bluuebunny/crossref_metadata_2025_split huggingface dataset:
Low temperature relaxation of DGEBA epoxy resins: A thermally stimulated discharge current (TSDC) study
Authors: Pangrle S. , Wu C. S. , Geil P. H. 
Published: December 2004

AbstractThe effect of curing conditions on the low temperature relaxation behavior of catalyst‐cured epoxy systems based on digliycidyl ether of bisphenol A (DGEBA) has been characterized by the thermally stimulated discharge current (TSDC) technique. In these chemically relatively simple epoxy systems, five relaxation processes, designated as γ, β, β′, βOH, and β″, have been observed: Their molecular origins are discussed in detail. The results are in agreement with prior suggestions of an inhomogeneous cross‐link density morphology.
Failure of composite laminae under biaxial loading
Authors: Neale K. W. , Labossière P. 
Published: December 2004

AbstractThe failure of thin, fiber‐reinforced composite laminae is considered. A parametric failure criterion applicable to plane stress loading conditions is presented. Both static and fatigue‐type loadings are treated. In general, the formulation of failure criteria for composite materials has closely followed the development of yield criteria in metal plasticity. The parametric failure criterion presented here was inspired by a general formulation recently proposed for the plastic yielding of sheet metals. The criterion satisfies the essential conditions that must be met in developing phenomenological strength criteria for composite materials. This entirely general formulation encompasses all previously proposed failure theories for fiber‐reinforced orthotropic laminae. The inherent advantages and drawbacks of the proposed parametric approach are discussed. An example of application for static loading is presented in detail. Possible extensions of the approach to fatigue‐type loading are also suggested.
Numerical and experimental evaluation of the Mode III interlaminar fracture toughness of composite materials
Authors: Becht G. J. , Gillespie J. W. 
Published: December 2004

AbstractThe Crack Rail Shear (CRS) specimen is a proposed test method to characterize the interlaminar Mode III critical strain energy release rate (GIIIc) of continuous fiber‐reinforced composite materials. The specimen utilizes the two rail shear test fixture and contains embedded Kapton film between designated plies to provide a starter crack for subsequent fracture testing. Analytical expressions for specimen compliance and GIII are based upon Strength of Materials (SM) principles. The model identifies important material and geometric parameters and provides a simple data reduction scheme. A quasi‐three‐dimensional, linear elastic finite element stress analysis verifies the purity of the Mode III fracture state and identifies admissible crack lengths to be used in the experimental study. A fully three‐dimensional linear elastic finite element analysis of the CRS is employed to investigate the influence of edge effects on the fracture state for the finite length sample. Results based upon a uniform crack extension indicate a small region of mixed mode behavior at traction free edges which decay to a pure Model III fracture state in the interior of the sample. Furthermore, the GIII distribution along the crack front decreases at the free edges from a maximum plateau region in the interior. The three‐dimensional analysis allows edge effects to be minimized by selecting appropriate specimen lengths. Compliance and strain energy release rates are in good agreement with the SM model. An experimental program was performed to measure GIIIc of two graphite epoxy systems. GIIIc results for AS4/3501‐6 were found to be 1.6 times the Mode II fracture toughness, while IM7/8551‐7 exhibited equivalent Mode II and Mode III fracture toughnesses. Mode III fracture surfaces revealed microstructural deformations characteristic of Mode II fracture.
The effect of processing variables on microstructure of injection molded short fiber reinforced polypropylene composites
Authors: Singh P. , Kamal M. R. 
Published: December 2004

AbstractInjection molded composites of polypropylene reinforced with short glass fibers were obtained under a variety of injection molding conditions. The microstructure of the moldings was determined using a variety of experimental techniques, including optical and scanning electron microscopy, differential scanning calorimetry, Fourier transform infra‐red spectroscopy, and thermogravimetry. Thus, it was possible to obtain a detailed characterization of the crystallinity, morphology, and orientation distribution in the matrix, in addition to the distribution of fibers and their orientation of the fibers in the composite. The influence of molding conditions on the above microstructural characteristics is summarized in an effort to explain the experimental observations.
Effect of60Co gamma radiation on the mechanical properties of epoxy blends and epoxy‐graphite fiber interface
Authors: Netravali A. N. , Manji A. 
Published: December 2004

AbstractThe effect of60Co gamma radiation of up to 100 Mrads on an IM6‐G graphite fiber‐epoxy interface was studied using the single‐fiber‐composite (SFC) technique. Flexible epoxy blends were formulated using diglycidylether of bisphenol‐A (DGEBA) based and polyglycol diepoxide epoxies which were cured with aliphatic and aromatic curing agents. Bulk epoxy specimens and graphite fibers were tension tested to obtain their tensile properties. The fragment length distribution from SFC tests, single fiber strength data, and a Monte Carlo simulation of Poisson/Weibull model for fiber strength and flaws were used to obtain the effective interfacial shear strength values. The results indicate that while graphite fiber strength is not affected by radiation, the tensile properties of the epoxies used are adversely affected by the radiation. The interfacial shear strength, however, increases significantly with the radiation dose. The study also supports the earlier results of many workers that the interfacial shear strength for flexible epoxies is much higher than the shear yield strength of the epoxies.
Kinetics of strain‐induced crystallization during injection molding of short fiber composites of poly(ether ether ketone)
Authors: Mishra Ajit Kumar , Schultz Jerold M. 
Published: December 2004

AbstractCrystallization kinetics of short glass and carbon fiber composites of poly(ether ether ketone) (PEEK) under melt‐strain conditions have been obtained for the first time, using in‐situ wide angle X‐ray scattering, and have been correlated to a model based on the Avrami equation in order to enable minimization of the processing time for injection molding of these materials. It has been demonstrated that increased flow rate of the melt in the mold and, consequently, increased shear rate accelerates the crystallization process of PEEK composites, analogous to similar trends observed previously in PEEK resin. Short glass fiber composites of PEEK crystallize slower than the resin under identical processing conditions, while short carbon fiber composites crystallize faster than the resin, except at the highest mold temperatures and the lowest flow rates. A model based on the Avrami equation has been proposed to fit the kinetics data obtained experimentally. The Avrami coefficient has been calculated and Arrhenius plots have been used to predict the crystallization kinetics at temperatures lower than those at which experimental data have been obtained here. Fiber orientation, flexural elastic modulus, and flexural fracture toughness of the composites have also been evaluated.
On the dynamic mechanical behavior of poly(methyl methacrylate) reinforced with Kevlar fibers
Authors: Calleja R. Díaz , Ribelles J. L. Gómez , Pradas M. Monleón , Greus A. Ribes , Colomer F. Romero 
Published: December 2004

AbstractThe dynamic mechanical relaxation behavior of poly(methyl methacrylate) reinforced by continuous parallel Kevlar‐49 fibers is investigated here on samples with several fiber volume fractions. The shifts in the temperature of the main relaxation of the matrix are interpreted according to free volume considerations and with the help of a thermomechanical block model. The dependence of the storage and loss moduli both on temperature and fiber content found experimentally can be reproduced by the model. It is not necessary to rely on the existence of an interphase to account for the modifications evidenced by the spectrum of the matrix, which can be explained on the basis of the two phase model.
In‐situ acoustic emission monitoring during electron microscopy of a model composite system
Authors: Siegmann A. , Kander R. G. 
Published: December 2004

AbstractThree‐point‐bend testing of a continuous unidirectional glass reinforced unsaturated polyester composite was chosen as a model to study the acoustic emission (AE) response and associated damage events in composite materials. Conventional three‐point‐bend samples were tested over a wide range of span‐to‐depth ratios, with failure modes established by post‐failure scanning electron microscope (SEM) analysis. In addition,in‐situAE monitoring with simultaneous SEM recording was undertaken during three‐point‐bend testing inside an SEM vacuum chamber. These two test methods, using different equipment and sample geometry, were found to yield similar mechanical and AE results. Thein‐situtests enabled the development of the various stages of damage to be observed while the AE response was simultaneously monitored. This enabled the AE signals to be unambiguously assigned to specific damage accumulation mechanisms. It was concluded that the AE amplitude distribution can be divided into three main ranges in this system: 60 to 65 dB, 75 to 85 dB, and larger than 90 dB corresponding to matrix damage, fiber‐matrix debonding, and fiber breakage, respectively. It has been demonstrated that the coupling of AE monitoring with SEM recording of a composite system undergoing mechanical loading is a very powerful technique in the study of damage accumulation in advanced composite materials.
The influence of processing on fiber orientation and creep in short carbon‐fiber reinforced low density polyethylene and polycarbonate
Authors: Bertilsson H. , Franzén B. , Klason C. , Kubát J. , Kitano T. 
Published: December 2004

AbstractThis paper is concerned with the creep behavior of short fiber‐reinforced thermoplastics, especially with regard to the role of fiber orientation. Rectangular samples of low density polyethylene (LDPE) and polycarbonate (PC) containing varying amounts of carbon fibers were prepared by compression and injection molding. The materials were compounded using a technique producing a concentration independent fiber length distribution. The orientation distribution, on the other hand, was found to be strongly influenced by fiber concentration. The creep parameters were measured for both LDPE and PC. The contraction ratio was determined for the PC samples. In the case of LDPE reliable data could not be obtained due to the low modulus of the matrix. The creep properties of the PC and LDPE samples varied significantly with the orientation of the fibers. The creep strain was measured as a function of time for both polymers for different fiber concentrations and orientations. The predictions of the Halpin‐Tsai equation underestimated the experimental strain figures somewhat when the stress direction coincided with that of the fiber orientation. When the stress acted across the fibers the theoretical and experimental results showed satisfactory agreement. A plausible explanation is that incorporation of carbon fibers changes the morphology of the matrix material. We conclude that the contraction ratio is an important measure of the volume and its changes during deformation, especially with regard to its relation to the free volume and similar quantities. We have shown that the necessary data can be obtained, in spite of experimental difficulties even for anisotropic samples.
Mechanism of damage and failure in an orthotropic glass/polypropylene composite
Authors: Kander R. G. , Siegmann A. 
Published: December 2004

AbstractThe mechanism of damage accumulation and failure in thin sheets of an orthotropic long discontinued glass fiber reinforced polypropylene composite was studied using optical and electron microscopy coupled with acoustic emission (AE) monitoring. The effect of strain rate (0.1 to 100 percent) was investigated, and a close correspondence was established between AE response and microscopic observations. Furthermore, simultaneous AE monitoring and optical microscopy performed during sample deformation substantiated the assignment of certain AE amplitude ranges with specific failure events in the composite. Specifically, the failure process was found to be very inhomogeneous in nature, and could be divided into three main stages of damage accumulation. Finally, cumulative AE energy curves were found to follow an interesting powerlaw behavior. Results based on the coupling of AE methods with optical and electron microscopy were found to be self consistent and in agreement with previous reports on thicker‐section composites manufactured from the same materials.
Cure kinetics of dicyanate matrix polymers
Authors: Zeng Shangying , Ahn Kyujong , Seferis James C. , Kenny J. M. , Nicolais L. 
Published: December 2004

AbstractThe cure kinetics of two dicyanate resins were investigated by differential scanning calorimetry under isothermal and nonisothermal conditions. An autocatalytic kinetic model was proposed and a set of general kinetic parameters was calculated from the isothermal experiments. Good agreement between experimental data and the kinetic model has been obtained under different processing conditions, which demonstrated the validity and the usefulness of the analytical procedure and of the kinetic expression employed. Consequently, in its current form, the modeling methodology is capable of describing the degree of cure during a typical processing cycle and has the potential for comparing different resin formulations as well as the manifestations of cure in property development. Specifically, in this work the modeling methodology was tested using two distinct dicyanate resin systems while the development of the cure was also observed through dielectric analysis (DEA).
Friction and wear bahavior of short fiber‐reinforced poly(amide‐imide) composites
Authors: Lee Kee H. , Youn Jae R. 
Published: December 2004

AbstractTribological behavior of short fiber‐reinforced thermoplastic composites was investigated experimentally and theoretically. Short carbon fiber and glass fiber reinforced poly(amide‐imide) composites were tested. Titanium oxide powder‐filled composite was also tested for comparison with the fiber composites. Block‐on‐ring type wear testing was performed for 24 h at three different sliding conditions. Frictional force was measured and stored by a data acquisition system and wear was measured as weight loss after the test. Wear tracks on the specimen and the counterface were examined with an optical microscope to observe fiber damage and formation of wear film. The equivalent stress distribution around each fiber at the sliding surface was calculated by employing a finite element program. The lowest friction and wear was obtained for the carbon fiber composite, the highest friction for the glass fiber composite, and the highest wear for TiO2‐filled one. It was observed that the glass fibers are damaged and removed from the surface more easily than the carbon fibers, and the finite element analysis also suggests easier debonding of glass fibers.
Fiber mat deformation in liquid composite molding. II: Modeling
Authors: Han K. , Lee L. James , Liou Ming 
Published: December 2004

AbstractMathematical models are proposed to simulate the flow induced fiber mat deformation during liquid composite molding. The fiber bed is treated as an elastic beam and the load acting on the bed causes its deformation. The lubrication approximation is used to simplify the resin flow equation in the fiber free region, while Darcy's law is used to calculate the pressure and velocity fields in the deformed fiber bed. The governing equations are solved using the control volume/finite element method. The numerical results show reasonable agreement with the experimental results from Part I.
Electrical degradation of blends and laminar composites of polyethylene and polystyrene
Authors: Gustafsson A. , Salot R. , Gedde U. W. 
Published: December 2004

AbstractPhysical blends and laminar composites of polystyrene (PS) and polyethylene (PE) were prepared with and without a tri‐block copolymer compatibilizer (poly(styrene‐block‐(ethylene‐co‐1‐butene)‐block‐styrene)), denoted SEBS. Dielectric strength and breakdown time of samples exposed to external partial discharges (PD) were measured and relationships were sought with composition, phase morphology, and phase bonding. The polymers were selected because they are incompatible and because the dielectric strength and stability towards PD are greater for PS than for PE. It was shown by adding small quantities of SEBS that a minimum amount of cohesive forces between the components was required to achieve good electrical properties. The major morphological factor controlling the electrical stability was which polymer constituted the continuous phase. Laminar composites with continuous sheets of stable PS as a top layer exhibited a stability equal to or better than that predicted from the upper bound rule of mixing.
Micromechanics prediction of the transverse tensilc strength of carobn fiber/epoxy composites: The influence of the matrix and interface
Authors: Blackketter D. M. , Upadhyaya D. , King T. R. 
Published: December 2004

AbstractCurrently, there is great interest in understanding and improving the bond between the fibers and matrix in high performcance composite materials. In many recently developed systems, fiber surface treatments have been developed to improve poor bonding. These treatments are often evaluated by measureing their effect on a composite property sensitive to the interfacial bond strength, typically the composite shear strength. This paper presents an evaluation of the influence of the matrix and interface properties on the transverse tensile strength. These effects were quantified by compring transverse flexural experimental data with results from a finite element micromechanics model. The results indicate that the transverse tensile strength is significantly more dependent upon sizing than is the shear strength. Finally, the transvere flexure test appears to provide an additional and complementary test for evaluating interface bond characteristics.
The effect of pre‐carbonization on the properties of PAN‐based carbon fibers
Authors: Ko Tse‐Hao , Day Tzyy‐Chin 
Published: December 2004

AbstractA continuous stabilization and two‐stage carbonization process was used to prepare polyacrylonitrile (PAN)‐based carbon fibers, The effect of pre‐carbonization (300 to 550°C) on the final properties and microstructure of carbon fibers was measured. Experimental results using an X‐ray diffractometer indicated the presence of a less ordered structure at 2Θ from 5 to 18° in the pre‐carbonized fibers and the final carbon fibers. This study found that the pre‐carbonization process strongly affects the microstructure of the resulting carbon fibers. The results also showed that a suitable pre‐carbonization was very conducive to improvement in tensile strength or in Young's modulus of the final carbon fibers. When the final carbon fiber was pre‐carbonized at 300 and 550°C, respectively, these fibers had a higher tensile strength and higher Young's modulus than carbon fibers pre‐carbonized at other conditions.
Physical modeling of the interphase in amorphous thermoplastic/glass bead composites
Authors: Alberola N. , Bergeret A. 
Published: December 2004

AbstractMechanical spectrometry was performed on polystyrene/glass bead and poly (styrene‐co‐methacrylic acid)/glass bead composites to test for the influence of the interphase on molecular mobility. To quantify these motion changes, a physical model was developed to predict the deformation of amorphous materials near Tg. Before applying this model, the dynamic mechanical behavior of the two phases (matrix and inclusions) must be separated to remove the reinforcement effect of the fillers and to keep only the physical crosslinking effect of the amorphous phase by the inclusions. It was shown that (i) the fillers can induce the nation of specific interactions, which act as physical ties, reducing molecular mobility and that (ii) the decrease in molecular motion with increasing filler content is enhanced for fillers coated by a silane coupling agent.
The application of fracture mechanics to short fiber composites
Authors: Huang Donald D. 
Published: December 2004

AbstractThe fracture performances of three short glass fiber‐reinforced polymer composite systems, PET with 30 wt% glass, nylon 6/6 with 33% glass fibers, and a nylon 6 and 6/6 copolymer with 33% glass, have been characterized using both standard mechanical characterization and fracture mechanics. These results have been compared to fracture tests of an experimental chair base. None of the characterizing techniques was successful in predicting the chair base fracture performances of the materials when the tests were conducted on standard 3‐mm‐thick test specimens. When larger specimens with comparable morphologies to the chair base were tested, the fracture mechanics tests compared favorably to the chair base fracture tests while the tensile test results were inconsistent in their predictive ability. The findings emphasize the importance of testing laboratory specimens that are similar in morphology to the final part and suggest that fracture mechanics methodologies can be used in materials selection of glass reinforced systems for structural applications. However, for quantitative design, it is necessary to address issues regarding the nature of the inherent flaw in the finished parts.
The effects of stress level on steady crack growth in an epoxy reinforced with long aligned glass fibers
Authors: Botsis J. , Caliskan A. , Beldica C. 
Published: December 2004

AbstractResults are reported of fatigue crack propagation experiments on an epoxy reinforced with long aligned glass fibers. The composite was prepared in such a way that fiber spacing was approximately the same in each specimen and the reinforcing fibers were sufficiently stronger than matrix. For a number of experiments with the same fiber spacing, fatigued under various stress levels, the crack speed as well as the rate of debonding reached steady values, i.e., independent of the crack length. In addition, the evolution of debonding followed a self‐similar growth pattern. The data implied that the applied load was a controlling parameter of the steady growth. Within the resolution of observations, no fiber fracture was observed in the bridging zone. Fiber debonding seemed to be the dominant mechanism of energy dissipation. Moreover, the crack front was not straight. Instead, it consisted of two branches growing on the specimen's surfaces first and then through the thickness of the specimen with a highly curved front. Stress intensity factor calculations showed that when the fibers in the bridging zone were under a uniform load, the total stress intensity factor was proportional to \documentclass{article}\pagestyle{empty}\begin{document}$ \sigma \sqrt \lambda $\end{document} (where σ is the applied stress and λ is the fiber spacing) and constant within the regime of steady crack growth. The steady values of crack growth and rate of debonding were correlated with the stress level, spacing, and fiber radius. The resulting power equations were found to have the same exponent.