In-situ non-destructive evaluation process monitoring for CFRP manufacturing

Abstract

Carbon fibre reinforced plastics (CFRPs) are increasingly used in the aerospace industry because they offer lightweight construction and design flexibility. As sustainability becomes more important in business and to consumers, these materials help vehicles use less fuel and become more durable. The aerospace industry started the development of CFRP materials in the 1970’s, after which were also introduced in other industries, such as marine and automotive, leading to higher volumes of CFRP materials in subsequent years. This thesis is focussed on prepreg CFRP manufacturing and the detection of specific production flaws found in an industry survey. During the CFRP prepreg manufacturing process, raw CFRP layers are stacked during the layup phase and then cured to reach the component’s design mechanical and geometric specifications. To assure the right quality of the end product, the product is tested for flaws in the non-destructive evaluation (NDE) phase. The criticality of any detected flaw needs to be evaluated and if required reworked or rejected. This research presents an industry survey of typical CFRP manufacturing flaws and evaluates possible NDE technologies to detect these flaws in-situ in the manufacturing process. Analysis is performed by literature review and experimental tests. NDE process monitoring system should decrease the number of rejected and repaired products and increase the efficiency of the manufacturing process. Three NDE techniques were investigated in depth in this thesis to make a detailed design of a monitoring system: Lamb waves, laser displacement sensing and fibre optic sensors. This thesis concludes that the two latter technologies are promising for industrialization to improve the CFRP manufacturing process. The costs of production flaws in the CFRP manufacturing process are normally hidden in the cost structure of the end product. To address this the research also investigated the financial impact of rework and rejection of products in a CFRP manufacturing process and the estimated financial benefits of implementing an NDE process monitoring system. Overall, this research shows that the potential to detect flaws in-situ, the impact of rework and rejection and the financial feasibility of implementing a novel NDE process monitoring system will increase the efficiency and effectiveness of the CFRP manufacturing process.