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When cured in a microwave, flat thin composite panels can experience even heat distribution throughout the laminate. However, as load and geometric complexity increase, the electromagnetic field and resulting heat distribution is altered, making it difficult to cure the composite homogeneously. Materials that absorb and/or reflect incident electromagnetic radiation have the potential to influence how the field behaves, and therefore to tailor and improve the uniformity of heat distribution. In this study, an absorber was applied to a composite with non-uniform geometry to increase heating in the location which had previously been the coldest position, transforming it into the hottest. Although this result overshot the desired outcome of temperature uniformity, it shows the potential of absorbing materials to radically change the temperature distribution, demonstrating that with better regulation of the absorbing effect, a uniform temperature distribution is possible even in non-uniform composite geometries.

The chapter investigates the effect of the essential manufacturing parameters on the surface quality of uncoated carbon fibre reinforced composites (CFRP) used as car body panels with visible surfaces (Class A properties). A series of CFRP laminates maunfactured by the RTM technique are investigated varying in the fibre volume content (30–60\(\%\)), reinforcement material (woven fabrics vs. unidirectional fibre reinforcements), curing temperatures (40–120 \(^{\circ }\)C), additives (SiO\(_2\)-nanoparticles as matrix fillers) and using a surface finish applied as an in-mould coating. The laminate surfaces are characterized by roughness analysis (white-light interferometry) and wave-scan measurement to quantify the influence of the different manufacturing parameters on the surface quality. Especially the used resins are intensively characterized concerning thermal properties (CTE) and total resin shrinkage. These results correlate very well with the performed analysis of surface roughness. It is found that the fibre print through effect is significantly reduced by realising low total resin shrinkage and an even distribution of resin and fibres at the surface. Thus, using of unidirectional fibre reinforcement (no weft or sewing threads; very fine filaments), low curing temperatures (slow curing processes) and an in-mould coating are most successful for reduction of fibre print through effect and getting surface similar to Class A properties. In addition, the surface quality is quite positively affected by the application of nanoparticles and also strongly controlled by roughness of tooling.

Thermochemical properties are needed to develop process models and define suitable cure cycles to convert thermosetting polymers into rigid glassy materials. Uncertainty surrounding the suitability of thermal analysis techniques and semi-empirical models developed for conventional composite materials has been raised for the new class of particle interleaf materials. This paper describes kinetics, conductivity, heat capacity and glass transition temperature measurements of HexPly® M21 particle interleaf material. Thermal models describing conventional, non-particle epoxy systems were fit to the data and validated through a thick-section cure. Results from curing experiments agree with heat transfer simulation predictions, indicating that established thermal analysis techniques and models can describe polymerisation and evolving material properties during processing of a material representing the class of interleaf toughened systems. A sensitivity study showed time savings up to about 20%, and associated energy-efficiency-productivity benefits can be achieved by using cure simulation for particle interleaf materials.

The aim of the present study has been to evaluate the effect of hybridization of montmorillonite (MMT) and multi-walled carbon nanotubes (MWCNT) on the thermal and viscoelastic properties of shape memory epoxy polymer (SMEP) nanocomposites. In this study, ultra-sonication was utilized to disperse 1%, 3%, and 5% MMT in combination with 0.5%, 1%, and 1.5% MWCNT into the epoxy system. The fabricated SMEP hybrid nanocomposites were characterized via differential scanning calorimetry, dynamic mechanical analysis, and thermogravimetric analysis. The storage modulus (E’), loss modulus (E”), tan δ, decomposition temperature, and decomposition rate, varied upon the addition of the fillers. Tan δ indicated a reduction of glass transition temperature (Tg) for all the hybrid SMEP nanocomposites. 3% MMT/1% MWCNT displayed best overall performance compared to other hybrid filler concentrations and indicated a better mechanical property compared to neat SMEP. These findings open a way to develop novel high-performance composites for various potential applications, such as morphing structures and actuators, as well as biomedical devices.

Geometric unconformities may arise due to residual stresses during the manufacturing process of polymer matrix composite materials. Compaction of the laminate, due to resin squeeze, is another phenomenon that occurs and it influences the mechanical behaviour of the laminate itself. In the past, models for spring-in or for compaction were developed separately, whereas in the present work a new kind of analysis is developed to take into account both residual stresses and compaction that take place during cure simultaneously. This analysis is composed by two different steps: in the former the compaction is predicted, in the latter the cure state and the residual stress condition are determined. Finally, the relationship between different degrees of compaction and the corresponding values of spring-in is studied, and it was found that a higher value of thickness reduction produces the smallest residual stresses for the composite structures with angled cross sections.

WOS; International audience; 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 presents a description of the evolution of the elastic and loss modulus during curing, which is correlated with cure shrinkage estimations and previous video results. The comparisons between these results lead to a clear proposal for a single long-fibre microbuckling scenario during the curing of an epoxy matrix. Novel results are that fibre instability is triggered at local heating rates higher than 3 °C/min and coincides with the maximal chemical shrinkage observed prior to glass transition. Similarly, the observation of the relaxation of partial fibre undulation relaxation is coherent with the viscoelasticity of the matrix during formation. The instability appears some time after exposure to a rubbery state. The analysis of single fibre undulation is an excellent indicator of cure quality and an appropriate testing structure for further chemical, thermal and mechanical models of the co-operative buckling of many fibres.

The paper investigates the effect of essential manufacturing parameters on the surface quality of uncoated carbon fibre-reinforced composites used as car body panels with visible surfaces (Class A properties). A series of carbon fibre-reinforced composites laminates were prepared by the resin transfer moulding technique varying the fibre volume content (30 to 60 %), reinforcement material (woven fabrics vs. unidirectional fibre reinforcements), curing temperatures (40℃ to 120℃), additives (SiO2 nanoparticles as matrix fillers) and using a surface finish applied as an in-mould coating. Laminate surfaces were characterised by roughness analysis (white-light interferometry) and wave-scan measurement to quantify the influence of the different manufacturing parameters on the surface quality. Especially, the used resins were intensively characterised concerning thermal properties and total resin shrinkage. These results correlate very well with the performed analysis of surface roughness. It is found that the fibre print through effect is significantly reduced by realising low total resin shrinkage and an even distribution of resin and fibres at the surface. Thus, using of unidirectional fibre reinforcement (no weft or sewing threads; very fine filaments), low curing temperatures (slow curing processes) and an in-mould coating are most successful for reduction of fibre print through effect and getting surface similar to Class A properties. In addition, the surface quality is quite positively affected by the application of nanoparticles and also strongly controlled by roughness of tooling.

Three different organo-modified clays have been incorporated by sonication into a high performance epoxy resin before the cross-linking reaction. The X-ray analysis indicated that, depending on the organoclay type, partially exfoliated and partially intercalated composites have been obtained. As shown by the DSC analysis, the clay addition seems to interact with the cross-linking reaction. The incorporation of organoclay into epoxy increased free volume and micro-voids in the samples. Sorption of water in the composite samples resulted higher than that of the pristine resin, whereas the diffusion coefficient is significantly lower. The lower value of diffusion makes the permeability at ambient conditions lower than the pristine resin. The elastic modulus of the composite sample results higher than that of the pristine resin, especially in the temperature region around the glass transition. The presence of organoclay in epoxy matrix decreased the glass transition temperature, whether the nanocomposites were in a dry or wet condition.

We report results on the development of an innovative fast-curing coupling method using a UV-curable epoxy primer based on a cycloaliphatic di-epoxide resin to bond metallic wires and a thermoplastic polyurethane matrix. The curing kinetics of the primer and its mechanical properties were analysed to optimize the formulation. Adhesion and durability were then tested by pull-out tests before and after hydrothermal ageing for several formulations and composites. The proposed UV-curable primer outperformed a conventional surface treatment and a thermally cured silane primer used for comparison in terms of processing time, adhesion and durability. (C) 2013 Elsevier Ltd. All rights reserved.

The sequential heat release (SHR) taking place in dual-curing systems can facilitate thermal management and control of conversion and temperature gradients during processing of thick composite parts, hence reducing the appearance of internal stresses that compromise the quality of processed parts. This concept is demonstrated in this work by means of numerical simulation of conversion and temperature profiles during processing of an off-stoichiometric thiol–epoxy dual-curable system. The simulated processing scenario is the curing stage during resin transfer moulding processing (i.e. after injection or infusion), assuming one-dimensional heat transfer across the thickness of the composite part. The kinetics of both polymerization stages of the dual-curing system and thermophysical properties needed for the simulations have been determined using thermal analysis techniques and suitable phenomenological models. The simulations show that SHR makes it possible to reach a stable and uniform intermediate material after completion of the first polymerization process, and enables a better control of the subsequent crosslinking taking place during the second polymerization process due to the lower remaining exothermicity. A simple optimization of curing cycles for composite parts of different thickness has been performed on the basis of quality–time criteria, producing results that are very close to the Pareto-optimal front obtained by genetic algorithm optimization procedures.