bluuebunny/crossref_metadata_2025_split huggingface dataset:
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

AbstractA 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

AbstractBlends 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

AbstractThis 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

AbstractMaleic 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

AbstractAn 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

AbstractFor 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

AbstractPorosity 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

AbstractIn 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

AbstractThe 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

AbstractThis 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

AbstractMechanical 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

AbstractThis 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

AbstractAs 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

AbstractThermoplastic 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

AbstractUltrasonic 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

AbstractThis 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

AbstractThe 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

AbstractThis 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

AbstractThe 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.