【作者】 刘继忠；

【导师】 周晓军；

【作者基本信息】 浙江大学 ， 机械制造及其自动化， 2005， 博士

【摘要】 论文以工程“内外升降副翼面板孔隙率无损测试技术研究”为依托，围绕碳纤维复合材料(CFRP)孔隙率定量测试，探讨了复合材料孔隙率超声无损测试技术及有关问题，进行了碳纤维复合材料孔隙率便携式超声智能检测系统的研制，给出了其系统实现。 第一章，绪论。简单介绍了超声学、超声无损检测以及超声信号处理技术，并从课题研究的社会背景和项目背景出发，指出了课题研究的意义及碳纤维增强复合材料孔隙率无损检测的重要性与存在的问题，引入了课题的主要研究内容。 第二章，碳纤维复合材料孔隙率超声测试技术研究。首先，介绍了复合材料的基本知识及其缺陷类型，探讨了复合材料孔隙率定量检测的重要性和必要性，指出：①孔隙缺陷是复合材料重要缺陷类型之一，完全没有孔隙的纤维增强复合材料是不存在的；②孔隙形状大小、含量多少对复合材料的物理、机械性能存在着重要的影响；③先进复合材料在高技术领域的应用，必要对复合材料孔隙率进行定量检测。其次，对复合材料孔隙率的传统测试方法和超声检测的有关理论研究进行了回顾和分析，指出：①破坏性孔隙率测试方法工序繁琐，成本较高，且不能满足现场实时检测的需要；②复合材料孔隙率超声测试方法是一种非常有效和实用的方法，可以满足现场实时检测的需要；③孔隙率测试理论的完善和发展有必要考虑孔隙自身的形态和分布特征与孔隙含量之间的关系。再次，利用显微照相分析系统，对复合材料孔隙形状和统计分布特征进行了观察和统计分析，结果表明：①孔隙含量与孔隙形态之间存在着关系，当孔隙率较小时，孔隙多呈圆星，且多发生在富树脂区域，当孔隙率较大时，孔隙呈椭圆形或延纤维方向的拉长形，当孔隙率更大时，孔隙多呈发生在层间的较大的扁平形；②孔隙的长度、面积尺寸在观察平面内近似服从对数正态分布，孔隙的宽度尺寸(即垂直于层间界面方向尺寸)变化不大。最后，对复合材料孔隙率超声测试进行了理论研究和实测分析：①基于脉冲反射方式建立了含孔隙形态分布特征的复合材料孔隙率超声相对衰减测试模型，并基于理论模型和实测数据建立了孔隙率相对衰减测试公式，对其精度进行了分析，指出超声信号时域幅值相对衰减测试公式可以用于复合材料实际孔隙率测试，并将其二次公式和三次公式进行了比较分析，结果显示二次公式可以代替三次公式，精度差别较小，而计算更为简单方便；②基于频谱技术和实测数据，对复合材料孔隙率测试进行了频域辅助分析，发现超声信号频率偏移与复合材料孔隙率近似存在着线性关系，可用超声信号相对频率偏移进行更多还原

【Abstract】 The research is supported by the Project "Porosity Nondestructive Evaluation of airfoil Panels". The main objective is to find a methodology for carbon fibre reinforced plastics (CFRP) porosity testing and set up a novel portable ultrasonic measuring system.Chapter one is introduction. The ultrasonic testing and the ultrasonic signal processing are briefly introduced. Combined with the Project, the research necessities are discussed. The main contents of the dissertation are also given.Chapter two is the research of CFRP porosity evaluation by ultrasonic method. Firstly the background and the basic knowledge of the composites are introduced briefly. It is demonstrated that: 1) Voids defect is a kind of important defect in composites and there is no composites without voids; 2) The morphology and content of voids have an important influence on the mechanical property of CFRP; 3) It is necessary to have a porosity evaluation for CFRP when being used in high-tech fields. Secondly the traditional methods of porosity test and the theory and empirical equations of ultrasonic porosity test are discussed in this chapter. It shows that: 1) The destroyed ways of porosity measuring methods are superfluous and complicated, and also have a high cost; 2) The porosity of nondestructive evaluation (NDE) of ultrasonic is an effective and practical porosity measuring method, and it can also meet the real-time testing conditions; 3) It is necessary to consider the voids’ morphology and its statistic features for further research of porosity evaluation theories. Thirdly a morphological study of voids and a statistical study of the morphological features in carbon fiber reinforced plastics are implemented using microscopy and image analyzing system. The result shows: 1) The voids morphological features are correlated with the CFRP porosity. They tend to be small and spherical when the porosity is low and often occur in the resin abundant regions. With the porosity increasing, the voids become elliptical or elongated along the carbon fibers, and even become much larger and flattened between layers; 2) The fraction of voids is nearly a logarithmic normal distribution with the voids’ size measured in the layer plane. Lastly the research of porosity evaluation theory of ultrasonic and the experimental analysis are carried out. 1) Based on the pulse-echo mode, an ultrasonic attenuation model of CFRP porosity testing is established in更多还原