bluuebunny/crossref_metadata_2025_split huggingface dataset:
An interface model for the prediction of Young's modulus of layered silicate‐elastomer nanocomposites
Authors: Shia D. , Hui C. Y. , Burnside S. D. , Giannelis E. P. 
Published: April 2004

AbstractRecent experiments on layered silicate‐elastomer nancomposites by Burnside and Giannelis have shown that there is a discrepancy between theoretical modulus predictions and experimental modulus measurements. A theory is proposed to explain this discrepancy. We hypothesize that the discrepancy is due to imperfect bonding between the matrix/inclusion interface which effectively reduces the aspect ratio and the volume fraction of the inclusion. We use a simple interface model to quantify the imperfect interfacial bonding. From this model, we introduce the concept of the effective aspect ratio and effective volume fraction of the inclusions. These effective quantities depends on a single material parameter, namely, the constant interfacial shear stress, τ. The interfacial shear stress for the elastomer‐silicate nanocomposites is found by fitting the theory to the experimentally measured modulus of Burnside and Giannelis. The interfacial shear stress is in the range of thousands of Pascals. For the elastomer‐silicate nanocomposite systems considered here, the interfacial shear stress can be decomposed into two parts; intrinsic shear stress τi and frictional shear stress τf. The intrinsic interfacial shear stress τi depends only on the volume fraction of inclusions and decreases with increasing volume fraction of inclusions. On the other hand, the frictional shear stress τf is found to increase linearly with the applied strain. Since the mean stress is also proportional to the applied strain, this gives rise to an effective coefficient of friction, which is found to be 0.0932 for the nanocomposite system considered here.
On the effect of the fiber orientation on the flexural stiffness of injection molded short fiber reinforced polycarbonate plates
Authors: Neves N. M. , Isdell G. , Pouzada A. S. , Powell P. C. 
Published: April 2004

AbstractThe through‐thickness fiber orientation distribution of injection molded polycarbonate plates was experimentally determined by light reflection microscopy and manual digitization of polished cross sections. Fiber length distribution was determined by pyrolysis tests followed by image analysis. A statistical analysis was done to determine the confidence limits of the fiber orientation results. The fiber orientation distribution was described by using second‐order orientation tensors. The through‐thickness stiffness variations were determined by the orientation averaging approach. This layer stiffness distribution was used to simulate the behavior of beams subjected to three point bending with a FEM Ansys model. The results were compared with experimentally determined flexural stiffness both in the flow direction and in the transverse flow direction. The effect of flow rate and melt‐temperature on stiffness and fiber orientation is discussed.
The influence of post‐cure on properties of carbon/phenolic resin cured composites and their final carbon/carbon composites
Authors: Ko Tse‐Hao , Kuo Wen‐Shyong , Lu Yng‐Ren 
Published: April 2004

AbstractTwo‐dimensional (2D) carbon/carbon (C/C) composites were prepared with phenol‐formaldehyde resin and graphite fabric. After curing, polymer composites were post‐cured in air at 160°C and 230°C for several hours and then all polymer composites were carbonized up to 1500°C. The effect of post‐cure on the microstructure and fracture behavior of the resultant carbon/carbon composites was studied. The post‐cure process was characterized by weight loss. This process promoted the crosslinking and condensation reactions and led to the formation of long‐chain, cross‐linked polymeric structures in the matrix. The post‐cured composites had a greater density than the unpost‐cured composite. This study indicates that a longer post‐curing time and higher post‐curing temperature would limit the shrinkage for the post‐cured composites during carbonization. The improvement in linear shrinkage was 22% to 44%. This process also limited the formation of open pores and decreased the weight loss of the resultant C/C composites. The resultant C/C composites developed from post‐cured composites had a greater flexural strength by 7 to 26% over that developed from unpost‐cured composite.
New nanocomposite materials made of an insulating matrix and conducting fillers: Processing and properties
Authors: Flandin L. , Cavaillé J. Y. , Bidan G. , Brechet Y. 
Published: April 2004

AbstractThe work described in this paper deals with the preparation and the characterization of an homogeneous composite material composed of electrically conductive fillers dispersed in a thermoplastic insulating matrix. These fillers were chosen to have either a spherical shape or a high aspect ratio. Processing of these conductive polypyrrole particles, which were obtained either through a classical polymerization of pyrrole in the presence of stabilizer, or polymerization onto the surface of cellulose monocrystals is detailed. The relationship of filler content in the composite to electrical and mechanical properties was investigated. In order to characterize the connectivity of the fillers in the matrix, electrical measurements were performed and these results have been compared with the predictions of the statistical percolation theory. Further analysis was undertaken by considering the influence of the network of rigid particles on the viscoelastic properties of the composites. These results were compared with two models; first, with a mechanical percolation approach which was based on strong interactions between fillers, and second, with a mean field model, which in no way accounted for interactions bewteen fillers. In recent developments, it has been shown that these materials used as coating on various substrate could be good sensors, allowing to determine some specific features of the substrate deformation.
Modulus recovery kinetics and other insights into the payne effect for filled elastomers
Authors: Chazeau L. , Brown J. D. , Yanyo L. C. , Sternstein S. S. 
Published: April 2004

AbstractThe nonlinear viscoelastic behavior of filled elastomers is examined in detail using a variety of samples including carbon‐black filled natural rubbers and fumed silica filled silicone elastomers. New insights into the Payne effect are provided by examining the generic results of sinusoidal dynamic and constant strain rate tests conducted in true simple shear both with and without static strain offsets. The effect of deformation history is explored by probing the low amplitude modulus recovery kinetics resulting from a perturbation by a large strain deformation such as a sinusoidal pulse or the application or removal of a static strain. It is found that a static strain has no effect on either the fully equilibrated dynamic (storage and loss) moduli or the incremental stress‐strain curves taken at constant strain rate. The reduction in low amplitude dynamic modulus and subsequent recovery kinetics due to a perturbation is found to be independent of the type of perturbation. Modulus recovery is complete but requires thousands of seconds, and is independent of the static strain. The results suggest that deformation sequence is as critical as strain amplitude in determining the properties, and that currently available theories are inadequate to describe these phenomena. The distinction between fully equilibrated dynamic response and transitory response is critical and must be considered in the formulation of any constitutive equation to be used for design purposes with filled elastomers.
Modeling compression molding of all‐thermoplastic honeycomb core sandwich components. Part B: Model verification
Authors: åkermo Malin , Tomas åström B. 
Published: April 2004

AbstractThe compression molding process for manufacturing of all‐thermoplastic honeycomb core sandwich components is studied with the aim of verifying a previously proposed model describing the instantaneous face‐core bonding during molding. Experiments are performed with glass/polypropylene (PP) faces and PP honeycomb core and experimental data are compared to model predictions in terms of temperature and degree of face‐core interfacial contact with reasonable good agreement. Model predictions show that the face‐core interface bond strength may increase with up to 200% when molding at an interface temperature slightly above the crystal melting temperature of the matrix for only a few seconds. The influence of the major process parameters, including molding temperature, molding pressure and core viscosity, on the predicted bond strength is investigated using the model.
Polymer bonded magnets. II. Effect of liquid crystal polymer and surface modification on magneto‐mechanical properties
Authors: Xiao Jun , Otaigbe Joshua U. 
Published: April 2004

AbstractWe studied the effect of liquid crystal polymer (LCP) and surface modification of neodymium‐iron‐boron (Nd‐Fe‐B) magnetic alloy on the magneto‐mechanical behavior of poly (phenylene sulfide) (PPS) bonded Nd‐Fe‐B magnets to accelerate efforts to develop useful thermoplastic magnets with optimal performance. The results indicate that blending the LCP with PPS provides the required balance of properties for the targeted applications. These properties include superior magneto‐mechanical performance at elevated temperatures, minimal melt viscosity at optimal LCP volume fraction, high stiffness, and improved dimensional stability, making the thermoplastic magnets suitable for use at elevated temperatures and in chemically corrosive environments where commercial rare earth alloy magnets are not useable. Enhanced wetting of the magnetic Nd‐Fe‐B powders by the polymers, formation of reinforcing LCP domains, and interactions between the polymers and the magnetic powders are thought to be responsible for the beneficial function of the LCP and Nd‐Fe‐B surface modifier in the PPS bonded Nd‐Fe‐B magnets.
Properties of films from polypropylene and thermotropic liquid crystalline polymer blends
Authors: Incarnato L. , Scarfato P. , Motta O. , Acierno D. 
Published: April 2004

AbstractIn this paper the effect of the inclusion of two different thermotropic liquid crystalline polymers, namely Rodrun 3000 and Vectra A950, in a PP matrix is analyzed with particular attention to the gas transport and mechanical properties of the extruded blend films. The experiments, conducted on PP/Rodrun 3000 and PP/Vectra A950 films, have shown that the presence of TLCPs, also at low percentages, modify the properties of the thermoplastic matrix in a manner depending on the degree of compability and interfacial adhesion between the two components of the blends. Moreover, the effect of a maleic anhydride grafted PP (MAP), used as compatibilizing agent, on the properties and morphology of the PP/Rodrun 3000 system was examined. It was found that the addition of the MAP determines an increase in the barrier properties and in toughness of the films compared to those without MAP.
The need to re‐evaluate laminate design criteria
Authors: Piggott Michael R. 
Published: April 2004

AbstractThe aerospace industry uses carbon‐fiber epoxy laminates for structures to reduce weight and increase payload. The “standard” design criterion for strength is that proposed by Tsai‐Wu. For stiffness, which is generally more critical than strength, classical laminated plate theory (LPT) is used. The normal lay‐ups considered for commercial aircraft are made up from 0°, 90° and ± 45° orientations. Angle ply laminates, [± ϕ]ns, with ϕ fixed to some angle such as 20°, are not normally used (although this type of structure is employed with great success in the pressure vessel industry). According to the Tsai‐Wu criterion, such a structure should be extremely weak, which probably accounts for the absence of simple angle ply structures in aerospace designs. However if short and wide samples (aspect. ratio 0.5 or less) are tested, higher values are obtained for modulus and much higher values for strength than the long narrow samples used to develop the Tsai‐Wu criterion. The short and wide sample test results are in agreement with results from tests on tubes. These observations show that there is an “edge softening” effect: long narrow samples have a relatively large amount of this soft edge. Since design software normally uses Tsai‐Wu and LPT, large errors in strength and significant errors in stiffness are possible at this stage, and better lay‐up designs may be totally missed. The experimental work leading to these conclusions is described and innovative designs are discussed.
A fiber optic thermoset cure monitoring sensor
Authors: Giordano Michele , Nicolais Luigi , Calabrò Antonio Maria , Cantoni Stefania , Cusano Andrea , Breglio Giovanni , Cutolo Antonello 
Published: April 2004

AbstractCuring determines the chemical and physical properties of a reacting resin. Among these, the optical properties strongly correlate with the structural features of the developing polymeric network. By monitoring changes of the refractive index, it is possible to analyze the polymerization of thermoset resin. In this work, a fiber optic sensor system has been designed and developed (based on the optical time domain reflectometry principle) to measure the reflection coefficient at the interface between the fiber optic and the resin during a curing process. Correlation between the sensor output and conversion has been proposed, following the Lorentz‐Lorenz law. Isothermal data from the sensor have been compared with calorimetric analysis of an epoxy‐based resin.
The influence of fiber wetting in resin transfer molding: Scale effects
Authors: Binetruy C. , Pabiot J. , Hilaire B. 
Published: April 2004

AbstractResin transfer molding (RTM) has become a popular technique for fabrication of composite parts. During the mold filling stage, the resin is forced to flow into pore spaces between tow filaments and the between the tows themselves. Voids trapped in the composite during the filling stage are believed to be the consequence of the non‐uniform micro‐flows inside fiber bundles and macro‐flows between them. Thus, to minimize the void formation, the processing parameters should be determined to generate a uniform front. In this case, the flow inside tows is driven by both the injection pressure and the capillarity forces and matches the flow outside the tows, which is driven only by pressure. To control such a flow, both viscous and capillarity flows have to be known at all scales of the fibrous structure. For this purpose, the wetting effects at the different scales (ranging from the individual tow to the multi‐layers reinforcements) are investigated. Original experiments are carried out to visualize micro‐flows and to measure the capillarity flow rates. Wicking effects are quantified in terms of the overall and local effective permeabilities. A new parameter that accounts for interactions between flows splitting in macro‐ and micro‐flows is introduced. Practical ways to reduce voids entrapment are also discussed.
Applications of fiber‐metal laminates
Authors: Straznicky P. V. , Laliberté J. F. , Poon C. , Fahr A. 
Published: April 2004

AbstractAdvanced composite materials and fiber‐metal laminates (FMLs) have the potential to offer significant improvements in weight savings and durability in airframe structures. FMLs are an advanced hybrid material system consisting of metal layers bonded with fiber‐reinforced polymer layers. This paper presents an overview of the history of fibre‐metal‐laminates, describes several common types and also discusses the results of impact durability experiments conducted at the Structures, Materials and Propulsion Laboratory of the Institute for Aerospace Research (SMPL‐IAR) of the National Research Council Canada (NRCC). An impact fixture was developed specifically for FMLs and is also described. Numerous low velocity impact tests have been carried out that demonstrate the improved impact response of FMLs over traditional composite materials. This research builds upon earlier impact testing on carbon‐fiber‐reinforced polymers conducted by NRCC and Carleton University.
Glass fiber reinforced polyamide‐6 nanocomposites
Authors: Akkapeddi M. K. 
Published: April 2004

AbstractPolyamide 6 nanocomposites (PA6/NC) are novel type of composite materials comprising extremely thin, “nanometer scale” dispersions of smectitic silicate platelets. We prepared such PA6/NC materials via a melt compounding technique using suitably organomodified montmorillonite or hectorite type clays. The high surface to volume ratio of such thin silicate dispersions in PA6/NC leads to a high reinforcement efficiency even at 2 to 5 wt% of clay, achieving high specific modulus, strength and heat distortion temperature under load (DTUL). In addition, the platelet orientation and their surface nucleation effects seem to promote a faster crystallization and higher crystallinity in PA‐6/NC (particularly at the surface and in thin‐wall injection moldings), as compared to the standard PA‐6. Such morphological features in PA‐6/NC also result in improved moisture resistance. Recognizing these benefits, we investigated the use of PA‐6/NC as a matrix for making both short and long glass fiber (GF) reinforced composites. Significant improvements in modulus were achievable in both the dry and the moisture conditioned state for PA‐6/NC compared to standard PA‐6, at any given level of glass fiber reinforcement. In general a small amount (3‐4 wt%) of the nanometer scale dispersed clay is capable of replacing up to 40 wt% of a standard mineral filler or 10‐15 wt% of glass fiber in PA‐6 composites to give equivalent stiffness at a lower density or a lower part weight advantage. In addition, improved moisture resistance, permeation barrier and fast crystallization/mold cycle time contribute to the usefulness of such composites.
Characterization of interfacial properties of composite materials by acoustic emission
Authors: Ndiaye I. , Maslouhi A. , Denault J. 
Published: April 2004

AbstractThe global mechanical properties of composite structures in service depend on fiber/matrix interface and interlaminar strength. The paper proposes to use Acoustic Emission (AE) and advanced signal processing to evaluate the interlaminar performance of polymeric composites. A delaminating process simulated with a Double Cantilever Beam (DCB) in opening mode (Mode I) coupled with an Acoustic Emission (AE) technique has been employed. Different samples were analyzed to observe the damage evolution and to evaluate the interlaminar decohesion processes. The resistance to delamination growth is expressed in terms of the interlaminar DCB mode (mode I) fracture toughness, measured by strain energy release rate, GI, dissipated per unit area of delamination growth in composite. Three categories of samples were used: two unidirectional carbon fiber/epoxy resins with one degraded by heat and one with a commercially used resin. It was found that sample that was exposed at a temperature greater than the glass transition temperature Tg of the epoxy had a higher cumulative energy release rate than the two other samples types. The original type having the lowest release rate. Acoustic emission parameters have been found to be powerful indicators of the intensity of the damage. Multivariate analysis of up to 49 parameters was performed in order to group classes of AE signals with matching characteristics. A correlation was established between the energy release rate and the acoustic emission energy.
Fatigue behavior of continuous glass fiber composites: Effect of the matrix nature
Authors: Bureau M. N. , Denault J. 
Published: April 2004

AbstractThe effect of the matrix morphology on the fatigue behavior of a continuous glass fiber/polypropylene (GF/PP) composite system was studied by means of stress‐life and mode II cyclic delamination tests. The stress‐life behavior of a GF composite is considerably affected by the nature of the matrix. A two‐stage fatigue damage curve was observed in the composite made with a PP matrix, whereas a three‐stage curve was observed in the composite made with a thermoset polyester matrix. For a fatigue stress higher than 50% of the yield stress, the PP matrix composite showed a considerably longer fatigue life than the thermoset polyester matrix composite. Mode II cyclic delamination tests showed that the morphology itself of the PP matrix also played an important role. Higher fatigue delamination growth rates, at given strain energy release rates, and lower strain energy release rates at failure were obtained for a composite showing a coarse spherulitic morphology and well‐marked interspherulitic regions than for a composite showing a finer spherulitic morphology and less‐marked interspherulitic regions. While the fatigue mode of the composite with a coarse spherulitic morphology was interspherulitic, that of the composite with a finer spherulitic morphology was transpherulitic.
Raman study of the microstructure changes of phenolic resin during pyrolysis
Authors: Ko Tse‐Hao , Kuo Wen‐Shyong , Chang Ying‐Huang 
Published: April 2004

AbstractAfter curing, phenol‐formaldehyde resins were post‐cured at 160°C, and then carbonized and graphitized from 300°C to 2400°C. The structure of the resulting carbonized and graphitized resins were studied using X‐ray diffraction and Raman spectroscopy. Thermal fragmentation and condensation of the polymer structure occurred above 300°C. The crystal size of the cured phenolic resins increased with an increase in temperature. The crystal size increased from 0.997 nm to 1.085 nm when the heat‐treatment temperature rose from 160°C to 500°C. Above 600°C, the original resin structures disappeared completely. Below 1000°C, the stack size (Lc) increased very slowly. The values increased from 0.992 to 1.192 nm when the heattreatment temperature rose from 600°C to 1000°C. Above 1000°C, the stack size showed an increase with the increase in heat‐treatment temperature. The values increased from 1.192 to 2.366 nm when the temperature rose from 1000°C to 2400°C. The carbonized and graphitized resins were characterized using Raman spectroscopy. The Raman spectrra were recorded between 700 and 2000 cm−1. Below 400°C, there were no carbon structures in the Raman spectra analysis. Above 500°C, G and D bands appeared. Raman spectra confirmed progressive structure ordering as heat‐treatment temperature increased. The frequency of the G band of all carbonized and graphitized samples shifted to 1600 cm−1 from the 1582 cm−1 of graphite. At the same temperature, the D band shifted to 1330 cm−1 from the 1357 cm−1 of the imperfect carbon. In the curve fitting analysis of the Raman spectra, a Gaussian shaped band centered at 1165 cm−1 was included. This band has not been described before in the literature and is attributed to disordered structures, which are formed from the original polymeric structures. These polymeric structures formed unknown disordered structures and remained in the carbonized phenolic resins. Above 1800°C, this band disappeared completely. But, a weak peak is present near 1620 cm−1. This indicated that those disoriented molecules and some disordered carbons were removed as volatiles or repacked into the glassy carbon structures during graphitization. The carbonized and graphitized phenolic resins were found to correspond to low order sp2 bonded carbon, but cannot be considered as truly glassy or amorphous carbon materials since they have some degree of order in the basal plane.