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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]

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]

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]

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]

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]

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]