Abstract
This paper explores the performance of low-cost unidirectional carbon fibre towpregs with respect to line production speed and fibre volume fraction. Using an automated production line, towpregs were produced at different production speeds, resulting in modified fibre volume fractions. The towpregs were used to manufacture unidirectional composite plates, which were then tested to evaluate mechanical performance. The fibre straightness and interfacial void ratio of the composite plates were determined by statistical analysis of the samples’ optical micrographs. The results demonstrate that adjusting the line production speed enables targeted fibre volume fractions (FVF) to be reached, resulting in the composites having different mechanical performances (2039 MPa and 2186.7 MPa tensile strength, 1.26 and 1.21 GPa flexural strength for 59.8% and 64.4% FVF, respectively). It was shown that at lower production speeds and FVF, composites exhibit good consolidation and low porosity, which is highlighted by the better interlaminar shear strength performances (8.95% increase), indicating the limitations of manufacturing very high FVF composites. Furthermore, it was concluded that fibre straightness plays a key role in mechanical performance, as samples with a lesser degree of fibre straightness showed a divergence from theoretical tensile properties.
Highlights
Out-of-autoclave (OOA) towpreg epoxy composites are ideal candidates to provide adequate strength and stiffness for large composite structures, such as tidal/wind turbine blades and marine or automotive applications, while being cost-effective due to the scalability and compatibility with inexpensive mould heating systems [1]
This study investigates the relationship between the production speed, fibre volume fraction (FVF), and mechanical performance of the powder–epoxy-based carbon fibre towpregs
It was observed that increasing the production speed may lead to inferior mechanical characteristics, higher FVF values can be achieved
Summary
Out-of-autoclave (OOA) towpreg epoxy composites are ideal candidates to provide adequate strength and stiffness for large composite structures, such as tidal/wind turbine blades and marine or automotive applications, while being cost-effective due to the scalability and compatibility with inexpensive mould heating systems [1]. The powder can be stored at room temperature thanks to its thermal stability, and little to no volatile organic compounds (VOC) are released during the production [6] In this context, a novel powder–epoxy-based pilot towpregging line has been developed [7] to manufacture unidirectional carbon fibre towpregs (or tapes) that are compatible with advanced composite manufacturing methods such as Automated Fibre Placement (AFP), pultrusion, or filament winding. The powder–epoxy system used in this study is solid and stable at ambient temperature and will not start to cure before 145 ◦C, due to its heat-activated curing mechanism [7] It has excellent storage performance at room temperature; a consistent FVF can be obtained by carefully adjusting the towpreg line process parameters such as speed, tension, or temperature. For the carbon fibre tows, commercially available Toray T700S-24K-50C (1% sizing agent) was used, as it showed the best performances comparatively to other fibre systems [14]
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