bluuebunny/crossref_metadata_2025 huggingface dataset:
Mechanical properties and morphology of glass bead–filled polypropylene composites
Authors: Liang J. Z. , Li R. K. Y.
Published: April 2004

The effects of the filler content and size on the mechanical properties such as tensile modulus, Ec, yield strength, σyc, and impact strength, SIC, of glass bead–filled polypropylene (PP) composites have been investigated employing an Instron materials tester and a Ceast impact tester at room temperature. With increasing concentration of glass beads, Ec and SIC increase, but σyc decreases non–linearly, within a filler volume fraction range of 0%−20%; under the same test conditions, the values of EC and σyc for PP with bigger beads are somewhat lower than those of PP with smaller ones; the maximum values of SIC for the composites are about 1.4 times as high as the unfilled PP; the interface between the matrix and the beads is a weak bond. The results indicate that the stiffness and the toughness of the PP composites are effectively improved by addition of glass beads.
Resin transfer molding of BMIs and polymides
Authors: Colton Jonathan S.
Published: April 2004

Bismaleimdes (BMI) and experimental polyimides were resin transfer molded into carbon fiber fabrics using a custom‐built injection mold placed within a vacuum hot press. This represents the first time that the latter type of materials has been resin transfer molded. This is a critical stage in developing materials and processing methods for future aerospace applications, such as the High Speed Civil Transport (HSCT).
Interfacial properties of two SiC fiber–reinforced polycarbonate composites using the fragmentation test and acoustic emission
Authors: Park Joung‐Man , Chong Eui‐Min , Yoon Dong‐Jin , Lee Joon‐Hyun
Published: April 2004

Interfacial shear strengths (IFSS) between the fiber and the matrix in two SiC fiber–reinforced polycarbonate (PC) composites (TFC) were investigated through the fragmentation method and the acoustic emission (AE) technique. Statistical analysis of SiC fiber tensile strength was performed mainly in terms of a Weibull distribution. The tensile strength and elongation for SiC fiber decreased with increasing gauge lengths, because of the heterogeneous distribution of flaws on the fiber surface. Using an amino‐silane coupling agent, the IFSS showed significant improvement, in the range of 150%, under dry conditions. On the other hand, in the aspect of the environmental effect, the IFSS was improved about 170% under wet conditions (immersed in hot water at 85°C for 75 min). This is probably due to chemical and hydrogen bonds in the two different interphases in the SiC fiber/silane coupling agent/PC matrix system. In‐situ monitoring of AE during straining of microspecimens showed the sequential occurrence of two distinct groups of AE data. The first group may result from SiC fiber breakages, and the second probably results from mainly PC matrix cracking. Characteristic frequencies coming from the failures of the fiber and the PC matrix were shown via fast Fourier transform (FFT) analysis. By setting an appropriate threshold level, a one‐to‐one correspondence between the number of AE events and fiber breakages was established. This AE method could be correlated successfully to the IFSS via the fragmentation technique, which can also applied to nontransparent specimens.
Effect of processing on the positive temperature coefficient of resistivity in lead metaplumbate/polyethylene composites
Authors: Huang Z. Z. , Yue R. , Chan H. L. W. , Choy C. L.
Published: April 2004

The positive temperature coefficient of resistivity (PTCR) effect of a barium metaplumbate/polyethylene [(BaPbO3)/PE] composite with 12 vol% of BaPbO3 was studied. The composite samples were prepared by hot‐pressing a mixture of BaPbO3 ceramic and high‐density polyethylene powders around the melting point of polyethylene. The composites exhibit a pronounced PTCR effect of up to a six‐decade increase in resistivity within a narrow range of temperature (∼10°C). The dependences of the room temperature resistivity and the magnitude of the resistivity jump on the pressing and annealing temperature, and the electrical behavior after repeated heating‐cooling cycles were investigated. The fracture surfaces of the composite samples were examined in a scanning electron microscope in order to correlate the electrical behavior with the microstructure.
Measurement and modeling of flow and mechanical properties of ASR‐filled polymer composites
Authors: Narh K. A. , Guo J. , Li Z.
Published: April 2004

Screw extrusion process was used to evaluate the flow properties of ASR/LDPE composite whose rheological properties cannot be obtained from the conventional capillary rheometer measurements. The results show that the viscosity of the mixture increases with increasing automobile shredder residue (ASR) content. Although there exists significant scatter in the results because of the non‐homogeneity of the mixtures, the result can be used to roughly predict the flow properties of the materials. Thus, based on linear regression fits of the flow data, a second order polynomial relationship was established between the viscosity of ASR/LDPE composite and ASR concentration. HDPE was used in the mechanical tests. The results also show that the tensile modulus can be predicted, accurately, using a conventional composite model.
Comparative study of interlaminar fracture toughness of GFRP with different fiber surface treatments
Authors: Korjakin A. , Rikards R. , Buchholz F.‐G. , Wang H. , Bledzki A. K. , Kessler A.
Published: April 2004

This investigation is focused on the influence of glass fiber surface treatment on the interlaminar fracture toughness of unidrectional laminates. Three different fiber surface treatments were considered: polyethylene treated fibers to get poor adhesion, silance treated fibers to get good bond strength, and industrial fibers without special treatments with the coupling agents. The interlaminar fracture behavior of unidirectional glass fiber reinforced composites with different fiber surface treatments has been investigated in mode I, mode II, and for the fixed mixed mode I/II ratio 1.33. Double cantilever beam (DCB), end notched flexure (ENF), and mixed mode flexure (MMF) specimens were used. The data obtained from these tests were analyzed by using different analytical approaches and the finite element method. For the fibers treated with the silane coupling agent, a value about 2.5 times higher of mode II interlaminar fracture toughness for crack initiation was obtained in comparison with the polyethylene sized composite. For the composite made from the industrial fibers, a value about 2 times higher was obtained. Because of extensive fiber bridging and pullout in the composites with poor fiber/matrix adhesion, the results of mode I and mixed mode I/II tests did not characterize the interphase quality. In order to determine the interphase quality, the mode II tests are recommended.
Mold filling analysis in vacuum‐assisted resin transfer molding. Part I: SCRIMP based on a high‐permeable medium
Authors: Sun Xiudong , Li Shoujie , Lee L. James
Published: April 2004

Mold filling in SCRIMP based on a high‐permeable medium is complicated because of the considerable difference in the permeabilities of the fiber reinforcement, the peel ply and the high permeable medium. The objectives of this paper are to understand the flow mechanism through flow visualization experiments and to present models that can be used to predict the filling time and flow pattern. Permeabilities of a stitched fiber mat, a high‐permeable medium and a peel ply were measured. Flow visualization of SCRIMP mold filling was carried out under various molding conditions. It was found that although the resin flowed faster in the high‐permeable medium than in the fiber reinforcement, the flow front lead‐lag was not very large and it remained nearly constant through the entire mold filling process. A three‐dimensional Control Volume/Finite Element Method (CV/FEM) was adopted to solve the flow governing equations, i.e. the Darcy's law, and the influences of the flow properties of the high‐permeable medium, the fiber reinforcement and the peel ply on filling time were investigated. Based on experimental observations and CV/FEM simulation, a simplified leakage flow model is also presented. The comparison of experimental and simulation results show good agreement.
Mold filling analysis in vacuum‐assisted resin transfer molding. Part II: SCRIMP based on grooves
Authors: Ni Jun , Li Shoujie , Sun Xiudong , Lee L. James
Published: April 2004

Compared with SCRIMP based on the high‐permeable medium, SCRIMP based on grooves has the advantage of a much higher mold filling rate. This paper analyzes the influences of various molding conditions on mold filling and presents models that can be used to predict the filling time and flow pattern in SCRIMP based on grooves. Mold filling experiments were carried out to investigate the effect of various factors such as the size of the groove, groove spacing, number of fiber layers and resin viscosity on mold filling. A leakage flow model was developed to simplify the simulation of the mold filling process in SCRIMP based on grooves. An “equivalent permeability” was introduced to represent the average flow capacity in the grooves. Compared with the Control Volume/Finite Element Method (CV/FEM) model, the leakage flow model greatly reduced computation time and yet provided simulation results that were in good agreement with experimental observations.
Analytical stress model for a composite prosthetic intervertebral disc
Authors: Hudgins R. Garryl , Muzzy John D.
Published: April 2004

This research develops an analytical stress model for a composite prosthetic intervertebral disc (PID) composed of an elastomeric core placed inside a braided flexible composite sleeve. The model is used to investigate the effects of interference between the core and sleeve on the axial compression behavior of the prosthesis. The model closely replicates the PID's compressive stress‐strain curve. The model combines textile crimp analysis and a newly proposed rubber elasticity constitutive relation. The stress model can be used to optimize the compressive behavior of a PID having a textile composite reinforcing phase.
Effect of volume loading and surface treatment on the thixotropic behavior of polypropylene filled with calcium carbonate
Authors: Wang Yeh , Yu Ming‐Jiann
Published: April 2004

The rheological properties of calcium carbonate‐filled polypropylene were examined using a Rheometrics dynamic analyzer. The study included steady shear test, transient stress growth test with sequential deformation history, and two‐step dynamic oscillatory shear flow. Thixotropic behavior was observed in transient tests for highly filled compounds when volume loading exceeding a critical value at about 20%. The material responses of these viscoelastic thixotropic materials depend on the duration of shear as well as on the rate of shear. The effects of filler on the rheological behavior of highly filled compounds are dominant at low strain rates; however, the effects of activity of the filler are almost negligible at high strain rates because of complete breakdown of the filler network. The timescales for structural changes in filled systems often become long compared with the viscoealstic time constants of the unfilled melt. The magnitudes of rheological properties and the degree of hysteresis appear to increase with increasing volume loading of filler particles. Conversely, surface treatment of fillers, which presumably reduces interaction between filler particles and the extent of agglomeration, results in major reductions of both rheological properties and the degree of hysteresis. The diverse experimental observations are interpreted in terms of a system forming a filler network due to weak interparticle forces. The thixotropy resulting from breakdown and recovery of the filler network is dependent on the characteristic time of the individual test.
Piezoresistivity in continuous carbon fiber polymer‐matrix composite
Authors: Wang Shoukai , Chung D. D. L.
Published: April 2004

Piezoresistivity involving the volume resistivity of a continuous unidirectional carbon fiber epoxy‐matrix composite in the fiber direction decreasing reversibly upon tension in the fiber direction was observed by the four‐probe method, due to an increase in the degree of fiber alignment. Use of the two‐probe method resulted in measurement of the contact resistance rather than the volume resistance. The contact resistance increased reversibly upon tension.
On predicting elastic moduli and natural frequencies of multi‐phase composites with randomly distributed short fibers
Authors: Chao Lu‐Ping , Huang Yung‐Sung
Published: April 2004

This study presents a formulation to determine the overall stiffness of an n‐phase short fiber composite to include the inclusions' aspect ratio ranging from less than one to greater than one. The Mori‐Tanaka theory is initially employed to investigate the overall stress‐strain relation of a multi‐phase short‐fiber‐reinforced composite material, particularly whether or not the fibers and the matrix are isotropic, cubic, or transversely isotropic material. The effective stiffness tensor of a multi‐phase composite is then denoted as a function of the matrix's elastic moduli, the n‐phases' inclusions' elastic moduli, the n‐phases' inclusions' Eshelby tensor, and the n‐phases' inclusions' volume fractions. Utilizing the equivalent inclusion method allows us to model inclusions of n‐phases that consist of fictitious eigenstrains. In addition, the corresponding Eshelby tensors' values for ellipsoidal inclusion embedded in the isotropic matrix with the variation of aspect ratio are presented. Numerical results of the proposed formulation in solving a two‐phase composite closely correspond to the Halpin‐Tsai Equation. Results presented herein provide valuable information on the appropriate manufacturing requirements of multi‐phase composite materials or the design and optimization of multi‐phase composite structures.
Analysis of the vacuum infusion molding process
Authors: Hammami A. , Gebart B. R.
Published: April 2004

The vacuum infusion molding process is becoming increasingly popular for the production of large composite parts. A comprehensive model of the process has not been proposed yet, making its optimization difficult. The flexible nature of the vacuum bag coupled to the varying pressure inside the mold cavity results in a variation of the cavity thickness during the impregnation. A complete simulation model must incorporate this phenomenon. In this paper, a complete analysis of the vacuum infusion molding process is presented. The analysis is not restricted to the theoretical aspects but also reviews the effect of the main processing parameters. The parameters investigated in this paper are thought to be those of most interest for the process, i.e. the compaction of the reinforcement, the permeability, the infusion strategy and the presence of flow enhancement layers. Following the characterization experiments, a 1‐D model for the vacuum infusion molding process is presented. This model is derived assuming that an elastic equlibrium holds in the mold cavity during mold filling. Even though good agreement was found between simulation results and experiments, it is concluded that additional work is needed on the numerical model to integrate interesting findings from the experimental part.
Performance evaluation of synthesized acrylic acid grafted polypropylene within CaCO3/polypropylene composites
Authors: Rahma F. , Fellahi S.
Published: April 2004

A polymeric coupling agent acrylic acid grafted polypropylene (AAgPP) was synthesized and its efficiency in CaCO3/PP composite was investigated. The grafting of acrylic acid monomer (AA) onto polypropylene was performed using an internal mixer. The effect of peroxyde, acrylic acid monomer content, temperature and RPM was studied. A grafting reaction between the polypropylene and the acrylic acid was evidenced through FTIR, UV, DSC and MFI testing. The highest grafting yield was obtained at 0.85 phr peroxide and 5 phr acrylic acid. The selected mixing temperature was 200°C, the rotor speed 150 rpm and the residence time 5 min. The obtained coupling agent (AAgPP) was used with 30 wt% CaCO3 filled polypropylene. Strong interactions with the composite were observed. The effect of increasing the coupling agent content on Izod impact and tensile properties was investigated. A maximum in the above properties is attained at 15 wt% AAgPP. The most important effect is clearly shown in the Izod test. In fact, a threefold increase has been observed for either notched and untoched specimen. The 15 wt% AAgPP is considered to be a critical concentration for the composite considered. This corresonds to maximum interactions occurring between the matrix and the filler. SEM analysis clearly shows strong interactions between the filler and the matrix in the presence of acrylic acid grafted polypropylene. This is another proof of the efficiency of the synthesized AAgPP as a potential coupling agent for CaCO3 filled PP.
A comparative study of using allyl alcohol based copolymers in the preservation of wood: Oak vs. cedar
Authors: Dilek Ş. , Olgun G.
Published: April 2004

Wood is an important raw material that is cheap and easily worked. However, wooden objects are subject to environmental attack and mechanical shocks. In this study, our aim is to preserve wooden objects against envrironmental deterioration and mechanical shocks on to consolidate objects already degraded. Allyl alcohol (AA), acrylonitrile (AN), methyl methacrylate (MMA) and AA/AN, AA/MMA monomer mixtures were impregnated into oak and cedar. Polymerization was accomplished by gamma irradiation. The mechanical properties and the dimensional stability of the wood‐copolymer composites were determined. The presence of polymer and copolymer in the wood increased the mechanical durability of the wood. The results of the hardness tests and the compressive strengths determined in parallel and perpendicular directions to the fibers revealed that P(AA/MMA), P(AA/AN) copolymers are effective in increasing the mechanical durability of pristine‐oak and cedar woods. Similar results were also obtained from hardness tests. The decrease in the mechanical durability of pristine‐oak and cedar woods after aging for 28 days is slight. The water uptake capacity of wood + copolymer composites was observed to decrease by more than 50% compared with the original samples. In the cedar wood, where the density is low and the quantity of copolymer is high, this decrease ranged from 100% to 50%.
Processing and properties of solution impregnated carbon fiber reinforced polyethersulfone composites
Authors: Wu G. M. , Schultz J. M.
Published: April 2004

Carbon fiber reinforced polymer composites are attractive because of their high stiffness and strength‐to‐weight ratios. In order to fully utilize the stiffness and strength of the reinforcement fiber, it is necessary to bring the polymer matrix and the reinforcement fiber together with homogeneous wetting. In this paper, a solution processing technique and the mechanical properties of carbon fiber reinforced polyethersulfone composites were investigated. The polymer was dissolved in cyclopentanone and fed onto a continuous carbon fiber tow using a drum winder. The solution‐processed composite prepregs were then layed up and compression molded into unidirectional composite panels for evaluation. The composite samples showed uniform fiber distribution and reasonably good wetting. The longitudinal flexural modulus was as high as 137 GPa, and longitudinal flexural strength 1400 MPa. In addition, the effects of polymer grade and processing conditions on the mechanical properties of the composites were discussed. It is suggested that the transverse properties and interlaminar fracture toughness could benefit from higher polymer matrix molecular weight. A careful design in the spatial distribution of the molecular weight would be necessary for practical applications.
Rate‐Dependent function in the correlation between hardness and yield stress of polyethylene composites
Authors: Suwanprateeb J.
Published: April 2004

A study of the validity of a correlation between compressive yield stress and Vickers hardness of CaCO3/high density polyethylene composites was carried out. Composites with calcium carbonate in the range of 0–0.40 were produced by twin screw extrusion followed by compression molding. Hardness was implemented by indenting the samples with Vickers indenter and compression test were carried out at various crosshead speeds in the range of 0.2–50 mm min−1. It was found that increasing calcium carbonate content increased both hardness and yield stress. In addition, compressive yield stress increased with increasing crosshead speed. The correlation between hardness and yield stress was observed to be independent on filler content and valid when the deformation rate employed in both tests were within the similar ranges which was in the order of 10−1 mm min−1. Tabor's equation was modified to take into account for the rate‐dependent behavior of composites and was found to be applicable and yield relatively accurate results.
Fractal permeation characteristics of preforms used in liquid composite molding
Authors: Ramakrishnan B. , Pitchumani R.
Published: April 2004

Preform permeability plays a critical role in the analysis of mold filling during liquid composite molding processes. Because of the complex structure of the preform pore network, a quantitative description of the pore structures, and consequently, the evaluation of the permeabilities presents a major challenge. In this article, a fundamental description of the disordered preform pore structures based on fractal techniques is utilized to relate the preform permeabilities to the actual microstructures in terms of two fractal dimensions. Comparison of the fractal permeation model predictions with experimentally‐measured permeabilities demonstrates excellent agreement over a wide range of fiber volume fractions, injection pressures, and isotropic and anisotropic preform architectures.
Viscosity characterization of highly filled photopolymerizable liquid encapsulants for microelectronic devices
Authors: Baikerikar Kiran K. , Scranton Alec B.
Published: April 2004

In this paper the viscosity of novel photopolymerizable liquid encapsulants (PLEs) for microelectronic devices was characterized as a function of the particle size distribution of the fused silica filler. Microelectronic devices are typically encapsulated using a transfer molding process in which the molding compound flows over the leadframe and wire bonds as it fills the mold. The molding compound should have a low viscosity to minimize problems such as: (1) incomplete mold filling; (2) lead frame movement during cavity filling; and (3) displacement of the wires that connect the die with the leadframe (wire sweep). We have developed a photopolymerizable liquid encapsulant using an epoxy novolac‐based vinyl ester resin that may alleviate these problems. In this contribution, we have investigated the blending of two different particle size distributions of fused silica to tailor the viscosity of PLEs for microelectronic applications. We have characterized the viscosity of highly filled PLEs containing 70.0, 72.0, and 74.0 wt% silica, and found that a blend of particle size distributions with a particle size ratio of 3.13 resulted in the best viscosity reduction. In addition, the PLE viscosity decreased slightly with increasing concentration of a silane coupling agent. The resulting PLEs exhibit low viscosities at ambient temperature while maintaining desirable material properties for microelectronic applications.
Processability and mechanical properties of ternary composites PP/EPDM/GF
Authors: Barbosa Silvia E. , Capiati Numa J. , Kenny José M.
Published: April 2004

The enhancement of the mechanical properties of neat PP is achieved by the addition of glass fibers and EPDM rubber. The Young's modulus and notched Charpy impact strength of the composites obtained are improved with respect to the original polymer, leading to a new composite material with a very good balance of toughness and rigidity properties. The tensile behavior of these multiphase systems is successfully compared with theoretical predictions using the Halpin‐Tsai/Nielsen theory for uniaxially short fiber composites, which considers the matrix as a blend with spherical particles and can predict the tensile modulus considering an average fiber orientation angle. An accurate morphological study performed by scanning electron microscopy (SEM) shows a very good dispersion of the rubbery phase into the neat matrix. No special affinity between the rubber and the fibers is reported. The good dispersion and the small particle diameter indicate the good processability of the ternary systems studied.
Chemical modification and adhesion in carbon fiber/epoxy micro‐composites; coupling and surface coverage
Authors: Földes Enikő , Gulyás János , Rosenberger Stefánia , Pukánszky Béla
Published: April 2004

Four compounds were used to improve adhesion between carbon fibers and an epoxy matrix. Triglycidyl isocyanurate (TGIC) and 3‐glycidoxy‐propyl‐triethoxysilane (EPS) contained reactive epoxy groups, while N‐(3‐trimethoxysilane‐propyl)ethylene diamine (AMS) a primary and a secondary amino group. The fourth coupling agent was 4,4' diphenylmethane‐diisocianate (MDI). The interaction of the fiber and the coupling agents was studied by dissolution experiments. Chemical reactions taking place on the surface of the fiber were followed by FTIR spectroscopy. Interfacial shear stress determined by fragmentation was used for the characterization of matrix/fiber adhesion. Beside coupling to the surface, EPS, AMS and MDI formed a polymer layer on the surface, but TGIC also entered into secondary reactions during the treatment. Both the type and the amount of the coupling agent affects strongly interfacial adhesion, which is determined by the thickness and properties of the formed coupling agent layer. The combination of dissolution experiments with the fragmentation test yields valuable information about the processes taking place on the surface of the fiber, facilitate the selection of the best coupling agent, as well as the development of surface treatment technology.
Structure development in thermoset recyclate‐filled polypropylene composites
Authors: Bream C. E. , Hornsby P. R.
Published: April 2004

Polypropylene containing comminuted fiber reinforced thermoset recyclate has been shown to exhibit enhanced mechanical properties relative to particulate‐filled materials. Optimum mechanical performance in these recyclate‐filled materials is achieved in compositions made from rubber‐modified polypropylene containing maleic anhydride‐modified PP in conjuction with silane coupling agent. Although matrix crosslinking was found to enhance properties in both filled and unfilled systems, composite properties are dominated by the development of strong interfacial bonding between polypropylene and recyclate reinforcement. A mechanism for the formation of interfacial bonding is proposed involving reaction between maleic anhydride functionalized PP, formation of trisilanol groups and their subsequent condensation with hydroxyl groups on the recyclate surfaces, together with molecular entanglement and co‐crystallization of the grafted and ungrafted polypropylene molecules. Furthermore, in the absence of treatment there is evidence that the elastomer particles encapsulate the filler particles. However, this effect is strongly hindered when functionalized‐PP is added, either in isolation or in combination with the silane co‐treatment. The crystalline nucleation of PP by thermoset recyclate and treatment is also considered. The treatment system investigated was found to promote interfacial bonding to both the polyester (DMC) and woven glassreinforced phenolic recyclates investigated, suggesting it may be suitable for treating mixed composite scrap.
Sensor placement study for online flow monitoring in liquid composite molding
Authors: Kueh Sylvia R. M. , Advani Suresh G. , Parnas Richard S.
Published: April 2004

On‐line sensing can play an important part in controlling the quality of the final product in any manufacturing environment, including liquid composite molding (LCM). Having a sensor embedded within the part itself is often the most effective means of monitoring its condition at various stages of manufacturing and even throughout its useful life. However, given their intrusive nature, there are practical limitations imposed upon their size, quantity and trajectory within the part. This study explores the possibility of using a single lineal sensor to monitor the resin flow front during the mold filling stage of LCM, and to detect the onset of void formation and the presence of dry spots within the mold. Experiments were conducted to characterize the response of a fiber optic system previously developed for cure monitoring. Simulations were then performed to determine the optimal placement of just one such sensor in a mold to demonstrate that sufficient information on the mold filling process could be obtained. The purpose of the simulation work was to learn how to interpret the sensor response and, subsequently, use it to control the LCM process.
E‐Glass/DGEBA/m‐PDA single fiber composites: The effect of strain rate on interfacial shear strength measurements
Authors: Holmes G. A. , Peterson R. C. , Hunston D. L. , McDonough W. G.
Published: April 2004

Precise measurements of fiber break regions have been made during the single fiber fragmentation test (SFFT) procedure on E‐glass/diglycidyl ether of bisphenol‐A (DGEBA)/meta‐phenylenediamine (m‐PDA) test specimens. From these measurements, the location and size of each fiber fragment was determined, and the resulting information was used to construct fragmentation maps of the tested fiber. By comparing these maps, the fragmentation process supports random fragmentation along the length of the fiber. Since the interfacial shear strength (IFSS) or the interfacial shear stress transfer coefficient (I‐STC) is obtained from the fragment length data at the end of the test (saturation), frequency histograms of the fragment length data were constructed to determine the repeatability of the fragmentation process. Since the SFFT is performed by sequential step‐strains of the test specimen, test protocols were developed by controlling the step size of each strain increment and the time between each step‐strain (dwell time). For the testing protocols used in this research, the E‐glass/DGEBA/m‐PDA frequency histograms of the fragment lengths were found to be generally repeatable. However, when the effective strain rate of the test was altered by changing the dwell time between strain increments, the fragment distribution at saturation of the E‐glass/DGEBA/m‐PDA SFFT specimens changed. The direction of the change was found to be inconsistent with the effect one might expect when only the nonlinear viscoelastic behavior of the matrix is considered. However, the magnitude of the change observed in the E‐glass/DGEBA/m‐PDA SFFT specimens is not universal. Fragmentation data obtained on E‐glass/polyisocyanurate SFFT specimens revealed a much smaller change in fragment length distributions with the same change in testing protocols. Consistent with the results obtained on the E‐glass/DGEBA/m‐PDA, fiber fragmentation occurs when the polyisocyanurate matrix exhibits nonlinear viscoelastic behavior. The implication of these results for interfacial shear strength measurements is discussed.
Nondestructive evaluation methods for damage assessment in fiber‐metal laminates
Authors: Fahr A. , Chapman C. E. , Forsyth D. S. , Poon C. , Laliberté J. F.
Published: April 2004

The Structures, Materials and Propulsion Laboratory of the NRC Institute for Aerospace Research (IAR) is engaged in a collaborative project with Bombardier Aerospace. The main objective of the project is to evaluate the potential of applying fiber‐metal laminates (FML) to aircraft types manufactured by Bombardier. As a part of this project, nondestructive evaluation (NDE) procedures have been developed and used at IAR to determine the extent of damage caused by impact, corrosion and fatigue loads in a commercial FML material (GLARE). X‐rays using radioopaque fluids as well as conventional and air‐coupled ultrasonic and eddy current methods have been investigated. This report describes the NDE procedures employed at IAR to assess damage in FML and provides examples of the results obtained utilizing each of the inspection methods and the damage types investigated. Also, the ability of the investigated NDE methods to determine damage size and the accuracy of damage measurements is discussed.
Polyester cure monitoring by means of different techniques
Authors: Ton‐That M.‐T. , Cole K. C. , Jen C.‐K. , França D. R.
Published: April 2004

The cure of a set of polyester resin samples having different styrene contents has been monitored by means of Fourier transform infrared (FTIR) spectroscopy, differential scanning calorimetry (DSC), rheometry, and ultrasonic measurements. FTIR and DSC experimental data were used to calculate the cure kinetics using a freeradical polymerization model (multiple steps) and also an empirical model that considers the curing to involve only a single step. The dependence of viscosity on the degree of curing has been investigated at different shear rates. Finally, correlations among the results from the different techniques have been established and discussed in terms of the curing mechanism.
Electron beam curing of polymer composites
Authors: Raghavan J. , Baillie Mark R.
Published: April 2004

Electron‐beam (E‐Beam) curing of an epoxy polymer matrix and its composite (reinforced with IM7 Carbon fibers) was studied using a cationic photoinitiator. Photoinitiator concentration, dose, and process temperature were varied to understand their influence on E‐beam curing. Optimal photoinitiator concentration was found to be 5 phr. The curing was due to a primary α reaction with a strong dependence on dose, and a secondary β reaction with a weak dependence on dose and a strong dependence on initiator concentration. The extent of cure increased rapidly with dose until 100 kGy and it approached a plateau value beyond 100 kGy. This plateau value corresponded to incomplete curing by 27% for resin and 22% for composite at a process‐temperature of 22°C. The causes for incomplete curing appear to be the secondary β reaction and diffusional limitation. Increase in process temperature resulted in higher extent of cure at a dose level. The material used in this study was also found to be thermally curable and the reaction onset temperature (measured in a DSC ramp experiment) reduced from about 150°C at 0 kGy to about 50°C at 30 kGy. This indicates that simultaneous thermal curing during E‐beam curing of resin and composite is possible. After thermal post‐curing, the Tg of the E‐beam cured resin increased from 130°C at 200 kGy to a value greater than 370°C and the modulus decreased by 10%. The service temperature and the modulus of the 100% thermally cured resin and the thermally post‐cured (after E‐Beam irradiation) resin were comparable.
Surface quality characterization of textile‐reinforced thermoplastics
Authors: Neitzel M. , Blinzler M. , Edelmann K. , Hoecker F.
Published: April 2004

To allow cost effective mass production of reinforced thermoplastics for visible parts, in‐situ a surface quality with “Class‐A” standard must be achieved. Furthermore, after the application of varnish, an appearance (gloss, waviness, color) similar to that of the traditional metal component is required. Porosity and fiber readout are the common surface defects. Fiber readout results from the significantly higher volume shrinkage of the thermoplastic resin (higher CLTE) in comparison to that of the reinforcement during the cooling process in production combined with the uneven distribution of resin and fibers. While glass mat reinforced thermoplastic (GMT) parts show a disorderly readout influenced (among other factors) by fiber length, processing and fiber content of the semi‐finished material, the fabric reinforced thermoplastics (organic sheets) suffer from a regular print‐through—a display of the textile reinforcement. Modern tools of measurement enable one to quantify gloss, roughness, and waviness of the surfaces. Thus parameters significantly influencing the surface characteristics can be identified. This leads to the development of procedures for improving the surface quality.
The hierarchical structure and flexure behavior of woven carbon fiber epoxy composite
Authors: Elleithy Rabeh H.
Published: April 2004

The hierarchical structure and flexure behavior of woven carbon fibers epoxy composite were investigated in this work. First, the hierarchical structure of the composite is characterized on three levels: composite, ply, and yarn. Structura imperfections,

In this paper, “structural imperfections” is used to describe the inherent structural characteristics of the actual composite, which deviate from the theoretically ideal and perfect composites, control, that are used in composite theories.

such as, ply‐ply misalignment, ply‐ply offset, and resin pockets, are identified and described. Second, a four‐point bending arrangement is used to study the flexure properties of the composite. Additionally, in‐situ traveling microscope and acoustic emission (AE) techniques are utilized to gain insight to the failure proceses during flexure test. AE showed early stages of matrix cracking before visual observation, which makes it a valuable tool for early failure detection.
Composition dependence of the magnetic properties of bonded magnets of strontium hexaferrite‐polyvinyl chloride
Authors: Matutes‐Aquino J. , Ríos‐Jara D. , Ayala‐Valenzuela O. , Sifuentes Gallardo P. , Ramos De Valle L. F. , Rodríguez Fernández O. S.
Published: April 2004

A systematic study of the magnetic properties of strontium ferrite‐polyvinyl chloide plastoferrites as a function of composition is presented. Plastoferrites were manufactured by hot compression of a mixture of commercial powders of strontium ferrite (SrFe12O19) and polyvinyl chloride. In order to explain the dependence of the volumetric density and the saturation magnetization with composition, an additive model for these properties is considered. The intrinsic coercivity shows a decrease with increasing strontium ferrite content, which is interpreted as a magnetizing‐like effect due to the increasing interaction between the magnetic particles. The maximum energy products are lower than 1 MGOe and increase with the second power of the strontium ferrite content. The best maximum energy product and specific saturation magnetization were obtained for the plastoferrite with a 85 weight percentage of ferrite.
Mechanical properties of E‐glass fiber reinforced siliconized epoxy polymer composites
Authors: Alagar M. , Thanikai Velan T. V. , Ashok Kumar A.
Published: April 2004

Siliconized epoxy‐matrix systems have been developed by an interpenetrating mechanism using epoxy resins GY 250 and LY 556 (Ciba‐Geigy) and hydroxyl terminated polydimethylsiloxane with γ‐aminopropyltriethoxysilane as crosslinker in the presence of dibutyltindilaurate catalyst. Aliphatic amine (HY 951, Ciba‐Geigy), aromatic amine (HT 972, Ciba‐Geigy) and polyamidoamine (HY 840, Ciba‐Geigy) are used as curing agents for epoxy resins. The tentative level of 10% siloxane introduction into epoxy resin has been ascertained from experimental studies to obtain reasonable improvements in the impact behavior without compromising other mechanical properties. The impact behavior of E‐glass reinforced composites made from the siliconized epoxy resin is enhanced to 2–4 times over that measured on the composites made from a pure epoxy resin. Composites cured with aromatic amine impart better mechanical properties than those cured with aliphatic amine and polyamidoamine.
The influence of crystallinity on interfacial properties of carbon and SiC two‐fiber/polyetheretherketone (PEEK) composites
Authors: Park Joung‐Man , Kim Dae‐Sik
Published: April 2004

The influence of the degree of crystallinity on interfacial properties in carbon and SiC two‐fiber reinforced poly(etheretherketone) (PEEK) composites was investigated by the two‐fiber fragmentation test. This method provides a direct comparison of the same matrix conditions. The tensile strength of the PEEK matrix and the interfacial shear strength (IFSS) of carbon or SiC fiber/PEEK exhibited the maximum values at around 30% crystallinity, and then showed a decline. The tensile modulus increased continuously with an increase in the degree of crystallinity. Spherulite sizes in the PEEK matrix became larger as the cooling time from the crystallization temperature increased. Transcrystallinity of carbon fiber/PEEK was developed easily and more densely than with SiC fiber/PEEK. This might have occurred because the unit cell dimensions of the crystallite in the fiber axis direction on the carbon surface was more suitable for making nucleation sites. The IFSS of carbon fiber/PEEK was significantly higher than that of SiC fiber/PEEK because it formed transcrystallinity of IFSS more favorably.
Fatigue life prediction of matrix dominated polymer composite materials
Authors: Lee C. S. , Hwang W.
Published: April 2004

Fatigue life prediction is investigated analytically for matrix dominated polymer composite laminates having nonlinear stress/strain response, based on the fatigue modulus concept. Fatigue modulus degardation rate at any fatigue cycle was assumed as a power function of number of fatigue cycles. A new stress function describing the relation of initial fatigue modulus and elastic modulus was used to account for material non‐linearity at the first cycle. It was assumed that fatigue modulus at failure is proportional to the applied stress level. A new fatigue life prediction equation as a function of applied stress is proposed. The prediction was verified experimentally using cross‐ply carbon/epoxy laminate (CFRP) tube under torsional fatigue loading. It is shown that the proposed equation has wide applicability and agrees well with experimental data.
Thermotropic liquid crystal polymer fabric reinforced polyimide composite materials
Authors: Kim Seong Hun , Lim Dong Keun , Yi Sung Chul , Oh Kyung Wha
Published: April 2004

An aromatic copolyeste thermotropic liquid crystal polymer (LCP) fabric was used to reinforce a polyimide (PI) matrix to produce composites. The LCP/PI composite was made to eliminate directional difference in the mechanical properties of LCP by controlling the individual reinforcement fabric alignment in different directions without losing any mechanical properties. As a result, a transversely isotropic LCP composite material could be obtained from the highly anisotropic LCP fiber. Interfacial adhesion between the LCP and polyimide was greatly improved by a NH3/H2 plasma treatment on the LCP fabric, thereby the significantly improving mechanical properties of the composite. Moreover, inter‐laminar shear strength of the LCP/PI composite was further increased after heat treatment at 220°C for 1 hour. The LCP/polyimide composite retains stable mechanical properties up to 250°C.
Comparison of the roles of two shrinkage‐controlled low‐profile additives in water aging of polyster resin–glass fiber composites
Authors: Camino G. , Ya. Polishchuk A. , Luda M. P. , Revellino M.
Published: April 2004

A model previously formulated or water sorption in polyester resin‐glass fiber composites has been applied to the kinetic analysis of experimental data for two composites containing a hydrolysable (polyvinyl acetate‐PVAc) and a non‐hydrolyzable (polystyrene‐PS) shrinkage‐controlling low‐profile additive (LPA) respectively. It was found that the equilibrium water uptake in the composites and their unreinforced matrix is not drastically affected by the type of LPA. The kinetics of water sorption in the composites, however, were substantially different. The PVAc composite displayed a two‐stage sorption process, the first stage being attributed to diffusion combined with hydrolysis, and the second to matrix swelling and plasticizing. A maximum in the kinetic curve was observed, and was due to changes in water solubility inside the matrix during sorption. In contrast, the PS composite displayed the typical kinetics of materials with slowly increasing hydrophilicity.
Compression molding of glass reinforced thermoplastics: Modeling and experiments
Authors: Dweib M. A. , Brádaigh C. M. Ó
Published: April 2004

The shearing and extensional behavior of glass mat‐thermoplastic (GMT) material under compression molding was investigated with a special model being developed for the case of non‐lubricated mold‐plate surfaces. Mathematical expressions for the radial and through‐thickness flow velocities were derived that enabled the derivation of extensional and shear strain rates. The GMT non‐lubricated (no‐slip wall conditions) compression molding was modeled as a combination of extensional and shearing flow and the two extensional and shear viscosities were determined. Scott's approach was used in this work to determine the radial velocit in the r‐direction, which depends on the shear power‐law expression. The velocity component in the z‐direction was then calculated using the continuity equation. The velocity profiles were used to calculate the shear and extensional strain rates. Scott's shear viscosity did not satisfy the constitutive equation for the extensional part, but a power‐law expression with new parameters depending on the deformation tensors was successfully used to calculate an independent extensional viscosity using the same non‐lubricated squeezing experiment. Lubricated squeezing flow was carried out for the same material to achieve a pure extensional flow, and the extensional viscosity calculated using this approach agreed with the extensional viscosity determined using the non‐lubricated experiment. GMT material used in this study is confirmed to have two layers of continuous long fibers orientated randomly inplane, separated by short chopped fibers in the middle, which suggests that the material can be treated as an isotropic material, and the fiber‐matrix separation is seen to be high at the extremities of the flow.
In‐situ reinforcement of PBT/ABS blends with liquid crystalline polymer
Authors: Tjong S. C. , Jiang Wei
Published: April 2004

Ternary in‐situ poly(butylene terephthalate) (PBT)/poly(acrylonitrile‐butadienestyrene) (ABS)/liquid crystalline polymer(LCP) blends were prepared by injection molding. The LCP used was a versatile Vectra A950, and the matrix material was PBT/ABS 60/40 by weight. Maleic anhydride (MA) copolymer and solid epoxy resin (bisphenol type‐A) were used as compatibilizers for these blends. The tensile, dynamic mechanical, impact, morphology and thermal properties of the blends were studied. Tensile tests showed that the tensile stregth of PBT/ABS/LCP blend in the longitudinal direction increased markedly with increasing LCP content. However, it decreased sharply with increasing LCP content up to 5 wt%; thereafter it decreased slowly with increasing LCP content in the transverse direction. The modulus of this blend in the longitudinal direction appeared to increase considerably with increasing LCP content, whereas the incorporation of LCP into PBT/ABS blends had little effect on the modulus in the transverse direction. The impact tests revealed that the Izod impact strength of the blends in longitudinal direction decreased with increasing LCP content up to 10 wt%; thereafter it increased slowly with increasing LCP. Dynamic mechanical analyses (DMA) and thermogravimetric measurements showed that the heat resistance and heat stability of the blends tended to increase with increasing LCP content. SEM observation, DMA, and tensile measurement indicated that the additions of epoxy and MA copolymer to PBT/ABS matrix appeared to enhance the compatibility between PBT/ABS and LCP.