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Design guidelines for hybrid continuous/discontinuous carbon fibre laminates

Evans, Anthony D.; Turner, Thomas A.; Harper, Lee T.; Warrior, Nicholas A.

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Authors

Anthony D. Evans

LEE HARPER LEE.HARPER@NOTTINGHAM.AC.UK
Associate Professor - Composites Manufacturing

NICHOLAS WARRIOR NICK.WARRIOR@NOTTINGHAM.AC.UK
Professor of Mechanical Engineering & Head of Research Division



Abstract

Combining discontinuous carbon fibre moulding compounds with unidirectional (UD) non-crimp fabric has been studied as a potential solution for producing cost effective composite structures, with short cycle times via compression moulding. The tensile stiffness and strength of a composite with a hybrid fibre architecture were found to be up to 60% and 110% higher, respectively, than the baseline discontinuous fibre moulding compound, when 20% (by vol.) of UD fibres were aligned in the primary loading direction. However, stress concentrations arising from the dissimilar material properties can result in the strength of the hybrid architecture being reduced to below that of the baseline composite if the UD fibres are not incorporated effectively. This paper focusses on optimising the stress transfer within the transition zone (inter-material interface) between the UD material and the discontinuous fibre moulding compound, when local isolated patches of continuous fibre are used rather than full coverage plies. This is key if hybrid architectures are to be adopted for structural applications, minimising the stress concentration effects from the UD ply ends, whilst maintaining the low cycle times and costs associated with compression moulding. Following aerospace laminate design guidelines, a range of step sizes and joint configurations have been considered for different ply drop strategies, minimising the magnitude of the stress concentration at the UD ply ends. Results indicate that the step length must be at least 20 times the thickness of the UD ply to ensure the bending strength at the joint is the same as the baseline discontinuous fibre material. An ‘alternating joint' yields 18% higher bending strengths than a conventional ‘stepped joint’ design, as the stress concentrations at the dropped ply ends are reduced in comparison to the inherent stress concentrations within the discontinuous fibre material.

Citation

Evans, A. D., Turner, T. A., Harper, L. T., & Warrior, N. A. (2022). Design guidelines for hybrid continuous/discontinuous carbon fibre laminates. Journal of Composite Materials, 56(10), 1513-1527. https://doi.org/10.1177/00219983221078786

Journal Article Type Article
Acceptance Date Jan 21, 2022
Online Publication Date Mar 20, 2022
Publication Date 2022-05
Deposit Date Mar 26, 2022
Publicly Available Date Mar 29, 2022
Journal Journal of Composite Materials
Print ISSN 0021-9983
Electronic ISSN 1530-793X
Publisher SAGE Publications
Peer Reviewed Peer Reviewed
Volume 56
Issue 10
Pages 1513-1527
DOI https://doi.org/10.1177/00219983221078786
Keywords Materials Chemistry; Mechanical Engineering; Mechanics of Materials; Ceramics and Composites
Public URL https://nottingham-repository.worktribe.com/output/7651456
Publisher URL https://journals.sagepub.com/doi/10.1177/00219983221078786

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