Abstract Analysis of the fibre dominated properties of composite materials typically assumes, often implicitly, the perfect alignment of fibres. Increasingly, however, it is acknowledged that waviness (in-plane misalignment) and wrinkling (out-of-plane misalignment) play an important role in both manufacturing and structural response. In this paper, a previously developed experimental method to measure fibre misalignment has been improved and extended to also determine fibre excess length. Results are presented for two unidirectional aerospace grade prepregs (8552 and 8552–1 resins reinforced by AS4 fibre). The fibre alignment distributions are well fitted by an analytical model that allows for a distribution of excess lengths; the fibre excess length is not constant at the end of the prepregging process. It is shown that only with a distribution of excess lengths can the experimental unimodal misalignment distributions be analytically modelled. Misalignment distributions presented in this paper are consistent with those reported elsewhere, and furthermore it is shown that the fibres were significantly more aligned out-of-plane than in-plane. Finally, contrary to the best working hypothesis in the literature, samples prepared using a thermal cure process saw no correlation between fibre misalignment and initial location on a prepreg roll.
Abstract Unidirectional (UD) carbon fibre reinforced polymers offer high specific strength and stiffness but they fail in a catastrophic manner with little warning. Gas-texturing and non-constrained annealing were used to introduce fibre waviness into UD polyamide 12 composites produced by wet-impregnation hoping to produce composites with a more gradual failure mode and increased failure strain. Both methods increased the variation of fibre alignment angle compared to the control samples. The c...
This paper investigates the effect of nanosilica on the fibre waviness or misalignment angle distribution of carbon fibre reinforced polymer composite unidirectional laminates. The quality of the laminates was evaluated using image analyzer technique. The polished specimens were examined using Polyvar B-met optical microscope and analysed using KSRUN ZEISS software. The effect of 3, 7 and 13 vol.% nanosilica on the fibre misalignment angle distribution was determined. The results showed that, th...
Last. Kevin Potter(UoB: University of Bristol)H-Index: 9
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Abstract The formation of out-of-plane ply deformation causes significant reductions in the mechanical properties of composites. In-plane fibre misalignments also cause reductions in the compressive strength, yet the origins of these defects are misunderstood. This paper presents a new mechanism for the formation of wrinkles, which is based upon the shear forces generated as a result of mismatches in the coefficient of thermal expansion of composite and tool, as well as the process of ply slippa...
#2Jinhuo Wang(UoB: University of Bristol)H-Index: 4
Last. Kevin Potter(UoB: University of Bristol)H-Index: 9
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Abstract This paper presents an experimental study on the effect of localised wrinkling defects on the strength of glass reinforced epoxy laminates. A method for generating wrinkles based on the ‘natural’ mechanism of formation was developed and used to make larger scale laminates, with the aim of being representative of industrial components. Wrinkle severity was characterised using optical microscopy and correlated to the results obtained from tensile testing, which showed that the most seriou...
Abstract The microporomechanical approach (via homogenization schemes) has been used and combined with triaxial tests to verify the Biot theory for the perfectly straight unidirectional fiber assembly in a previous paper [Tran T, Binetruy C, Comas-Cardona S, Abriak NE. Microporomechanical behaviour of perfectly straight unidirectional fiber material: theoretical and experimental. Compos Sci Technol 2009;69:199–206.]. The comparison of theoretical and experimental results is in good agreement, i....
In this paper, the development of physical and mechanical properties of a thermosetting composite which are relevant to the modelling of residual stresses and process induced deformations are discussed. Findings of previous work on cure kinetics and cure shrinkage of the composite are summarized. The development of resin modulus throughout the Manufacturer’s Recommended Cure Cycle (MRCC) is modelled by Group Interaction Modelling (GIM). The moduli of AS4/8552 composite are calculated by two micr...
Frequency tables are often constructed on intervals of irregular width. When plotted as bar charts, the underlying true density information may be quite distorted. The majority of introductory statistics texts recommend tabulating data into intervals of equal width, but seldom caution the consequences of failing to do so. An occasional introductory text correctly emphasizes that area rather than frequency should be plotted. Nevertheless, the correctly scaled density figure is often visually less...
Abstract Recently, real-time video images of the appearance of undulations on a long T300 single carbon fibre during the curing of a LY556 epoxy matrix were proposed by Jochum et al. [Jochum Ch, Grandidier JC, Smaali M. Experimental study of long T300 carbon fibre undulations during the curing of LY556 epoxy resin. Compos Sci Technol 2007;67:2633–42]. The correlation of the fibre undulation with cure kinetics has established that undulations appear prior to glass transition. The present study pr...
Abstract A novel approach has been developed to measure in situ the through-the-thickness strains during processing of epoxy composites. The technique captures the thermal expansion during the heating stages, the laminate consolidation throughout the cure process, and also the cure shrinkage. The tests were performed on 45 mm × 45 mm × 4 mm samples, for both unidirectional and cross-ply laminates. A ply pull-out technique was used to determine the position of the gel point of the AS4–8552 compos...
#1Anh Dung Tran(TU Wien: Vienna University of Technology)H-Index: 3
#2Thomas Koch(TU Wien: Vienna University of Technology)H-Index: 19
Last. Patrick Knaack(TU Wien: Vienna University of Technology)H-Index: 8
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In this study, a new type of prepreg technology has been established using a dual curing system consisting of 1,6-hexanediol diacrylate (HDDA) and frontally polymerisable components based on the epoxide resin. The study of the polymerisation of HDDA revealed (tert-butylcyclohexyl)peroxydicarbonate (BCPC) as the most suitable radical thermal initiator. The presence of BCPC resulted in a fast radical polymerisation of HDDA and no cationic ring-opening reaction of the epoxy, which was observed by m...
#1Kangyi Lu(Huada: Beijing University of Chemical Technology)H-Index: 2
#2Wenmo Zhu(Huada: Beijing University of Chemical Technology)
Last. Xiaoping Yang(Huada: Beijing University of Chemical Technology)H-Index: 44
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Abstract Epoxy matrix with high modulus was synergistically designed by organic amide acid (AA) and inorganic nano silica (SiO2) as well as stiffened interphase of carbon fiber composite, and the effects of matrix modulus on longitudinal compressive strength and failure mechanism of composites were investigated. The elastic and shear modulus of matrix was enhanced by increased chemical cross-linking cites of AA and mechanical restraint of SiO2, contributing to improved interfacial properties fro...
#1Ying-Guo Zhou(Henan University of Technology)H-Index: 11
#2Chao-Yang Wang(Henan University of Technology)H-Index: 1
Last. Hai-Hong Wu(Henan University of Technology)H-Index: 3
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Abstract Unidirectional laminate made from ply prepreg is commonly used to evaluate the mechanical performance of carbon fiber-reinforced composites (CFRCs), which is often calculated using the classical law of mixtures based on the fraction of dual-phases components. The thinning of the ply prepreg presents some special influences on composite structures and mechanical properties, leading to the deviation of the results between calculation and the experiment. In this work, four CFRC laminate wi...
#2Mehrzad Mortezaei(MUT: Malek-Ashtar University of Technology)H-Index: 1
Last. Iraj Amiri Amraei(MUT: Malek-Ashtar University of Technology)H-Index: 2
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Abstract Dual-curable formulation was used to prepare epoxy prepregs with tailored tack and drape. The obtained formulation had enhanced stability during the storage which eliminates the instability as the main drawback of prepregs. Diethylenetriamine was used as a low-temperature curing agent in the off-stoichiometry ratio for pre-curing and dicyandiamide was used as a latent curing agent for final curing. DSC Tests showed that simultaneous presence of two curing agents with different reactivit...
Carbon fiber-reinforced polymer (CFRP) is increasingly used for aero-structure applications due to their high strength-to-weight ratio. The integration of the on-board electrical power system (EPS) with CFRP is challenging due to the requirement to thermally and electrically isolate these systems to meet existing safety standards. By capturing the thermal characteristics of CFRP at a macro (component) scale for CFRP components, it is possible to understand, and design for, the increased integrat...