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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.

The paper deals with the influence of the convection coefficient and laminate thickness on multi-objective optimisation of the vacuum assisted resin transfer moulding cure stage for the manufacturing of wind turbine components. An epoxy resin system widely used in the wind turbine industry has been chemically characterised and the correspondent finite element implementation validated. The optimisation methodology developed links the finite element solution with a genetic algorithm and identifies a set of optimal cure cycles for a range of thicknesses (10–100 mm) able to minimise cure time (t cure ) and the maximum degree of cure gradient developed through thickness (Δα max ) during the cure stage as a measure of quality of the product. The results highlight that, by adding convection coefficient as design parameter of the process, significant benefits could be obtained when insulation is applied at the vacuum bag side for all thicknesses.

This study investigated the feasibility of using an electron beam (EB) process to cure chemically impregnated wood products. Maple wood planks were impregnated with the low-viscosity resins 1,6 hexanediol dimethacrylate (HDDA) and trimethylolpropane trimethacrylate (TMPTA). The addition of nanoparticles into the formulation was also studied. The impregnated wood was then cured by EB irradiation. The EB curing method utilizes highly energetic electrons at a controlled energy level to polymerize and cross-link the polymeric materials. The thermal analysis results of differential scanning calorimetry (DSC) confirmed that the curing of chemically impregnated wood by electron beam radiation was validated. Polymerization exotherms were observed for the neat acrylate resin and formulations of acrylate/nanoparticles impregnated maple samples. No polymerization exothermal peaks were observed for both EB-cured impregnated maple and control maple samples, confirming that EB irradiation can serve as an efficient curing method to polymerize acrylate-impregnated wood products. The surface hardness of the EB-cured impregnated maple wood was improved up to 200%.

The thermochemical and the thermomechanical phenomena that happen during the cure process of a composite material laminate are responsible for the rise of residual stresses and, consequently, for the deformation at the end of the manufacturing process. In this work, the influence of some parameters, such as the laminate thickness, the stacking sequence and the mold radius, on the spring-in angle of a U-shaped laminate was studied exploring a full factorial plan through numerical simulations. Moreover, the influence of the laminate shape on the deformation was investigated. First of all, a numerical model appropriate for cure simulation was introduced and its suitability to simulate the deformation behavior was demonstrated. Using a simulation model instead of running experimental test was important for analyzing the parameters influence without reduce the full factorial plan to a fractional one and without wasting a lot of time and material. As a result, only the stacking sequence influenced the spring-in value, while the effect of the tool radius and laminate thickness was minimal. Finally, a comparison between U-shaped and L-shaped laminates evidenced that the spring-in value was independent of part shape, while this parameter affected the flange warpage.

peer-reviewed The development of a novel hot-stage microscopy technique to measure the level of cure shrinkage that occurs in an epoxy thermoset microdroplet with different epoxy-to-hardener ratios is presented. The equipment setup, sample preparation, and experimental procedure are described in detail. A comparable method to characterise cure shrinkage, a modified rheometry technique, is also reviewed. Shrinkage measurements using the hot-stage microscopy method are shown to characterise the full range of shrinkage that occurs both before and after the resin gel point, hence producing values greater than those found previously in the literature. However, when used in conjunction with the gel point values for the different ratios, measured using rheometry, the technique produces results for shrinkage post-gelation that concur well with literature values. The modified rheometry technique showed potential for measuring the level of cure shrinkage with a varying cure temperature profile, with more work required to perfect the method in defining the cross-over point for sample loading for different epoxy-to-hardener ratios.

The aim of this study was to prepare and characterize a ceramic matrix cement of hydroxyapatite (HAp) and galactomannan (Gal) extracted from Adenanthera pavonina L. seed. Three composites were prepared: the solid phases used were 75 wt% HAp and 25 wt% Gal (HAG) both powder adding to composite 0.30 ml distilled water. The composite HAGJET consists of 0.10 mL catalyst commercial JET® (methyl methacrylate and dimethyl-p-toluidine) and 0.20 mL distilled water (see table 1). The HAGLS composite was composed of 60 wt% HAp powder, liquid phase of 40% Gal solution and 0.10 mL of catalyst commercial LS® (phosphoric acid, zinc oxide, aluminum hydroxide and water) (see table 1). The solid phase in each material was dissolved in the liquid corresponding to each composite formed. The phases of HAp and Gal were characterized by X-ray diffraction. The setting time, flow and solubility were tested according to ISO 6876/2001. Furthermore, the amount of water that each material absorbs was determined, as well as their microhardness and morphology. The data were analyzed using 1-way ANOVA with Student’s t-test (p < 0.05). All of the materials exhibited good setting time and flow above that allowed by the ISO (p < 0.05). The HAGLS composite had solubility of less than 3% (p < 0.05), absorbed less water (p < 0.05) and had the highest hardness value. The HAG and HAGLS composites showed roughened surfaces, while the HAGJET exhibited a smooth surface. These results suggest that there is potential to develop a sealer using HAp and Gal. Este estudo refere-se à caracterização de um compósito a base de hidroxiapatita (Hap) e galactomanana (GAL) extraída da semente de Adenanthera pavonina L. Três compósitos foram preparados: o primeiro compósito é formado por 75% em massa de Hap e 25 % de GAL em fases sólidas utilizando 0,30 mL de água destilada como fase liquida (HAG). O segundo compósito é formado pela mesma proporção de Hap e Gal adicionando 0,20 mL de água destilada e 0,10 mL de catalisador commercial JET® (HAGJET) (ver tabela 1). O terceiro compósito (HAGLS) é compost de 60% em massa de Hap em fase sólida e 40 % de GAL em fase líquida e 0,10 mL de catalisador commercial LS® (ver tabela 1). A fase sólida de cada material foi dissolvida no líquido de cada compósito formado. As fases de Hap e GAL foram caracterizadas por difração de raios-X. Os compósitos foram caracterizados por técnicas de tempo de secagem ou cura, fluxo e solubilidade de acordo com a ISO 6876/2001. Além disso, a quantidade de água absorvida em cada compósito foi observada pelas técnicas de microdureza e morfologia. Os dados foram analisados estatísticamente utilizando o teste t-student com p < 0,05. Todos os compósitos apresentaram bons tempode de cura e fluxo. O HAGLS solubilizou abaixo de 3% com baixa absorção de água e um alto valor de microdureza. HAG e HAGLS apresentaram superficies rugosas, enquanto o HAGJET apresentou superfície lisa. Esses resultados sugerem que os compósitos de Hap e Gal são potencialmentes favoráveis a selantes.

During the cure process of CFRP laminates, some geometrical unconformities can arise, due to several thermomechanical and thermochemical phenomena that make residual stress rise. Among these unconformities, one of the most studied is the spring-in, that is the deviation of the flange-to-flange angle from the design value. In this work a numerical model suitable to determine the spring-in value was developed and verified. The proposed model considered both the thermo-chemical and thermo-mechanical phenomena that happen during the cure process. Then, the numerical model was used for calculating the spring-in angle of lots of different laminates in order to evaluate the influence of the thickness, the corner radius and the layup sequence on the laminate deformation. For evaluating the influence of the above mentioned parameter on the spring-in a full factorial plan was designed, and the FEM analysis allowed a saving of time, energy and material. It was found that only the layup sequence influenced the spring-in. Finally, a preliminary analysis stated the possibility to extend the proposed model also to other geometries, such as U-shaped laminates.

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.

In NSM-CFRP installations, the mechanical behaviour of the strengthening system is strongly influenced by the epoxy adhesive, particularly at early ages. In the present work, the influence of temperature on the curing process of the epoxy was investigated. Three distinct temperatures were studied: 20, 30 and 40 °C. The elastic modulus of the adhesive was monitored through EMM-ARM (Elasticity Modulus Monitoring through Ambient Response Method). Direct pull-out tests with concrete specimens strengthened with NSM CFRP strips were carried out at the same three distinct temperatures to compare the evolution of bond performance with the E-modulus of epoxy since early ages. The results showed that increasing the curing temperature significantly accelerated both the curing process of the epoxy adhesive and the evolution of bond performance. The EMM-ARM technique has revealed its ability in clearly identifying the hardening kinetics of epoxy adhesives, allowing also thermal activation analysis. Finally, existing models for predicting temperature-dependent mechanical properties were extended to also describe the bond behaviour of NSM-CFRP applications., This work is supported by FEDER funds through the Operational Program for Competitiveness Factors - COMPETE and National Funds through FCT - Portuguese Foundation for Science and Technology under the projects FRPreDur FCOMP-01-0124-FEDER-028865 (FCT no. PTDC/ECM-EST/2424/2012) and VisCoDyn FCOMP-01-0124-FEDER-041751 (FCT no. EXPL/ECM- EST/1323/2013). The authors also like to thank all the companies that have been involved supporting and contributing for the development of this study, mainly: S&P Clever Reinforcement Ibérica Lda., Artecanter - Indústria de Transformação de Granitos, Lda., Vialam – Indústrias Metalúrgicas e Metalomecânicas, Lda. The second and third authors also acknowledge the grants SFRH/BD/80338/2011 and SFRH/BD/80682/2011, respectively, provided by FCT.

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.

During the curing process, the exothermic cross-linking reaction inside epoxy resin-based composites causes overheating and, eventually, a thermal degradation of the matrix. Thick sectioned epoxy composites require an optimized curing cycle in order to minimize the temperature raise inside the composite. However, the recommended cycle for thin laminates is often wrongly used also for thick sectioned composites, resulting in an overheating. In this work, the mechanical behaviour of laminates having different thicknesses was investigated. Specimens were cured according to a curing cycle optimal for thin laminates which causes overheating in thicker laminates. The curing temperature histories at several positions inside the laminates were monitored and recorded and, following a new methodological approach, a series of comparative interlaminar shear tests was performed. Experimental results show a decrease of the interlaminar shear strength in thicker laminates. A simple model to account for the detrimental effect of the exothermic peak on the interlaminar shear strength is proposed. © 2016 Springer-Verlag London

The present paper describes the application of an innovative technique (termed EMM-ARM: Elasticity Modulus Monitoring through Ambient Response Method) for continuous monitoring of the stiffening process of an epoxy adhesive used in near-surface mounted (NSM) fibre reinforced polymer (FRP) reinforcements. A simultaneous study of direct pull-out tests with concrete specimens strengthened with NSM carbon FRP laminate strips was carried out to compare the evolution of bond performance with the E-modulus of epoxy since early ages. A relationship between the evolution of epoxy E-modulus and the maximum pull-out force is assessed, highlighting the potential of applying EMM-ARM for quality control and decision-making assistance of NSM systems., This work is supported by FEDER funds through the Operational Program for Competitiveness Factors - COMPETE and National Funds through FCT - Portuguese Foundation for Science and Technology under the projects CutInDur PTDC/ECM/112396/2009 and VisCoDyn EXPL/ECM-EST/1323/2013. The authors also like to thank all the companies that have been involved supporting and contributing for the development of this study, mainly: S&P Clever Reinforcement Iberica Lda., Artecanter - Industria de Transformacao de Granitos, Lda., Vialam - Industrias Metalurgicas e Metalomecanicas, Lda. The first and second authors also acknowledge the grants SFRH/BD/80338/2011 and SFRH/BD/80682/2011, respectively, provided by FCT.

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.