Rework signature: assessing quality of reworked defects in automated fibre placement composites

This paper examinesthe assessment of reworking techniques in the realm of composite materials, going beyond conventional cosmetic pass-fail criteria commonly employed by practitioners. The findings of this study indicate that these criteria are not sufficient in ensuring the quality of reworked laminates. An ultrasonic Non-Destructive Testing (NDT) method was employed to investigate the laminates after curing. Our study utilised a linear ultrasonic phased array roller probe to capture through-thickness, depth-wise images (known as B-scans) perpendicular to the orientation of the top ply surface. This provided insights into the volumetric structure of the samples. Comparisons were drawn between pristine samples, samples with embedded defects, and those subjected to the reworking process in terms of their out-of-plane ply waviness on the internal plies. Despite the successful completion of the rework process, a discernible difference between pristine and reworked samples, termed the "novel rework signature" was identified in some samples. This observation underscores the critical need for optimising reworking activities from a quality perspective. Our experimental approach utilises a novel BenchtopAutomated Fibre Placement (AFP) setup which establishes a robust research environment for simulating real-world conditions. The successful generation of laminates using this method demonstrates its potential as a democratised research environment free of the high capital costs traditionally associated with AFP research and development.This research contributes not only to the understanding of rework effectiveness but also emphasises the importance of a comprehensive approach to quality assessment in composite material manufacturing. Additionally, the quantitative method demonstrates an effective acceptance measure for rework analysis. The findings pave the way for future optimisation strategies, emphasising the necessity of considering both internal and surface characteristics in evaluating the integrity of composite materials.