bluuebunny/crossref_metadata_2025 huggingface dataset:
Characterization of the fracture toughness property (G1c) of composite laminates using the double cantilever beam specimen
Authors: Lee S. , Gaudert P. C. , Dainty R. C. , Scott R. F.
Published: December 2004

The results of a study on the interlaminar fracture toughness properties (G1c) of four unidirectional carbon fiber epoxy materials are presented. The selected materials included Narmco 5245C, Hexcel F584, and American Cyanamid 1806 resins reinforced with Hercules IM6 fibers and for a baseline material Narmco 5208 reinforced with T300 fibers. TheG1cvalues determined on Double Cantilever Beam specimens were found to range from 93 to 370 J/m2. The higher values may partly result from fiber bridging during fracture. This paper discusses specimen configuration, test procedure, and the Scanning Electron Microscope results.
Tensile properties of injection molded long fiber thermoplastic composites
Authors: Denault J. , Vu‐Khanh T. , Foster B.
Published: December 2004

This paper deals with the mechanical performances of a new class of injection molded long fiber composites based on PP and PBT matrices. Effects of material parameters such as fiber concentration, breakage, orientation, and matrix composition are analyzed. The critical fiber length, l, of the PP long fiber composite, evaluated from the pull‐out length of the tensile fracture surface, was found to be much higher than those previously reported. Tensile strength calculated from the measured ll and fiber length distribution in the molded samples was found to be in agreement with the measured values. From this work it is concluded that higher mechanical performances of the long fiber reinforced thermoplastics will be attained by the injection molding process to further reduce fiber breakage.
The prediction of flow and orientation behavior of short fiber reinforced melts in simple flow systems
Authors: Kamal M. R. , Mutel A. T.
Published: December 2004

A model for the prediction of changes in fiber orientation in simple flows of fiber suspensions is proposed. Fiber interactions are modeled as randomizing forces over the rotation of fibers in closed orbits in simple shear. The resulting Fokker‐Planck type convection‐diffusion equation in orientation space is solved using a finite difference technique. The solution technique permits the use of periodic boundary condition for the convection‐diffusion equation and different initial conditions for the orientation distribution. The model predictions for simple shear flow demonstrate the interaction between the structural changes and the bulk rheological properties. The effect of non‐Newtonian fluid properties on the orientation distribution was also incorporated at the slow flow limit. Structural changes are assumed to be irreversible. The irreversibility is incorporated through an orientation distribution dependent diffusion coefficient.
Injection molding of glass flake reinforced polypropylene: Flake orientation and stiffness
Authors: Bouti A. , Vu‐Khanh T. , Fisa B.
Published: December 2004

Three samples of silane treated glass flakes of different diameters were dry blended with polypropylene powder and injection molded into rectangular (32 mm × 127 mm) plaques using an edge‐gated mold cavity. The thicknesses of plaques were 1.6 mm, 3.2 mm, and 6.4 mm. Tensile and flexural specimens were machined from these plaques. Average flake diameters and thicknesses were determined. It was found that aspect ratios in finished moldings are quite similar, despite the initial (before processing) differences. The flake orientation varies across the thickness; it is parallel to the plane of the molding in the outer skin layer, changing gradually to perpendicular in the core. The relative thickness of the skin where the flake orientation is parallel increases with the decreasing thickness and flake concentration. It represents about 85% of the overall thickness in 1.6 mm moldings, between 70% and 85% when the plaque thickness is 3.2 mm, and between 50% and 60% in the thickest (6.4 mm) molding. Elastic properties can be interpreted using the modified rule of mixtures. Tensile moduli depends strongly on the flake orientation in the core and on the flake concentration, whereas the influence of the core on flexural moduli is insignificant. The flake orientation coefficients determined from micrographs are in good agreement with those calcuated from mechanical test. The coefficient accounting for finite flake aspect ratio, ηL was found to be about 0.3.
Crystallization of poly(aryl‐ether‐ether‐ketone): Effect of thermal history of the melt on crystallization kinetics
Authors: Deslandes Y. , Day M. , Sabir N.‐F. , Suprunchuk T.
Published: December 2004

Differential Scanning Calorimetry (DSC) and optical microscopy were used to investigate the effect of the thermal history of the melt on the crystallization of a commercial sample of poly(aryl‐ether‐ether‐ketone) (PEEK). Heating a film of PEEK at a temperature above the melt temperature for various periods of time changes the nucleation and crystal growth rate upon cooling the sample. Destruction of existing nuclei, formation of new nuclei, chain branching, cross linking, and chemical degradation of the macromolecular chains are all believed to take place at different times and to different extents during the thermal melt processing of the polymer. This study suggests that the thermal history of the melt plays an important role in the crystallization of PEEK samples.
Processing and characterization of new bismaleimide matrix advanced composites
Authors: Viot J.‐F. , Giraud Y. , Camberlin Y. , Lopez P. , Meissonnier J.
Published: December 2004

Bismaleimide polymers offer a thermostability that fills in the gap between epoxies and high temperature polyimides. Bismaleimides of the new generation overcome traditional problems of brittleness and difficult processing. The property transpositions from these tougher, hot‐melt processable resins to the corresponding carbond fiber composites are detailed, focusing on crack propagation behavior. Particularly, the mode I critical strain energy release rate (GIC) is compared to the mode I interlaminarGICof the corresponding composites (both unidirectional and woven laminates). Parameters of the transposition are tried to be identified.
Simultaneous measurements of permeability and capillary pressure of thermosetting matrices in woven fabric reinforcements
Authors: Ahn K. J. , Seferis J. C. , Berg J. C.
Published: December 2004

A simple apparatus was designed and constructed capable of measuring the unsteady‐state permeability and the capillary pressure simultaneously in a simulated composite impregnation experiment. It was found that the Kozeny‐Carman equation used to describe the permeability of composites during impregnation adequately described experimental results for woven fabric preform up to porosity values of 0.5. Above this value, observed deviations were attributed to interfacial effects between adjacent woven fabric layers. For woven fabric preforms made of T‐300 carbon fibers, a maximum capillary pressure of 3.7 × 104Pa (=5.4 psi) was observed at low porosity values. Thus, the capillary pressure may compete with other pressure sources in low pressure processes, such as the prepregging process. The woven fabric preform used in this study is observed to have a permeability similar to a unidirectional fibrous preform along the transverse direction. Furthermore, an existing modeling methodology capable of predicting permeability and capillary pressure through different preforms was found to be valid for fibrous preforms of complex orientation.
Permeability characteristics of multilayer fiber reinforcements. Part I: Experimental observations
Authors: Adams Kurt L. , Rebenfeld Ludwig
Published: December 2004

The fluid permeability characteristics of homogeneous and heterogeneous multilayer fabric assemblies were determined by a radial in‐plane flow technique. The permeabilities and flow anisotropies of multilayer assemblies generally differ from those of the constituent layers. In homogeneous assemblies, the creation of interlaminar pores can increase the effective in‐plane permeability. In heterogeneous assemblies, the effective in‐plane permeabilities and anisotropies are governed by the high permeability layers or directions. A transverse flow mechanism contributes to filling the low permeability layers and keeping the fluid front macroscopically uniform.
Ballistic response of polymer composites
Authors: Zee R. H. , Wang C. J. , Mount A. , Jang B. Z. , Hsieh C. Y.
Published: December 2004

A new microvelocity sensor unit was developed to measure the instantaneous velocity of a projectile during the penetration process. The concept of this device is based on the induced current generated in a coil resulting from the passage of a magnet. A special digital circuit was designed to yield a spatial resolution of better than 2.5 mm by elimiating the problem of signal overlap. The time delays obtained from these signals were used to determine the slowing down or energy loss of a high velocity projectile. A light gas gun was used to propel aluminum projectiles to velocities up to 320 m/s. Energy loss of these high velocity projectiles in composites reinforced with polyethylene, polyester, and graphite fabrics was investigated. Two distinct energy loss mechanisms were detected, one due to the actual fracture process and the other to the generation of frictional heat. Extensive delamination was observed in the more ductile PE and PET composites, but not in graphite. Low velocity instrumented drop‐tower impact tests were also conducted, using identical specimens and similar impact geometries.
A study of damage accumulation in unidirectional glass reinforced composites via acoustic emission monitoring
Authors: Kander R. G.
Published: December 2004

Damage accumulation in continuous unidirectional glass reinforced composites was studied by acoustic emission (AE) monitoring during three‐point‐bend loading. Results are presented for four composites monitored during quasi‐static break loading, and one composite also monitored during cyclic fatigue and static creep loading. AE response was correlated with the mechanical (stress‐strain) response and with visual observation of damage events to study the details of the damage accumulation process. Results show that the failure process is characterized by the sequential occurrence of three distinct damage mechanisms. Specifically, the failure process initiated with cohesive matrix damage, propagated with interfacial debonding, and ended with fiber breakage very near catastrophic failure. The same sequential damage process occurred in all four composites and all three test procedures examined. Results also demonstrate that AE analysis, in combination with mechanical testing and microscopic observation, is a valuable tool in understanding damage accumulation in composites.
Application of the J‐integral concept for the description of toughness properties of fiber reinforced polyethylene composites
Authors: Grellmann Wolfgang , Seidler Sabine , Lauke Bernd
Published: December 2004

For the determination of toughness properties of HDPE/glass fiber and HDPE/cotton fiber composites, an instrumented Charpy impact test has been used. The interpretation of impact load‐deflection curves has been carried out with several concepts of fracture mechanics. Here the limits of linear elastic fracture mechanic (LEFM) have been shown. The change of toughness properties with increasing fiber volume can be described for short fiber reinforced composites with the help of the J‐integral concept in a suitable mode. An application of the conventional Charpy impact test will result in an overestimation of material behavior because of the energy of crack propagation. With the help of a micromechanical model to describe failure processes, taking account of energy dissipative processes, it is possible to calculate fracture mechanical material parameters. Because of the peculiarities of deformation and fracture behavior, the application of elastic‐plastic fracture mechanic (EPFM)‐concepts for fiber reinforced polymers is required.
The failure morphology of PEEK/carbon fiber ±45° angle‐ply laminates
Authors: Burnett P. J. , Cervenka A.
Published: December 2004

The ultimate strength of certain thermoplastic matrix laminates is observed to be strongly dependent upon the stacking sequence. Such effects are thought to be due to the development and action of through‐thickness stresses at the edges of laminates. However, the action of such stresses is not normally considered in Classical Laminate Theory. This paper describes experimental studies of the development of damage in, and subsequent failure of, a family of laminates that exhibit “through‐thickness” effects. Important differences between the mode of failure and development of damage prior to failure are identified, and these observations correlated with other workers' predictions concerning the presence and actions of edge stresses.
Thermally stimulated current in glass‐laminated unsaturated polyester resins
Authors: Jelčič Ž. , Ranogajec F. , Babić L. , Ivanović Z.
Published: December 2004

Experimental results are reported on the electrical properties of glass‐laminated unsaturated polyester (UP) resins. Measurements of the poling current as a function of temperature reveal two different activated processes. Above 50°C the activation energy is 160 kJ/mol and has been associated with ionic condition, possibly by protons, while at lower temperatures (below −70°C) the activation energy is very low (less than 40 kJ/mol) and is associated with dipole relaxation. It is concluded that the laminated UP resin undergoes a phase transformation between low and high temperatures, which gives rise to a completely different electrical response. This phase transformation can be associated with the glass transition of UP resin phase. In view of the low activation energy, giving rise to a polarization peak, it is concluded that the low temperature range (glassy state) favors strictly localized motions of charges—most likely electrons. At higher temperatures, the behavior corresponds to d.c. conductivity and is associated with extended motions of charge carriers with limitations at contacts and at internal barriers. According to the air gap measurements, the pronounced dip found in the temperature dependence of the poling current (in the range from 20 to −30°C) may be due to separation of conduction and dipole relaxation current. Thermally stimulated depolarization (TSD) current measurements reveal the presence of high internal fields due to space charges accumulated at the phase boundaries of glass fibers.
Flow simulation in molds with preplaced fiber mats
Authors: Young W. B. , Fong K. Han. L. H. , Lee L. James
Published: December 2004

The primary goal of this study was to develop 2‐D and 3‐D computer simulation schemes for the mold filling processes of structural reaction injection molding (SRIM) and resin transfer molding (RTM) under isothermal conditions. The developed computer code was able to simulate the mold filling in molds with complicated geometry, Experiments were also carried out based on flow vitalizations. Experimental results were compared with the numerical simulations.
The consolidation of commingled thermoplastic fabrics
Authors: Van West B. P. , Pipes R. Byron , Advani S. G.
Published: December 2004

Commingled fabrics composed of yarns containing both the reinforcement and the matrix in fiber form are an innovative preform for thermoplastic composite materials. The material is consolidated into a rigid structure by the application of heat and pressure. A mathematical model of the consolidation process for commingled fabrics has been developed. The model predicts the variation of laminate thickness, fiber volume fraction, and void content during the consolidation process as well as the time required to reach full consolidation. Materials composed of initially separate, commingled or cowoven fiber bundles are considered. The influence of fiber velocity induced by compaction on the flow of matrix is accounted for. An equivalence factor has been derived so that a one‐dimensional flow analysis may be used to model the impregnation of elliptical bundles of varying aspect ratio. This permits an analytic solution to the governing equation for fiber bundle impregnation. The model was utilized to examine the influence of various material and processing parameters on consolidation behavior.
Elastic moduli and thermal conductivity of injection‐molded short‐fiber–reinforced thermoplastics
Authors: Choy C. L. , Leung W. P. , Kowk K. W. , Lau Felix P.
Published: December 2004

The nine independent stiffness constants of injection‐molded tensile bars of poly(phenylene sulfide) reinforced with 30 and 40% by weight of carbon or glass fibers have been measured by ultrasonic techniques. The thermal conductivities along the three principal directions of these thermoplastic composites have also been determined by the laser‐flash radiometry method. The elastic moduli (tensile and shear) and thermal conductivity increase with increasing fiber volume fraction,vf, with the tensile modulus and thermal conductivity along the mold flow direction showing the greatest change. For a composite, containing 40 weight % of carbon fibers, the Young's modulus and thermal conductivity along this direction exceed those of the polymer matrix by a factor of 8. Using the known values ofvfand the observed aspect ratio and orientation factor of the fibers, the elastic moduli and thermal conductivity have been calculated on the basis of the laminate theory. The agreement between theoretical predictions and experimental data is better than 10% on the average.
Effect of fuming nitric acid surface treatment of ultra‐high modulus polyethylene fibers on the mechanical properties of their composites
Authors: Taboudoucht A. , Opalko R. , Ishida H.
Published: December 2004

The effect of hot fuming nitric acid (FNA) treatment on the adhesion of ultra‐high modulus polyethylene fabrics to an epoxy resin has been investigated. Mechanical and molecular characterization of the interface has been attempted. Fourier transform infrared diffuse transmittance spectroscopy has been used to monitor the chemical changes introduced by the FNA treatment as well as the nature of the interface between the fibers and the epoxy resin on the molecular level. Scanning electron microscopy has been used to examine the morphological consequences of the FNA treatment. Flexural and interlaminar shear properties of the composites have been measured as a function of the extent of surface treatment. Esterification of the FNA treated polyethylene fibers is used to examine the role of surface functionality to the mechanical performance.
Material response of a semicrystalline thermoplastic polymer and composite in relation to process cooling history
Authors: Lawrence Wesley E. , Seferis James C. , Gillespie John W.
Published: December 2004

A model capable of predicting the process‐induced macroscopic in‐plane material response of semicrystalline thermoplastic matrices and their composites was developed. Thi sinvestigation focused on the material response of a single layer or ply of neat PEEK matrix and its carbon fiber composite (APC‐2) when subjected to various processing histories. Specifically, the response of the material moduli and processing strains as a function of temperature and the degree of crystallinity were studied. The kinetic‐viscoelastic response of the matrix was determined from a modified form of the Standard Linear Solid model. A constitutive relation was proposed to quantify resign shrinkage as a function of thermal history, which incorporated crystallization. For a specific process history, the effective composite mechanical properties were determined from micromechanics models. Both neat and composite processing strains were evaluated to show the effect of fibers on the matrix dominated response (90° direction). In addition, comparisons of model moduli predictions with experimental measurements were performed. This study demonstrated that an increase in the degree of crystallinity results in an asymmetric shift of the modulus in the glass transition region to higher temperatures. Also, strains due to crystallization were predicted to be much smaller in comparison to the strains resulting from thermal contraction of the PEEK matrix.
Compression molding simulation of chopped fiber reinforced polymeric composites in plate‐rib type geometry
Authors: Kim Junil , Shiau Y. C. , Lee L. James , Im Y. T.
Published: December 2004

A study on anisotropic material flow of polymeric composites in compression molding was conducted. Flow resistance and material anisotropy were measured by compression and tension tests to quantify the inhomogeneity of chopped fiber reinforced polymeric composites. The material was assumed to obey Hill's anisotropic yield criterion with its associated flow rule. An anisotropic finite element formulation was developed to simulate the material flow under various conditions. This two‐dimensional model was applied to plane strain compression in a mold with plate‐rib type geometry to substantiate the effect of fiber induced anisotropy. The predictions were compared with experimental results.
Mechanical and rheological properties of reinforced polyethylene
Authors: Malik T. M. , Farooqi M. I. , Vachet C.
Published: December 2004

The rheological and mechanical properties of a high density polyethylene (HDPE) filled with surface‐treated mica flakes are reported. Young's modulus decreases with different treatments, whereas break elongation and maximum strength slightly increase. Young's modulus increases with the addi ion of mica flakes, but the decrease in elongation is also quite significant. For 20% mica composites, hardly any change was observed in the properties. The high shear viscosity does not show any significant effect as a result of the surface treatment. Viscosity of composites increases with silane treatment and decreases with titanate treatment. It is suggested that the coupling agent, depending on its chemical structure and nature of the filler, may act as an adhesion promoter or as a lubricating agent.
Analytical model for prediction of the damping loss factor of composite materials
Authors: Crane Roger M. , Gillespie John W.
Published: December 2004

Numerous approaches have been undertaken to determine the damping of composites. These approaches can be grouped into micromechanical, macromechanical, and structural approaches. This paper describes a macromechanical approach that has been experimentally validated using various S‐2 glass/3501‐6 laminates. Our approach is an extension of the elastic‐viscoelastic approach, which accounts for the frequency dependence of the loss factor. The experimentally determined material loss factor for the glass/epoxy determined in a previous investigation is used as input to the model. The material complex moduli are then determined and used as input to the model. The loss factor of a quasi‐isotropic configuration is analytically determined in the frequency range of the experimental data. The loss factors for these beams are then experimentally determined using a cantilever beam configuration set into vibration with an impulse excitation. The loss factor at various frequencies are determined using the half power band width technique. The analytical values are within 15% of the experimental values in the frequency range of test. In addition, a parametric study is given on the effect of fiber orientation on loss factor. The analytically determined loss factor using the proposed model shows that inconsistencies documented in the literature on the fiber orientation at which a maximum in loss factor occurs can be resolved by incorporating the frequency dependence of the composite loss factor.
Surface modification of spectra™‐900 polyethylene fibers using RF‐plasma
Authors: Rostami Hossein , Iskandarani Bassel , Kamel Ihab
Published: December 2004

RF‐plasma polymerization and bonding of allylamine onto ultrahigh molecular weight polyethylene (UHMWPE) “Spectra™‐900” is described using an inductively coupled plasma reactor. This process was found to enhance the interfacial strength between the fibers (Spectra‐900) and room‐temperature‐cured epoxy matrix up to fivefold. Fibers covalently coated with allylamine plasma showed no loss in tensile strength, while argon gas plasma pretreatment of the same fibers caused up to 10% reduction in tensile strength depending on the energy and duration of the treatment. Optimum treatment was attained through a short argon plasma etching (15 s), followed by allylamine polymerization and coating for 3 min. The coating process was found to protect the fiber surface from etching by plasma ion bombardment. A loss of 19% of the original diameter was found during the 15 s precoating etching with argon plasma, indicating the sensitivity of the fiber structure to plasma etching.
Whiskers and short fiber technology
Authors: Milewski John V.
Published: December 2004

This paper presents the technology of whiskers and short fibers for use in polymer substances. It starts with a definition and examples of what a whisker is and how it differs from other short fibers such as micro fibers, mineral fibers, chopped fibers, and milled fibers. Then this paper discusses the problems in working with whiskers and short fibers and gives solutions to these problems. Next, various ways of improving the efficiency of short fiber reinforcements is given. This is done by reviewing details of the theory of short fiber reinforcements and how the use of packing theory helps in making a better short fiber composite. Finally, suggestions are given for designing an idealized molding compound using whiskers and short fibers in harmony with good packing theories.
Modulus prediction of a cross‐ply fiber reinforced fabric composite with voids
Authors: Farouk A. , Langrana N. A. , Weng G. J.
Published: December 2004

Voids or bubbles in polymer composites have a detrimental effect on the properties of the material. Such voids are found in PMR 15/graphite fiber (fabric type) composites. The matrix, PMR 15, is formed in‐situ during the molding process and undergoes two major stages of reactions, viz., imidization and crosslinking. Volatiles are formed as by‐products of these reactions and may remain trapped in the matrix to form voids or bubbles. Photomicrographs of composite cross sections suggested the classification of voids as two different phases in two different directions, each aligned with the fibers, resulting in a five phase model. The composites were tested in three‐point bending tests to obtain the flexural modulus. By combining Weng's inclusion approach (1) and Ishikawa and Chou's crimp method (2), an analytical model has been developed to predict the elastic moduli of such a multiphase composite material. Thus, the voids have been treated as inclusions in an enclosing matrix, which in turn is reinforced by woven fibers in two directions. The stiffness behavior obtained analytically was within 10% of the experimental values.
Theoretical determination of the optimal fiber volume fraction and fiber‐matrix property compatibility of short fiber composites
Authors: Pan Ning
Published: December 2004

Although the question of minimum or critical fiber volume fraction, beyond which a composite can then be strengthened due to addition of fibers, has already been dealt with by several investigators for both continuous and short fiber composites, a study of maximum or optimal fiber volume fraction at which the composite reaches its highest strength has not been reported. The present analysis has investigated this issue for short fiber case based on the well‐known shear lag (the elastic stress transfer) theory. Using the relationships obtained, the minimum spacing between fibers is determined upon which the maximum fiber volume fraction can be calculated. The effects on the value of this maximum fiber volume fraction due to such factors as the mechanical properties of the fiber and matrix, the fiber aspect ratio, and fiber packing forms are discussed. Furthermore. Combined with the previous analysis on the minimum fiber volume fraction, this maximum fiber volume fraction is used to examine the property compatibility of fiber and matrix in forming a composite. This is deemed to be useful for composite design. Some examples are provided as well to illustrate the results.
Measurement of fiber orientation in short‐fiber composites using digital image processing
Authors: Gadala‐Maria F. , Parsi F.
Published: December 2004

A technique that uses digital image processing to measure the orientation distribution function of the fibers in a plane of a short‐fiber composite is described in this work. Other orientation descriptors, such as the fiber orientation parameter, can be calculated from the measured fiber orientation distribution function. In this technique, the edges of the fibers in a digital image of the composite are first identified. Then, using Sobel operators, the orientation of the gradient vector is determined at each fiber orientation distribution function. The advantages of digital imaging over photography and the simplicity of the algorithms make this technique advantageous over previously developed methods to measure fiber orientation.
Fiber mat deformation in liquid composite molding. I: Experimental analysis
Authors: Han K. , Trevino L. , Lee L. James , Liou Ming
Published: December 2004

When a resin in injected into the mold in liquid composite molding, the preplaced fiber mat may deform near the inlet gate because of the high momentum carried by the injected fluid. A fiber free region near the gate followed by the fiber mat deformation may emerge. This phenomenon is most likely to occur when the stacked fiber mats have low permeability and the resin has high viscosity. A set of mold filling experiments were carried out using an instrumented metal mold and a small transparent mold to investigate the fiber mat deformation during mold filling. Experimental results showed that the fiber mat deformation was limited to a small region near the gate and that deformation greatly reduced the molding pressure. A forced fiber mat deformation employing a modified gate design was proposed to facilitate mold filling in liquid composite molding.
Mechanisms of degradation of polymer composites by galvanic reactions between metals and carbon fiber
Authors: Woo E. M. , Chen J. S. , Carter C. S.
Published: December 2004

Toughened and untoughened epoxy and BMI carbon fiber reinforced composites were evaluated in terms of their matrix chemical stability in galvanic reactions between metals and composites. It has been known that the presence of moisture and salts and contact between unprotected metals and BMI carbon fiber composition constitute prerequisite conditions for composite degradation. This study has further demonstarated that these conditions were necessary, but not sufficient. It was found that the OH species generated by galvanic reactions had to be concentrated in localized spots to induce composite degradation at a significant rate. A mechanism was proposed to elucidate how degradation took place under those necessary conditions with the aid of localized aggregation of the OH−species. Additionally, thoughening of BMI composite matrix resins resulted in poorer resistance to degradation by galvanic reactions. On the other hand, none of the eposy composites (toughened or untoughened) exhibited any degradation due to galvanic reactions at room temperature, nor did they degrade in a concentrated caustic NaOH solution (pH = 14,82°C) that simulated a highly accelerated galvanie reaction.
Tensile mechanical properties and reduced internal stresses of polymer optical fiber
Authors: Bosc D. , Toinen C.
Published: December 2004

A few years ago, polymer optical fiber (POF) emerged worldwide as a means for short optical transmission. This fiber type is generally made of poly(meth1 methacrylate) polymer and can be manufactured by a perform process using hot drawing in an oven. The mechanical properties, particularly the breaking stress, depend highly on the draw conditions. Recently, we have implemented the fabrication of very low diameter fiber, to take advantage of the electro‐optic properties of stumps of such single mode fiber. It turned out that the drawing conditions cause undesirable internal stresses, which, in turn, yield unfortunate refractive index variations in the fiber. We observed that increased shearing speed during the drawing operation of low diameter threads did provide high modulus fibers. To overcome the occurrence of the huge shrinkage at Tg, we have found that temperature and length of the oven are critical parameters: an increase in the temperature and also the length of the oven for a given drawing speed has resulted in quality POF.
Evaluation of fiber surfaces treatment and sizing on the shear and transverse tensile strengths of carbon fiber‐reinforced thermoset and thermoplastic matrix composites
Authors: Blackketter Donald M. , Upadhyaya Deepak , King Todd R. , King Julia A.
Published: December 2004

The mechanical performance of advanced composite materials depends to a large extent on the adhesion between the fiber and matrix. This is especially true for maximizing the strength of unidirectional composites in off‐axis directions. The materials of interest in this study were PAN‐based carbon fibers (XA and A4) used in combination with a thermoset (EPON 828 epoxy) and a thermoplastic (liquid crystal poymer) matrix. The effect of surface treatment and sizing were evaluated by measuring the short‐beam shear (SBS) and transverse flexural (TF) tensile strengths of unidirectional composites. Results indicated that fiber surface treatment improves the shear and trasverse tensile strengths for both thermosetting and thermoplastic matrix/carbon fiber‐reinforced unidirectional composites. A small additional improvement in strengths was observed as the result of sizing treated fibers for the epoxy composites. Scanning electron microscope photomicrographs were used to determine the location of composite failure, relative to the fiber‐matrix interface. Finally, the epoxy composites SBS and TF strengths appear to be limited to the maximum transeverse tensile strength of the epoxy matrix, while the thermoplastic composite SBS and TF strengths are limited by the LCP matrix shear and transverse tensile strengths, respectively.
On‐line consolidation of thermoplastic towpreg composites in filament winding
Authors: Wagner P. , Colton J.
Published: December 2004

A study of the use of thermoplastic powder coated towpregs in filament winding was conducted. A suitable technique for manufacturing parts with adequate on‐line consolidation was identified through an experimental investigation that compared several techniques. This process utilized a single compaction roller on‐line consolidation head with hot air guns to obtain consolidation at the lay‐down point on the mandrel. The addition of a heated pultrusion die between the creel system and the filament winder was found to produce the best process. Nylon 11/E‐glass towpreg was used in this study. The effect of winding speed and compaction force on the quality of the resulting parts was determined in order to optimize the process. Only the speed was found to have a significant effect, with better quality parts being made at higher speed. Observations were also made on parts manufactured with polypropylene and E‐glass towpreg, as well as on parts wound with helical patterns.
Universal aspects of composite viscoelastic behavior
Authors: Sullivan J. L. , Wen Y. F. , Gibson Ronald F.
Published: December 2004

The viscoelastic behavior of a series of vinyl ester resins and E‐glass fiber‐reinforced composites is discussed. It is shown that the temperature shift factors for these systems, and others, suggests a universal behavior. A similar observation is made for the aging shift rate. On the other hand, the temperature dependence of compliance components per se appear to differ from system to system. Finally, it is shown that the retardation spectra for the vinyl ester resin and composites systems are the same to within a multiplicative constant in the glassy and in the short time transition regions. This shows that the presence of fibers has no influence on the distribution of retardation times in those regions.
Fracture toughness characterization of phenolic resin and its composite
Authors: Charalambides M. N. , Williams J. G.
Published: December 2004

The aim of this study is to determine the fracture toughness of phenolic resin and its composite. Fracture tests on phenolic resin resulted in a fracture toughness close to values quoted for unmodified epoxy resins. Composite specimens of glass fiber reinforced phenolic were also tested. The interlaminar fracture toughness in both mode I and mode II failures was determined. The mode I initiation values were lower than the neat resin's toughness. Mode I propagation values were strongly influenced by fiber bridging. The mechanism of fiber bridging was found to be sensitive to specimen dimensions. The effect of fiber bridging on the mode I analysis is discussed. Fiber bridging was also evident in mode II failures. Two different geometries were used for the mode II tests (end loaded split and end notched flexure); a correlation between the results from the two geometries is made.
Experimental investigation of fatigue crack growth behavior and damage mechanisms of fiber/metal laminates under uniaxial and biaxial loading
Authors: Li K. , Chudnovsky A. , Kin Y. , Macheret J.
Published: December 2004

The response of the aramid reinforced aluminum‐epoxy‐laminate to uniaxial and biaxial fatigue loading has been investigated. The fracture process in the laminates propagates mainly in the form of cracks in aluminum layers, delaminations between the resin‐rich and fiber‐rich prepreg layers, splitting in prepreg layers and fiber fracture. Ultrasonic microscopy has been used to evaluate the shape and size of the damage zone. The ultrasonic images have been calibrated by means of SEM and optical microscopy of the laminates with sequential removal of the layers. Microscopic examination reveals a direct correlation between delamination, fiber fracture, and fatigue crack growth in the aluminum layer. The results of this investigation strongly suggest that the laminate resistance to tension‐tension biaxial fatigue is superior to that under uniaxial loading conditions.
Bending strength of composite laminates with an elliptical hole
Authors: Zhao Yi , Tripathy Aruna K. , Pang Su‐Seng
Published: December 2004

Great efforts have been made in analyzing the strength of notched laminates under in‐plane loadings. However, no work has been reported on notched laminates under bending, because of the complexity of theoretical stress analysis. In this study, a simplified approach has been used to analyze the notched strength of laminated composites with an elliptical hole under bending. This approach combines notched sample experiments and finite element results. Based upon the consideration that not only the stress distribution at one ply, but also the stress variation across the laminate thickness, should be taken into account, two failure models are presented: a modified point stress model and a modified average stress model. Two characteristic parameters are presented to evaluate the notched strength of the laminated plates.
A finite element method for flow in compression molding of thin and thick parts
Authors: Liang Erwin W. , Tucker Charles L.
Published: December 2004

Based on Barone and Caulk's model and a generalized variational functional, a finite element simulation was developed for the compression molding of thin and thick parts. For solving the u‐v‐p type equations, an element‐based penalty method and a mixed formulation were implemented. Numerical results show that the new model gives better accuracy in velocity and velocity gradient than the Hele‐Shaw formulation for cases where both models are appropriate. Predictions of velocity and its gradient by the model are compared with other FEM results and BEM solutions. Using a fixed base mesh that covers the mold cavity, a new technique was developed for tracking the moving flow front. Temporary elements and nodes are generated for the filled part of elements intersected by the flow front. This method allows a smooth representation of the flow front and has exact boundary conditions on the flow front. The scheme is demonstrated for compression molding of an elliptical and an L‐shaped charge.
Experimental study and finite element simulation of a glass fiber fabric shaping process
Authors: Boisse P. , Cherouat A. , Gelin J. C. , Sabhi H.
Published: December 2004

A finite element simulation is proposed for the shaping of glass fiber fabric. The overall mechanical behavior of the fabric is obtained by combining the tensile behavior of a single thread and the current position of threads in the fabric. The constitutive model for a single thread in tension is based on a statistical approach and is identified using tensile tests. Shear and tensile tests have been carried out on fabric specimens to demonstrate that the behavior of the fabric mainly results from the contribution of each thread, the sliding between fiber threads having a small effect on the energy for the deformation mechanism of these fabrics. A numerical model for the shaping process is obtained based on a finite element approach using three‐ and four‐node membrane shell elements. The formulation accounts for the large displacements and large strains involved in the process as well as the mechanical behavior. A drawing simulation is presented in the case of an hemispherical punch. The comparison with experimental results obtained in this case shows good agreement.
The effect of isothermal aging on transverse crack development in carbon fiber reinforced cross‐ply laminates
Authors: Pederson C. L. , Gillespie J. W. , McCullough R. L. , Rothschilds R. J. , Stanek S. L.
Published: December 2004

An investigation into the effect of isothermal aging on the development of transverse cracks in cross‐ply laminates of two high temperature composite systems was performed. The composite materials investigated were BASF X5260/640–800 and DuPont Avimid K/IM6. Changes in the glass transition temperature, composite weight loss, crack density, and mode I intralaminar fracture toughness were monitored during isothermal aging in air at 177°C for up to 2232 h. The two laminate configurations used in this study include two variations of the generic cross‐ply configuration [02/90n]s, in whichnequals 1 and 2. The results of this investigation show that a layer of degraded material forms at the surface of the X5260/640–800 bismaleimide laminates and that the thickness of the degraded layer increases with aging time. After 744 h of aging, transverse cracks form in the surface plies and an increasing crack density evolves as aging time is increased; however, transverse cracks do not form in the inner 90° ply groups with aging during the time period investigated. The Avimid K/IM6 thermoplastic polyimide laminates, which show evidence of cracking prior to aging, do not exhibit any significant change in crack density with aging. The results of the aging experiments also show that the bismaleimide system exhibits a weight loss of 1.5% and an increase in glass transition temperature from 250°C to 300°C after 2232 h of aging at 177°C, while the thermoplastic polyimide system shows a weight loss of only 0.05% and an increase in glass transition temperature from 280 to 285°C after 2232 h. Changes in the resistance to crack formation are also seen in these materials during aging. The mode I intralaminar fracture toughness, a measure of resistance to transverse crack formation, shows a 50% decrease after aging for 2232 h for the bismaleimide system, while the behavior exhibited by the thermoplastic polyimide shows little evidence of a reduction.
Interfacial bonding and optical transmission for transparent fiberglass/poly(methyl methacrylate) composites
Authors: Weaver Kevin D. , Stoffer James O. , Day Delbert E.
Published: December 2004

Evidence is presented relating the interfacial bonding strength and the optical transmission of transparent glass fiber reinforced PMMA composites. The temperature dependent (20° to 50°C) optical transmission of composites that contained uncoated 13 μm glass fibers and 13 μm glass fibers coated with divinyltetramethyl disilazane or 3‐(trimethoxysilyl)propyl methacrylate was found to decrease in the same order as the bond strength of the PMMA/glass fiber interface, namely, trimethoxy silane coated fiber, disilazane coated fiber, and uncoated fiber. SEM photographs showed similar fracture surfaces, clean fiber pull‐out, and no apparent bonding of the glass fiber to the PMMA for the composites containing uncoated and disilazane coated fiber, whereas, the composite containing trimethoxy silane coated fiber showed virtually no clean fiber pullout. Additional evidence for differences in the bonding strength is seen in the degradation (penetration of water and fiber whitening) on aging at 23°C in air or water for composites containing uncoated fiber (most degradation), disilazane coated fiber (slight degradation), and trimethoxy silane coated fiber (no degradation). The optical transmission between 20° and 30°C at 600 to 800 nm for the composite containing trimethoxy silane coated fiber decreased the least with increasing temperature (from ∼85% to 70%) while the composite containing uncoated fiber decreased the most (from ∼85% to 32%).
Fatigue behavior of quasi‐isotropic carbon fiber/PEEK laminates under tension‐tension loading
Authors: Ma C. C. M. , Lin S. H. , Tai N. H. , Wu S. H. , Wu J. F.
Published: December 2004

Fatigue behavior of carbon fiber reinforced poly(etheretherketone)(PEEK) laminates was investigated. The static tensile measurement, tension‐tension fatigue loading tests, and residual tensile strength measurement of the [0/45/90/‐45]2sAS‐4/PEEK laminates were performed at various levels of stress amplitudes. The influences of stress amplitude on the fatigue life and the residual tensile strength were investigated. The experimental results for fatigue life and residual tensile strength under different stress amplitudes are analyzed by the median rank method. TheS‐Ncurves at various survival probabilities are also presented by the pooled Weibull distribution function. Furthermore, a residual strength degradation model is used to predict the residual strength for the composites subjected to a number of fatigue cycles and to simulate the effects of the stress amplitude on the fatigue life. The agreement between experiment and theory is good.
Degradation behavior of mechanically fastened joints of glass‐reinforced crosslinked polyester immersed in hot water
Authors: Morii Tohru , Hamada Hiroyuki , Maekawa Zen‐Ichiro , Tanimoto Toshio , Hirano Takahiro , Haruna Kazushi
Published: December 2004

This study deals with the degradation of mechanically‐fastened GFRP joints immersed in hot water (80°C). The material used was randomly oriented E‐glass fiber continuous strand mat with a crosslinked polyester. Three kinds of joint geometries were adopted; thickness was 3 mm, hole diameter was 6 mm, the distance from hole center to top‐edge was 18 mm (3e), and specimen widths were 18 (3w), 30 (5w), and 42 mm (7w). Failure modes of original dry specimens were a function of joint geometry, The dominant failure mode of 3w3e joints was net‐tension, whereas 5w3e and 7w3e joints displayed bearing failure. As degradation progressed, the dominant failure mode gradually shifted from net‐tension to bearing failure. Strength reduction was marked in 5w3e and 7w3e joints, in which the dominant failure mode was bearing. Joint strength and failure mode were predicted from the combination of a macroscopic failure criterion and characteristic curves obtained from tensile testing of rectangular specimens with holes, bearing tests, and finite element analysis. Predictions agreed with experiment.