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The present study investigates the mechanical and tribological properties of an epoxy matrix filled with different graphitic particles deposited on an aluminum substrate by the electrostatic spray technique. Three different particles added to the epoxy matrix were the received graphite, the crushed graphite obtained by crushing the natural flake graphite particles using a ball mill, and graphite oxide obtained by oxidation treatment. Nanoindentation tests were conducted on the different coatings in order to evaluate the surface hardness and the contact elastic modulus. The effect of the oxidation treatment and the loading content on the tribological behavior of the above composites were also evaluated under dry-friction conditions. As expected, the smaller the particle size, the greater the reduction in the dynamic friction. The experimental findings showed that adding 5 wt % of crushed graphite (10 µm) provided a similar dynamic friction as the addition of 10 wt % of received graphite (20 µm). The epoxy filled with received graphite showed a lower wear rate than that filled with graphite oxide and crushed graphite. Moreover, both hardness and elastic modulus increased in the case of the epoxy filled with graphite oxide and crushed graphite.

International audience; Transparency is a crucial factor in developing functional and decorative thin films and coatings, but incorporation of nanoparticles into organic resins for improving their properties quite often makes them opaque. In this work, photophysical properties of epoxy/layered double hydroxide (LDH) nanocomposite coatings were correlated with the dispersion state of LDH in the epoxy resin. The quality of solid epoxy network was assessed in terms of the Cure Index (CI) in relation to the transparency of the films containing 0.1, 0.5, 0.7, 1.0, and 3.0 wt% Mg–Al–LDH and Zn–Al–LDHs. At high loadings, direct transmittance (YDirect) decreased, while the light scattering in the coatings improved with respect to the neat epoxy. The highest Zn–Al–LDH loading (3.0 wt%) slightly deteriorated the transparency (YDirect = 93.3), but it was still higher than that of epoxy nanocomposite containing 0.5 wt% Mg–Al–LDH (YDirect = 89.8). A Good label was assigned to the epoxy nanocomposites containing up to 1.0 wt% Zn–Al–LDH, while epoxy/Mg–Al–LDH nanocomposites were Poor in terms of the CI labeling when Mg–Al–LDH content was more than 0.1 wt%. An increase of about 28 °C in the Tg value after the addition of 0.1 wt% Zn–Al–LDH indicated that Zn–Al–LDH can make strong the interaction between the epoxy matrix and nanoplatelets. However, decrease in the Tg of the epoxy/Mg–Al–LDH nanocomposites was a signature of the weak interactions between the Mg–Al–LDH nanoplatelets ‎and epoxy matrix due to inappropriate dispersion. In general, it was revealed for the first time that the CI enables correlating the chemical crosslinking with the photophysical properties of the epoxy/LDH nanocomposites.

Carbon nanotubes (CNTs) have been widely studied in the literature for their potential benefits as reinforcement in epoxy matrices. However, the enhancement that these nano-materials can provide to the corresponding epoxy matrix is largely dependent on the manufacturing process and other factors such as the wt.% or the nanotube type, showing different effects on the resulting mechanical properties. In this study, five contents of multi-wall carbon nanotubes (MWCNTs) were introduced in an epoxy resin to analyse their effects on both tensile and fracture properties, with the fracture behaviour being characterised in cracked and in notched conditions (with various radii). The experimental results showed a drastic deterioration of the tensile strength for MWCNTs contents higher than 0.1 wt.%, and no benefit was found in the fracture resistance (only conducted for 0.1 wt.% due to the negative effect observed in the tensile results). Therefore, it seems that the CNTs do not always improve the fracture behaviour of the epoxy matrix. The authors of this work would like to express their gratitude to the Spanish Ministry of Science and Innovation for the financial support of the project PGC2018-095400-B-I00 “Comportamiento en fractura de materiales compuestos nano-reforzados con defectos tipo entalla”, on the results of which this paper is based.

Composite designing and airframe fabrication to develop a lightweight, robust, and high-endurance unmanned aerial vehicle (UAV) Aarush X2, next-generation urban unmanned aerial vehicle, are presented in this paper. The composite study investigated the structural feasibility of various lay-ups and fibre orientations using analytical model. The research is performed on the sandwich composite configuration of Divinycell, core, and carbon fibre-reinforced plastic (CFRP), facesheet, bonded with the epoxy matrix of AY-105 (resin) and HY-951 (hardener). The study presented five plies, [0/90/Divinycell/0/90], lay-up to sustain structural loads with the least gross take-off weight (GTOW) for manufacturing the UAV. The fabrication of the UAV was carried out using vacuum-assisted wet lay-up method (VAWLM) and demonstrated a total weight of the airframe 12.1 kg. The flight tests of around 30 h validated the structural capability of the designed sandwich composite along with the fabrication technique selected. The averaged flight time of 2.8 h on a two-stroke gasoline engine, DLE-61, with fuel tank capacity of 1.8 litres was recorded.

There are two parts by which epoxy coatings are generally packaged. These two parts which are mixed before application consist of (1) an epoxy resin be cross-linked and (2) a toughening agent or hardener. The formulation of epoxy coatings is done on the basis of performance required for the end product. On proper catalyzation, a hard, chemical and solvent resistant finish can be produced by epoxies. To protect concrete and steel from water, alkali and acids, epoxy coatings are generally given on them. Unfortunately, it is seen that highly cross-linked networks are brittle in nature and as a result, they cannot be applied widely for the cases where high impact fracture strength is required. This limited utility can be overcome by toughening the easily broken composites through the incorporation of rubbery materials into them. Specific selection and combination of the epoxy and the hardener are the key factors to determine the characteristics and suitability of epoxy coating for a given situation.

The improvement of engines is one of the ways to diminish the fuel consumption in civil aircrafts, and Open Rotors engines are one of the best promises in order to achieve a sensible efficiency increment. These engines have large composite blades that could, in the event of failure, impact against the fuselage, totally or partially. In this case, composite fragments could behave as impactors. In order to design fuselages for this event and adopt these new engines in the future, it is necessary to understand the impact behaviour of a composite fragment against a deformable structure. To this end, unidirectional and woven composites fragments were impacted at high velocity (up to 150 m/s) against aluminium panels at different impact velocities. The composite fragments were made using AS4/8552 (UD) and AGP-193PW (woven) prepregs manufactured by Hexcel Composites, both using AS4 fibres and 8552 epoxy matrix. High speed video cameras were used to record the impact process and to measure both the impact and the residual velocity and hence the energy absorbed.

The current research will discuss on the low velocity impact properties of kenaf/jute/kenaf hybrid composites treated with sodium hydroxide solution. The after impact damage properties will be observed through ultrasonic C-scan and compression after impact analyses. Kenaf/jute/kenaf sequence with 30 wt% fibre loading was laid up in epoxy matrix and cured in room temperature. The hybrid composites can withstand up to 30 J impact energy without full penetration, but appeared to be severely damaged. The visual inspection through the naked eyes clearly shown the cracks propagated towards the sides of the samples. However, limitations occurred through the C-scan technique, as the damages captured were not fully in parallel to the visual inspection. This is due to the properties of natural fibres. The compression after impact testing showed a maximum force of 42 kN needed to break the samples, impacted with low impact energy. The maximum compression force reduced as the impact energy increased.

This article deals with the thermal oxidation mechanisms and kinetics of epoxy-diamine (EPO-DA) networks used as composite matrices reinforced with carbon fibers in the aeronautical field. The first part of this article is devoted to a detailed presentation of the new analytical kinetic model. The so-called “closed-loop” mechanistic scheme, developed in the last 3 decades in our laboratory in order to accurately describe the thermal oxidation kinetics of saturated hydrocarbon polymers, is recalled. Its main characteristics are also briefly recalled. Then, the system of differential equations derived from this oxidation mechanism is analytically solved without resorting to the usual simplifying assumptions that seriously degrade the reliability of all kinetic models. On the contrary, the generalization of the proportionalities observed between the steady concentrations of the different reactive species (i.e., hydroperoxides and alkyl and peroxy radicals) to the entire course of thermal oxidation gives a series of much sounder equations. From this basis, the kinetic model is completed by considering new structure/property relationships in order to predict the consequences of thermal oxidation on the thermomechanical properties, in particular on the glass transition temperature (Tg). To reach this second objective, the two main mechanisms responsible for the alteration of the macromolecular network structure are recalled: chain scissions and crosslinking. Like any other chemical species, their kinetics are directly expressed from the oxidation mechanistic scheme using the classical concepts of chemical kinetics. The second part of this article is devoted to the checking of the kinetic model reliability. It is shown that this latter accurately simulates the experimental curves of carbonyl build-up and Tg decrease versus time of exposure determined in our laboratory for three EPO-DA networks under study, exposed in a wide variety of thermal oxidative environments. The values determined by inverse solving method for the different model parameters are discussed and their temperature dependence are elucidated. Finally, an end-of-life criterion is proposed for predicting the lifetime of EPO-DA networks involving a predominant chain scission process.

Coarse-grained molecular dynamics (CG-MD) simulations were conducted to characterize the molecular structure and mechanical properties in the epoxy matrix around fibers in polymer matrix composites (PMCs). From these simulations, the molecular structure was quantified by measuring the free-volume hole radius distribution as a function of position from the matrix-fiber interface. Additionally, correlations between the epoxy mechanical properties and the average free-volume hole radius were established for different degrees of cross-linking. These results were then upscaled into a finite element model (FEM) of a PMC representative volume. The results from the CG-MD-informed FEM model were compared to conventional FEM simulations that assume uniform epoxy mechanical properties, and the results indicate that conventional FEM simulations overestimate the strength of PMCs and predict a symmetric damage evolution in the matrix. On the other hand, the CG-MD-informed FEM simulations predict a more realistic localization of damage around the fiber-matrix interface.

This work focuses on the modeling of acoustic emission (AE) in a microcomposite made of carbon fiber and epoxy matrix. The main objective of this thesis is to quantify the influence of the propagation medium and of the sensor on the acoustic signal related to the breakage of a fiber, via finite element simulations carried out using the ABABQUS® software. Several studies, based on pattern recognition techniques, have shown that it is possible to correlate each AE signal to the different damage mechanisms (fiber breakage, matrix cracking, interfacial fiber / matrix debonding, delamination, etc. ). However, the acoustic signature is not universal; it strongly depends on the material, the structure, the sensors and the acquisition system. In the AE qualitative analysis, propagation and signal modifications are not taken into account. In this context, the validation of the acoustic signature is delicate and the results are difficult to generalize. A quantitative approach based on the simulation of AE and the entire acquisition chain is necessary in order to make the use of AE more reliable and to give robustness to the diagnosis and prognosis. In this work, a numerical model of the carbon fiber failure embedded in an epoxy matrix is established. This numerical model is validated by comparison with the experimental results. A parametric study is carried out in order to identify the effect of the different parts of the AE chain, in particular the effect of the propagation medium and of the sensor. An extension of this numerical model is also proposed in order to simulate another AE source, the interfacial fiber / matrix debonding. These numerical AE signals can be used in addition to experimental data to build libraries for life prediction approaches, based on machine learning methods in a PHM (Prognosis Heath management) type approach., Ce travail porte sur la simulation de l’émission acoustique (EA) dans un microcomposite constitué d’une fibre de carbone et de matrice époxy. L’objectif principal de cette thèse est de quantifier l’influence du milieu de propagation et du capteur sur le signal acoustique lié à la rupture d’une fibre, via une simulation par Eléments Finis réalisée à l’aide du logiciel ABABQUS®. De nombreuses études, basées sur des techniques de reconnaissance de formes, ont montré qu’il est possible de relier chaque signal d’EA aux différents mécanismes d’endommagement (rupture de fibre, fissuration matricielle, décohésion interfaciale fibre/matrice, délaminage, …). Cependant, la signature acoustique n’est pas universelle, elle dépend fortement du matériau, de la structure, des capteurs et du système d’acquisition. Dans l’analyse de EA qualitative, la propagation et les altérations du signal ne sont pas prises en compte. Dans ce contexte, la validation de la signature acoustique est délicate et les résultats difficilement généralisables. Une approche quantitative basée sur la simulation de l’EA et de toute la chaine d’acquisition est nécessaire afin de fiabiliser l’utilisation de l’EA et de donner de la robustesse au diagnostic et au pronostic. Dans ce travail, un modèle numérique de la rupture de fibre en carbone noyée dans une matrice époxy est établi. Ce modèle numérique est validé par comparaison avec les résultats d’essais. Une étude paramétrique est effectuée afin d’identifier l’effet des différents éléments formant la chaîne d’EA, notamment l’effet du milieu de propagation et du capteur. Une extension de ce modèle numérique est également proposée afin de simuler une autre source d’EA, la décohésion interfaciale fibre/matrice. Ces signaux virtuels d’EA pourront être utilisés en complément de données expérimentales afin de construire des bibliothèques pour des approches de prévision de durée vie basées sur des méthodes d’apprentissage automatique dans une approche de type PHM (Pronostic Heath management).

International audience; To perform predictive crash simulations on composite structures, it is necessary to provide reliable input data for the cohesive material models often used to describe delamination processes in composite materials. For quasi-static loadings, the mode I fracture toughness measurement has been standardized. However, for high-rate of loading, additional challenges arise. Consequently, no test standard has yet been defined for the mode I fracture toughness evaluation under high rates of loading. Therefore, this research aims at developing an experimental procedure to characterize the dynamic fracture toughness of a fast running crack in carbon fiber-reinforced epoxy matrix composite T700/M21. The dynamic fracture toughness is characterized using the Double Cantilever Beam test under several loading rates up to 17 m.s−1. An experimental protocol has been developed to identify the dynamic energy release rate GID for the mode I crack opening with various crack speeds å.

Graphene oxide (GO) incorporation in natural fiber composites has recently defined a novel class of materials with enhanced properties for applications, including ballistic armors. In the present work, the performance of a 0.5 vol % GO-incorporated epoxy matrix composite reinforced with 30 vol % fabric made of ramie fibers was investigated by stand-alone ballistic tests against the threat of a 0.22 lead projectile. Composite characterization was also performed by Fourier-transform infrared spectroscopy, thermal analysis and X-ray diffraction. Ballistic tests disclosed an absorbed energy of 130 J, which is higher than those reported for other natural fabrics epoxy composite, 74&ndash, 97 J, as well as plain Kevlar (synthetic aramid fabric), 100 J, with the same thickness. This is attributed to the improved adhesion between the ramie fabric and the composite matrix due to the GO&mdash, incorporated epoxy. The onset of thermal degradation above 300 &deg, C indicates a relatively higher working temperature as compared to common natural fiber polymer composites. DSC peaks show a low amount of heat absorbed or release due to glass transition endothermic (113&ndash, 121 &deg, C) and volatile release exothermic (~132 &deg, C) events. The 1030 cm&minus, 1 prominent FTIR band, associated with GO bands between epoxy chains and graphene oxide groups, suggested an effective distribution of GO throughout the composite matrix. As expected, XRD of the 30 vol % ramie fabric-reinforced GO-incorporated epoxy matrix composite confirmed the displacement of the (0 0 1) peak of GO by 8&deg, due to intercalation of epoxy chains into the spacing between GO layers. By improving the adhesion to the ramie fabric and enhancing the thermal stability of the epoxy matrix, as well as by superior absorption energy from projectile penetration, the GO may contribute to the composite effective ballistic performance.

Flax epoxy composites can be massively adopted in internal applications of automobiles and aircraft. This research work mainly deals with flax fiber composite in which unidirectional flax fibers are reinforced in epoxy matrix and are used in combination with CNT fillers. Such composite plate structures are manufactured and are tested using a smart actuation system. This experimental research work aims to find out the variations of the natural frequencies of composite plates made of flax fibers and CNT fillers. The consequence of various parameters like size, number of layers, etc. on CNT reinforced flax epoxy composite is discussed. The percentage of CNT fillers is varied and results for several parametric studies are presented.

In recent years, natural fiber reinforced composites have become an alternative to synthetic fiber reinforced composites in some areas due to their properties like low cost, biodegradability and lightness. In this study, abrasive wear tests were applied to jute fabric reinforced epoxy matrix composites filled with graphene nanoplatelets (GNPs) at different filling ratios (0, 0.5, 1, 2 wt.%), produced with vacuum assisted resin transfer molding (VARTM) method. Tribotests were carried out using a pin-on-disk type tribotest device on the counterface of 400 grit SiC emery paper with 5 N, 10 N and 15 N loads at a sliding speed of 1 m s-1 and a sliding distance of 200 m. In the tests carried out, the interface temperature and specific wear rate values were followed. It has been found that the specific wear rate is minimal at 1 wt.% GNPs filler and the interface temperature generally increases with increasing load., Son yıllarda düşük maliyet, biyobozunurluk, hafiflik gibi özelliklerinden dolayı doğal elyaf takviyeli kompozitler bazı alanlarda sentetik elyaf takviyeli kompozitlere alternatif hale gelmiştir. Bu çalışmada, vakum destekli reçine transfer kalıplama (VDRTK) metodu ile üretilen jüt kumaş takviyeli ve farklı dolgu oranlarında (ağırlıkça % 0, 0.5, 1, 2) grafen nanoplatelet (GNP) dolgusu yapılmış epoksi matrisli kompozitlere abrazif aşınma testleri uygulanmıştır. Tribotestler pim-disk tipi tribotest cihazı kullanılarak 400 grit SiC zımpara kağıdı karşı yüzeyi üzerinde 5 N,10 N ve 15 N yüklerde 1m s-1 kayma hızında ve 200 m kayma mesafesinde gerçekleştirilmiştir. Yapılan testlerde ara yüzey sıcaklığı ve spesifik aşınma oranı değerleri takip edilmiştir. Spesifik aşınma oranının ağırlıkça %1 GNP dolgusunda minimum olduğu ve ara yüzey sıcaklığının genel olarak artan yük ile arttığı görülmüştür.

A basic characterization of novel epoxy matrix composites incorporated with up to 40 vol% of processed leaf fibers from the Copernicia prunifera palm tree, known as carnauba fibers, was performed. The tensile properties for the composite reinforced with 40 vol% of carnauba fibers showed an increase (40%) in the tensile strength and (69%) for the elastic modulus. All composites presented superior elongation values in comparison to neat epoxy. Izod impact tests complemented by fibers/matrix interfacial strength evaluation by pullout test and Fourier transformed infrared (FTIR) analysis revealed for the first time a significant reinforcement effect (&gt, 9 times) caused by the carnauba fiber to polymer matrix. Additional thermogravimetric analysis (TG/DTG) showed the onset of thermal degradation for the composites (326 ~ 306 &deg, C), which represents a better thermal stability than the plain carnauba fiber (267 &deg, C) but slightly lower than that of the neat epoxy (342 &deg, C). Differential scanning calorimetry (DSC) disclosed an endothermic peak at 63 &deg, C for the neat epoxy associated with the glass transition temperature (Tg). DSC endothermic peaks for the composites, between 73 to 103 &deg, C, and for the plain carnauba fibers, 107 &deg, C, are attributed to moisture release. Dynamic mechanical analysis confirms Tg of 64 &deg, C for the neat epoxy and slightly higher composite values (82&ndash, 84 &deg, C) due to the carnauba fiber interference with the epoxy macromolecular chain mobility. Both by its higher impact resistance and thermal behavior, the novel carnauba fibers epoxy composites might be considered a viable substitute for commonly used glass fiber composites.

This paper presents the results of research concerning multilayered epoxy composites reinforced with different materials. The strength of multilayered composites depends, to a large extent, on the reinforcing material. The authors decided to compare the low velocity impact response and perform tensile strength tests on several composites, to ascertain the mechanical properties of the prepared composites. Five different reinforcing materials were provided for the research (two fabrics made from aramid fibers, two fabrics made from carbon fibers and one fabric made from polyethylene fibers). The composites were manufactured by the vacuum supported hand laminating method. The low velocity impact response tests were conducted with the use of a pneumatic launcher. Three strikers with different geometry (conical striker, hemispherical striker and ogival striker) were used. A comparison of the resulting damage to the composites after the impact of the strikers was based on the images obtained using an optical microscope, tensile tests were also performed. The experimental investigation showed significant differences in the mechanical properties of the composites, depending on the applied reinforcing material. It was found that, as a result of the impacts, less damage occurred in the composites which were characterized by a lower Young&rsquo, s modulus and a higher tensile strength.

Epoxy resin samples were prepared using cycloaliphatic resin and anhydride curing agents. Response Surface Methodology (RSM) was applied to determine the effect of five independent variables (Silbond W12EST, MoldXA400, CSR, PC1000 and BYK3701) at 5 levels on the dependent variables thermal shock crack resistance (TSR) and track resistance. 33 experimental samples were prepared according to experimental design made by RSM. It was observed that not only an increase in the amount of MoldX A400 in the compound improved the tracking, but also amount Silbond W12EST had positive effect on it. The results showed that if the total filler amount in the formulation is lower than 60% the time-to-track is less than 300 min, even with using a high amount of MoldXA400 (30%). Increasing the amount of Silbond W12EST as well as core-shell toughening agent (CSR) microparticles can improve the TSR because of crack propagation inhibition caused by particles. On the other hand, an increase in MoldX A400 deteriorated TSR due to the creating weak bonds with epoxy matrix.

Cyclic olefin copolymer (COC) particles were dispersed in various amounts in an epoxy matrix, and the resulting blends were used to impregnate unidirectional carbon fibers (CF) by hand lay-up. The thermal stability was not substantially modified by the presence of COC particles. The mixture of the two polymers resulted in a phase separated blend and the flexural modulus and interlaminar shear strength progressively decreased with the addition of COC particles in the laminates. Mode I fracture toughness tests were executed on double cantilever beam specimens. The opened crack was then thermally mended at 190 &deg, C for 1 h. The laminates containing 30 wt.% of COC particles showed a healing efficiency of ~180%.

This research article investigated the effect of stacking sequence of glass fibers on the notched and unnotched tensile strength of glass fibers plies reinforced epoxy matrix composites fabricated by the hand lay-up technique. The orientation of glass fabrics was kept at [(0/90)]5, [(45/-45)]5 and [(0/90), (45/-45), ]s and all the laminates were prepared using five plies for different stacking sequences with fiber volume content of 38.6 vol.% with different ratios of the specimen hole diameter to the specimen width with three different values (0.1, 0.2, 0.5). The notch sensitivity of these composites was evaluated applying Whitney-Nuismer mathematical model. The results indicated that the composites with [(0/90)]5 stacking sequence displays the highest tensile unnotched strength, whereas the composites with [±45°]5 stacking sequence displays the least strength. Moreover, the notch sensitivity of [±45°]5 composites is almost higher than those of other stacking sequences with different D/W ratios. On the other hand, the notch sensitivity of [(0/90), (45/-45), ]s composites is slightly lower than those of [(0/90)]5 composite structures for different D/W ratios. Moreover, SEM micrographs indicates the most common failure modes for [(0/90), (45/-45), ]s and [(45/-45)]5 are more significant delamination and matrix cracking than that of [(0, 90)]5.

Delamination resistance and epoxy matrix brittle fracture have been the main issues in carbon/epoxy composites laminates. Various studies have been reported to complement the brittle fracture of epoxy matrix. Conventional methods of fabricating toughened carbon/epoxy composite laminates were thermo-plastic veils and films interleaving methods, directly toughening the matrix resin and dispersing nanoparticles in the matrix. In this study, the carbon/epoxy composites laminates were manufactured using carbon fiber/polyamide fiber braided fabrics. The chemical interactions between polyamide and epoxy matrix resin were investigated by Fourier transform infrared spectroscopy, which resulted in ring opening of the epoxide group by the amide group. The compression after impact strength and the interlaminar toughness of the carbon/epoxy composite laminate were increased by 31%, and the strain energy release rates were increased by 120% compared to the virgin interface composite. In the case of carbon/epoxy composite laminates interlaced with polyamide fibers, the mechanical properties, such as the tensile strength and fatigue properties, were improved as tensile modulus decreased.

Wind energy is a conventional energy source of power generation and a significant player in the today’s energy market. As an unlimited and free energy source, wind is available in majority areas of the world. Wind energy driven turbines uses a variety of composite materials. The details of wind turbine technology along with structure are discussed in this chapter. The historical development of wind turbine technology along with overall structure is briefed. This chapter focuses on the conventional composite materials for wind turbine blades (glass fibers/epoxy matrix composites), natural composites, hybrid and nano-engineered composites technology. A thorough insight in these topics results in appropriate selection of composite materials for wind turbine blade.

Prosopis Juliflora (Kikar Wood), also known as Vilayati babul commonly known in India, is commonly available all over the country. Its branches are mainly used as wood fuel and fodder in saw dust form. The current research focuses on extracting fibers from Kikar wood by chemi-thermomechanical pulping process and using as reinforcement in Epoxy Matrix polymer composites. Several mechanical tests such as tensile test, compressive test, hardness test, and impact test were conducted to study the mechanical properties of the developed composites.

The experimental study aimed to understand the effect of the highly polymerized thermoplastic epoxy matrix and of the submicron diameter glass fibres content on the impact and compression after impact (CAI) performance of woven carbon fibre reinforced composites. A thermoset epoxy system was also considered for the sake of comparison. The comparison highlighted the better impact performance of the composites with the thermoplastic epoxy matrix of higher weight-average molecular weight (Mw), which is further improved by the proper content of micro glass fibres. The enhanced impact damage tolerance was also demonstrated observing the damage imparted with surface laser morphology, infrared thermography and X-ray μ-CT.

A computational micromechanics based Finite Element (FE) analysis methodology is presented to predict the bi-axial failure envelope of a unidirectional (UD) carbon-epoxy composite ply. In order to estimate the effect of various microscale parameters that are influencing the macroscopic stress–strain behavior, under individual load cases, detailed numerical studies are conducted using a 3D RVE (Representative Volume Element) model. The constituent epoxy matrix plastic deformation in the RVE is captured using the linear Drucker-Prager plasticity model. The effect of the fiber–matrix interface damage, followed by frictional sliding of the constituent materials on the computed interface tractions is captured using the cohesive zone damage model combined with the Coulomb friction law, which is implemented into Abaqus using VUMAT. From the detailed FE analysis of the RVE under individual load cases, it is observed that the predicted macroscopic stress–strain behavior is sensitive to the fiber–matrix interface properties as well as the in-situ epoxy stress–strain behavior. Hence, using a coupled experimental-computational micromechanics approach the interface and the in-situ epoxy material properties are calibrated and validated. Using the calibrated interface and in-situ epoxy material properties, the bi-axial (transverse tension/transverse compression – in-plane shear) failure envelope of a UD composite ply is estimated. Comparing the predicted damage profiles and the failure envelope with the experimental results leads to good agreement and validates the proposed numerical methodology.

The extraction of glycyrrhizin from licorice root and stolon with ethanol/water solutions leaves a lignocellulosic residue, which could be potentially applied in biocomposites. This process proved difficult in principle, given the considerable hardness of this material as received, which impedes its use in polymer resins in large amounts. After ball milling, up to 10% of this fibrous residue, which shows very variable aspect ratio, was introduced into an epoxy matrix, to investigate its possible future application in sustainable polymers. Of the three composites investigated, containing 1, 5 and 10 wt% of licorice waste, respectively, by performing flexural testing, it was found that the introduction of an intermediate amount of filler proved the most suitable for possible development. Thermal characterization by thermogravimetry (TGA) did not indicate large variation of degradation properties due to the introduction of the filler. Despite the preliminary characteristics of this study, an acceptable resin-filler interface has been obtained for all filler contents. Issues to be solved in future study would be the possibility to include a larger amount of filler by better compatibilization and a more uniform distribution of the filler, considering their orientation, since most of it maintains an elongated geometry after ball milling.

This paper demonstrates the effectiveness of parametrically-upscaled continuum damage mechanics (PUCDM) models for multiscale damage analysis of S-2 glass fiber/SC-15 epoxy matrix composite beams subjected to single-edge notched bending (SENB) tests. The SENB experiments with [ 0 12 / 9 0 12 ] double-ply and [ 0 8 / 9 0 8 / 0 8 ] triple-ply composite beams use synchrotron X-ray phase-contrast imaging for in-situ damage characterization. PUCDM models represent a class of thermodynamically-consistent multiscale constitutive models that bridge length-scales through explicit incorporation of representative aggregated microstructural parameters (RAMPs) in constitutive coefficients. Functional forms of RAMPs are generated through machine learning tools, operating on a micromechanical analysis database. The efficient PUCDM-based FE simulations reveal multiscale damage phenomena in the SENB experiments.

Nowadays there is an increasing tendency to reuse industrial residues in order to reduce their environmental impact. A typical alternative for a residue is to be incorporate into a productive process that could be economically viable. In this work, 80 wt% of residues, quarry dust and chamotte from brick industries, were incorporated into 20 wt% of epoxy resin for the production of a novel artificial ornamental stone to be used in civil construction. For preparation of test specimens the granulometric composition associated with the best packaging of residues was determined by the Simplex method. Artificial stone plates were produced using vibration and vacuum processes. Specimens were tested for mechanical, physical and thermal properties as well as chemical resistance. The developed artificial stone presented mechanical properties within the standard expected range, with rupture stress of 30 MPa. Density and thermal behavior were also found to comply with values of natural ornamental stones applied in civil construction. This artificial stone was resistant to chemical attack by HCl, one of the most aggressive acid, which caused a weight loss of only 0.08 g. According to wear test, the thickness reduction indicated that the artificial stone could be used for high traffic pavement. Keywords: Artificial stone, Residue, Chamotte, Quarry dust, Technical properties

The mallow fiber (Urena lobata, linn) is demonstrating a great potential as reinforcement in polymer matrix composites. The difficulty in the use of the mallow, as in other natural lignocellulosic fibers (NLFs), is its hydrophilic compatibility with polymeric matrices that are typically hydrophobic. In order to improve the adhesion between the fiber surface and polymeric matrices, mallow fibers were subjected to mercerization treatment. In this work composites were produced with epoxy matrix reinforced with 30 vol% of mallow fibers, both untreated and mercerized. By means of XRD analysis it was verified the variation of crystallinity in fibers treated with different NaOH solutions as well as immersion times and agitation. After this XRD preliminary analysis, a treatment of 5% NaOH solution for 24 h without agitation was selected. The objective was to compare the Charpy impact energy of composites specimens produced with untreated mallow fibers and treated for the higher crystallinity obtained after the selected mercerization. For the analysis of impact energy the Tukey test was applied from which it could be assured, with a confidence level of 95%, that the epoxy specimens reinforced with 30 vol% of untreated mallow fibers, had the best performance. Keywords: Mallow fibers, Epoxy composite, Mercerization, Charpy impact test

The thermal coefficient of linear expansion, the electrical conductivity and dielectric permittivity of fabric reinforced hybrid composites with filled stratified epoxy matrix were investigated. The measurements of electrical conductivity and dielectric permittivity had been performed, using standard method regarding electrical resistance and electrical capacity. In order to point out the effect of filler and of the spatial distribution of reinforcement layers, the medial layer of fabric was especially prepared by introducing copper wires in the woven. So, the medial layer is made of different types of tows (carbon, aramid, glass). This attempt is made in order to design a composite able to provide information about its state during various loading. The results showed that the fillers did not improve the electrical parameters of epoxy matrix, but they led to reduce the thermal coefficient of linear expansion. The thermal and electrical behavior of hybrid composites varied in dependence of number of carbon layers and fiber orientation.

The potential of carbon nanotubes (CNT) as multifunctional filler in poly(epoxy)-based structural composites has been investigated. In a first step the reinforcement effect of CNT has been studied by tensile and three points bending tests, which evidenced significant improvements of stress and strain at break (respectively +17% and +30% for tensile tests on unidirectional carbon fibre-epoxy composites). Moreover, fracture experiments have also revealed a positive effect of CNT on the toughness (G1c) of carbon fibres-epoxy composites (+105% of improvement at the initial stage). In a second step, the health monitoring capability quantum resistive strain sensors (sQRS) made of CNT filled epoxy nanocomposite, incorporated in the core of glass fibres-epoxy composites has been studied. It was shown that during cyclic tensile tests, following the evolution of the relative resistance amplitude (Ar) of sQRS with strain gives a pertinent information on non-reversible phenomena such as plastic deformation and cracks’ development within the composite. In particular, the evolution of the sQRS sensitivity (gauge factor GF) under and over the elastic limit, allows to track damage accumulation throughout the composite. These results suggest a possible use of sQRS for the structural health monitoring (SHM) of composites in fields such as boating, wind energy, aeronautics and automotive.

In this novel work the EMI shielding properties of low density, low cost and less explored carbon nano fiber (CNF) nanofiller embedded in the epoxy matrix is investigated for its potential use in electromagnetic interference (EMI) shielding of sensitive electronic equipment’s applied in industrial, military applications and also in protection of human health. The CNF nanocomposite with filler concentrations 1, 5, 10 and 15 wt.% epoxy are synthesized via ultrasonication method. The EMI shielding efficiency of all the nanocomposites prepared are investigated in the X-band using VNA and the result shows that nanocomposite with CNF as 15 wt. % of epoxy achieved maximum EMI shielding efficiency of 35.53 dB in X-band at 2 mm thickness. Hence this lightweight CNF based nanocomposite can be potentially applied in many application such as military, industrial and civil application, where high shielding efficiency is required.

The interfacial shear strength (IFSS) is commonly used for evaluating the adhesion at the interface between fibre and matrix. A glass fibre/epoxy matrix system was investigated. The surface coatings applied to glass fibres may result in a discrepancy in the amine:epoxide group ratio between the interface and the bulk matrix, consequently moving the ratio away from the optimum stoichiometric ratio most often used. The amine:epoxide group ratio in the matrix was varied to obtain the optimum ratio at the interface. The study found that the amine:epoxide ratio influenced the IFSS with an optimum just below the stoichiometric ratio. The microbond test was conducted in a thermal mechanical analyser (TMA) to determine the IFSS thus revealing an inverse dependency on the testing temperature: an increased testing temperature yields a decrease of IFSS. IFSS determined at temperatures below the glass transition temperature displays a decreasing trend at high amine:epoxide ratio whereas IFSS measured at testing temperatures above the glass transition temperature steadily increases as the amine:epoxide ratio increases. The microbond test was conducted using both a tensile tester and a TMA setup. The two microbond test setups yielded results with same behaviour of the IFSS as a function of the amine:epoxide ratio.

The influence of voids on the moisture uptake of epoxy matrix has been studied. Specimens with void contents from 0 to about 50% were prepared. Void geometry and content were analyzed using microscopy and density methods. Void-containing samples were characterized by differential scanning calorimetry and dynamic mechanical analysis which verified consistency of chemistry. The moisture uptake of specimens immersed in distilled water at 40℃ was monitored. The rate of absorption and saturation moisture content increased with increasing void content. Mass balance calculations revealed that only 6–8% of the void volume is occupied by water at saturation. The moisture uptake of void-free and void-containing specimens was non-Fickian. The Langmuir model provided better fits to the experimental results, although the high void content specimens showed substantial deviations from the Langmuir diffusion model. The moisture diffusivity of the void-free and void-containing specimens agreed reasonably with the Maxwell inclusion model.