bluuebunny/crossref_metadata_2025_split huggingface dataset:
Characterization of modulus and glass transition phenomena in poly(L‐lactide)/hydroxyapatite composites
Authors: Fambri Luca , Kesenci Kemal , Migliaresi Claudio 
Published: April 2004

AbstractIn order to study the dynamic‐mechanical properties of Poly(L‐lactide)/Hydroxyapatite (PLLA/HA) composites, two different molecular weight (inherent viscosity (ηinh): 4.0 (dL/g), and 7.8 (dL/g)) poly(L‐lactide) (PLLA) were synthesized by bulk polymerization and filled with 10%, 30%, and 50% (w/w) with medical grade HA (size range: 25–45 μm and Ca/P = 1.69). The plain PLLA polymers and PLLA/HA composites were compression molded and machined to yield 50 × 3 × 2 mm3 specimens. The composites were investigated by dynamic mechanical thermal analyzer (DMTA) of imposed bending load on rectangular specimens over a temperature range from 30 to 120°C using multiple frequencies (0.3–50 Hz). The results showed that the bending storage modulus (E′) of the composites increased linearly with the percentage of the filler, reaching at 37°C and 0.1 Hz about 2.5, 3.7 and 5.0 GPa with 10, 30 and 50% of HA respectively. The glass transition temperature, evaluated at the tan δ peaks, were in the range 70–80°C and 50–70°C for PLLA matrix and PLLA composites respectively. The activation energies at the glass transition temperature were calculated from the Arrhenius plot in the range of 102–111 Kcal/mol for the composites, whereas 132 and 148 Kcal/mol were found for low and high molecular weight of PLLA respectively. The content of amorphous phase was evaluated from the intensity of tan δ peak. Results showed that HA causes an amorphous phase with a greater mobility with respect to the pure PLLA.
Processability of LCP‐nylon‐glass hybrid composites
Authors: Pisharath Sreekumar , Wong Shing‐Chung 
Published: April 2004

AbstractA hybrid composite consisting of rubber toughened nylon 6,6, short glass fibers and thermotropic LCP was investigated by varying the content of LCP. It was found that a hybrid composite offered better processability over the glass fiber reinforced polymers alone. The total torque in melt mixing increased with short glass fiber addition but decreased with an increase in LCP content. The thermal stability of the glass fiber reinforced composite was improved by blending with LCP. However, a minimum of 15 wt% LCP was required to realize reinforcement effect from the hybrid composite. The fracture morphology was examined using SEM techniques. Some LCP fibrils could be observed on the tensile fracture surface.
Interfacial interactions in calcium carbonate–polypropylene composites. 1: Surface characterization and treatment of calcium carbonate: A comparative study
Authors: Wang Yeh , Lee Wei‐C. 
Published: April 2004

AbstractCalcuium carbonate (CaCO3) was modified with two types of coupling agents based on fatty acid and titanate. The efficiency of the surface treatment was studied through a dissolution method. The change in surface properties was characterized by inverse gas chromatography at both infinite dilution and finite concentration. It was found that a small amount of coupling agents caused a drastic decrease in surface energy, which varied as a function of bonded coupling agents. The completely covered CaCO3 exhibited a surface of little polarity. Infrared analysis showed that stearic acid reacted extensively with the filler surface to produce chemically bound organic salt compound, in addition to the increase in peak intensity due to the methylene vibration of the alkyl chain. However, instead of directly observing the transesterification reaction between LICA 12 and the filler, only an increase in the peak intensity due to absorption of the phosphate stretching was detected.
Morphology and compression‐after‐impact strength relationship in interleaved toughened composites
Authors: Derkowski B. J. , Sue H.‐J. 
Published: April 2004

AbstractMorphology and compression after impact (CAI) strength relationships in interleaved toughened high performance composites are investigated using a quantitative two‐dimensional image analysis approach. A group of six quasi‐isotropic carbon fiber‐epoxy composites with identical compositions, but having variations in CAI strengths, were analyzed to study how the interleaf particle size, particle size distribution, and location of particles in the interlaminar region affect the CAI strength values and the corresponding damage mechanisms. It is found that the CAI strength of interleaved‐toughened composites is significantly affected by the size and size distribution of toughener particles in the interlaminar regions of the composite. In general, high CAI strength composites exhibit more uniform particle size distribution throughout the interlaminar regions. Whereas, for low CAI strength composites, the interleaf particles tend to cluster together and have varied size distribution.
Adhesion improvement in glass fiber reinforced polyethylene composite via admicellar polymerization
Authors: Somnuk Usa , Yanumet Nantaya , Ellis John W. , Grady Brian P. , O'Rear Edgar A. 
Published: April 2004

AbstractAdmicellar polymerization (polymerization of monomer solubilized in adsorbed surfactant bilayers) has been used to form a thin film of polyethylene onto the surface of milled glass fibers using sodium dodecyl sulfate as the surfactant. The decrease in ethylene pressure was used to follow the solubilization and adsolubilization processes as well as the reaction processes. An increase in initiator (Na2S2O8) to surfactant ratio gave thicker and more uniform coatings of polymer onto the glass fiber surface according to SEM micrographs. Although a substantial amount of ethylene polymerized in solution according to the pressure drop, the decrease in pressure attributed to admicelle polymerization corresponded to the amount of polymer formed on the glass fiber, indicating little, if any, solution polymer deposited on the fibers. The admicellar‐treated glass fiber was used to make composites with high‐density polyethylene. The composites showed an increase in tensile and flexural strength over composites made from as‐received glass fiber, indicating an improvement in the fiber‐matrix adhesion of the admicellar‐treated glass fiber.
Hot water resistance of glass‐fiber and glass‐bead reinforced thermoplastics
Authors: Kawaguchi Takafumi , Nishimura Hiroyuki , Ito Kazunori , Kuriyama Takashi , Narisawa Ikuo 
Published: April 2004

AbstractThe hot water resistance of three kinds of short glass fiber or glass bead‐reinforced plastics [polyphenyleneether (PPE), polyphenylenesulfide (PPS), and polyoxymethylene (POM)] was studied by hot water immersion testing, tensile testing and water‐hammer fatigue testing. It was found that the degradation of the strength was observed only for the reinforced plastics under hot water immersion and that the change of the tensile strength was most drastic in glass fiber‐reinforced PPS (GFPPS). Scanning electron microscope (SEM) observations of the tensile fracture surface revealed that the change in tensile strength was attributable to the deterioration of the interface between the glass fiber and the matrix resin. The results of acoustic emission analysis also supported the conclusion that the change in strength was due to the deterioration of the interface. Although the change in the tensile strength of glass fiber‐reinforced PPE (GFPPE) was small compared with that of GFPPS, debonding between the glass fiber and the matrix resin and surface cracks was observed on the surface of the GFPPE specimens.
Effect of nylon66 addition on the mechanical properties and fracture morphology of poly(phenylene sulfide)/glass fiber composites
Authors: Lee Bo Sun , Chun Byoung Chul 
Published: April 2004

AbstractIn this study, the toughening effect of nylon66 on the PPS/glass fiber composite at various nylon66 contents and testing temperatures was analyzed using tensile and notched Izod impact test. Also, the corresponding fracture surface morphology was observed and analyzed. Mechanical properties such as strain at break and impact strength decreased at all testing temperatures when nylon66 was a dispersed phase. However, when PPS was a dispersed phase, improved interfacial bonding between matrix and fiber resulted in a mechanical property increase. Thus, when nylon66 was a dispersed phase (minor component), negative deviation from the rule of mixture relationship was found. In order to improve these deficiencies, compatibilizer EGMA was used. Optimum EGMA content which can improve the strain at break and impact strength was found to be between 3∼5%.
Resin infusion of triaxially braided preforms with through‐the‐thickness reinforcement
Authors: Sayre Jay R. , Loos Alfred C. 
Published: April 2004

AbstractVacuum assisted resin transfer molding (VARTM) has shown potential to significantly reduce the manufacturing cost of high‐performance aerospace composite structures. In this investigation, high fiber volume fraction, triaxially braided preforms with through‐the‐thickness stitching were successfully resin infiltrated by the VARTM process. The preforms, resin infiltrated with three different resin systems, produced cured composites that were fully wet‐out and void free. A three‐dimensional finite element model was used to simulate resin infusion into the preforms. The predicted flow patterns agreed well with the flow patterns observed during the infiltration process. The total infiltration times calculated using the model compared well with the measured times.
Nonisothermal healing and interlaminar bond strength evolution during thermoplastic matrix composites processing
Authors: Yang F. , Pitchumani R. 
Published: April 2004

AbstractThermoplastic‐matrix composite products are fabricated by applying heat and pressure to contacting thermoplastic surfaces, and consolidating the interface. The combined processes of interfacial contact area increase, referred to as intimate contact, and polymer interdiffusion (healing) across the interfacial areas in contact are responsible for the development of interlaminar bond strength in the composite products. In this paper, a model for the healing process under nonisothermal conditions is presented starting from a fundamental formulation of the reptation of polymer chains. The healing model is coupled with an intimate contact model based on a fractal representation of the asperity structures on thermoplastic tow surfaces, to provide a comprehensive description of the interfacial bond strength evolution during nonisothermal processing. Nondimensional analysis is used to identify the ranges of a parameter, introduced as the fusion bonding number, which correspond to the interfacial bonding process being healing‐limited, intimate‐contact‐limited, or equally dominated by both mechanisms.
Tailoring viscoelastic and mechanical properties of the foamed blends of EVA and various ethylene‐styrene interpolymers
Authors: Liu I‐Chun , Tsiang Raymond Chien‐Chao 
Published: April 2004

AbstractFoamed materials (EVA/ESI) have been prepared from blends of ethylene‐vinyl acetate copolymer (EVA) and ethylene‐styrene interpolymers (ESI) in the presence of various amounts of dicumyl peroxide (DCP). Four ESIs of different compositions were employed in this study; their styrene contents ranged from 30 to 73 wt% and their Tg ranged from −2 to 33°C. It has been found that microcellular morphology, degree of crosslinking and expansion ratio were strongly affected by the DCP concentration and the type of ESI employed. A minimum degree of crosslinking was required for making good foams and the same degree of crosslinking could be achieved by employing a smaller amount of DCP for an EVA/ESI blend having a higher styrene content. In contrast to other EVA blends, such as EVA/LDPE, these EVA/ESI blends exhibited no existence of any optimum DCP concentration, and the α glass transition temperatures of the foams varied with the ESI type, covering a wide span from 0°C to 37°C. Therefore, it was possible to tailor the Tg of an EVA/ESI blend by choosing an appropriate type of ESI. Furthermore, by correctly tailoring the Tg, the EVA/ESI foam could be made into a rubbery material with a custom‐designed damping factor. Tensile strength and modulus of the EVA/ESI foams increased generally with an increase in the styrene content, with the exception that ESIs with very low styrene content will confer on the blend a high modulus at small strain and a large elongation at break.
Preparation and linear rheological behavior of polypropylene/MMT nanocomposites
Authors: Jian Li , Zhou Chixing , Gang Wang , Wei Yu , Ying Tao , Qing Liu 
Published: April 2004

AbstractMaleic anhydride grafted low isotactic homopolypropylene elastomer (LiPP‐g‐MAH) is used as a compatibilizer in the melting mixing of polypropylene (PP) and clay. The microstructures of the composites of PP/clay (PPCN) are investigated using a wide‐angle X‐ray diffractometer (WAXD) and transmission electron microscope (TEM) as well as parallel rheometer, which show that PPCN with different phase morphologies have been obtained. It is found that the weight ratio of LiPP‐g‐MAH to clay and the weight content of LiPP‐g‐MAH in PPCN have a strong effect on the final dispersibility of the clay. The rheological response to small amplitude oscillatory shear (SAOS) shows that the storage modulus (G′) at the low frequencies is greatly sensitive to the microstructures in comparison with WAXD measurements. The investigation further indicates that the virgin clay particles, intercalated silicate crystallites, and exfoliated layers may coexist in the matrix at the same time, resulting in the great enhancement of G′ plateau at low frequency region.
Carbon fiber reinforced melamine‐formaldehyde
Authors: Voigt B. , Rychwalski R. W. , McCarthy D. M. C. , Den Adel J. C. , Marissen R. 
Published: April 2004

AbstractNew composites based on carbon fiber (cf) and melamine‐formaldehyde (MF) are presented. Composites were manufactured by pressing stacked planar random veils (webs) or unidirectionally (UD) arranged fibers, and MF impregnated thin cellulose sheets. Non‐vented pressing for 60 s was used. Also, planar random, UD and bidirectional fiber composites with or without alumina trihydrate (ATH) were manufactured by conventional compression molding using much longer times (up to 20 min). Tensile strength of about 500 MPa and stiffness of 60 GPa was obtained for the UD composite containing 23 vol% fiber, and no ATH. Practically the same strength was measured for the bidirectional composite containing 46 vol% fiber and no ATH. Tensile strength and modulus of 130 MPa and 28 GPa, respectively, was obtained for the random fiber composite containing 16 vol% fiber. Measurements showed that replacement of ATH with cellulose in a composite containing 6 vol% carbon fibers increased the strength (2.5 times) without any penalty on stiffness, and increased strain at break. Cf‐MF interfacial strength is low. This was estimated for clean fibers by means of transverse tensile testing and in‐situ scanning electron microscopy (SEM), and for fibers with an epoxy compatible coating by using the interlaminar shear strength (ILSS) test. The cf/MF/cellulose composite performed well up to 200°C. Within this temperature range it retained 80% of its stiffness compared to about 60% in the case of a representative epoxy with a higher content of carbon fibers.
Analysis of dynamic flows through porous media. Part II: Deformation of a double‐scale fibrous reinforcement
Authors: Bréard Joël , Henzel Yann , Trochu François , Gauvin Raymond 
Published: April 2004

AbstractPorous media are encountered in numerous applications from Soil Mechanics to composite materials manufacturing. Part I of this article investigated the flow behavior in a double‐scale porous medium, i.e., in a material with a bimodal distribution of pore sizes. Typical examples of such medium are the dry fibrous reinforcements used in composite manufacturing through which resin is injected. This type of porous medium contains two types of pores: microscopic voids inside the fiber tows and macroscopic ones between the tows. Because of this double‐scale structure, the saturation of such reinforcing materials is not instantaneous during resin injection. Part I has shown that the notion of saturation must be taken into account in order to describe accurately transient unsaturated flows during the filling of double‐scale fibrous materials. Part II of this investigation is concerned with the transient flow behaviors that can be observed once the reinforcement is saturated. In permanent regime, saturated resin flows are governed by Darcy's law, which describes the purely linear pressure drop observed in fully saturated reinforcements. However, this model cannot be applied to transient saturated flows unless they are considered as a succession of quasi‐stationary flows. Simple macroscopic measurements during transient flow regimes permit us to derive important information on the microscopic characteristics of the flow in connection with the deformations of the porous medium under the effect of fluid pressure. The pressure variations in time observed in permanent flow regimes, when the flow rate is changed, are connected with the double‐scale porosity structure of the fibrous reinforcement. Therefore the second part of this analysis is focused on the stress‐stain behavior of fibrous reinforcements deformed by the pore pressure. A physical model based on Kelvin‐Voigt visco‐elastic material is proposed here to describe the dynamic compaction and relaxation behaviors of saturated fibrous reinforcements. This approach is not only in good agreement with experiments, but it shows also that double‐scale effects are intimately connected with the pressure variations observed in transient saturated flows.
Modeling and simulation approaches in the resin transfer molding process: A review
Authors: Shojaei A. , Ghaffarian S. R. , Karimian S. M. H. 
Published: April 2004

AbstractA review of current approaches in modeling and simulation of the resin transfer molding (RTM) process is presented. The processing technology of RTM is discussed and some available experimental techniques to monitor the process cycle are presented. A master model is proposed for the entire process cycle consisting of mold filling and curing stages. This master model contains the fundamental and constitutive sub‐models for both stages. The key elements of the master model discussed in this study are: flow, heat and mass balance equations for fundamental sub‐models, permeability, cure kinetics, resin viscosity and void formation for constitutive sub‐models. At the end, numerical methods widely used to simulate the filling process are presented and published simulation results of mold filling and process cycle are reviewed.
Moisture absorption by cyanate ester modified epoxy resin matrices. Part IV: Effect of curing schedules
Authors: Karad Sunil K. , Attwood David , Jones Frank R. 
Published: April 2004

AbstractThe cure schedule (time and temperature) has a profound effect on the physical properties of thermosetting materials. For hydrophilic systems, it can also influence the rate of diffusion of moisture and the equilibrium concentration. The effect of post‐cure time and temperature on the moisture sorption behavior and the viscoelastic properties of cyanate ester modified epoxy resin has been investigated. Moisture absorbed at 96% R.H. (relative humidity) and 50°C under isothermal conditions was found to increase with post‐cure temperature, but the diffusion coefficient decreased in line with the crosslink density. Resins of high crosslink density and high glass transition temperature appeared to exhibit a larger reduction in glass transition temperature on plasticization by moisture in comparison to those with lower crosslink density.
Prediction of flow–induced process variables based on similarity analysis in the liquid molding process
Authors: Um Moon‐Kwang , Byun Joon‐Hyung 
Published: April 2004

AbstractIn general, a numerical scheme is a widely accepted technique for estimating resin flow in the liquid molding process. A numerical mold filling analysis is essential to optimize the manufacturing process of a composite. However, finding an optimal condition from the numerical analysis requires many numerical calculations. The efforts can be greatly reduced if a similarity solution replaces the repeated numerical calculations. In this study, similarity relations are proposed to predict the flow‐induced process variables. such as resin pressure, resin velocity, and flow front evolution time, during mold filling. Numerical simulations are performed for two cases where a material property, an injection condition or a part shape is different. The model is verified by applying the similarity relation for two numerical results obtained from the thin shell structure.
Fiber orientation control of short‐fiber reinforced thermoplastics by ram extrusion
Authors: Sanomura Yukio , Kawamura Munehiro 
Published: April 2004

AbstractIn this study we examine the fiber orientation distribution, fiber length and Young's modulus of extruded short‐fiber reinforced thermoplastics such as polypropylene. Axial orientation distributions are presented to illustrate the influence of extrusion ratio on the orientation state of the fibrous phase. Fibers are markedly aligned parallel to the extrusion direction with increasing extrusion ratio. The orientation state of extruded fiber‐reinforced thermoplastics (FRTP) is almost uniform throughout the section. The control of fiber orientation can be easily achieved by means of ram extrusion. Experimental results are also presented for Young's modulus of extruded FRTP in the extrusion direction. Young's modulus follows a linear trend with increasing extrusion ratio because the degree of the molecular orientation and the fiber orientation increases. The model proposed by Cox, and Fukuda and Kawada describes the effect of fiber length and orientation on Young's modulus. The value of the orientation coefficient is calculated by assuming a rectangular orientation distribution and calculating the fiber distribution limit angle given by orientation parameters. By comparing the predicted Young's modulus with experimental results, the validity of the model is elucidated. The mean fiber length linearly decreases with increasing extrusion ratio because of fiber breakage due to plastic deformation. There is a small effect on Young's modulus due to fiber breakage by ram extrusion.
Mechanical characterization of woven carbon fiber composites with poly(methyl methacrylate)–modified epoxy matrices
Authors: Fernández B. , Mujika F. , De Benito A. , Mondragon I. 
Published: April 2004

AbstractThe influence of the modification of epoxy matrices with poly(methyl methacrylate) (PMMA) on the fracture behavior of composite laminates based on woven carbon fibers has been investigated. Three‐point flexural, short beam shear (SBS) and end‐notched flexural tests (ENF) have been carried out. Microstructural features have been investigated by atomic force microscopy (AFM) and scanning electron microscopy (SEM). Dynamic mechanical thermal analysis of the different epoxy matrices and their corresponding composites shows the power of this technique for microstructural studies. Fracture behavior is compared with that shown by similar bifunctional (DGEBA) epoxy matrix composites. In spite of the two‐phase structure obtained in tetrafunctional (TGDDM) epoxy matrix‐based systems for all PMMA contents, only a small improvement in fracture toughness and interlaminar shear strength properties was obtained. In contrast, for DGEBA bulk matrices and composites, a higher enhancement of fracture toughness was obtained, as a consequence of the lower crosslink densities of bifunctional matrices.