Defect Development during the Preforming of Non-Crimp Fabrics

这个博士试图解决的研究问题是，在纺织增强材料的预成型过程中，皱纹等缺陷是通过什么机制产生的，以及如何表征和最大限度地减少这些缺陷。纺织增强材料是复合材料制造中的一个关键研究领域，因为它们为航空航天和汽车工业提供了一条更经济、更快生产复合材料部件的途径。然而，目前在制造工艺的预成型步骤中出现的缺陷构成了一个重大障碍，因此本博士试图解决这个问题。所考虑的纺织增强物是无卷曲织物（NCF），其是缝合在一起而不是编织的新型多层纺织物。该博士学位的方法是开发一种新型的实验预成型装置，该装置能够在各种边界条件下使用3D数字图像相关（DIC）跟踪和测量NCF中皱纹和相关纤维应变的发展。然后，将使用这些数据来建立应变和起皱幅度之间的关系，以便尝试建立起能够根据所引起的应变来确定特定织物增强物的起皱开始的起皱成形极限图（WFLD）。该研究将强调一种合理的标准化方法，用于通过一系列简单测试通过实验获得特定织物的起皱极限，然后将其应用于一系列织物，并显着简化织物选择过程及其后续制造。此外，在这些实验中获得的形成过程中的皱纹发展的理解将被用来通知的NCF的形成的微观力学模型有限元（FE）模型的发展。该模型将能够预测褶皱的位置和幅度以及相关的应变，并且可以直接用于开发特定织物的WFLD，而不需要任何实验测试。最终，博士将尝试根据实验和模拟数据进行优化研究，以优化预成型过程，最大限度地减少缺陷。该项目属于EPRSC的“材料工程-复合材料”研究领域。'

The research questions that this PhD is trying to address are by what mechanisms do the defects such as wrinkles develop during the preforming of textile reinforcements and how can these defects be characterised and minimised. Textile reinforcements are a critical area of research within composite manufacturing as they provide a pathway towards more cost effective and faster production of composite components for the aerospace and automotive industries. However, currently the defects that develop during the preforming step of the manufacturing process pose a significant hurdle and thus this PhD attempts to address this issue. The textile reinforcements that are considered are non crimp fabrics (NCFs) which are novel multi-layered textiles that are stitched together instead of being woven. The approach for this PhD is to develop a novel experimental preforming rig that is able to track and measure the development of wrinkles and the associated fibre strains in the NCFs using 3D digital image correlation (DIC), under a variety of boundary conditions. This data will then be used to develop relationships between the strains and wrinkle amplitudes in order to attempt to develop a wrinkling forming limit diagram (WFLD) that is able to characterise the onset of wrinkling for a particular textile reinforcement in terms of the strains induced. The research will highlight a plausible standardised methodology for experimentally obtaining the wrinkling limits of a particular fabric from a series of simple tests, which can then be applied to a range of fabrics and significantly simplify the fabric selection process and their subsequent manufacture. Furthermore, the understanding of wrinkle development during forming obtained in these experiments will be used to inform the development of a micromechanical model finite element (FE) model of the forming of NCFs. This model will be able to predict the locations and amplitudes of wrinkles and the associated strains, and can be used directly to develop the WFLD for a particular fabric, without the need for any experimental tests. Ultimately, the PhD will attempt to conduct an optimisation study based on both experimental and simulation data that is able to optimise the preforming process with regards to minimising defects. This project fits within the EPRSC research area of 'Materials engineering - composites.'