Non-destructive Testing And Recognizing Methodologies Of Major Defects In Carbon Fiber Composites

During manufacturing process, contributed to the accuracy of processing parameters or human errors, defects are easily formed inside the composites, which affect its mechanical properties and sometimes may result in disastrous consequences. NDT(Non-Destructive Testing) is an analytical approach based on certain physical principles, usually utilized to test physical properties, certain characteristic status and its internal structures inside or on the surface of certain material, without doing any damage to it. It’s a reliable method to detect defects inside products, in order to qualify the product and evaluate its usability. On the basis of practical engineering applications, combining and comparing two NDT approaches(reflection A-scan and transmission C-scan), common defects in structure components made of CFRPs(Carbon Fiber Reinforced Polymers) were closely examined in this article, and criterions of various types of defects were systematically studied.(1) Theoretical Studies. Principles, calculations and characteristic signal analysis of reflection A-scan and transmission C-scan were evaluated; criterions of various types of defects were studied.(2) Sample Preparation. According to HB and features of practical products, simulating samples were designed to simulate various types of defects, for comparing and contrasting purpose. Samples with five different types of defects, such as delamination, mixing, detaches, voids and loose, were prepared via compression moulding method, following respective industry standards.(3) NDT of Samples and Analysis. Results from reflection A-scan and transmission C-scan of the samples contrasted with classic oscillograms. First, location of defect planes were deduced from transmission C-scan; and then defect properties were deducted from reflection A-scan analysis and contrasted with theoretical oscillograms. In addition to NDT, CT or metallographic analysis was performed, verifying the concluded defect type and criterions of various types of defects.(4) NDT of Practical Products. Reflection A-scan and transmission C-scan were performed over three practical products. The results were contrasted with defects’ recognition methods and oscillograms obtained from reflection A-scan of simulating samples, to determine the defect type. In combination of other analytical approaches, such as CT, thermal infrared imaging and metallographic analysis, a variety of defect types existing in practical products were verified, and assertions were made regarding sources of defects, providing references for further research and manufacture process.