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Diffusion of water in epoxy composites with different sequential arrange ments of woven roving (WR) and chopped strand mat (CSM) reinforcements was studied on immersion in water at 298 K and 323 K. Laminates with CSM as skin layers showed higher diffusivity and equilibrium moisture content than WR as skin layers. The diffusion parameters obtained from the experiment conducted up to saturation limits of 323 K showed good correlation with the data computed using a moisture absorption programme written on lines suggested by G. S. Springer. Hence data at lower temperatures are also generated by using the above programme, thus shortening the time to reach saturation levels. [ABSTRACT FROM PUBLISHER]

The moisture diffusion characteristics of simple (E-glass, Graphite and Kevlar) and hybrid (E-Glass-Graphite, Graphite-Kevlar and Kevlar-E-Glass) unidirectional com posites have been studied at 296 K and 343 K under water immersion conditions. The equilibrium moisture content (Mm) and diffusion coefficient (Dx) of Kevlar fibre com posites are respectively as high as 5 and 10 times those of E-glass/Graphite fibre com posites. The hybridization of impermeable fibres (E-Glass and Graphite) in a com posite does not cause significant changes in the Mm and D x values of their simple com posites. Hybridization of impermeable fibres with permeable fibres (Kevlar), however, has a significant effect on the diffusion characteristics of their simple composites. The experimental data for simple and hybrid composites comprising both impermeable and/or permeable fibre composites show good correlations with the analytical Fickian Diffusion plot. The effect of edge coating on the moisture absorption is quite signifi cant in the impermeable fibre composites. [ABSTRACT FROM PUBLISHER]

The influence of internal factors like the fibre volume fraction and its orientation to the diffusion path on the moisture absorption trends of both the permeable (Jute-Epoxy) and the impermeable types (glass-epoxy) of composites were studied. The equilibrium moisture level (Mm) and the diffusion coefficient (DJ of the glass-epoxy composite decreased as expected, with an increase of the glass fibre fraction (V f) and its orientation («), while those of the Jute-epoxy composite (ie Mm and D/) were found to increase with an increase in the resin impregnated jute fibre fraction (V/) and remain practically uninfluenced by the variations in the fibre orientation angle. These observed trends were explained in terms of typical fibre permeabilities and the diffusion paths preferred by the moisture in these composites. A term called "dif- fusivity index (DI)" was introduced to quantify the relative permeabilities of polymer composites to moisture. [ABSTRACT FROM PUBLISHER]

The influence of external factors like relative humidity (0) and ambient temperature (T) on the moisture absorption behaviour of permeable (Jute-Epoxy) and impermeable (Glass-Epoxy and Graphite-Epoxy) types of composites were reported. The respective equilibrium moisture contents (Mm and Mm) increased exponentially with relative humidity. The diffusion coefficients of both type of composites (D~'and D,) increased with ambient temperature and could be represented by an Arrhenius relationship. The permeable composite showed a higher exponential power on the relative humidity term than the impermeable composite (2.64 for Jute composite as compared to 2.0 reported by Shen and Springer for a graphite composite) and a lower activation energy for diffusion (0.9 x 101 cal. mole-' for the jute composite as compared to 4.429 x 103 cal. mole-1 obtained for a glass composite). These trends were attributed to the fibre permeability leading to different diffusion barriers in such composites. [ABSTRACT FROM PUBLISHER]

Braided and filament wound CFRP were fabricated with varied fiber orientations. These composites exhibited not only similar trends in their experimental strength and stiffness properties but also good correlations with predictions made by CLT. [ABSTRACT FROM PUBLISHER]

Studies were conducted on the degradation of short beam shear (SBS) and impact strength (Izod) properties of glass epoxy composite specimens with sequential ar rangements of woven roving (WR) and chopped strand mat (CSM) reinforcements, (Figure 1 of Part A) immersed in water at two different temperatures (298 K, 323 K).It was found that composites with higher fibre content, though possessed of a higher ini tial shear strength, degraded faster than those with low fibre content. This was attributed to a thin resin layer separating the glass layers and a consequential increased surface area around the fibres for the moisture absorption. Further, it was noted that while the impact strength too degraded with exposure period, the degradation patterns are almost identical in all types of laminates within the limits of fibre resin ratio chosen. [ABSTRACT FROM PUBLISHER]

A comparative study was made between the moisture absorption behaviours of sisal and jute fibre composites in an epoxy matrix under immersion conditions. Sisal fibres, in spite of possessing more compact structure than jute fibres, exhibited higher moisture absorp tion levels in their composite form, contrary to expectations. This tendency was attributed to the high cellulose content and a possible interfacial effect in the former. [ABSTRACT FROM PUBLISHER]

A brief description of the Fickian diffusion behaviour in polymer composites, con taining impermeable fibres (glass and graphite) is presented. The applicability of such a model to composites based on a permeable fibre phase (jute) is verified, both under the influence of varied internal (fibre volume fraction) and external (ambient temperature) factors. Very good correlations are found between the experimental data and a modified Fickian diffusion plot. The significance of a resin impregnated fibre volume fraction in such a composite is highlighted. [ABSTRACT FROM PUBLISHER]

In order to investigate the durability of fiber-reinforced polymer composites in hygrothermal environments, hygrothermal accelerate aging tests, for 360 days at 70 °C, RH70%; 70 °C, RH85%; 85 °C, RH70%; and 85 °C, RH85% and natural storage for 2 years in Guangzhou, China, were carried out for composite laminates. Then, the moisture absorption and interlaminar shear strength were measured. The hygrothermal damage mechanism of the composite was studied by Fourier transform infrared (FTIR), differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), and field emission scanning electron microscopy (FSEM). A dual stress storage life prediction model and the equivalent relationship between natural storage and hygrothermal acceleration were established. The results show that the order of moisture absorption rates, moisture absorption contents, and the severity effect order on the interlaminar shear strength is RH85%; 85 °C > 70 °C; RH85% > 85 °C; RH70% > 70 °C; and RH70%. The time to achieve an effective moisture absorption balance is opposite to this. The moisture absorption rate meets Fick's law before the effective moisture absorption balance, and then shows a linear trend. The interlayer shear strength still decreases exponentially with aging, which is mainly caused by the resin plasticization and interface weakening. Hygrothermal accelerated aging for 13.4831 days at 85 °C; RH85% is equivalent to that for one-year actual storage in Guangzhou. According to the failure criterion of shear strength decreasing to 77%, the storage life of T700/epoxy in Guangzhou is 14.4661 years. [ABSTRACT FROM AUTHOR]

This study focuses on examining the influence of bast fibers on the flammability and thermal properties of the polylactide matrix (PLA). For this purpose, Urtica dioica and Vitis vinifera fibers were subjected to two types of modifications: mercerization in NaOH solution (M1 route) and encapsulation in an organic PLA solution (M2 route). In a further step, PLA composites containing 5, 10, and 15 wt% of unmodified and chemically treated fibers were obtained. The results of the tests show that only biocomposites containing mercerized fibers had a nearly 20% reduced flammability compared to that of PLA. Moreover, the biofiller obtained in this way belongs to the group of flame retardants that generate char residue during combustion, which was also confirmed by TGA tests. The M2 modification route allowed to achieve higher mass viscosity than the addition of unmodified and M1-modified fibers. The reason is that fibers additionally encapsulated in a polymer layer impede the mobility of the chain segments. The inferior homogenization of the M2-modified fibers in the PLA matrix translated into a longer combustion time and only a 15% reduction in flammability. [ABSTRACT FROM AUTHOR]

Epoxy resins find extensive utility across diverse applications owing to their exceptional adhesion capabilities and robust mechanical and thermal characteristics. However, the demanding reaction conditions, including extended reaction times and elevated reaction temperature requirements, pose significant challenges when using epoxy resins, particularly in advanced applications seeking superior material properties. To surmount these limitations, the conventional approach involves incorporating organic catalysts. Within the ambit of this investigation, we explored the catalytic potential of metallic powders, specifically bismuth (Bi) and silver (Ag), in epoxy resins laden with various curing agents, such as diacids, anhydrides, and amines. Metallic powders exhibited efficacious catalytic activity in epoxy–diacid and epoxy–anhydride systems. In contrast, their influence on epoxy–amine systems was rendered negligible, attributed to the absence of requisite carboxylate functional groups. Additionally, the catalytic performance of Bi and Ag are different, with Bi displaying superior efficiency owing to the presence of inherent metal oxide layers on its powder surfaces. Remarkably, the thermal and mechanical properties of uncatalyzed, fully cured epoxy resins closely paralleled those of their catalyzed counterparts. These findings accentuate the potential of Bi and Ag metal catalysts, particularly in epoxy–diacid and epoxy–anhydride systems, spanning a spectrum of epoxy-based applications. In summary, this investigation elucidates the catalytic capabilities of Bi and Ag metal powders, underscoring their ability to enhance the curing rate of epoxy resin systems involving diacids and anhydrides but not amines. This research points toward a promising trajectory for multifarious epoxy-related applications. [ABSTRACT FROM AUTHOR]

Featured Application: Multifunctional protective layer for fiber reinforced composites. In the aerospace sector, structural and non-structural composite components are usually subjected to a wide range of environmental conditions. Among all, moisture can seriously damage these materials' performance, reducing their mechanical, thermal, electrical, and physical properties as well as their service time. Lightweight protective barrier coatings capable of reducing the diffusion of gases and/or liquids in a material can improve the material's resistance in humid environments. In this work, nanolamellar nanocomposites characterized by a high in-plane orientation of nanoplatelets have been employed as protective coatings for Kevlar sandwich panels, reproducing the construction of a nacelle engine. The effectiveness of the protection against water uptake of nanocomposites reinforced with graphite nanoplatelets (GNPs) at high filler contents (70, 80 and 90 wt%) has been investigated using moisture uptake and Ground-Air-Ground (GAG) tests in an environmental chamber. GNP coatings effectively work as barrier by generating highly tortuous paths for molecule diffusion. Results showed a dependence of the absorption on the coating composition and inner structure. Films @70 wt% GNPs showed the best protection against moisture uptake by delaying the phenomenon and reducing the absorption by −80% after 3 days and −35% after 41 days. [ABSTRACT FROM AUTHOR]

This paper presents an experimental and numerical investigation on the influence of pre-existing impact damage on the low-velocity impact response of Carbon Fiber Reinforced Polymer (CFRP). A continuum damage mechanics-based material model was developed by defining a user-defined material model in Abaqus/Explicit. The model employed the action plane strength of Puck for the damage initiation criterion together with a strain-based progressive damage model. Initial finite element simulations at the single-element level demonstrated the validity and capability of the damage model. More complex models were used to simulate tensile specimens, coupon specimens, and skin panels subjected to low-velocity impacts, being validated against experimental data at each stage. The effect of non-central impact location showed higher impact peak forces and bigger damage areas for impacts closer to panel boundaries. The presence of pre-existing damage close to the impact region leading to interfering delamination areas produced severe changes in the mechanical response, lowering the impact resistance on the panel for the second impact, while for non-interfering impacts, the results of the second impact were similar to the impact of a pristine specimen. [ABSTRACT FROM AUTHOR]

Purpose: Rapid tooling (RT) integrated with additive manufacturing technologies have been implemented in various sectors of the RT industry in recent years with various kinds of prototype applications, especially in the development of new products. The purpose of this study is to analyze the current application trends of RT techniques in producing hybrid mold inserts. Design/methodology/approach: The direct and indirect RT techniques discussed in this paper are aimed at developing a hybrid mold insert using metal epoxy composite (MEC) in increasing the speed of tooling development and performance. An extensive review of the suitable development approach of hybrid mold inserts, material preparation and filler effect on physical and mechanical properties has been conducted. Findings: Latest research studies indicate that it is possible to develop a hybrid material through the combination of different shapes/sizes of filler particles and it is expected to improve the compressive strength, thermal conductivity and consequently increasing the hybrid mold performance (cooling time and a number of molding cycles). Research limitations/implications: The number of research studies on RT for hybrid mold inserts is still lacking as compared to research studies on conventional manufacturing technology. One of the significant limitations is on the ways to improve physical and mechanical properties due to the limited type, size and shape of materials that are currently available. Originality/value: This review presents the related information and highlights the current gaps related to this field of study. In addition, it appraises the new formulation of MEC materials for the hybrid mold inserts in injection molding application and RT for non-metal products. [ABSTRACT FROM AUTHOR]

Epoxy-acrylate-maleate of bisphenol-C (ECAM), unsaturated polyester resin of phthalic anhydride, maleic anhydride and propylene glycol (PMP) were synthesized. ECAM, PMP and their varying compositions (25-75 wt%) were cured using MEKP and cobalt naphthenate and characterized by IR, DSC and TGA techniques. Interpenetrating networks possess intermediate thermal stability of ECAM (300°C) and PMP (227°C) and followed single step degradation with fractional order kinetics (0.6-2.4) leaving 10-25% residue above 400°C. Low magnitudes of energy of activation and frequency factor of interpenetrating networks indicated improvement in flexibility due to toughening of PMP by ECAM of varying compositions. [ABSTRACT FROM AUTHOR]

The objective of the work was to investigate the effect of addition of various weight percentages of Acrylonitrile-Butadiene-Styrene in to Bismaleimide resin on mechanical properties. Matrix material and their blends were characterized for viscosity and glass transition temperature. Modified and unmodified carbon composites were prepared and tested for tensile, flexural and impact strengths. Tensile (11%) and impact properties (29%) were found to be highest at 6% weight of ABS. In the case of flexural strength was found to be increasing with increase of ABS. The morphology of the BMI modified resin systems were also studied by scanning electron microscopy. [ABSTRACT FROM AUTHOR]

Cyanate ester (CE) -3,3-bis (3-maleimidophenyl) phenyl phosphine oxide (BMI)-modified epoxy matrices were made by using epoxy resin (DGEBA) and 1,3-dicyantobenzene and diaminodiphenyl methane as a curing agent. The properties of BMI-CE epoxy matrices were characterized by differential scanning calorimetry (DSC), thermogravimetric analysis, scanning electron microscopy, water absorption behavior and heat deflection temperature. The matrices were also characterized for their mechanical properties such as tensile strength, flexural strength and unnotched Izod impact strength by ASTM methods. The mechanical and tensile properties were improved by increasing the percentage of the CE in the epoxy resin. DSC thermograms of 1,3-dicyantobenzene as well as BMI-modified epoxy resin showed an unimodal reaction exothermicity. [ABSTRACT FROM AUTHOR]

Polybenzoxazine, poly(B-a), was hybridized with polysiloxanes by synchronizing two reactions ring-opening polymerization of benzoxazine (B-a) and the sol-gel process of diethoxysilanes. As diethoxysilanes, mixtures of diethoxydimethylsilane and diethoxydiphenylsilane in various ratios were used to prepare polysiloxane copolymers, poly(dimethylsiloxane-co-diphenylsiloxane), P(DMS/DPS). The effect of diphenylsiloxane (DPS) content of polysiloxane copolymer on the optical, mechanical, and thermal properties of the hybrids was studied. The progress of the sol-gel process was confirmed by IR, ¹H-NMR and size exclusion chromatography. Opaque poly(B-a)-P(DMS/DPS) hybrid films were obtained at high dimethylsiloxane (DMS) content corresponding to the phase separation. The domain size of the polysiloxane was evaluated from the scanning electron microscope. Meanwhile, transparent hybrid films were obtained at high DPS content, corresponding to the homogeneous phase as observed from the scanning electron microscope. The hybrid films revealed higher tensile strength and elongation at break than pristine poly(B-a) as a function of DPS content. Dynamic viscoelastic analyses of the hybrids at high DMS content revealed two glass transition temperatures (Tg) corresponding to polysiloxane and poly(B-a) components, while one Tg was observed at high DPS content. Thermogravimetric analysis of the hybrids revealed that the thermal stability of the poly(B-a)-polysiloxane hybrids was higher than pristine poly(B-a) depending on the DPS content. [ABSTRACT FROM AUTHOR]

Epoxidized soybean oil at various concentrations was cured with amine curing agent. The prepared matrices were chemically modified with three types of bismaleimides, namely N,N'-bismaleimido- 4,4′-diphenylmethane (BMI-1), 1,3-bis(maleimido)benzene (BMI-2) and 3,3′-bis(maleimidophenyl) phenylphosphine oxide (BMI-3). The interpenetrating networks thus developed were characterized for glass transition temperature, thermal stability, dynamic mechanical analysis, heat distortion temperature, flame retardancy and water absorption behavior. The incorporation of bismaleimides in the soy-based epoxy matrices significantly enhanced thermal stability and flame retardancy. The excellent flame retardant properties of the BMI-3 incorporated system were also demonstrated by high char yield and high limiting oxygen index. Dynamic mechanical analysis studies showed that the storage modulus increased with the increase in the concentration of bismaleimides and a reduction in the tan δ value for the bismaleimide-modified, 30 wt.% soy-based epoxy system due to enhanced cross-linking density and rigidity. [ABSTRACT FROM AUTHOR]

Dielectric barrier discharges (DBD) in ambient air are used on carbon fiber to improve the carbon fiber surface activity. Carbon fibers with length of 75 um are placed into the plasma configuration. The tribological properties of polypropylene filled with untreated and DBD treated carbon fiber are comparatively investigated. Results show that DBD treatment greatly improve the friction and wear properties of carbon fiber reinforced polypropylene composite (CF/PP). [ABSTRACT FROM AUTHOR]

Organoclay-filled polyethylene glycol (PEG)/1,8-octanediol (OCT)-modified epoxy matrices were developed. Epoxy systems modified with 10, 20, and 30wt% of PEG/OCT were made by using diglycidyl ethers of bisphenol A epoxy resin and PEG/OCT with 4,40-diaminodiphenylmethane as curing agent. The PEG/OCT-modified epoxy systems were further modified with 1, 3, and 5wt% of organoclay. The thermal behavior of organoclay-filled PEG/OCT-modified epoxy matrices were characterized using differential scanning calorimeter, thermogravimetric analysis, and dynamic mechanical analysis. Mechanical properties were studied as per ASTM standards. Three percent organoclay-filled PEG-modified epoxy possesses high storage modulus (6240 MPa) compared to 3% organoclay-filled OCT-modified epoxy (5064 MPa). The values of impact strength for 3% organoclay filled PEG and OCT modified epoxy systems are 122 and 85.5 J/m, respectively. Homogeneous and heterogeneous morphology was ascertained from scanning electron microscope. From the X-ray diffraction analysis, it was observed that the absence of d001 reflections in organoclay-filled PEG/OCT-modified epoxy systems indicated the formation of exfoliated nanohybrids. The significant improvement in impact strength was achieved without any reduction in glass transition temperature (Tg) due to the addition of organoclay. Thermal stability with better char yield and improved impact strength were attained during the formation of nanocomposites due to the increment of organoclay in PEG/OCT-modified epoxy systems. [ABSTRACT FROM AUTHOR]

Experiments have indicated that the diffusion properties of a penetrant organic matrix composite system may change with time due to evolution of the internal mechanical strain states experienced by the constituting matrix of the composite plies. A multi-scale approach coupling the internal mechanical states, predicted by continuum medium mechanics, and their localization at the ply-constituent scale to the traditional Fick's law governing the moisture diffusion process was used in order to achieve the modeling of the response of composite laminates submitted to environmental hygroscopic loads, from the transient part of the diffusion process to its permanent stage. Various numerical practical cases were considered: the effects of the internal swelling strains on the time- and space-dependent diffusion coefficient, maximum moisture absorption capacity, moisture content, and states of internal stresses are extensively studied and discussed. [ABSTRACT FROM AUTHOR]

Inorganic—organic hybrid nanocomposites were prepared by the following steps: (1) homogeneous dispersion of various percentages (1 to 5% w/w) of organically modified montmorollonite clay in epoxy matrix resin; (2) the resulting homogeneous epoxy—clay hybrids were modified with 10 wt.% of hydroxyl-terminated polydiemthyl siloxane (HTPDMS) using γ -aminopropyltriethoxysilane (γ APS) as coupling agent in the presence of dibutyltindilaurate catalyst; and (3) the siliconized epoxy—clay prepolymers were further modified separately with 10 wt% of three different cyanate ester monomers and cured with diaminodiphenylmethane. The chemical interactions between epoxy, clay, HTPDMS and cyanate ester were confirmed by Fourier transform infrared spectral analysis. The values obtained from differential scanning calorimetry and dynamic mechanical analysis showed that there was a significant loss of glass transition temperatures in the resulting hybrid epoxy nanocomposite systems compared with that of neat epoxy system. The inorganic clay mineral and the formation of thermally stable oxazolidinone structures and siloxane linkages during curing led to significant improvement in the thermal properties of the resulting nanocomposites. A decreasing trend was identified in the resulting nanocomposites from their values of dielectric constant and dielectric loss by the incorporation of clay, HTPDMS and cyanate ester in the epoxy resin. The intercalation/exfoliation structure was studied using X-ray diffraction analysis and the homogeneous/heterogeneous morphology was studied using scanning electron microscopy analysis in the resulting nanocomposites. [ABSTRACT FROM AUTHOR]

Bismaleimides (BMI) modified polyethersulfone (PES)-epoxy interpenetrating networks were developed. Epoxy systems modified with 4%, 8%, and 12% (by wt) of polyethersulfone were made by using epoxy resin (DGEBA) and polyethersulfone with diaminodiphenylmethane as curing agent. The polyethersulfone-toughened epoxy systems were further modified with 4%, 8%, and 12% (by wt) of bismaleimides, namely 1,3-bismaleimiobenzene and 1,1'-bis(4-maleimidophenyl) cyclohexane. BMI-PES-Epoxy matrices were characterized using differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), and heat deflection temperature (HDT) analysis. The DSC thermograms of polyethersulfone-modilied epoxy and BMI-modified epoxy during cure show unimodal reaction exotherms. The studies indicate that thermal stability and resistance to water absorption of epoxy resin has been enhanced by the introduction of polyethersulfone. The incorporation of bismaleimide into unmodified epoxy and PES-epoxy enhanced the thermal and mechanical properties according to its percentage content. The morphologies of fractured surfaces of modified epoxy systems were compared with that of unmodified epoxy system. [ABSTRACT FROM AUTHOR]

Epoxy polyhedral oligomeric silsesquioxane (POSS)-based hybrid nanocomposites were prepared by in situ polymerization of a homogeneous blend of the diglycidylether of bisphenol-A and 4,4'diaminodiphenylmethane (DDM) in the presence of octa(maleimidophenyl)silsesquioxane. The reaction of a maleimido-functionalized POSS cube with the epoxy resin was studied by Fourier transform infrared analysis and the formation of nanocomposites was confirmed by wide-angle X-ray diffraction and scanning electron microscopy. Dynamic mechanical analysis studies indicated that the crosslinking structures of the nanocomposite networks were predominantly formed between the terminal maleimide double bonds and the amino groups of DDM through a Michael addition reaction to form an aspartimide. The values of the glass transition temperatures (Tg) decreased with increasing POSS-maleimide content and this was likely to be due to the inclusion of POSS cages into the system and the consequent increase in free volume. The dynamic thermal stability of the cured polymers was increased by increasing the POSS content in the hybrid epoxy matrices as evidenced from thermogravimetric analysis data. [ABSTRACT FROM AUTHOR]

The dynamic response of E-glass/epoxy composite laminates under low velocity impact was experimentally investigated. Uni-directionally reinforced E-glass/epoxy laminates with the stacking sequence of [0°/-45°/45°/0°/ 90°/0°/45°/-45°/0°]s were studied with the aim of an impact test. The impact tests performed at impactor mass (30 kg) for three different impact velocities (2.0, 2.5, and 3.0m/s) were conducted with a specially developed vertical drop weight testing machine. The radius of the impactor with a semispherical nose was 12 mm. Sample plate specimens that had dimensions of 180 x 50, 180 x 100, and 180 x 150mm were clamped from two opposite sides while the other two sides were free. The center of each plate was exposed to impact loading. The differences in the impact responses of specimens with varying width are characterized. Moreover, it was shown that the peak force increased with the increase of the width of the specimen. [ABSTRACT FROM AUTHOR]

Although economic, ecological, processing and property considerations suggest that it is very attractive to use lignocellulosic fibers as reinforcement in polymer matrix composites, moisture can strongly and deleteriously affect their properties. In this work the water absorption behavior of sisal/cotton, jute/cotton and ramie/cotton hybrid fabric reinforced composites is evaluated. The effect of the temperature of immersion, fiber volume fraction, and predrying of the fabrics before their incorporation onto the composites are evaluated. Sisal was shown to be the most hygroscopic of the fibers analyzed, and its presence leads to higher values of the maximum water content and of the diffusion coefficient of sisal/cotton reinforced composites. Under the range of temperatures analyzed (30-60°C) the volume fraction of the fibers, rather than the temperature itself, was shown to be the main parameter governing water absorption. Predrying usually lowers maximum water content, although for sisal/cotton reinforced composites a reverse trend was observed for the composites with higher volume fractions. This behavior was again attributed to the higher hydrophilic behavior of sisal fibers. [ABSTRACT FROM AUTHOR]

This study assesses the effect of porosity in the moisture absorption of polymeric composites. The preparation of composites samples with porosity, control, and measurement of void content, and moisture absorption behavior of carbon/epoxy laminates are discussed. Rheological analyses are used to characterize the viscosity behavior of prepregs either in the presence or absence of moisture. Polymeric composites with different levels of voids were produced and submitted to hygrothermal conditioning to study the moisture absorption behavior. It was found that the rate of water uptake and the maximum level of moisture absorption in carbon/epoxy composites depends on the void content and specimen geometry. The dependence on the void content may be quite significant. The nature of the matrix system was also verified to affect the moisture absorption properties of the composite. [ABSTRACT FROM AUTHOR]

Knitted structures occupy a special position in composite preforming due to their inimitable characteristics. An insight into the knitted structures with respect to their composite preforming characteristics is presented in this article. Directionality of knitted structures and requirements of high performance fibers for knitting have been discussed. Contourability, net-shape preforming, high dynamic mechanical properties along with easy and rapid manufacturability are the important features of knitted structures to match the composite preform requirements. In this article, the work done in the above areas of research have been critically reviewed. [ABSTRACT FROM AUTHOR]

This study proposes a procedure that integrates the grey relational analysis and principal component analysis (PCA) to optimize a multi-response problem. The procedure is demonstrated by investigating the energy at failure in single impact, and the impact fatigue life of the injection molded 30 wt% glass fiber reinforced poly(butylene terephthalate) (PBT). The results show that the influence of the injection molding condition on the product's impact performances are quite significant. The signal-to-noise (S/N) ratios of impact performances of the recommended injection molding condition are larger than the averages of experimental runs. This demonstrates that the proposed procedure is effective for the optimization of multi-response problems. [ABSTRACT FROM AUTHOR]

Composites were fabricated by impregnating the jute nonwoven fabric in a bath of acrylonitrile-butadiene (NBR) latex. The effects of different pickup ratios (dry-to-dry weight) of jute nonwoven fabric to NBR latex viz., 1:0.5, 1:1, 1:1.5, 1:2, and 1:2.5 on the performance of composites have been studied. The fabricated composites have been evaluated for physico-mechanical properties and chemical resistance. Percent water absorption of composites has been determined both at room temperature and boiling water. Effects of different relative humidity on the equilibrium moisture content of the natural jute nonwoven fabric-NBR composites have been evaluated. [ABSTRACT FROM AUTHOR]

The hygrothermal diffusion and degradation behavior of a high-temperature cured glass-epoxy (Epoxy Novolac -- EPN) composite system was studied under two environmental conditions (i.e. 323°K and 343°K immersion in distilled water). Samples immersed at 343°K showed higher diffusivity (Dc) value and lower saturation time (tm) than those of 323°K immersion while the maximum moisture content (Mm,) remained the same, good Fickian correlation were observed for the composite system. As regards the degradative effects, the glass transition temperature (Tg) of the composite decreased with increased moisture content showing a maximum drop of 30°C at full saturation, while the mechanical properties (ILSS and IPS) of saturated specimens degraded upto 26 and 33% respectively. Further these mechanical properties obtained at 70°C/85%RH test condition showed good correlations with those predicted by a theoretical equation (Chamis et al. An Intergrated Theory for Predicting the Hydrothermo Mechanical Response of Advanced Composite Structural Components, Lewis Research Center, Cleveland, Ohio, NASA Technical Memorandum 73812). [ABSTRACT FROM AUTHOR]

Low-velocity (≅ 1.2-2.4 m/s) repeated drop weight impact tests were carried out on advanced composites (glass, carbon, kevlar in epoxy matrix -- LY 556, HT 972) using an instrumented impact test machine (DYNATUP 8250). The incident energies ranged from 3.5 to 15J (constant impactor mass 5.42 kg). Number of drops to failure (Nf) data were obtained for the above with simultaneous recording of the load-time and energy-time traces. The extent of impact damage for glass and kevlar composites was interpreted using final delamination area maps (tracings). Results for all the three composites showed that with an increase in drop numbers, the peak load (PL) steadily decreased while the total energy (Et) increased, until failure. Also, as the incident energy (Ein) was varied in arithmetic progression, the number of drops to failure (Nf) varied in harmonic progression. Finally it was concluded that repeated drop tests with final delamination area maps assist in understanding the impact damage tolerance of polymer composites. [ABSTRACT FROM AUTHOR]

Experimental studies were carried out to understand the impactor mass effects on glass-epoxy composites using an instrumented impact machine (DYNATUP 8250) under low-velocity test conditions. Repeated drop tests were carried out at pre-determined energy levels for selective mass height combinations. Number of drops to failure (Nf) was chosen as the damage criterion. Analysis of test results clearly showed that, at low incident energies, heavier impactors caused more damage to the laminates as reflected by their lower number of drops to failure. This effect diminished gradually at relatively higher incident energies. [ABSTRACT FROM AUTHOR]

Investigations were carried out on the moisture absorption behavior of RT-cured glass/epoxy composite specimens subjected to 333 K/Immersion in distilled water. Different laminate thicknesses (i.e., 0.25-2.25 mm) were studied for comparative evaluation of their moisture diffusion and distribution profiles across the thickness of the composite as a function of the exposure period. Moisture absorption data showed that the equilibrium moisture levels (Mm) remained practically the same for different laminates of the same fiber weight fraction (i.e., 0.62). Further, the times of saturation (tm) increased with the laminate thickness, while the absorption rates (slopes of the absorption curves) showed a reverse trend. It was also found that the Diffusion Coefficient (Dc) values of different thicknesses specimens ranged between 0.28 and 7.81(10 7)mm2/sec, indicating a negligible thickness effect on this diffusion parameter. The small variations of Dc (all of the order 10 7 mm2/sec) are attributed mainly to the variations in the edge areas for different thickness laminates. [ABSTRACT FROM AUTHOR]

An effort has been made to study the effects of variable incident impact energy and laminate thickness (obtained by varying the number of fabric layers at constant moulding pressure and also by varying the pressure for a fixed number of fabric layers), on the low velocity impact damage tolerance of GFRP composite laminates (woven E-glass fabric in a room temperature cure epoxy system LY556/HY951). Repeated drop tests were conducted using an in-house built drop weight impact tester. Number of drops to failure (Nf), was considered as the impact damage tolerance index. Correlations between Nf and composite material parameters (fiber weight fraction - Wf, laminate thickness - t, number of fabric layers - L) and a test parameter (incident impact energy - E) were found out and the bounding limits for these were defined. Critical values of impact energy (Ec) and laminate thickness (tc) were defined (for the particular resin - hardener system chosen for the study) which can quite possibly be used as designer's guidelines. A new ratio, (t/Wf), was introduced for the study of composite systems where both fiber weight fraction and laminate thickness get affected upon alteration of a process parameter (the pressure - P as in this case). [ABSTRACT FROM AUTHOR]

Epoxy system having 10% by vol. of fly ash fillers with their surfaces covered by paraffin oil was made and the responses to exposure by immersion in waterat 75C in one case and water containing smaller amounts of dilute acid in theother were monitored. Weight recordings up to 100 h were noted regularly on thetest coupons exposed to the two media. The samples exposed to 100 h duration were later on subjected to compression test to evaluate the strength. In one case, a set of samples were immersed in water for a prolonged period of 1000 h before subjecting these also to compression tests. The result showed increased absorption in acid bearing medium. The strength of the plain water exposed samples were lower than the dry counterparts. Samples that had an immersion in medium containing acid showed a further but marginaldrop in strength compared to the plain water case. However, the prolonged period plain water immersed sample exhibited considerable drop in strength. These are explained using scanning fractography where surface features of compression failed samples are recorded. The plain water as well as the acid media exposed ones show a plasticised matrix and in some places a cavity-like feature, left bythe separating ash particles, whose number showed a perceptible increase for the acid bearing system compared to the plain water case. Longer exposed samples showed the loss of fly ash due to the surface of the matrix holding them showing a step-like expanded appearance indicating the interfacial regions being affected by the prolonged exposure time. These and other features are discussed in this report. [ABSTRACT FROM AUTHOR]

Natural fiber–reinforced polyester matrix composite materials are evaluated both for strength performance and cost. The flexural strength of composites fabricated with untreated chopped natural fibers is comparable only to the performance of low-strength wooden agglomerates and plywood. Nevertheless, it is shown here that on a cost basis the composites fabricated with high-strength natural fibers can even compete with glass fiber–mat polyester matrix composites. The primary constraint is to maintain consistently low cost of the fibers. [ABSTRACT FROM AUTHOR]

E-glass fiber reinforced vinylester composites are attractive for use in civil infrastructure applications ranging from repair and rehabilitation to new structural systems due to their potential durability and low cost. However, these materials, generally cured under ambient conditions, must withstand changing and severe environmental conditions over extended periods of time. Data related to their degradation kinetics and property retention are largely anecdotal and lack the existence of both fundamental and mechanistic information and a data-base on the basis of which service life could be reasonably established. This study investigates the degradation of two E-glass architectures after exposure to salt solution, accelerated heat cycles based on a summer in Sydney, and actual outdoor weathering over an 18 month period in Sydney, Australia. It is seen that both tensile strength and modulus are reduced due to the various exposures with attendant degradation at the matrix, fiber, and interphase levels. Based on results of the study it is concluded that natural weathering can lead to rather severe degradation at the surface level, which if not corrected leads to rapid degradation through the thickness, emphasizing the criticality in use of surface coatings and/or veils/layers of mat. It is also shown that changes in Tg are due to both physical and chemical aging with overall effects to an extent being irreversible due to matrix hydrolysis and cracking, and fiber degradation. [ABSTRACT FROM PUBLISHER]

The effect of surface layer reinforcement with glass fibres of unidirectional jute-rein forced epoxy composite on the flexural properties has been investigated. Substantial increase in flexural modulus and strength with small amounts of reinforcement (for reinforcement ratio (t/d) < 0.3, where "t" and "d" are the respective thicknesses of glass reinforced plastic (GRP) shell and JRP core) were achieved. In addition, studies on the effect of moisture absorption of flexural properties revealed a significant im provement in moisture resistance of jute reinforced epoxy with hybridization. Though density analyses of these hybrids indicate an increase in density with hybridization, the considerable improvement of the normalized properties of jute-glass hybrids make them candidate materials for cost-effective applications. The work has also shown that the reinforcement (t/d) is more useful a parameter in the case of sandwich-type hybrid fibre composites. Analysis of failure modes of these composites loaded in flexure is also presented. [ABSTRACT FROM PUBLISHER]

Graphite as a solid lubricant was incorporated in a Al-Si eutectic alloy by a liquid metallurgy technique. The pin-on-disc wear test unit was used to determine the friction and wear characteristics of the composites in the speed and bearing pressure ranges of 0.9 to 4.4 ms-1 and 0.15 to 1.02 MPa respectively. The pins of the composites were slid against a hardened (63 HRC) AISI-SAE 52100 steel disc under dry conditions for a distance of 5000 m. SEM features of the worn surfaces were correlated with the ob served wear data. An attempt was made to determine the effect of graphite type, modification of the matrix and hot working on wear behaviour of the composites. It was found that more than the graphite type, the silicon size influences the wear. [ABSTRACT FROM PUBLISHER]

This work focuses on investigating the curing process of an epoxy-based resin—Aerotuf 275-34TM, designed for aerospace applications. To study the curing degree of Aerotuf 275-34TM under processing conditions, woven carbon fiber fabric (WCFF)/Aerotuf 275-34TM composite laminates were produced by compression molding using different processing temperatures (110, 135, 160, and 200 °C) during 15 and 30 min. Then, the mechanical behavior of the composite laminates was evaluated by tensile tests and correlated to the resin curing degree through Fourier-transform infrared spectroscopy (FTIR) analysis. The results show the occurrence of two independent reactions based on the consumption of epoxide groups and maleimide (MI) double bonds. In terms of epoxide groups, a conversion degree of 0.91 was obtained for the composite cured at 160 °C during 15 min, while the measured tensile properties of [±45°] WCFF/Aerotuf 275-34TM laminates confirmed that these epoxy resin curing processing conditions lead to an enhancement of the composite mechanical properties. [ABSTRACT FROM AUTHOR]