic aspect ratio roughness parameter which is related to the mechanical properties of metallic fracture sample, we will modify the theory and method for 3-Motif characterization；we will exam the interfeometry characterization methodology through experimental test on several typical kinds of fractures as fatigue, dimple, intergranular, cleavage, respectively. The SWLI has long measurement range, as long as the above difficulties are resolved, this technique possesses advantages of both large efficient view field and high longitudinal resolution and, combined with the 3-D characterization, can provide quantitative and objective evidences for the study of fracture process. This project will build the theoretical and technical foundation for the realization of computerized automatic identification of fracture.

断口表面微观三维形貌检测及定量分析对于研究断裂的产生及扩展具有重要价值，愈来愈受到人们的高度重视。本课题采用扫描白光显微干涉表征断口，由于断口表面起伏大，反射极微弱且不均匀，所以干涉信号退化严重，并大多被噪声淹没，造成很大重建误差。为此，项目拟研究如何进一步增强干涉信号、抑制噪声、提高信噪比改善，并就干涉信号大深度变化模糊退化和表面位相畸变退化机理及其对检测的影响进行分析，探索复原退化干涉信号和改进奇异数据修正的方法，从而降低检测误差；结合与断口材料力学性能相关的纵横比三维微观粗糙度参数，改进3D-Motif表征理论和方法；分别对金属断口样品的疲劳、韧窝、沿晶和解理等几类典型微观特征形貌进行干涉表征验证。扫描白光干涉术纵向测程范围大，只要相关难题得以解决，该技术兼顾有效视场和纵向精度，再结合三维表征，可为研究断裂机理提供量化且客观的依据。本项工作可为实现断口的计算机自动识别构筑理论基础。

1)对扫描白光干涉系统的设计进行了改进优化，完善了多帧自动采集系统；.2)提出一种并行积分与小波算法相融合的新算法，运用于多幅干涉图信息提取微弱干涉信号，能提高干涉信号信噪比，并能有效降低PZT扫描的非线性形变的影响;.3)采用Monte-Carlo方法对随机粗糙表面干涉场进行了数值模拟;.4)研究基于贝叶斯估计的微弱干涉信号处理方法，并将贝叶斯估计方法运用于三维重建形貌寄点数据的处理;.5)对结合数学形态学处理的3D-Motif表征进行了初步探索。