bluuebunny/crossref_metadata_2025 huggingface dataset:
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

Calcuium 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

Morphology 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

Admicellar 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

The 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

In 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

Vacuum 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

Thermoplastic‐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

Foamed 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

Maleic 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

New 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

Porous 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

A 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

The 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

In 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

In 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

The 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.
Joining composite pipes using hybrid prepreg welding and adhesive bonding
Authors: Li Guoqiang , Davis Dishili , Stewart Carlos , Peck Jerry , Pang Su‐Seng
Published: April 2004

A critical technology for composite piping systems in offshore platforms is the joining technique. This paper discusses the development of a hybrid joining approach by using heat‐activated prepreg welding and adhesive bonding. The joining procedure was demonstrated via specimens' fabrication. Four adhesives, with varying mechanical properties, were used to seal the gap between the two pipes. A glass fiber reinforced prepreg was used to wrap the pipes. A total of forty‐five specimens were prepared and evaluated using standardized internal pressure tests. A finite element analysis was conducted to aid in the understanding of the mechanisms of the hybrid joining method. Recommendations for further studies were made based on the test and finite element analysis results.
Blends of low‐density polyethylene and liquid crystalline polymer
Authors: Sahoo N. G. , Das C. K.
Published: April 2004

Blends of low‐density polyethylene (LDPE) and a glass‐filled thermotropic liquid crystalline polymer (LCP‐g) have been prepared by melt mixing techniques. The thermal transitions, dynamic behavior, morphology and crystalline properties of the blends have been measured by DSC, DMTA, SEM and XRD respectively. The crystallinity decreased with increase in LCP‐g content in the blends. At higher levels of LCP‐g, crystal growth is favored in the PE phase. From DSC, it is found that the thermal stability of the blends increased with the LCP‐g content. The variation of storage modulus, loss modulus and stiffness as a function of blend ratio suggested the phase inversion at the 40–50% level of LCP‐g in the blend. SEM studies revealed that with the increase in LCP‐g content, the flow of the matrix was restricted.
Cryogenic microcracking of rubber toughened composites
Authors: Nobelen Matthieu , Hayes Brian S. , Seferis James C.
Published: April 2004

This study investigated the influence of carboxyl‐terminated butadiene acrylonitrile (CTBN) liquid rubbers on the microcracking response of polymeric composite materials to cryogenic cycling. Matrices of carbon fiber/epoxy prepregs were modified with different concentrations of two CTBN liquid rubbers. The glass transition temperature and the interlaminar shear strength of the laminate systems were depressed as a result of the presence of CTBN in the epoxy phase. An increase in total rubber concentration with the continuous phase was found to decrease and in some cases eliminate microcracking in laminates exposed to cryogenic cycling.
Effects of processing conditions on the mechanical performance of maleic anhydride compatibilized in‐situ composites of polypropylene with liquid crystalline polymer
Authors: Meng Y. Z. , Tjong S. C.
Published: April 2004

Maleic anhydride compatibilized blends of isotactic polypropylene (PP) and thermotropic liquid crystaline polymer (LCP) were prepared either by the direct injection molding (one‐step process), or by twin‐screw extrusion blending, after which specimens were injection molded (two‐step process). The morphology and mechanical properties of these injection molded in situ LCP composites were studied by means of scanning electron microscopy (SEM), Izod impact testing, static tensile, and dynamic mechanical measurements. SEM observations showed that fine and elongated LCP fibrils are formed in the maleic anhydride compatibilized in situ composites fabricated by means of the one‐step process. The tensile strength and modulus of these composites were considerably close to those predicted from the rule of mixtures. Furthermore, the impact behavior of LCP fibril reinforced composites was similar to that of the glass fiber reinforced polymer composites. On the other hand, the maleic anhydride compatibilized blends prepared from the two‐step process showed lower mechanical performance, which was attributed to the poorer processing behavior leading to the degradation of PP. The effects of the processing steps, temperatures, and compatibilizer addition on the mechanical properties of the PP/LCP blends are discussed.
Two‐dimensional mapping of tensile strength for injection molded composites of glass fiber reinforced polypropylene
Authors: Karian Harutun G. , Stoops Ken
Published: April 2004

An array of polypropylene composites were injection molded into rectangular plaques having a single side gate. As a consequence of non‐symmetrical flow patterns, giving complex distribution of fiber orientations, measured tensile strength of test specimens cut along X‐Y directions produced nonlinear and anisotropic trendlines. Chemical coupling, glass fiber content, and the choice of short or long glass fiber reinforcement are shown to be material variables influencing the magnitude of the tensile strength at any given localized position. These data verify the notion that tensile strength evaluation along just the flow direction is insufficient for anticipating end use performance.
The correlation between packing efficiency and tensile properties for polymer composites in SMC formulation
Authors: Chaturvedi Manish
Published: April 2004

For polymer composites that find application as sheet‐molding compounds (SMCs), the fiber aspect ratio l/d and the size ratio R (the ratio of the diameter of the spherical filler and the diameter of the fiber) are important parameters. A study of various composite formulations of different combinations of l/d and R has been made to examine the correlation between the packing efficiency of these fibers and fillers in air, and the properties of resulting composites. Samples containing a total of 32 wt% fibers and spherical fillers (in 1:3 proportion) were tested. The tensile modulus was seen to represent behavior similar to packing efficiency. Sources of experimental errors are discussed.
Self‐adhesive honeycomb prepreg systems for secondary structural applications
Authors: Hayes Brian S. , Seferis James C. , Edwards Richard R.
Published: April 2004

Porosity in cured honeycomb parts was investigated using model prepreg systems and compared with a commercial solvent produced prepreg. Woven glass fabric was used as the reinforcement in both of the systems. Three main solvents were identified in the commercial prepreg. These solvents were found to cause porosity or reduce thermal properties in model solvent prepreg based laminates when used either separately or in combination. Lowering the solvent content reduced the porosity in the prepreg but was limited by resin staging. The high level of porosity, resulting from solvents, found in these commercial prepreg systems motivated the investigation of the feasibility of changing the method of impregnation from solvent to hot‐melt. Hot‐melt model prepreg produced essentially void‐free laminates as well as honeycomb parts. Model prepreg produced by hot‐melt impregnation was found to be more robust, providing the capability of changing the degree of resin impregnation in the fiber bed. A low level of impregnation resulted in the best fillets to the honeycomb core, while still producing essentially void free parts. The use of both solid and liquid carboxyl‐functional elastomers was incorporated in the epoxy based resin to provide flow control and self‐adhesive characteristics. Mechanical properties of both the model hot‐melt and commercial prepreg based honeycomb structures and laminates were compared. The model hot‐melt prepreg was found to have better cured properties along with the necessary prepreg characteristics providing an optimized self‐adhesive controlled flow prepreg system.
Numerical simulation of unsaturated flow in woven fiber preforms during the resin transfer molding process
Authors: Pillai K. M. , Advani S. G.
Published: April 2004

In this paper, the unsaturated flow encountered in the woven or stitched fiber mats used in RTM is simulated using an adaptation of the Finite Element Method/Control Volume (FEM/CV) technique. The movement of resin through such fiber mats is modeled as flow through dual scale porous media and the mass balance in such media creates a sink term in the equation of continuity of the macroscopic flows. Combining this equation with Darcy's law leads to a non‐homogeneous non‐linear elliptic partial differential equation for pressure that is solved iteratively. First the simulation is used to study simple flows encountered during the characterization of preforms, such as the constant injection pressure 1‐D flow and the constant flow rate radial injection flow. Previously observed experimental results of relatively flatter pressure histories for the latter type of flows in wove fiber mats are replicated, both numerically and analytically, by the pressure equation with the sink term. A quantity called pore volume ratio is shown to play an important role in such flows. Finally, the unsaturated flow in a typical RTM mold, packed with woven fiber mats, is simulated numerically, and inlet pressures, fill times, and mat saturation are studied.
Dynamic rheological properties of binary PP/PA and ternary PP/PA/GF blends
Authors: Benderly D. , Siegmann A. , Narkis M.
Published: April 2004

The dynamic rheological behavior was investigated for binary polypropylene (PP) ‐ polyamide‐6 (PA‐6) and ternary PP‐PA‐6‐glass fiber (GF) blends. The observed trends are related to the blend morphology and the partitioning of the GF within the three component blends. The dynamic and shear viscosity results show a good overlap for the PP homopolymer, within the shear rates studied. The addition of PA‐6 and/or glass fibers to the PP causes significant deviations between the two rheological behaviors. This reflects the fibrillation of PA‐6 and the orientation of glass fibers during shear rheometry, which reduce the blends' shear viscosity. The effect of PA‐6 content on dynamic viscosity is less significant than for shear viscosity, owing to the absence of morphological structuring. The addition of PA‐6 to PP increased the principal relaxation time of the binary blends. The addition of GF to these binary blends gave a further increase in the principal relaxation time.
Static and fatigue behavior of adhesive joints in SMC‐SMC composites
Authors: Mazumdar S. K. , Mallick P. K.
Published: April 2004

This paper discusses the static and fatigue behavior of adhesively bonded single lap joints in SMC‐SMC composites. Effects of lap length and adhesive thickness on the static and fatigue strength of SMC‐SMC adhesive joints are studied. Effects of SMC surface preparation and test speed on the joint performance are evaluated. Finally, the effect of water exposure on the joint durability is also investigated. Results show that the static behavior of adhesive joints in SMC‐SMC composites is significantly influenced by the lap length and adhesive thickness. With an increase in lap length from 12.7 mm to 38.1 mm, the joint failure load increases by 37%. The joint failure load also increases with the adhesive thickness, but it reaches a maximum at an adhesive thickness of 0.33 mm and then decreases. However, lap length and adhesive thickness have negligible effect on the ratio of fatigue strength to static strength. The fatigue strength at 106 cycles is approximately 50% to 54% of the static strength for various adhesive thicknesses and lap lengths investigated in this study. Adhesive failure, fiber tear or combination of these two failure modes are observed during both static and fatigue tests.
Short fiber reinforced thermoplastic polyurethane elastomer composites
Authors: Corrêa R. A. , Nunes R. C. R. , Filho W. Z. Franco
Published: April 2004

Mechanical properties of thermoplastic polyurethane elastomer (TPE) reinforced with short fibers were studied. Two types of fibers were used as the discontinuous phase: an aromatic polyamide (Twaron, diameter: 12 μm) and carbon fiber (FCI 140/90‐R33—diameter: 8–10 μm). Because of processing limitations, the maximum length of both fibers, after incorporation in the composites, was reduced to 3 mm. The TPE (continuous phase) was a polyol‐polyester type [Elastollan—glass transition of short fiber segments: −42°C (1)]. Both types of composites had fiber concentration of 10, 20, and 30 phr. Component interaction is discussed, as well as the application of a third power polynomial to establish a relationship between the amount of fiber added and stress at break data. Stress‐strength, tear resistance, shore A and B hardness, abrasion resistance, and compression set tests were performed. Composites reinforced with aromatic polyamides showed higher values in most of the tests, except in the abrasion resistance test, in which a smaller material loss was observed.
Impact response of 3‐D woven composites reinforced by consolidated rods
Authors: Kuo Wen‐Shyong , Lee Lin‐Chyuan
Published: April 2004

This paper examines the impact response of three‐dimensionally woven fabric composites using consolidated rods in the axial direction. The material processing includes fabrication of the 1‐mm rods by pultrusion, formation of the fabrics, and impregnation of the resin. A weaving setup incorporating the rods in the axial direction has been developed. Using the setup, three types of orthogonal fabrics with varying the tow sizes have been made. The microgeometry of yarns and the distribution of fibers were examined. Impact tests were carried out using an instrumented drop‐weight impactor. Matrix cracks and rod debonding are the principal damage modes on the top and bottom surfaces. However, the crack configurations on these surfaces are very different. Formation of these damage modes and the associated influencing factors have been discussed. One feature not found in conventional composites is rod pull‐in, which is a result of rod debonding and sliding. The pull‐in creates a zone of holes on the specimen edge, revealing how the stress wave propagates from the impact to the non‐impact sides. It is found that the pull‐in is more pronounced near the non‐impact side. The load‐time and energy‐time histories have been examined and related to how the specimens respond to the impact.
Compaction of textile reinforcements for composites manufacturing. I: Review of experimental results
Authors: Robitaille François , Gauvin Raymond
Published: April 2004

As new developments are brought to the group of manufacturing processes for composite parts known as liquid composites molding (LCM), the compaction behavior of the textile reinforcements is increasingly seen as an important parameter of the definition of these processes. The evolution of the permeability tensor of the reinforcements with time, the general kinetics of the manufacturing operations, and the modelization of these processes depend on a large extent on the compaction behavior of the reinforcements used, especially in flexible‐wall RTM and autoclave molding. Also, more research efforts are devoted toward the development of a complete analytical model of the properties of heterogeneous textile reinforcements. In this paper the published experimental data related to the compaction and relaxation of random mats and woven reinforcements are gathered. Observed parameters are defined, which allow numerical comparisons of the experimental curves to be made, as well as the identification of general trends seen with most tested reinforcements. The effects of various processing parameters are identified, and relations to published analytical models of the mechanical properties of fibrous assemblies are discussed.
Polypropylene matrix composites reinforced with pre‐stressed glass fibers
Authors: Zhao Jianhong , Cameron John
Published: April 2004

Thermoplastic matrix composites have recently emerged as promising engineering materials because of their desirable properties such as high service temperatures, high impact resistance, and processing advantages. However, residual stresses in composites introduced during fabrication are cited as one of the most significant problems in the processing of composites. In some instances these stresses have been shown to significantly degrade the strength of the material, resulting in matrix cracking, debonding, reduced fracture toughness, and delamination. In this work, studies have been carried out on glass fiber reinforced polypropylene composites formed by compression molding process from co‐mingled fabrics. The fibers were pre‐stressed during the process to produce high performance composite products with low residual microstresses, which are harmful to the properties of the composite. Mechanical tests showed that pre‐stress can increase the tensile, flexural and interlaminar shear properties of the composites, and there exists an optimum pre‐stress level to gain best properties for each external loading condition.
Ultrasonic evaluation of graphite/epoxy composites with different curing conditions
Authors: Chen J.‐Y. , Hoa S. V. , Jen C.‐K. , Viens M. , Monchalin J.‐P.
Published: April 2004

Ultrasonic evaluation of AS4/3501‐6 graphite/epoxy composites and Hercules 3501‐6 epoxies with different curing conditions has been carried out. A differential scanning calorimeter and a dynamic mechanical analyzer were used to characterize the cure status of these materials. The anisotropic elastic moduli, through‐thickness longitudinal wave dispersion and attenuation were measured by different ultrasonic techniques. Effects of curing conditions on the mechanical properties of the composites and corresponding epoxies were discussed.
Life prediction for composite laminates submitted to service loading spectra
Authors: Aboussaleh M. , Boukhili R.
Published: April 2004

This paper deals with the prediction of the fatigue life of composite laminates subjected to service loading spectra. Assuming that the spectrum loading is a Gaussian stationary and ergodic process, a model that predicts the fatigue life is proposed. This model requires the results of the constant amplitude fatigue test and is based on a combination of the Palmgreen‐Miner damage rule and the peak‐counting method to define and count the cycles. To compare the model predictions to experimental results, random loading was simulated in three different manners: block programming, random sequence block programming and individual cycles method. It is shown that the three simulation methods agree reasonably well with the experimental results; however, the best agreement is obtained with the individual cycle simulation method. All the constant amplitude and random fatigue tests were performed in three point bending on a digitally controlled servohydraulic fatigue machine that permits random simulation. The material used is a quasi‐isotropic graphite epoxy composite [± 45/0/90]3s.
Specimen design, manufacturing and testing procedures for flat carbon fiber reinforced plastic laminates under biaxial loading
Authors: Youssef Y. , Labonté S. , Roy C. , Lefebvre D.
Published: April 2004

The optimization of a specimen design allowing the investigation of the biaxial strength of composite laminates over the full range of failure strain was the primary objective of this work. Multiaxial strength criteria are often found unreliable mainly as a result of the inherent complexity of biaxial tests and, in many cases, as a result of inefficient specimen designs. As a result of a development program combining numerical simulations and experimental measurements, a flat cruciform‐shaped specimen has been developed for carbon fiber reinforced plastic (CFRP) laminates. The design fulfills the basic criteria for such a specimen, namely allowing for a uniform biaxial stress/strain state to exist in the gauge area and for testing the virgin material up to failure in both the tension‐tension and tension‐compression quadrants of the strain/stress space. The fabrication of the specimen is described and a three‐step testing procedure for generating biaxial strength data is proposed. Typical results obtained from specimens of the proposed configuration tested in accordance with this procedure are presented. Results compare well with those obtained from tubular specimens, thus confirming the effectiveness of the proposed design. Experimental data obtained for the AS4/3501‐6 carbon/epoxy composite system are finally compared against strength predictions of recognized failure theories.
Interfaces in polyolefin/cellulosic fiber composites: Chemical coupling, morphology, correlation with adhesion and aging in moisture
Authors: Gauthier R. , Joly C. , Coupas A. C. , Gauthier H. , Escoubes M.
Published: April 2004

This paper details the characteristics of pure cellulose and wood fibers when associated with thermoplastic matrices for composite applications. Chemical modification of the cellulose is performed to allow a good compatibilization, and the most efficient compatibilizing agents must possess: (i) a function highly reactive with the OH groups of the cellulose and (ii) a non‐polar chain with preferably a polymeric structure. Polypropylenes grafted with maleic anhydride are thus efficient agents. Smaller compatibilizing agents, especially if reacted with cellulose in swelling media, react with the bulk of the fiber and lead to dimensional stability. All treatments, even when performed with low degrees of grafting or small alkyl chains, significantly modify the hydrophilicity of the cellulose surface and play a role in a better wettability of the fiber by the matrix leading to improved adherence. The global mechanical properties are then improved, but the effect is preferably studied at the scale of a single filament composite. The morphology of the matrix in the vicinity of the non‐treated fiber shows that, in some cases, the fiber acts as a nucleating agent involving the formation of a transcrystalline phase. Aging in moisture is generally detrimental to the mechanical properties. This phenomenon is limited by the chemical treatment performed on the fibers.
Thermoformed glass fiber reinforced polypropylene: Microstructure, mechanical properties and residual stresses
Authors: Youssef Y. , Denault J.
Published: April 2004

The objective of this work was to characterize the microstructure, mechanical properties and residual stresses in glass fiber reinforced polypropylene (PP) composites with respect to the thermoforming parameters and as a function of the fiber‐matrix interface quality. First, differential scanning calorimetry (DSC) was used to investigate the crystallization behavior of the PP matrix. Second, short beam shear tests and tensile tests in the ±45° directions have been conducted to characterize respectively the interfacial strength and the matrix properties in the composites. Finally, residual stresses were measured via the curvatures of unsymmetric cross‐plied laminates. The cooling rate was found to be a critical parameter of the molding process since the matrix crystallization temperature, the interfacial strength as well as the residual stresses showed large variations with various cooling rates. At slow cooling, the crystallization process initiates at higher temperatures and covers longer time periods resulting in more spherulitical matrix structures. In this case, the composites becomes stiffer but also fragile indicating a decrease in the stress transfer efficiency at the interface level. This effect was also observed in the improved interface system, suggesting that the fiber‐matrix interaction operates through the amorphous phase surrounding the fibers. The fiber‐matrix interface improvement was accompanied by an increase in residual stresses, possibly due to the inhibition of some stress relief mechanism.
Simulations of cyclic, transient variations of mold temperatures in the SMC compression molding process
Authors: Hu Sheng Yan , Chen Shia Chung , Twu Jun‐Tien , Lee L. James
Published: April 2004

The dual reciprocity boundary element technique is used to simulate the cyclic SMC compression molding process, taking into account the heat transfer within the whole mold. The cyclic, transient variations in mold temperatures at different mold locations are illustrated through the analysis of a plate mold. The transient temperature fluctuation near the mold cavity surface is much larger than that away from it. It was also found that owing to the high heating fluid temperature (compared with the ambient air temperature), the heat transfer at the mold exterior surface shows a significant effect on the mold temperature distribution, especially when the mold is a small or medium size. The present method provides a complete and more accurate description of the mold temperature variation during the whole cycle history by including the mold as the analysis domain, meanwhile minimizing the computation time. Other analysis methods, including the constant mold wall temperature approach, the hybrid shape‐factor/finite element method, as well as the cycle‐averaged boundary element technique imposed with 1‐D transient analysis, basically overestimate mold wall temperatures and the associated charge conversion rate.
Shrinkage anisotropy in fiber reinforced injection molded products
Authors: Jansen K. M. B. , Van Dijk D. J. , Freriksen M. J. A.
Published: April 2004

This paper includes a systematic study of the effect of fiber concentration and molding conditions on fiber orientation and shrinkage in injection molded composites. Closed‐form expressions were derived to relate shrinkage and internal stresses to the molding pressure and fiber orientation. The shrinkage predictions were seen to agree well with experimentally measured shrinkages.
Modeling of injected pultrusion processes: A numerical approach
Authors: Kommu S. , Khomami B. , Kardos J. L.
Published: April 2004

Injected pultrusion (IP) is an attractive process for high volume, high performance, and low cost manufacture of continuous fiber reinforced polymer matrix composites. In this work we focus our attention on development of a computer simulation model for the IP process. First, the governing equations for conservation of mass, momentum, and energy are developed using a local volume averaging approach. In turn, a computer simulation model of the IP process is developed using finite element/control volume (FE/CV) and finite difference techniques. Specifically, the equation of continuity and conservation of momentum are solved in 2‐D using a Galerkin FE/CV technique. The energy and chemical species balance equations are solved in 3‐D, where streamline upwind Petrov‐Galerkin (SUPG) or streamline upwind (SU) FE/CV are used to discretize the equations in two dimensions while finite differences have been used in the third dimension. The chemical species balance equation is solved in the Lagrangian frame of reference using finite differences. Different numerical formulations (Galerkin, Lagrangian, SU, and SUPG) are used to solve a number of benchmark problems to determine the best numerical formulation. It is shown that for coarse discretization, Streamline Upwind methods perform consistently better than the other methods. However, for refined meshes, the Lagrangian method produces the best solution for a given CPU time. Also, using the simulation model, the effect of fiber pull speed, reinforcement anistropy, and taper of the die on the quality of the product is studied. It is shown that the simulation model can be effectively used to design the die geometry as well as to optimize the operating conditions for a given product.