Showing papers in "Composites Part A-applied Science and Manufacturing in 2010"
TL;DR: In this paper, a review of the current understanding of carbon nanotubes and CNT/polymer nanocomposites with two particular topics: (i) the principles and techniques for CNT dispersion and functionalization and (ii) the effects of CNT-based functionalization on the properties of polymers.
Abstract: Carbon nanotubes (CNTs) hold the promise of delivering exceptional mechanical properties and multi-functional characteristics. Ever-increasing interest in applying CNTs in many different fields has led to continued efforts to develop dispersion and functionalization techniques. To employ CNTs as effective reinforcement in polymer nanocomposites, proper dispersion and appropriate interfacial adhesion between the CNTs and polymer matrix have to be guaranteed. This paper reviews the current understanding of CNTs and CNT/polymer nanocomposites with two particular topics: (i) the principles and techniques for CNT dispersion and functionalization and (ii) the effects of CNT dispersion and functionalization on the properties of CNT/polymer nanocomposites. The fabrication techniques and potential applications of CNT/polymer nanocomposites are also highlighted.
2,849 citations
TL;DR: In this paper, the authors review the recent progress in using silane coupling agents for NFPCs, summarizes the effective silane structures from the silane family, clarifies the interaction mechanisms between natural fibers and polymer matrices, and presents the effects of silane treatments on the mechanical and outdoor performance of the resulting composites.
Abstract: Natural fiber reinforced polymer composites (NFPCs) provide the customers with more alternatives in the material market due to their unique advantages. Poor fiber–matrix interfacial adhesion may, however, negatively affect the physical and mechanical properties of the resulting composites due to the surface incompatibility between hydrophilic natural fibers and non-polar polymers (thermoplastics and thermosets). A variety of silanes (mostly trialkoxysilanes) have been applied as coupling agents in the NFPCs to promote interfacial adhesion and improve the properties of composites. This paper reviews the recent progress in using silane coupling agents for NFPCs, summarizes the effective silane structures from the silane family, clarifies the interaction mechanisms between natural fibers and polymer matrices, and presents the effects of silane treatments on the mechanical and outdoor performance of the resulting composites.
1,725 citations
TL;DR: Bast fibres are defined as those obtained from the outer cell layers of the stems of various plants and find use in textile applications and are increasingly being considered as reinforcements for polymer-matrix composites as they are perceived to be sustainable as mentioned in this paper.
Abstract: Bast fibres are defined as those obtained from the outer cell layers of the stems of various plants. The fibres find use in textile applications and are increasingly being considered as reinforcements for polymer–matrix composites as they are perceived to be “sustainable”. The fibres are composed primarily of cellulose which potentially has a Young’s modulus of ∼140 GPa (being a value comparable with man-made aramid [Kevlar/Twaron] fibres). The plants which are currently attracting most interest are flax and hemp (in temperate climates) or jute and kenaf (in tropical climates). This review paper will consider the growth, harvesting and fibre separation techniques suitable to yield fibre of appropriate quality. The text will then address characterisation of the fibre as, unlike man-made fibres, the cross section is neither circular nor uniform along the length.
556 citations
TL;DR: In this paper, Ramie fiber reinforced poly(lactic acid) (PLA) composites were prepared by a two-roll mill and Ramie was treated by alkali and silane (3-aminopropyltriethoxy silane and γ-glycidoxypropyltrimethoxysilane).
Abstract: Ramie fiber reinforced poly(lactic acid) (PLA) composites were prepared by a two-roll mill. Ramie was treated by alkali and silane (3-aminopropyltriethoxy silane and γ-glycidoxypropyltrimethoxy silane). Effect of surface treatment on the properties of the composites was studied. The tensile, flexural and impact strength of the composites have a significant improvement. Dynamic mechanical analysis (DMA) results show that the storage moduli of the composites with treated ramie increase with respect to the plain PLA and the composites with untreated fiber whereas tangent delta decreases. The Vicat softening temperature of the composites with treated fiber is greatly higher than that of the composites with untreated fiber. The results of thermogravimetric analysis (TGA) show that fiber treatment can improve the degradation temperature of the composites. Moreover, the morphology of fracture surface evaluated by scanning electron microscopy (SEM) indicates that surface treatment can get better adhesion between the fiber and the matrix.
404 citations
TL;DR: Bast fibres are defined as those obtained from the outer cell layers of the stems of various plants and are increasingly being considered as reinforcements for polymer matrix composites as they are perceived to be sustainable.
Abstract: Bast fibres are defined as those obtained from the outer cell layers of the stems of various plants. The fibres find use in textile applications and are increasingly being considered as reinforcements for polymer matrix composites as they are perceived to be “sustainable”. The fibres are composed primarily of cellulose which potentially has a Young’s modulus of ∼140 GPa (being a value comparable with man-made aramid [Kevlar/Twaron] fibres). The plants which are currently attracting most interest are flax and hemp (in temperate climates) or jute and kenaf (in tropical climates). Part 2 of this review will consider the prediction of the properties of natural fibre reinforced composites, manufacturing techniques and composite materials characterisation using microscopy, mechanical, chemical and thermal techniques. The review will close with a brief overview of the potential applications and the environmental considerations which might expedite or constrain the adoption of these composites.
289 citations
TL;DR: In this paper, an intralaminar damage model, based on a continuum damage mechanics approach, is presented to model the damage mechanisms occurring in carbon fiber composite structures incorporating fibre tensile and compressive breakage, matrix tensile fracture, and shear failure.
Abstract: An intralaminar damage model, based on a continuum damage mechanics approach, is presented to model the damage mechanisms occurring in carbon fibre composite structures incorporating fibre tensile and compressive breakage, matrix tensile and compressive fracture, and shear failure. The damage model, together with interface elements for capturing interlaminar failure, is implemented in a finite element package and used in a detailed finite element model to simulate the response of a stiffened composite panel to low-velocity impact. Contact algorithms and friction between delaminated plies were included, to better simulate the impact event. Analyses were executed on a high performance computer (HPC) cluster to reduce the actual time required for this detailed numerical analysis. Numerical results relating to the various observed interlaminar damage mechanisms, delamination initiation and propagation, as well as the model’s ability to capture post-impact permanent indentation in the panel are discussed. Very good agreement was achieved with experimentally obtained data of energy absorbed and impactor force versus time. The extent of damage predicted around the impact site also corresponded well with the damage detected by non destructive evaluation of the tested panel.
286 citations
TL;DR: A coupled thermal-electrical analysis of carbon fiber reinforced polymer composites (CFRP) exposed to simulated lightning current was conducted in order to elucidate the damage behavior caused by a lightning strike with the numerical results being compared to experimental results as discussed by the authors.
Abstract: A coupled thermal–electrical analysis of carbon fiber reinforced polymer composites (CFRP) exposed to simulated lightning current was conducted in order to elucidate the damage behavior caused by a lightning strike with the numerical results being compared to experimental results. Based on the experimental results and a preliminary analysis, the specific mechanism of electrical conduction through the thickness direction of CFRP following thermal decomposition was revealed to be a key parameter for accurate numerical simulation. In particular, assuming the electrical conductivity in the thickness direction to be linear with respect to temperature in the range from the epoxy decomposition temperature to carbon sublimation temperature produced reasonable numerical results. The delamination area and damage depth were estimated from numerical results and thermal decomposition behavior of CFRP with the estimated damage area agreeing qualitatively with the experimental results. Numerical results suggest that Joule heat generation significantly influences lightning strike damage.
280 citations
TL;DR: In this article, the potential of grain by-products such as wheat husk, rye husk as reinforcements for thermoplastics as an alternative or together with wood fibres was investigated.
Abstract: The main objective of this research was to study the potential of grain by-products such as wheat husk, rye husk as reinforcements for thermoplastics as an alternative or together with wood fibres. Thermal degradation characteristics, bulk density, water absorption and solubility index were also investigated. The particle morphology and particle size was investigated by scanning electron microscopy. Water absorption properties of the fibres were studied to evaluate the viability of these fibres as reinforcements. The chemical composition of fibre such as cellulose, hemicellulose, lignin, starch, protein and fat were also measured. Surface chemistry and functionality of grain by-products was studied by EDX and FT-IR. Polypropylene composites were fabricated using a high speed mixer followed by injection moulding with 40 wt.% of fibre load. Tensile and Charpy impact strength of resulting composites were investigated.
259 citations
TL;DR: Wang et al. as discussed by the authors examined the evolution of damage in graphite/epoxy composite laminates due to lightning strikes to clarify the influence of lightning parameters and specimen size.
Abstract: This study examines the evolution of damage in graphite/epoxy composite laminates due to lightning strikes To clarify the influence of lightning parameters and specimen size, artificial lightning testing was performed on a series of laminated composite specimens Damage was assessed using visual inspection, ultrasonic testing, micro X-ray inspection, and sectional observation The results showed that the damage modes can be categorized into fiber damage, resin deterioration, and internal delamination modes Damage progression is governed by the strong electrical orthotropic properties of the laminates, and the lightning parameters defining impulse waveform show strong relationship with certain damage modes, though specimen size and thickness variation barely affect damage size
254 citations
TL;DR: In this article, a comparison of substantial published data for 3D woven, stitched and pinned composites quantifies the advantages and disadvantages of these different types of through-thickness reinforcement for in-plane mechanical properties.
Abstract: A comparison of substantial published data for 3D woven, stitched and pinned composites quantifies the advantages and disadvantages of these different types of through-thickness reinforcement for in-plane mechanical properties. Stitching or 3D weaving can either improve or degrade the tension, compression, flexure and interlaminar shear properties, usually by less than 20%. Furthermore, the property changes are not strongly influenced by the volume content or diameter of the through-thickness reinforcement for these two processes. One implication of this result is that high levels of through-thickness reinforcement can be incorporated where needed to achieve high impact damage resistance. In contrast, pinning always degrades in-plane properties and fatigue performance, to a degree that increases monotonically with the volume content and diameter of the pins. Property trends are interpreted where possible in terms of known failure mechanisms and expectations from modelling. Some major gaps in data and mechanistic understanding are identified, with specific suggestions for new standards for recording data and new types of experiments.
247 citations
TL;DR: In this article, a bio-based polylactic acid (PLA) composite with improved flame retardancy was developed, utilizing the unique properties of sepiolite nanoclay (Sep) and multiwalled nanotubes (MWNT).
Abstract: This work aims to develop a fully bio-based polylactic acid (PLA) composite with improved flame retardancy, utilising the unique properties of sepiolite nanoclay (Sep) and multiwalled nanotubes (MWNT). The pyrolysis combustion flow calorimeter (PCFC) also known as the microcalorimeter was used to screen the various PLA nanocomposites with respect to their potential flammability performance. The heat release capacity (HRC) which is an indicator of a materials fire hazard, reduced by 58% for the PLA ternary system based on sepiolite and MWNTs. Thermal gravimetric analysis (TGA) showed significant improvements to the residual char towards the later stages of the thermal ramp. The PLA ternary nanocomposite showed a 45% reduction in peak heat release (PHRR) when tested in the cone calorimeter. A further noteworthy observation was the 25% reduction in PHRR upon the introduction of hemp fibre into the PLA nanocomposite system.
TL;DR: In this paper, the value of some commonly available tropical fibres for the composite industry is assessed by determination of the strength, E-modulus and strain to failure through single fibre tensile tests.
Abstract: Natural fibres are studied as alternatives for man-made fibres to reinforce composites while keeping the weight lower. The assessment of the value of some commonly available tropical fibres for the composite industry starts with the determination of the strength, E-modulus and strain to failure through single fibre tensile tests. The mean strength and standard deviation is calculated following the normal and Weibull distribution resulting in the questionable benefit of applying the Weibull distribution. Furthermore, a correction method assesses the real fibre elongation from the measured clamp displacement. This procedure seems to be useful for strong, brittle fibres to produce more reliable results for the E-modulus and strain to failure.
TL;DR: In this paper, a short (random and aligned) and long (aligned) industrial hemp fibre reinforced polylactic acid (PLA) composites were produced by compression molding.
Abstract: The focus of this work was to produce short (random and aligned) and long (aligned) industrial hemp fibre reinforced polylactic acid (PLA) composites by compression moulding. Fibres were treated with alkali to improve bonding with PLA. The percentage crystallinity of PLA in composites was found to be higher than that for neat PLA and increased with alkali treatment of fibres which is believed to be due to the nucleating ability of the fibres. Interfacial shear strength (IFSS) results demonstrated that interfacial bonding was also increased by alkali treatment of fibres which also lead to improved composite mechanical properties. The best overall properties were achieved with 30 wt.% long aligned alkali treated fibre/PLA composites produced by film stacking technique leading to a tensile strength of 82.9 MPa, Young’s modulus of 10.9 GPa, flexural strength of 142.5 MPa, flexural modulus of 6.5 GPa, impact strength of 9 kJ/m2, and a fracture toughness of 3 MPa m1/2.
TL;DR: In this article, carbon nanotubes (CNTs) were grafted on IM7 carbon fibres using a chemical vapour deposition method, which resulted in a threefold increase of the surface area compared to the original CNT fibres.
Abstract: Carbon nanotubes (CNTs) were grafted on IM7 carbon fibres using a chemical vapour deposition method. The overall grafting process resulted in a threefold increase of the BET surface area compared to the original primary carbon fibres (0.57 m 2 /g). At the same time, there was a degradation of fibre tensile strength by around 15% (depending on gauge length), due to the dissolution of iron catalyst into the carbon; the modulus was not significantly affected. The wetting behaviour between fibres and poly(methyl methacrylate) (PMMA) was directly quantified using contact angle measurements for drop-on-fibre systems and indicated good wettability. Single fibre fragmentation tests were conducted on hierarchical fibre/PMMA model composites, demonstrating a significant (26%) improvement of the apparent interfacial shear strength (IFSS) over the baseline composites. The result is associated with improved stress transfer between the carbon fibres and surrounding matrix, through the grafted CNT layer. The improved IFSS was found to correlate directly with a reduced contact angle between fibre and matrix.
TL;DR: In this paper, the effect of machining parameters (feed, speed and drill diameter) on the thrust force and machinability of woven glass fiber-reinforced epoxy (GFRE) composites was investigated.
Abstract: The present paper deals with the effect of machining parameters (feed, speed and drill diameter) on the thrust force and machinability of woven glass fiber-reinforced epoxy (GFRE) composites. The selected machinability parameters were delamination size, surface roughness, and bearing strength. The results show that, delamination-free in drilling GFRE composites was not observed, in the range of the investigated cutting parameters. Surface roughness instrument can be used as an indication for the position of the internal delamination damage in drilling GFRE composites. The high values of correlation coefficients between thrust force and the machinability parameters confirm the importance of reducing the thrust force to improve the load carrying capacity of composite structure assembled by rivets or bolted joints.
TL;DR: In this paper, sisal fibers were mercerized, under tension and no tension, to improve their tensile properties and interfacial adhesion with soy protein resins, which is known to minimize fiber shrinkage and to lower the microfibrillar angle by aligning them along the fiber axis.
Abstract: Sisal fibers were mercerized, under tension and no tension, to improve their tensile properties and interfacial adhesion with soy protein resin. Mercerization of fibers under tension is known to minimize fiber shrinkage and to lower the microfibrillar angle by aligning them along the fiber axis. Mercerization improved the fracture stress and Young’s modulus of the sisal fibers while their fracture strain and toughness decreased. Mercerized sisal fiber-reinforced composites with soy protein resin showed improvement in both fracture stress and stiffness by 12.2% and 36.2%, respectively, compared to the unmercerized fiber-reinforced composites. Scanning electron microscope (SEM) photomicrographs of the composite fracture surfaces showed shorter fibrils protruding in the mercerized fiber-reinforced composites resulting in better sisal fiber/soy adhesion. Changed fiber surface properties were also responsible for better adhesion.
TL;DR: In this article, carbon nanotubes (CNTs) were integrated in glass fibres epoxy composites by either including CNTs in the fibre sizing formulation, in the matrix, or both.
Abstract: Carbon nanotubes (CNTs) were integrated in glass fibres epoxy composites by either including CNTs in the fibre sizing formulation, in the matrix, or both. The effects of such controlled placement of CNTs on the thermophysical properties (glass transition temperature and coefficient of thermal expansion) and the Mode I interlaminar fracture toughness of the composites were studied. The present method of CNT-sizing of the glass fibres produces an increase of almost +10% in the glass transition temperature and a significant reduction of −31% in the coefficient of thermal expansion of the composites. Additionally, the presence of CNTs in the sizing resulted in an increased resistance of crack initiation fracture toughness by +10%, but a lowered crack propagation toughness of −53%. Similar trends were observed for both instances when CNTs were introduced only in the matrix and in combination of both matrix and sizing.
TL;DR: In this paper, a carbon-phenolic ablative TPS was developed, manufactured and tested with the aim of fulfilling the thermal and mechanical requirements corresponding to the actual loads experienced by a vehicle during a moon-earth re-entry.
Abstract: Thermal protection systems (TPS) are designed to protect re-entry space vehicles from the severe heating encountered during hypersonic flight through a planet’s or the earth’s atmosphere. A carbon–phenolic ablative TPS was developed, manufactured and tested with the aim of fulfilling the thermal and mechanical requirements corresponding to the actual loads experienced by a vehicle during a moon-earth re-entry. Experimental activities were carried out on two different composite systems (a resole resin coupled with a graphitic felt and a graphitic foam), and were aimed to the optimization of the manufacturing procedure and to the characterization of the mechanical behaviour and of the insulation performance of the fabricated composites.
TL;DR: In this paper, the thermal conductivity of epoxy composites with hybrid filler system is higher than that of any single filler system (functionalized MWCNTs or modified SiC np ), which is due to the effective combination of multi-walled carbon nanotubes (MWCNTs) to MWCNT and SIC np -to-SiC np conductive networks.
Abstract: Multi-walled carbon nanotubes (MWCNTs) were first treated by a 3:1 (v/v) mixture of concentrated H 2 SO 4 /HNO 3 , and then triethylenetetramine (TETA) grafting was carried out. Nano-sized silicon carbide particles (SiC np ) were modified by the silane coupling agent. Epoxy nanocomposites filled with hybrid filler system containing TETA-functionalized MWCNTs and silane-modified SiC np were prepared. The investigation on the thermal conductivity of epoxy nanocomposites filled with single filler system and hybrid filler system was performed. Chemical surface treatment is conducive to the enhancement of thermal conductivity of epoxy composites. The thermal conductivity of epoxy composites with hybrid filler system is higher than that of epoxy composites with any single filler system (functionalized MWCNTs or modified SiC np ), which is due to the effective combination of MWCNT-to-MWCNT and SiC np -to-SiC np conductive networks. Hybrid filler system could provide synergistic effect and cost reduction simultaneously.
TL;DR: In this paper, an integrative joining technology between steel and carbon fiber reinforced plastics (CFRP) is presented for lightweight design applications in aviation industries, where small spikes are welded onto metal surfaces via "cold-metal transfer" which then build up a fibre-friendly fixation through form-closure with co-cured composites.
Abstract: An integrative joining technology between steel and carbon fibre-reinforced plastics (CFRP) is presented for lightweight design applications in aviation industries. Small spikes are welded onto metal surfaces via “cold-metal transfer” which then build up a fibre-friendly fixation through form-closure with co-cured composites. Manufacture of such reinforced hybrid specimens and results of static tensile testings are discussed. Video-extensometry is applied to characterize the hybrid joints in terms of strength and failure history. Comparisons with epoxy bonded references show improvements in ultimate load, maximum deformation and energy absorption capacity.
TL;DR: In this article, the effect of maleated polypropylene (MAPP), two surfactants (stearic acid and cellulose palmitate) and the chemical modification of wood (benzylation) on interfacial adhesion, homogeneity, processability and water absorption was compared.
Abstract: Four different approaches were used for the modification of interfacial interactions in polypropylene (PP)/wood flour composites. We compare the effect of maleated polypropylene (MAPP), two surfactants (stearic acid and cellulose palmitate) and the chemical modification of wood (benzylation) on interfacial adhesion, homogeneity, processability and water absorption. Interfacial adhesion and reinforcement improves upon the addition of a maleated polymer as expected. Non-reactive surface modification leads to a moderate decrease of interaction, while benzylation decreases interfacial adhesion quite considerably. MAPP does not influence any other property of interest; homogeneity, viscosity and water absorption remain practically unchanged independently of the amount of coupling agent used. Surfactants improve homogeneity and processability, while the chemical modification of wood by benzylation decreases water absorption significantly. The results clearly prove that the proper selection of the approach and level of surface modification may lead to considerable improvement in targeted properties.
TL;DR: In this paper, the authors presented a new in situ Structural Health Monitoring (SHM) system able to identify the location of acoustic emission (AE) sources due to low-velocity impacts and to determine the group velocity in complex composite structures with unknown lay-up and thickness.
Abstract: This paper presents a new in situ Structural Health Monitoring (SHM) system able to identify the location of acoustic emission (AE) sources due to low-velocity impacts and to determine the group velocity in complex composite structures with unknown lay-up and thickness. The proposed algorithm is based on the differences of stress waves measured by six piezoelectric sensors surface bonded. The magnitude of the Continuous Wavelet Transform (CWT) squared modulus was employed for the identification of the time of arrivals (TOA) of the flexural Lamb mode ( A 0 ). Then, the coordinates of the impact location and the flexural wave velocity were obtained by solving a set of non-linear equations through a combination of global Line Search and backtracking techniques associated to a local Newton’s iterative method. To validate this algorithm, experimental tests were conducted on two different composite structures, a quasi-isotropic CFRP and a sandwich panel. The results showed that the impact source location and the group speed were predicted with reasonable accuracy (maximum error in estimation of the impact location was approximately 2% for quasi-isotropic CFRP panel and nearly 1% for sandwich plate), requiring little computational time (less than 2 s).
TL;DR: In this paper, the application of cohesive zone interface elements to modeling discrete matrix dominated failures in polymer composites is reviewed, and it is shown that because they can accurately represent the physical mechanisms controlling damage development and failure, they are able to give excellent simulations of a wide variety of phenomena including delamination, laminate in-plane failure, behaviour at notches, impact damage and structural failure due to debonding.
Abstract: The application of cohesive zone interface elements to modelling discrete matrix dominated failures in polymer composites is reviewed. It is shown that because they can accurately represent the physical mechanisms controlling damage development and failure, they are able to give excellent simulations of a wide variety of phenomena including delamination, laminate in-plane failure, behaviour at notches, impact damage and structural failure due to debonding.
TL;DR: The physico-mechanical properties of coir reinforced polypropylene (PP) composites were investigated in this article, where coir was chemically treated with o-hydroxybenzene diazonium salt.
Abstract: The physico-mechanical properties of coir reinforced polypropylene (PP) composites been investigated. In order to attain improved mechanical properties of the composites coir was chemically treated with o-hydroxybenzene diazonium salt. Both raw and treated coir samples were utilized for the fabrication of the composites. The mechanical properties of the composites prepared from chemically treated coir are found to be much better compared to those of untreated ones. Tensile strengths of the composites of both raw and chemically treated coir-PP composites showed a decreasing trend with increasing filler content. However, the values for the chemically treated coir-PP composites at all mixing ratios are found to be higher than that of neat PP. The surface morphologies of the fractured surfaces of the composites were recorded using scanning electron microscopy (SEM) to gain information about the fiber–matrix interfacial adhesion in the composites.
TL;DR: In this paper, the effect of the molecular nature of the interface between an epoxy matrix and multi-walled carbon nanotubes (CNTs) on the mechanical properties of the resultant nano-composites, with emphasis on toughness, was studied.
Abstract: We study the effect of the molecular nature of the interface between an epoxy matrix and multi-walled carbon nanotubes (CNTs) on the mechanical properties of the resultant nano-composites, with emphasis on toughness. A number of samples based on variously functionalized CNTs, namely, pristine, carboxylated, and aminated CNTs are examined, with different qualities of dispersion. Nano-composite toughness is found to increase with enhanced interfacial adhesion, an effect that is opposite to what is usually observed in traditional fiber-based composites. The classical pull-out energy model is shown to effectively explain this result. It is thus possible to tune the toughness of a nano-composite by adjusting the molecular nature of its interface and the CNT characteristics, namely its strength and its length relative to its critical length.
TL;DR: In this article, the dispersibility of unfunctionalized and three differently functionalized multi-walled carbon nanotubes (MWNTs) in the presence of anionic, cationic, and non-ionic surfactants was investigated.
Abstract: The dispersibility of unfunctionalized and three differently functionalized multi-walled carbon nanotubes (MWNTs) in the presence of anionic, cationic, and non-ionic surfactants was investigated. Significant differences in their dispersibility were revealed by UV–vis spectroscopy of the dispersed MWNTs. X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy, streaming potential measurements as well as pH measurements were conducted to characterize the MWNTs and their dispersions. Based on this information, possible interaction mechanisms between the surfactants and the differently functionalized MWNTs are proposed in order to account for the distinct dispersibility observed. Aqueous sizings containing low weight fractions of MWNTs were used for on-line modification of glass fibre (GF) sizings and preparation of GF/polypropylene composites, resulting in enhanced mechanical properties.
TL;DR: In this paper, the behavior of glass fibres reinforced polymer (GFRP) under low velocity impact with infrared thermography was investigated with a modified Charpy pendulum by varying shape (ogival and hemispherical) and diameter (18 and 24 mm).
Abstract: The aim of the present paper was to investigate the behaviour of glass fibres reinforced polymer (GFRP) under low velocity impact with infrared thermography. Several specimens were considered which include unidirectional E-glass fibres embedded in epoxy resin matrix with symmetrical stacking sequence [02/902]S. These specimens were impacted with modified Charpy pendulum by varying shape (ogival and hemispherical) and diameter (18 and 24 mm) of the hammer and the impact energy in the range 4–25 J. The side opposite to impact was monitored by infrared cameras. Sequences of images were acquired with starting and ending times set so as to include the evolution of thermal phenomena from thermo-elastic to thermoplastic phases. Infrared thermography was also used for non-destructive evaluation of specimens before and after impact. The obtained results show that on-line monitoring of the impact is useful for material characterization. In particular, it is shown that the onset of heat generation loci corresponds to the onset of impact damage. From the analysis of temperature maps it is possible to get information about damage threshold and extension. One main finding regards the relationship between the damaged area and the effective striking surface.
TL;DR: In this paper, the authors reported on a novel toughening concept based on dissolvable phenoxy fibres, which are added at the interlaminar region in a carbon fiber/epoxy composite.
Abstract: This paper reports on a novel toughening concept based on dissolvable phenoxy fibres, which are added at the interlaminar region in a carbon fibre/epoxy composite. The composites were prepared by resin infusion of carbon fibre fabric with the phenoxy introduced as a chopped fibre interleaf between the carbon fibre plies. The thermoplastic phenoxy fibre dissolved in the epoxy during curing at elevated temperatures and a phase separated morphology with phenoxy-rich secondary phase was formed upon curing. It was found that the average Mode-I fracture toughness value, G1c increased tenfold with only 10 wt.% (with regard to the total matrix content) phenoxy fibre added. Other properties such as Young’s modulus, tensile strength and thermal stability were not adversely affected. The mechanical and thermal properties of the neat epoxy–phenoxy blends were also studied for comparison.
TL;DR: In this article, the authors used a microencapsulated healing agent and paraffin wax microspheres containing 10 wt% Grubbs' catalyst for self-healing of impact damage in composite materials.
Abstract: In this study autonomic self-healing of impact damage in composite materials is shown using a microencapsulated healing agent. The components for self-healing, urea‐formaldehyde microcapsules containing dicyclopentadiene (DCPD) liquid healing agent and paraffin wax microspheres containing 10 wt% Grubbs’ catalyst, have been successfully incorporated in a woven S2-glass-reinforced epoxy composite. Lowvelocity impact tests reveal that the self-healing composite panels are able to autonomically repair impact damage. Fluorescent labeling of damage combined with image processing shows that total crack length per imaged cross-section is reduced by 51% after self-healing. A testing protocol based on compression after impact reveals significant recovery of residual compressive strength (RCS) in self-healing panels. Self-healing panels show a higher threshold impact energy before RCS reduction, and as impact energy increases, RCS recovery decreases. Qualitative inspection shows that crack separation increases with increasing impact energy, indicating that self-healing performance depends on the ability to adequately fill damage volume.
TL;DR: In this article, the effects of surface modification of AlN nanoparticles on morphology, glass transition, electrical property and thermal conductivity of the epoxy composites were investigated, and it was found that the surface modification not only improved the dispersion of the nanoparticles, but also showed an enhancement in electrical and thermophysical properties.
Abstract: The traditional epoxy resin used for electrical and electronic industry has a poor thermal conductivity and no longer meets the increasingly cooling requirements of electric equipments and electronic devices. Ceramic nanoparticles with high thermal conductivity and low dielectric constant represent good candidates to improve the thermophysical properties of epoxy resin. This paper reports the effects of surface modification of AlN nanoparticles on morphology, glass transition, electrical property and thermal conductivity of the epoxy composites. Gamma-aminopropyl triethoxysilane was used as a silane coupling agent for the surface modification of the AlN nanoparticles. It was found that the surface modification of the nanoparticles not only improved the dispersion of the nanoparticles, but also showed an enhancement in electrical and thermophysical properties of the epoxy composites. The surface modification technology presented a strategy to prepare nanocomposites having high thermal conductivity simultaneously with low dielectric loss.