Structure tensor-based analysis method for quantitative assessment of fibre waviness in fibre-steered laminates manufactured by continuous tow shearing

Producing fibre-steered laminates require the use of automated tape deposition techniques. Although the Automated Fibre Placement (AFP) is the state-of-the-art fibre steering technology, its tape handling mechanism causes various defects such as tape buckling. Continuous tow shearing (CTS) was developed to eliminate such defects by in-plane shearing prepreg tapes, demonstrating superior fibre steering quality. However, the inherent fibre misalignments within the tape material may result in micro-level fibre waviness during shearing. It is important to measure the fibre waviness level in CTS-steered prepreg layups or laminates. The existing fibre waviness measuring processes requires high-fidelity microscope images, limiting scanning area and processing time. This paper presents a new method utilising Structure Tensor Analysis (STA) for 100 mm wide, CTS-steered prepreg tapes scanned using a contact image sensor. The effects of the processing parameters of the STA on the accuracy of the analysis result were investigated, by comparing the results against microscopic analysis using the High Resolution Misalignment Analysis (HRMA). The analysis results have demonstrated that the STA has the potential for fast and cost-effective fibre-waviness inspection to verify layup quality of fibre-steered layups and laminates.