bluuebunny/crossref_metadata_2025 huggingface dataset:
The flow of suspensions
Authors: Van De Ven T. G. M.
Published: May 2005

Most rheological and rheo‐optical properties of suspensions such as viscosity and light‐scattering intensities can be expressed in terms of the average orientation and/or the average concentration distribution of the suspended particles. In general one can distinguish several distinct regimes: (i) infinitely dilute, (ii) dilute, (iii) semi‐dilute or moderately concentrated, and (iv) concentrated suspensions. Cases (i) and (ii) are regimes in which particle interactions are either absent or only two‐body interactions are important. These cases can, in general, be well described theoretically. Regime (iii) is characterized by n‐body (n ≥ 2) interactions and is the least understood. Regime (iv) can often be described in terms of a cell model in which the motion of a reference particle, or the fluid motion around it, is described.
Dynamic mechanical properties of particulates: Application to iron‐epoxy composites
Authors: Sideridis E. , Theocaris P. S. , Kontou E.
Published: May 2005

The dynamic mechanical properties of composite materials, consisting of an epoxy matrix filled with iron particles, were determined over a temperature range. The storage‐ and loss moduli were evaluated in a Dynastat apparatus, with the parameters being the volume fraction of filler and the test frequency. A theoretical model was developed for comparing the experimental results with the theoretical predictions. A satisfactory correlation was obtained for the glassy region of the composite.
The influence of temperature on the impact behavior of unidirectional glass fiber‐epoxy composite
Authors: Golovoy A. , Van Oene H.
Published: May 2005

The influence of temperature on the impact behavior of unidirectional glass fiber‐epoxy composite was studied in the range of −20 and 150°C using a 3‐point drop weight test at a constant impact velocity of 2.2 m/s (5 mph). The impact energy per unit deformed volume was found to be very sensitive to the ratio length/thickness of the specimens. When the ratio was 4, the impacted specimens exhibited extensive delamination (shear failure) and the energy absorbed by the composite was about 14 MJ/m3between −20 and 100°C, and 18 MJ/m3at 150°C. At length/thickness above 16 the failure was mostly in tension, and the impact energy approached a constant value of about 3.5 MJ/m3, independent of temperature.
Microdielectric monitoring of prepreg cure
Authors: Zukas Walter X. , Wentworth Stanley E.
Published: May 2005

The feasibility of using a microdielectric sensor to characterize the cure behavior of a commercial prepreg roving was investigated. Chemical and physical characterization methods were first used to determine the uniformity of the prepreg material. Thermal, dynamic mechanical, and dielectric methods were then utilized to monitor the cure cycle. The dielectric response was found to be independent of the glass fibers of the prepreg and to show reproducible changes in the early part of cure over a temperature range of 80 to 135°C. The manufacturer's recommended cure temperature of 121°C (250°F) was found to correspond to the onset of the ultimate glass transition of the material. Variations in the dielectric response in the latter part of cure at this temperature and above were attributed in part to this event.
Nondestructive evaluation of polymers with optically generated thermal waves
Authors: Busse G. , Rief B. , Eyerer P.
Published: May 2005

Periodic illumination of an absorbing sample results in a surface temperature modulation which propagates into the sample as a highly attenuated and slow “thermal wave”. Thermal wave propagation depends on thermal properties and on their anisotropy. Boundaries affect both the phase and magnitude of the temperature modulation. Since thermal wave detection can be performed in a remote way, one can monitor the orientation of fibers and molecules without touching the sample. Scanned local inspection allows mapping of layer delamination caused by mechanical stress or electrical heating.
Damage tolerance in graphite‐epoxy composite: Comprehensive monitoring method
Authors: Tasnon M. , Roy C.
Published: May 2005

A failure model is proposed to calculate the minimum expected lifetime of a graphite‐epoxy structure under cyclic loading conditions. The theoretical approach is based on the statistical theory of strength and the mechanical redistribution of stresses between piles of a damaged laminate. The use of the acoustic emission technique has permitted the development of internal damage to be monitored during cyclic loading of unidirectional laminates. The experimental results indicate that the composite can withstand greater damage at low level cyclic loading than observed during monotonic loading to failure. The theoretical modeling under development aims at predicting this behavior.
Thermoforming of ordered polypropylenes
Authors: Iaboni S. , Woodhams R. T.
Published: May 2005

Uniaxial molecular ordering of polyolefin billets by a process of roll‐drawing produces clear, transparent sheets having greatly increased strength and modulus in the draw direction whereas the strength and modulus in the transverse direction remain essentially unaltered. Such sheets may be laminated together by means of ultrasonic welding, electromagnetic induction heating or simple pressure lamination using adhesive tie layers to produce multiply laminates with controlled biaxial properties. These self‐reinforced laminates have mechanical properties which compare favorably with advanced aramid or carbon fiber composites. Conventional thermoforming techniques may be employed to convert these highly ordered sheets into shaped products having potential commercial value. In these investigations examples are presented to illustrate the methods of laminating and thermoforming of ordered polypropylene sheets. Examples are also presented to demonstrate the feasibility of pressure forming of ordered polypropylene laminates into more complex three‐dimensional shapes without loss of their mechanical properties. The techniques described in this paper may be applied to other crystalline polymers to create a new spectrum of self‐reinforced plastics capable of approaching the limits of performance.
High temperature liquid crystalline copolyester composites. Part I: A review and new data for the self‐reinforced matrix phase
Authors: Frayer Paul D.
Published: May 2005

Our work concerns structure‐processing‐morphology‐property (SPMP) relationships in fibrous composites where the polymeric matrix may be self‐reinforced. Composites have been made using a commerically available thermotropic liquid crystalline polymer (TLCP) with nematic and isotropic transitions at 693 and 738 K, respectively. To understand the behavior of such composites one must first understand the composite nature of the matrix resin. Thus, this article covers the SPMP relationships for the self‐reinforced matrix phase alone. A review and new data are presented on the molecular dynamics of wholly aromatic copolyesters in the solid state to help clarify the nature of the temperature dependence of mechanical properties. Subsequent papers concern short (Part II) and continuous (Part III) fiber reinforced composites.
Electrical properties of exfoliated‐graphite filled polyester based composites
Authors: Foy John V. , Lindt J. Thomas
Published: May 2005

Work has been done to develop and optimize a procedure for the preparation of electrically conductive exfoliated‐graphite filled unsaturated polyester composites. The exfoliated graphite flakes impart excellent electrical properties to the polyester composite. EMI (electromagnetic interference) shielding effectiveness, comparable to that of exfoliated graphite alone, has been observed over a frequency range of 0 to 1000 MHz with composite samples containing as little as 4 weight percent of exfoliated graphite. The resistivities approached the value for exfoliated graphite in the c‐direction (0.03 μ‐cm) at a graphite loading of 11 weight percent. It has been observed that the mechanical integrity of the composite remained good up to graphite loadings of some 17 weight percent. The polyester readily wets the graphite and penetrates most of the graphite open pore volume during processing. Flow visualization measurements have been made in a transparent compression molding apparatus. No effect of the flow conditions on the apparent electrical properties has been found.
High intensity compounding of mica‐filled thermoplastics
Authors: Cacoutis Spyridon , Woodhams Raymond T. , Van De Poll Peta Gay Kleyn
Published: May 2005

High‐speed turbine mixers have been adapted for compounding filled thermoplastics by the partial flux method. The extreme shearing forces exerted by the mixing impellors simultaneously mixes and delaminates mica fillers to form finely dispersed compounds in a granular, partially fused state which can be directly injection molded without pelletizing. In practice, one turbine mixing unit can be employed for compounding all types of resins and fillers. The partial flux method permits compounding to be accomplished at peak sensor temperatures that are considerably below the resin softening or melting transitions, frequently 50°C less than normal compounding temperatures. The short residence times and reduced energy requirements possible with partial fluxing results in substantial cost reduction without compromising quality or performance. Examples are provided for polypropylene, nylon 66, poly(butene terephthalate), poly(ethylene terephthalate) and poly(phenylene oxide) alloys. Impact modifiers derived from carboxylated polyolefin waxes may be dispersed by the intense shearing action to form highly subdivided submicron particles, which promote crazing and shear deformation during fracture testing, thereby contributing to increased composited toughness with minor sacrifice in modulus and strength. The mechanical properties of micafilled thermoplastics have also been compared with those of short glass fiber composites. In certain applications requiring stiffness and dimensional stability at elevated temperatures, mica composites prepared by intensive mixing in a turbine mixer may be economically substituted for glass fiber counterparts.
A study of low‐energy impact of continuous carbon‐fiber‐reinforced composites
Authors: Moore D. R. , Prediger R. S.
Published: May 2005

Low‐energy instrumented falling weight impact tests were used to study the failure mechanisms in various multiangle laminates of continuous carbon‐fiber‐reinforced composites. C‐scans of impacted specimens were conducted to monitor an area for delamination damage. Photography of the tension surface during impact enabled the onset of tension surface cracking to be detected. These techniques were employed for composites based on thermoplastic, poly(ether ether ketone) (PEEK), and thermoset (epoxy system 934) matrix materials. In addition, a range of ply numbers (8 to 40) were used in preparation of the multiangle laminates. Tension surface splitting can be shown to be the first failure mechanism during impact. Initiation of a tension crack occurs at a lower absorbed impact energy than that for the onset of delamination damage.
Monitoring progression of mode II delamination during fatigue loading through acoustic emission in laminated glass fiber composite
Authors: Roy C. , El Ghorba M.
Published: May 2005

Acoustic emission (AE) was used to monitor damage development in a glass fiber/epoxy composite during monotonic and cyclic Mode II loadings of DCB specimens. AE parameters such as event count rates and accumulative event counts together with the distribution of events by time and location in the DCB specimen were used as proper indicators of the damage growth at various stages during testing. AE proved to be a powerful technique to predict in real time the interlaminar failure stress (delamination in Mode II) in both the static and the dynamic tests. An S‐N curve constructed entirely on the AE signatures recorded during fatigue testing exhibits three distinct stages enabling delineation of period of damage initiation, the period of damage growth, and finally the occurrence of delamination. A generalized expression based on the nonlinear cumulative damage model was developed to correlate AE activity with the damage development in the composite during cyclic loading. The fatigue data to date agree well with this method of prediction of the fatigue life.
Role of morphology and coupling agent in fracture performance of glass‐filled polypropylene
Authors: Denault J. , Vu‐Khanh T.
Published: May 2005

The effect of silane coupling agent on the morphology and fracture performance of particulates‐filled polypropylene was investigated. The onset of the crystallization at the filler‐matrix interface was observed by optical microscopy. This analysis shows that the silane alters the matrix morphology by inducing nucleation at the filler‐matrix interface. This effect was attributed to the physisorbed layer of silane on the filler. The fracture performance of the composites was analyzed by the post yield fracture mechanics approach. The effect of coupling agent on the fracture performance was found to occur at a very low concentration, whereas subsequent increase in silane concentration had no effect. Furthermore, the effect of coupling agent depended on concentration of filler. Silane treatment had a detrimental effect at low concentration of filler. However, at high concentration of filler, an improvement in the filler‐matrix adhesion had a beneficial effect on the fracture performance. Two phenomena, the morphological effect and the competition between the contribution of the matrix‐filler interface and the contribution of the matrix, were found to be possible explanations for the variation of KRmax with filler concentration and adhesion at the matrix‐filler interface.
Effects of cellulose fibers in polypropylene composites
Authors: Bataille P. , Ricard L. , Sapieha S.
Published: May 2005

A systematic study of the effect of surface pretreatment of cellulosic fibers and the processing time and temperature on the mechanical properties of the cellulose‐containing polypropylene was undertaken. Using non‐treated fibers, the elastic modulus increased gradually with the cellulose content, typically doubling its value at 30 phr fiber content. Treatment of fibers with coupling agent improves significantly the interfacial adhesion and therefore the mechanical properties of composite. Scanning electron micrographs reveal that the shear stress is sufficiently high to break and delaminate the cellulosic fibers. Addition of maleic anhydride modified polypropylene also improves the properties of resulting composites.
Micromechanical characterization of composite materials based on poly(styryl pyridine) thermoset resin
Authors: Caux X. , Coulon G. , Escaig B.
Published: May 2005

The purpose of this paper is to propose a micromechanical characterization of composite materials through measurement of the work‐hardening rate K in the preyield stage during compression tests at constant strain‐rate. This method belongs to a more general framework where the non‐elastic deformation of glassy polymers is analyzed from a metallurgical point of view. The parameter K varies as the inverse of the nucleation rate of dislocations which are responsible for the non‐elastic deformation. The method is used, here, to characterize a model composite material : PSP resin (poly(styryl pyridine)) filled with glass beads. K measurements show that introducing glass beads in the PSP resin enhances its ability to deform plastically, i.e. the presence of glass beads increases strongly the nucleation rate of dislocations. K‐measurements and scanning electron microscopy investigations seem to show that the coupling agent A1100 is not appropriate to the PSP matrix.
Thermal expansivity and bulk modulus of polymer composites: Experiment versus theory
Authors: Simha R. , Papazoglou E. , Maurer F. H. J.
Published: May 2005

Correlations between the thermal expansivity, αc, and the compressibility, Kc, of particulate‐filled polymer melts are explored in terms of two different theories and in connection with experiments. Both theories employed [an interlayer approach based on micromechanics (IM), and a molecular one starting from the statistical thermodynamics of mixtures (MM)] account for the effect of filler‐matrix interactions, viewed as a system‐dependent parameter. The concentration dependences of αc and Kc calculated using either IM or MM agree well with experiments on polyurethane and epoxy composites, and it is possible to predict αc based on Kc experimentation. In MM this is always true, but in IM it depends on a knowledge of relations between α and K of the constituents. This point remains to be explored further.
Liquid flow in molds with prelocated fiber mats
Authors: Molnar J. A. , Trevino L. , Lee L. J.
Published: May 2005

The mechanism associated with mold filling in the manufacture of structural RIM (SRIM) and resin transfer molding (RTM) composites is studied by means of flow visualization and pressure drop measurements. To facilitate this study, an acrylic mold with a variable cavity was constructed and the flow patterns of nonreactive fluid flowing through various layers, types, and combinations of preplaced glass fiber reinforcement mats were photographed for both evacuated and nonevacuated molds. The pressure drops in the flow through a single type of reinforcement (e.g., a continuous strand random fiber mat) and also a combination of reinforcement types (e.g., a stitched bidirectional mat in combination with a random fiber mat) were recorded at various flow rates to simulate high‐speed feeding processes (e.g., SRIM) and low‐speed feeding processes (e.g., RTM). By changing the amount of reinforcement placed into the mold, the permeabilities of the different types and combinations of glass fiber mats were obtained as a function of porosity. It is shown that partially evacuating the mold cavity decreases the size of bubbles or voids in the liquid, but ultimately increases the maximum pressure during filling. The results also show that glass fiber mats exhibit anisotropic permeabilities with the thickness permeability, Kz, being extremely important and often the determining factor in the pressure generated in the mold during filling.
Rheological and mechanical characteristics of poly‐p‐phenylene terephthalamide/nylon molecular and particulate composites
Authors: Park H.‐S. , Kyu T.
Published: May 2005

Poly‐p‐phenylene terephthalamide (PPTA) and nylons (nylon 6, 66, 11, and 12) molecular and particulate composites were examined with emphasis on rheological, mechanical, and morphological characteristics. These molecular composites were prepared by coagulation in water from isotropic ternary sulfuric acid solutions. Upon heating above the crystal melting temperatures of nylons, the molecular composites undergo phase separation and become two‐phase particulate composites. Shear viscosity measurements indicate that the viscosity of nylon 6 and 66 systems has increased for an order of magnitude because of the presence of PPTA, but decreased in the case of nylon 11 and 12 systems. PPTA/nylon 6 and 66 systems exhibit yield behavior, particularly with high PPTA contents. Measurements show an extrudate swell of around 1 in all composition ranges and shear rates. Scanning electron microscopic investigations of low PPTA content particulate composites reveal spherical or long fibrillar morphology of PPTA phase dispersed in nylon matrices. Wide angle X‐ray diffraction investigations show no preferred orientation in the extrudates, but biaxial orientation in the case of compressed films. The study on mechanical properties of extrudates of 5 to 10 wt.% PPTA compositions exhibits significant improvement in tensile modulus and tensile strength. The heat‐treated extrudates show further increase in tensile modulus and tensile strength, as compared with the unannealed samples, but the elongation at break decreases.
Interlaminar shear test by hybrid sandwich specimen under distributed load
Authors: Rosensaft M. , Marom G.
Published: May 2005

A new method is proposed for the determination of the interlaminar shear strength of composites. The method is particularly pertinent to composites of high interlaminar shear strengths, where the ratio of tensile (compressive) strength to shear strength is relatively low. In such materials, including unidirectional composites with improved fiber/matrix bond strength and angle‐ply laminates, an analysis based on a short beam interlaminar shear test is highly problematic and may, in fact, be erroneous. The test method is based on the use of a sandwich composite structure with a core made of layers of the tested composite and skins made of an elastic, strong unidirectional composite. A proper design procedure determines the choice of the skin material and of the relative thicknesses, so that flexural testing under distributed load leads to the intended core failure in shear. Calculations of the stress profile in a hybrid sandwich beam in bending and of the stress ratios under distributed load are presented. Also presented are experimental results recorded with sandwich hybrids made of unidirectional carbon‐fiber‐reinforced epoxy skins and a ±θ aramid‐fiber‐reinforced epoxy angle‐ply core.
Processing and structural optimization of PEEK composites
Authors: Lustiger A. , Uralil F. S. , Newaz G. M.
Published: May 2005

The objective of this experimental program was to understand how changes in processing conditions affect the morphology and ultimately, the performance of polyetheretherketone (PEEK)‐based carbon fiber composites. Based on some initial differential scanning calorimetry (DSC) work, various molding and aging conditions were implemented on compression molded plaques made from PEEK APC‐2 prepreg. These conditions included samples that were physically aged, annealed just below the melting point, slow cooled, prepared under low pressure, and under fast cooling. Using DSC, the crystallinity of plaques prepared according to the ICI procedure, low pressure, and physical aging conditions were found to be 31–33 percent, while the slow cooling and annealing conditions resulted in crystallinity of 42 percent, with slow cooling displaying a „shoulder”︁ on the primary melting endotherm. Optical and plasma etching/scanning electron microscopy on faster cooled plaques generally revealed a mixture of isolated and graphite fiber nucleated spherulites, while the slow‐cooled condition revealed larger fiber nucleated spherulites exclusively. Fracture toughness and impact delamination as measured by ultrasonic C‐scan indicates that slow cooling resulted in the lowest properties, while simultaneously resulting in the highest compression strength, all of which suggests reduced matrix toughness. The annealing condition, which allowed high crystallinity but in a matrix of smaller spherulites, resulted in properties intermediate between slow and fast cooling, suggesting that both spherulite size and degree of crystallinity are important in characterizing these materials. In contrast, physical aging resulted in no degradation in mechanical properties.
Application of digital image processing to the analysis of two‐phase materials with spherical inclusions
Authors: Parsi F. , Husband D. M. , Lisk J. S. , Gadala‐Maria F. , McNeill S. , Sutton M.
Published: May 2005

Digital image processing was used to experimentally determine the two‐dimensional pair distribution function of suspensions of solid spheres (cross‐linked polystyrene spheres in silicone oil) and of composite materials with spherical inclusions (surface‐treated glass spheres in unsaturated polyester resin). An assembly of optical devices and computers was used to obtain and store images of two‐phase materials. Software was developed to analyze the information in the images in order to determine the pair distribution function. The technique developed is simple yet powerful, and with some modification could easily be adapted for the analysis of other multiphase systems.
A numerical simulation of short fiber orientation in compression molding
Authors: Advani Suresh G. , Tucker Charles L.
Published: May 2005

A computer simulation has been developed to predict the orientation of fibers in a thin, flat part that is compression molded from sheet molding compound. The simulation combines a finite element/control volume simulation of the mold filling flow, a second order tensor representation of the fiber orientation state and a finite element calculation for the transient orientation problem. Sample results and comparison with experiments are presented. Predictions compare favorably with experiments on SMC (sheet molding compound) plaques and a model suspension of nylon fibers and silicon oil.
A study of the impact behavior of chopped fiber reinforced composite
Authors: Kau H. T.
Published: May 2005

The impact behavior of sheet molding compound (SMC) plaques was determined by using an instrumented Instron puncture test machine and the failure mechanism was qualitatively assessed by examining the damage. The impact response of SMC in terms of the load‐deflection curve is fairly consistent and shows the characteristics of a composite, intermediate between a brittle and a ductile material. At the speed of 2 m/s (about 5 miles per hour) the fracture energy, i.e., energy to break, was determined to be about 10 J for a regular 3 mm thick R‐25 SMC panel. This value decreases exponentially with a decrease in the thickness of the panel (power of 2.7). The failure process could also be affected by the material factors (resin and fibers used in the composite). For instance, an examination of the length distribution of the fibers in the damage region indicates that a combination of fiber pull‐out and severe fiber breakage have contributed to the impact resistance. Also, the fiber length in the composite could alter the failure modes. With the 25 mm fibers, the damage consists of an even mixture of fiber breakage and fiber pull‐out, but with a mixture of equal numbers of longer (38 mm) and shorter (13 mm) fibers in the composite, the damage is shifted to predominantly breakage of the longer fibers.
Fracture behavior of hybrid composites containing both short and continuous fibers
Authors: Lin T. L. , Jang B. Z.
Published: May 2005

A method for improving the fracture resistance of brittle polymer composites was explored. This method involved the incorporation of short fibers in a thermosetting resin before being used for impregnating the continuous fibers or fabrics. The impact fracture energy and the maximum load experienced by the hybrid can be associated with the parameters of short fibers (e.g., volume fraction and mechanical properties). Electron micrographs of the fracture surfaces of the specimen loaded under mode I and mode II conditions indicate that the short fiber modified composites have a significantly greater fracture surface area and higher level of plastic deformation than the unmodified composites. The data from all the tests demonstrate that adding a small amount of short fibers can significantly improve the interlaminar fracture toughness and impact resistance of graphite/epoxy composites. However, a high volume fraction of added short fibers could make it difficult to out‐gas during compression‐molding, leading to a high void content and reduced mechanical properties of composites.
A micro/macro approach to fracture in composites
Authors: Kollé J. J. , Lin K. Y. , Mueller A. C.
Published: May 2005

The results of an integrated microscopic/macroscopic finite element analysis of fracture in fiber‐reinforced composites are presented. A macroscopic analysis of a composite double‐cantilever‐beam (DCB) fracture toughness test specimen was carried out using a singular finite element method. The effects of fiber layup angle on strain energy release rate are discussed. Results from this analysis were input as boundary conditions to a microscopic model used to calculate J‐integral values in the crack tip region. Nonhomogeneity in this region causes the elastic strain energy release rate to vary with crack tip location and geometry. Elastic‐plastic calculations showed that significant matrix plasticity occurs near fibers away from the crack tip region. The constitutive equation chosen for the matrix plasticity was shown to have an important effect on the J‐integral value. The results show how the microscopic J‐integral is related to the macroscopic strain energy release rate.
Random glass mat reinforced thermoplastic composites. Part III: Characterization of the tensile moudulus
Authors: Stokes Vijay K.
Published: May 2005

Random glass mat thermoplastic composites, which can be thermostamped to form complex deep‐drawn parts with ribs and bosses, are excellent materials for making low‐cost stiff parts with relatively high impact strength. An earlier efforts, aimed at understanding the scatter in the mechanical properties of these materials showed that the tensile modulus in these materials can vary by a factor of two over a 12.7‐mm distance. To better characterize the local tensile modulus for such materials, measurements of the local tensile moduli of long, thin, 12.7‐mm wide strips along both thin edges (left and right) of the specimen and across the face are used to show that the tensile modulus is well approximated by the arithmetic mean of the local left‐ and right‐edge tensile moduli. This arithmetic mean modulus, which is shown to correlate with the local density, is a better practical measure of the response to tensile loads.
Effect of processing parameters on compression molded PMR‐15/C3K composites
Authors: Farouk Alamgir , Kwon Tai Hun
Published: May 2005

The consolidation and curing history during the processing of composite materials affects the final properties of a part in various inter‐related ways. In order to improve the quality of composites, these process‐property relations must be understood in detail. Using a computer‐controlled compression molding and data acquisition system, the processing of PMR‐15/C3k composites has been investigated. The process parameters considered were the pressure, the time at which it was applied and the crosslinking temperature. Parts were tested for inter‐laminar shear strength and flexural modulus, and measurements were made for void content and thickness. Full compaction strength, optimum compaction strength and void sensitivity factor have been defined.
Controlled energy dissipation in fibrous composites. II: Microscopic failure mechanisms
Authors: Lieu Y. K. , Shih W. K. , Jang B. Z.
Published: May 2005

Mechanical properties and microscopic fracture mechanisms of continuous fiber reinforced polymer composites were investigated. Perforated polyimide films (e.g. Kapton®) were added between composite prepreg layers to modify the interlaminar bonding strength. Addition of highly perforated films can increase the toughness of unidirectional glass/epoxy composites without an appreciable reduction in strength. The fibrous composites studied exhibit two fracture modes (compressive and tensile) when failed by three‐point bending. In general, the compressive failure mode preceded the tensile failure mode. Real‐time acoustic emission (AE) analysis was found to provide more fracture information which is otherwise not discernible from mechanical testing alone. The crack initiation stress level and the subsequent crack propagation mode were identified by real‐time AE during deformation and by post‐failure scanning electron microscopy fracture surface analysis.
Instrumented puncture impact characterization of composite laminates for printed circuit board applications
Authors: Rodriguez Ernesto L.
Published: May 2005

One sided copper glass/epoxy laminates for printed circuit board (PCB) applications were examined using an instrumented puncture impact technique. The effect of the diameter of the support ring, the initial impact velocity, and the preence of a stress concentrator on the impact parameters were evaluated. The orientation of the copper film with respect to the impacter was also varied. The PCB laminate showed brittle failure under the different conditions examined. Results showed that a higher degree of toughness was found for the condition where the copper layer was directly impacted by the dart. The maximum force and the total impact energy were found to be independent of the strain rate. The effect of a stress concentrator on the impact parameters was also found to be minimial. Total impact energies were found to be in the range of 8.8 to 12.6 J for the different testing conditions.
Radiation‐curable prepreg composites
Authors: Saunders Chris B. , Carmichael Alistair A. , Kremers Walter , Lopata Vince J. , Singh Ajit
Published: May 2005

Advanced composites, specifically carbon‐fiber‐reinforced epoxies, are used extensively for a variety of demanding structural applications, primarily because of their high strength‐to‐weight and stiffness‐to‐weight ratios, corrosion resistance, and damage tolerance characteristics. Electron beam (EB) treatment can be used to produce useful physical and/or chemical changes in plastics and composites by initiating various polymerization and crosslinking reactions. The advantages of using EB rather than thermal curing for carbon‐fiber‐reinforced epoxy composites include curing at ambient temperature, reduced curing times, and fewer volatiles. An EB‐curable carbon fiber‐acrylated epoxy composite is being developed for various applications. The tensile properties of the 14‐ply EB‐cured epoxy laminate were comparable with the properties of the thermally cured laminates used in the aircraft industry. Research is continuing to develop resin formulations and select coupling agents to improve the compression properties of EB‐cured laminates.
Dynamic mechanical properties of N‐phenylnadimide modified PMR polyimide composites
Authors: Pater Ruth H.
Published: May 2005

Temperature‐frequency dependence of α, β, and γ transitions was determined using a Rheometrics dynamic spectrometer on a series of unidirectional Celion 6000/N‐phenylnadimide (PN) modified PMR polyimide composites. The objective was to see if any correlations exist between crosslinked network structure and dynamic mechanical properties. Variation in crosslinked network structures was achieved by altering the polyimide formulation through addition of various quantities of PN into the standard PMR‐15 composition. As a control, PMR‐15 composite system exhibited well‐defined α, β, and γ transitions in the regions of 360, 100, and −120°C, respectively. Their activation energies were estimated to be 232, 60, and 14 kcal/mole, respectively. Increasing the amount of PN concentration caused (a) lowering of the activation energies of the three relaxations, (b) a decrease of the glass transition temperature, and (c) increasing intensities of the three damping peaks, compared to the control PMR‐15 counterpart. These dynamic mechanical responses were in agreement with formation of a more flexible co‐polymer from PN and PMR‐15 prepolymer.
Processing parameters for filament winding thick‐section PEEK/carbon fiber composites
Authors: Colton J. , Leach D.
Published: May 2005

The consolidation pressure and winding speed for thermoplastic filament winding were studied. Thermoplastic composite parts were manufactured from tape prepreg (APC‐2); powder‐coated, semi‐consolidated towpreg; and commingled fiber towpreg. The material used was carbon fiber (AS‐4) (60 vol%) in a PEEK matrix. The parts made were open‐ended cylinders of the three materials, 177.8‐mm ID, 228.6 mm long, 17 plies thick with a 0° lay‐up angle; and rings, 50 plies of APC‐2 thick, 6.35 mm wide (one strip wide), 177.8‐mm ID, and a lay‐up of 0°. Their quality was determined by surface finish and void percentage. The tubes made from APC‐2 appeared to have the best quality of the three prepregs. For the rings, the speed of lay‐down had a significant effect (at a 99% confidence level) on both the final width of the parts and on the percentage of voids. The pressure of the roller had a significant effect on the final widths at a 99% confidence level, but a significant effect on the percentage of voids at only a 95% confidence level.
Compression molding of sheet molding compounds in plate‐rib type geometry
Authors: Xu Jingyi , Kim Junil , Ho Ted , Lee L. James
Published: May 2005

The flow of fiber‐reinforced composite materials in a plate‐rib type mold geometry during compression molding was investigated using a series of sheet molding compounds (SMC). Material anisotropy in relation to the amount and the length of reinforcing fibers was analyzed. The influence of the interfacial friction between SMC charge and the mold surface on the flow and sink mark formation was also examined. The results were explained qualitatively by computer simulation.
A modeling approach to thermoplastic pultrusion. II: Verification of models
Authors: Åstroöm B. Tomas , Pipes R. Byron
Published: May 2005

A set of mathematical models as a thermoplastic pultrusion process is evaluated. The predictions of the models are compared to experimentally obtained data in terms of composite temperature and pressure and process pulling force. The comparisons between predictions and experiments are made for two different material systems, two different die configurations, and a range of processing temperatures and speeds. The correlations between predictions and data are found to be favorable, indicating the soundness of the models.
The effect of pyrolysis on the mechanical properties and microstructure of carbon fiber‐reinforced and stabilized fiber‐reinforced phenolic resins for carbon/carbon composites
Authors: Ko Tse‐Hao
Published: May 2005

Carbon/carbon composites were prepared with phenol‐formaldehyde resin, one kind of commercial carbon fiber, and a stabilized fiber that was developed in our laboratory. The effect of pyrolysis on the microstructure, fracture behavior, and flexural strength of the composites during the carbonization process was studied. During the pyrolysis of the composites a chemical reaction at the fiber/resin interface apparently took place. A thermogravimetry (TG) study indicated that the use of stabilized fiber reinforced composites inhibited decomposition reactions and thermal fragmentation in the matrix resin, and reduced the weight loss of the final composites. The X‐ray reflection of the resin and the two composites showed a reflection appearing at 2θ ≈ 12° when the samples were carbonized above 600°C. The intensity of this reflection in the composites made with stabilized fiber was higher than that of the composite made with carbon fiber. Because of the formation of strong bonding in the fiber‐matrix interface, the composites made with stabilized fiber showed catastrophic failure and low flexural strength below carbonization temperatures of 600°C. Above 600°C, the flexural strength of the composites increased with an increase in the carbonization temperatures, even if the fracture behaviors showed catastrophic failure. The flexural strength of the composites made with carbon fiber showed pseudo‐plastic patterns and debonding with very little fiber pullout. Above 800°C, these composites showed a catastrophic failure and smooth failure surfaces. During pyrolysis the flexural strength decreased with an increase in the carbonization temperature.
Determination of initiation value of mode I interlaminar fracture toughness of unidirectional polymer composites
Authors: He Tianbai , Zhou Jiang , Liu Weilian
Published: May 2005

The use of interlaminar fracture tests to measure the delamination resistance of unidirectional composite laminates is now widespread. However, because of the frequent occurrence of fiber bridging and multiple cracking during the tests, it leads to artificially high values of delamination resistance, which will not represent the behavior of the laminates. Initiation fracture from the crack starter, on the other hand, does not involve bridging, and should be more representative of the delamination resistance of the composite laminates. Since there is some uncertainty involved in determining the initiation value of delamination resistance in mode I tests in the literature, a power law of the formGIC=A· Δab(whereGICis mode I interlaminar fracture toughness and Δais delamination growth) is presented in this paper to determine initiation value of mode I interlaminar fracture toughness. It is found that initiation values of the mode I interlaminar fracture toughness.GICini, can be defined as theGICvalue at which 1 mm of delamination from the crack starter has occurred. Examples of initiation values determined by this method are given for both carbon fiber reinforced thermoplastic and thermosetting polymers.
Mechnical properties of thermoplastic film/metallic glass composites with improved interfacial strength
Authors: Sidhu A. S. , Varin R. A.
Published: May 2005

The mechanical properties of the uniaxial and continuous composite with high strain to fracture PP matrix reinforced with the Fe40Ni40B20 (at%) and Metglas 2605SC metallic glass ribbons have been determined and compared with the rule of mixtures. The reinforcing ribbons were coated with PVA (polyvinlyl alcohol) to improve interfacial bonding. The experimental fracture strength results for both types of reinforcement deviate from the values predicted. The strength of composite at the fracture strain of ribbon determined experimentally obeys a modified rule of mixture (isostrain condition) for both types of reinforcement over the entire volume fraction range of reinforcement (up to 16%). The experimental composite eleastic modulus results for composite reinforced with relatively narrow Fe40Ni40B20 ribbons are found to be generally near the values predicted by the rule of mixtures, but for the Metglas 2605SC wide the modified rule of mixtures, which takes into account the thermally induced tensile stresses at the interface resulting from the mismatch of the coefficients of thermal expansion.
Microstructure‐based processing parameters of thermoplastic composite materials. Part I: Theoretical models
Authors: Yang Heechun , Colton Jonathan S.
Published: May 2005

Processing parameters for composites are predicted by new models which are based on the microstructure of the composite. Three types of termoplastic prepregs are considered, ICI tape, BASE commingled two, and CCMI powder coated tow. The permeability of the composites depends on their fiber distribution. The elastic behavior of the fiber network compression depends on the fiber oreientation. These two are integrated to predict the processing parameters.
Prediction of mechanical properties of short kevlar fiber‐nylon‐6,6 composites
Authors: Yu Z. , Brisson J. , Ait‐Kadi A.
Published: May 2005

Injection molded short Kevlar (DuPont) fiber/nylon‐6,6 composites have been studied. Fiber length and length distribution were measured as a function of processing variables. Critical fiber length was measured by an embedded single‐fiber method. Tensile modulus of the molded composites was predicted by an adapted classical lamination analogy. Fiber and matrix orientation factors, derived from X‐ray diffraction, were introduced to modify Kelly Tyson equation to estimate the composite tensile strength. It has been found that fiber length is dramatically shortened by the injection molding process, and is affected by processing conditions. Predictions gave reasonable agreement with data for tensile modulus and strength.
Simulation of the fracture behavior of elastomeric composites: Mechanical interactions at material interfaces
Authors: Khan M. B. , Briscoe B. J.
Published: May 2005

The fracture mechanics of multilayered elastomeric composites was simulated by the Blister Test using a polyurethane (PU)/A1 base plate interfacial assembly. In the various systems studies, and hard or soft intrposed layer (∼50 μm) separated the bulk matrix (∼ 1000 μm) from the metal counterface, with a hard‐to‐soft modules ratio of 1.70. Debonding was performed at a constant pressurization rate 1 × 10−8 m3/s corresponding to an average delamination rate of 0.25 m/s. Lateral hardening of the composite modules (negative transversal gradient of modulus) improved the fracture resistance (by 35%) at the material interface, in conformance with analytical predictions. Particle‐dispersed and liquid‐doped systems exhibited a sharp attenuation (40 to 90%) in the debond pressure. The latter results were substantiated by subjective assessement using optical microscopy, and were found consistent with stress concentration and weak conhesive fracture at the resin‐substrate interface, respectively.
Effect of two stage pressure molding on surface quality of sheet molding compounds
Authors: Dziewatkoski Nicholas A. , Xu Jingyi , James Lee L. , Castro Jose
Published: May 2005

The goal of this work was to investigate the effect of two stage pressure molding on the compression molding of a sheet molding compound (SMC). It has been shown in previous studies that a rapid drop in pressure during SMC curing significantly reduced severity of sink marks. This study concentrated on a method of predicting the optimum time during curing to release pressure by examining material behavior through process data from in‐mold sersors. A simple control scheme was them applied for automatic pressure release at the optimum time corresponding with the peak of the material expansion and the onset of the reaction exotherm.
Studies on a fiber reinforced plastics honeycomb structure
Authors: Mukherjee G. S. , Saraf M. N.
Published: May 2005

Based on an adhesive and fabric screening program, a rubber‐modified resole adhesive and a flexible grade plain weave glass fabric were found appropriate for the fabrication of a glass‐reinforced plastics honeycomb core material. Sandwich structures of different densities were fabricated. A linear regression analysis was performed to correlate the mechanical properties (S) with the density (p) for a wide range of sandwich structures based on honeycomb and cellular plastic core materials. An analytical model of the formS=Kρnwas derived, with two empirical constantsKandn. The density exponentnwas between 1 ≤n≤ 2 in all cases. An equation was also derived to relate density with thermal conductivity. The dynamic mechanical analysis (DMA) results revealed that the glass transition temperature of the resin matrix associated with the sandwich structure was higher than that of the corresponding facing laminate or near resin casting.
Deformation studies of polystyrene/poly(vinyl methyl ether) blends by mechanical‐vibrational spectroscopy
Authors: Lu F. J. , Burchell D. J. , Li X. , Hsu S. L.
Published: May 2005

We have analyzed the deformation behavior of compatible and incompatible polystyrene (PS) and poly(vinyl methyl ether) (PVME) blends by a combination of mechanical and vibrational spectroscopy. Macroscopic properties and segmental orientation were found to be sensitive to molecular weight, strain rate, and temperature of measurement above the glass‐transition temperature. Considerably different orientation functions were found for the PS and PVME components. For the experiments carried out above the Tg of the blends, the deformation behavior measured was consistent with expectations of a rubbery network.
Predicting conversion using temperature as the measured variable in the reaction injection molding process. Part II: Implementation of the on‐line corrective algorithm
Authors: Pino Oscar Del , Romagnoli José A. , Castro José M.
Published: May 2005

In the reaction injection molding process, we need to know the evolution of the conversion field with a high level of confidence in order to minimize the mold opening time. Thus, the mold can be opened as soon as there is conversion everywhere in the mold above the value needed for the part to become dimensionally stable. Since conversion can not be determined readily by experimental measurements, and since a thermocouple can provide reliable dynamic temperature data, it is best to predict the conversion field from the solution of a state estimation problem using temperature as the measured variable. Here, we develop an on‐line corrective system which uses temperature to correct the model predictions. It is shown that by measuring at the center and at the mold wall, both of which are physically possible, the performance of the corrective algorithm is fairly good.