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Parametric study of piezoresistive structures in continuous fiber reinforced additive manufacturing
(2024)
Recent advancements in fiber reinforced additive manufacturing leverage the piezoresistivity of continuous carbon fibers. This effect enables the fabrication of structural components with inherent piezoresistive properties suitable for load measurement or structural monitoring. These are achieved without necessitating additional manufacturing or assembly procedures. However, there remain unexplored variables within the domain of continuous fiber-reinforced additive manufacturing. Crucially, the roles of fiber curvature radii and sensing fiber bundle counts have yet to be comprehensively addressed. Additionally, the compression-sensitive nature of printed carbon fiber-reinforced specimens remains a largely unexplored research area. To address these gaps, this study presents experimental analyses on tensile and three-point flexural specimens incorporating sensing carbon fiber strands. All specimens were fabricated with three distinct curvature radii. For the tensile specimens, the number of layers was also varied. Sensing fiber bundles were embedded on both tensile and compression sides of the flexural specimens. Mechanical testing revealed a linear-elastic behavior in the specimens. It was observed that carbon fibers supported the majority of the load, leading to brittle fractures. The resistance measurements showed a dependence on both the number of sensing layers and the radius of curvature, and exhibited a slight decreasing trend in the cyclic tests. Compared with the sensors subjected to tensile stress, the sensors embedded on the compression side showed a lower gauge factor.
The integration of continuous fibers into additively manufactured plastic components greatly enhances their mechanical properties. Nonetheless, a challenge lies in the limited adaptability of these properties to specific loading scenarios. To address this issue, present research aims to exploit the hybridization of additively manufactured composites, combining diverse fiber materials within a single component. Specifically, fabricating continuous fiber-reinforced hybrid composites through material extrusion enables high flexibility in adapting local fiber materials. To further the understanding of the effects of hybrid fiber reinforcement in additively manufactured plastic parts, this study investigates how distinct stacking sequences in hybrid and non-hybrid PA6-based composite components, reinforced with carbon and glass fibers, affect deformation and failure behavior. Mechanical properties are assessed using tensile, flexural, and impact tests, in conjunction with an analysis of cost and weight efficiency. The results unveil a distinct correlation between stacking sequences and the mechanical properties of additively manufactured composites. While the hybrid samples predominantly exhibit slight negative hybrid effects, a positive hybrid effect of 96.4 % is achieved in terms of impact toughness with an optimized stacking sequence. With the exception of impact strength, specimens reinforced solely with carbon fibers frequently demonstrate a remarkable ratio between mechanical properties, weight, and cost, whereas hybrid composites exhibit a balanced compromise across all tested mechanical properties. Building upon the obtained results, three comprehensive design approaches are introduced and applied, demonstrating the new design possibilities arising from the combination of hybrid composites and additive manufacturing. The developed design approaches and material combinations can be used for a wide range of lightweight construction applications.
