bluuebunny/crossref_metadata_2025_split huggingface dataset:
Determination of elastic constants of transversely isotropic materials by combining vibration testing and numerical method
Authors: Hwang Shun‐Fa , Chang Chao‐Shui , Chang Kung‐Lin 
Published: April 2004

AbstractSince it is nondestructive and can produce global properties, the method combining vibration testing and numerical analysis is a potential approach to determine elastic constants of materials. In order to simplify the modeling process and reduce the complexity of the numerical analysis, both the direct determination method and the inverse determination method are presented in this work. In the direct determination method, two special natural frequencies of an X mode and a ring mode are obtained by the vibration testing of a plate with special dimensions decided from another arbitrary plate. Five natural frequencies obtained from both plate specimens can be used to determine four elastic constants of transversely isotropic materials by substituting them into the existing formulas. In the Inverse determination method, the combination of finite element analysis and optimum design is adopted to inversely calculate the elastic constants. Thin plates of steel and carbon/epoxy composites are selected to demonstrate the procedures and to compare the application of both methods. The results indicate that the elastic constants predicted by both methods are in good agreement with the reference values. Even though the steel plate is treated as a transversely isotropic material, these predicted constants also satisfy the conditions of isotropy. However, it is always difficult and cumbersome to find the X and ring modes in the direct determination method, especially for composite materials. Therefore, the inverse determination method is generally recommended because of its single test and versatility.
Effects of water, salt solution and simulated concrete pore solution on the properties of composite matrix resins used in civil engineering applications
Authors: Chin Joannie W. , Aouadi Khaled , Haight Michael R. , Hughes William L. , Nguyen Tinh 
Published: April 2004

AbstractOne of the obstacles hindering the acceptance of polymer composites in civil engineering applications is the susceptibility of the polymeric matrix to degradation that is initiated by moisture, temperature, and corrosive chemical environments. The objective of this study was to characterize chemical and physical changes in polymer matrix resins following exposure to these environments. Resin systems studied were vinyl ester and isophthalic polyester, both of which are proposed for use in construction applications. Unreinforced free films were exposed to water, alkaline and saline environments at ambient and elevated temperatures for extended periods of time. Changes in strength and thermophysical properties were evaluated through tensile testing, dynamic mechanical thermal analysis (DMTA) and thermogravimetric analysis (TGA). Chemical degradation of the polymers was characterized using Fourier transform infrared (FTIR) spectroscopy. Energy dispersive X‐ray (EDX) analysis of specimens following exposure was carried out to determine if ion diffusion into the bulk polymer occurred. Only minor changes in the glass transition temperatures of the polymers were observed after prolonged exposure at elevated temperature, but more substantial changes were noted in tensile strength, particularly in the case of the isophthalic polyester. Examination of the polymers following immersion in salt solution and alkaline solution showed essentially no ionic penetration into the bulk, with the exception of specimens that were visibly degraded. Spectroscopic analysis of chemical structure prior to and following exposure revealed varying degrees of ester hydrolysis.
Analysis of an image processing method for fiber orientation in polymer composites
Authors: Vahlund C. Fredrik , Gebart B. Rikard 
Published: April 2004

AbstractThe errors in fiber orientation distribution measurements of compression molding materials have been investigated, for generated as well as for real distributions. Because of the size of the sample, only a finite number of fibers are visible in a picture leading to a statistical error in the measurement. A method is proposed to express this error as function of the number of visible fibers and the number of subintervals the distribution is divided into. Studies of the error In a Fraunhofer/FT based fiber orientation distribution analysis have been performed, including effects of increasing number of fibers (fiber‐fiber intersections) in generated pictures and investigation of the errors in real fiber images. All steps in a fiber orientation distribution analysis of SMC/GMT kind of material are described, including suitable equipment, image enhancement methods and investigation of the errors present in analysis of a real image as well as comparisons to hand–measured data.
Effect of reinforcement structure on compaction behavior in the vacuum infusion process
Authors: Hammami A. 
Published: April 2004

AbstractThe Vacuum infusion molding process is gaining Increased popularity for its relatively short cycle time, low equipment cost and low labor requirements. Furthermore, for large and complex structures, it offers a high potential of integration In addition to the complete elimination of volatile organic compound (V.O.C.) emissions, which are considered to be a major health concern for employees within the composite Industry. Successful implementation of the process, especially for large structures such as boat hulls where large amounts of raw materials are involved, requires the completion of the impregnation phase in the shortest time possible. This can be achieved by the integration of a highly permeable layer to the reinforcement stack. However, this will strongly affect the compaction behavior of the resulted stack. This paper investigates the effect of the reinforcement structure on the overall compaction behavior. More specifically, the investigation is oriented toward the effect of the flow enhancement layer on the compaction response.
Influence of the steel core of composite squirrel cage rotor on motor performance
Authors: Chang Seung Hwan , Lee Dali Gil 
Published: April 2004

AbstractSince the critical whirling vibration frequency of high speed built‐In type motor spindle systems is dependent on the rotor mass of the built‐In motor and the spin‐die specific bending modulus, the rotor and the shaft were manufactured using magnetic powder contained epoxy and high modulus carbon fiber epoxy composite, respectively. In order to enhance the magnetic flux of the composite squirrel cage rotor of an AC induction motor, a steel core was inserted into the composite rotor. The motor parameters of the developed composite rotor system were obtained from the no‐load and blocked rotor tests and the effect of thickness of the steel core on the motor performance was investigated. From the magnetic analysis, the optimal steel core size for the dynamic characteristics of the rotor system mounted on the carbon fiber epoxy composite spindle was determined.
Fundamental investigation of cure‐induced microcracking in carbon fiber/bismaleimide cross‐ply laminates
Authors: Lincoln Jason E. , Morgan Roger J. , Shin E. Eugene 
Published: April 2004

AbstractTransverse microcracks are present in carbon fiber/bismaleimide (BMI) cros: composite laminates composed of 4, 4′‐bismaleimidodiphenylmethane (BMPM)/diallyl bisphenol A (DABPA) matrices after standard cure and fabrication condit and grow in width upon subsequent postcure. This investigation characterizes cure‐induced microcracking in terms of the critical fundamental macroscopic croscopic, and molecular damage mechanisms and thresholds, and a cure cycle modification that prevents microcrack formation under standard processing conditions tions for [0°/90°]s laminates is examined. A unique in‐situ technique is utilized which cure of the laminate is performed inside the chamber of an environim scanning electron microscope (ESEM), allowing for (i) physical observation of microcrack crack growth and formation mechanisms and (ii) characterization of microcracking onset time‐temperature thresholds. The cure cycle modification that prevents microcracking is an extended initial cure time at 177°C prior to higher temperature; cure regimes. Effects of this modification are examined through network structure property‐processing interrelationships by way of (i) dynamic mechanical analysis (DMA), (ii) optical and electron microscopy, (iii) differential scanning calorimetry (DSC), and (iv) our previous work on carbon fiber/bismaleirnide composites. The aforementioned analysis it was concluded that an extended initial cure time 177°C prior to higher temperature cure steps prevents microcracking under standard; fabrication postcure conditions for [0°/90°]s laminates; no microcracking observed until an additional postcure of 6 h at 300°C. This microcrack resist was independent of initial BMPM:DABPA monomer stoichiometry for the monomer ratios examined and associated with an improved fiber‐matrix interface and lower composite residual stress.
Solid state bonding of graphite/thermoset composites via interchain transesterification reaction (ITR)
Authors: López Alfonso , Economy James 
Published: April 2004

AbstractThick section composite laminates are expensive and difficult to manufacture because of problems with porosity, large reaction exotherms from epoxies and residual strains. The copolyester thermosets described here can eliminate these problems. Through interchain transesterification reactions, individually cured prepreg plies of graphite reinforced copolyester can be bonded with each other in the solid state. ITR bonding is shown to produce well‐consolidated laminates with less than 2% void volume and mechanical properties comparable to those of current high‐end polymer matrix composites. DMA testing showed the glass transition to begin at 190°C for a 45% fiber volume fraction composite. Tensile testing of 55% fiber volume composites at room temperature showed modulus, strength and elongation to failure averages of 105.4 GPa, 1.02 GPa and 1.0% respectively.
Modification of thermosetting resins and composites through preformed polymer particles: A review
Authors: Hayes Brian S. , Seferis James C. 
Published: April 2004

AbstractA review is presented that focuses on preformed particle modification of high performance thermosetting resins and composite systems. The modifiers reviewed consist of thermoplastic and rubber preformed particles with no size limitations. Both organic and inorganic preformed polymer particles are considered but not glass or hollow spheres. In this text, preformed particles are defined as those which do not require phase separation and remain in the shape in which they were added to the neat resin or composite. Therefore, these particles may be developed prior to the resin formulation and then added to the thermosetting resin or developed in situ (during resin formulation) before the resin is catalyzed or cured. This technical review of preformed particle modification of thermosetting resins and composite systems summarizes the utilization of these materials and their performance.
The influence of fiber surface modification on the mechanical properties of coir‐polyester composites
Authors: Rout J. , Tripathy S. S. , Misra M. , Mohanty A. K. , Nayak S. K. 
Published: April 2004

AbstractCoir, an important lignocellulosic fiber, can be incorporated in polymers like unsaturated polyester in different ways for achieving desired properties and texture. But its high level of moisture absorption, poor wettability and insufficient adhesion between untreated fiber and the polymer matrix lead to debonding with age. In order to improve the above qualities, adequate surface modification is required. In our present work, fiber surface modification was effected through dewaxing, alkali (5%) treatment, aqueous graft copolymerization of methyl methacrylate (MMA) onto 5% alkali treated coir for different extents using CuSO4 – NaIO4 combination as an initiator system and cyanoexhylation with a view to improve the mechanical performance of coir‐polyester composites. Mechanical properties like tensile strength (PS), flexural strength (ES) and impact strength (IS) of the composites as a function of fiber loading and fiber surface modification have been evaluated. Composites containing z5 wt% of fiber (untreated) improved tensile and flexural strength by 30% and 27% respectively in comparison to neat polyester. The work of fracture (impact strength) of the composite with 25 wt% fiber content was found to be 967 J/m. The elongation at break of the composites exhibits an increase with the introduction of fiber, All types of surface modification result In improved mechanical properties of the composites. Significant improvement in mechanical strength was also observed for composites prepared from 5% PMMA grafted fiber.
Investigation of unsaturated flow in woven, braided and stitched fiber mats during mold‐filling in resin transfer molding
Authors: Slade J. , Pillai K. M. , Advani S. G. 
Published: April 2004

AbstractIn Resin Transfer Molding (RPM), which is a process to manufacture polymer composites, the impregnation of fibrous reinforcement In the form of mats by a thermosetting resin is modeled as the flow of a Newtonian liquid through a single length‐scale porous medium. While this approach is sufficiently accurate for random fiber‐mats, it can lead to appreciable errors when applied to woven, braided, or stitched fiber‐mats that contain two length scales. This work investigates the primary factors governing the isothermal unsaturated flow through such dual‐scale porous media. Two studies were conducted to better understand this phenomenon: the first experimenatally investigated the flow, while the second theoretically modeled the flow and identified important parameters affecting such a flow with the help of dimensionless analysis. In the first study, one‐dimensional constant injection rate experiments were performed using various fiber mats. The unsaturated flow behavior of various mats was characterized using a constant “sink” term in the continuity equation. Results indicated that for a given fiber‐mat, the magnitude of the sink effect was a function of the capillary number. In the second study, a numerical model was developed to describe flow through dual‐scale preforms in which the two flow domains, the inter‐ and intra‐tow regions, were coupled. We identified a dimensionless number called the sink effect index ψ that characterizes the magnitude of liquid absorption by the tows and is a function of the relative resistance to flow in the tow and inter‐tow regions, and the packing density of the tows. The parametric study of this index with the help of numerical simulations reveals its influence on the flow and identifies the distinct transient and steady‐state flow regimes.
Prediction of failure and fracture mechanisms of polymeric composites using finite element analysis. Part 2: Fiber reinforced composites
Authors: Ghassemieh E. , Nassehi V. 
Published: April 2004

AbstractA robust finite element scheme for the micro‐mechanical modeling of the behavior of fiber reinforced polymeric composites under external loads is developed. The developed model is used to simulate stress distribution throughout the composite domain and to identify the locations where maximum stress concentrations occur. This information is used as a guide to predict dominant failure and crack growth mechanisms in fiber reinforced composites. The differences between continuous fibers, which are susceptible to unidirectional transverse fracture, and short fibers have been demonstrated. To assess the validity and range of applicability of the developed scheme, numerical results obtained by the model are compared with the available experimental data and also with the values found using other methods reported in the literature. These comparisons show that the present finite element scheme can generate meaningful results in the analysis of fiber reinforced composites.
Inferring the degradation of pultruded composites from dynamic nonlinear resonance measurements
Authors: Van Den Abeele K. , Carmeliet J. , Van De Velde K. 
Published: April 2004

AbstractThe Chemical resistance of pultruded polyester composites to various chemical immersion solutions is investigated as a function of the exposure time, and the observations from static tests are compared with the results from nonlinear dynamic vibration experiments. The mechanical properties were measured according to ASTM standards, both in flexural and tensile tests. Barcol hardness and sorption measurements provide complemntary information. In addition, a novel nondestructive (NDE) method, called Single Mode Nonlinear Resonance Acoustic Spectroscopy (SIMONRAS), was applied to measure the linear and nonlinear dynamical properties of the samples as a funtion of exposure time. This new NDE method focuses on the strain amplitude dependence of the resonance frequency while driving a sample at relatively low excitation levels. The obtained relative frequency shift is a measure of the internal microstructural properties of the material. The correlation between this nonlinearity parameter and the mechanical properties is extremely good, which implies that the SIMONRAS technique can be applied to predict the chemo‐mechanical degradation of composites in a nondestructive manner.
Mechanical properties and morphology of flax fiber reinforced melamine‐formaldehyde composites
Authors: Hagstrand P.‐O. , Oksman K. 
Published: April 2004

AbstractThe mechanical performance of natural fiber reinforced polymers is often limited owing to a weak fiber‐matrix interface. In contrast, melamine‐formaldehyde (MF) resins are well known to have a strong adhesion to most cellulose containing materials. In this Paper, nonwoven flax fiber mat reinforced and particulate filled MF composites processed by compression molding are studied and compared to a similar MF composite reinforced with glass fibers. Using flax instead of glass fibers has a somewhat negative effect on tensile performance. However, the difference is relatively small, and if density and material cost are taken into account, flax fibers become competitive. Tensile damage is quantified from the stiffness reduction during cyclic straining. Compared to glass fibers, flax fibers generate a material with a considerably lower damage rate. From scanning electron microscopy (SEM), it is found that microcracking takes place mainly in the fiber cell walls and not at the fiber‐matrix interface. This suggests that the fiber‐matrix adhesion is high. The materials are also compared using dynamic mechanical thermal analysis (DMTA) and water absorption measurements.
A thermoviscoelastic analysis of process‐induced internal stresses in thermoplastic matrix composites
Authors: Sunderland Paul , Yu Wonjae , Månson Jan‐Anders 
Published: April 2004

AbstractA numerical tool for predicting the evolution of internal and residual stresses during the processing of thermoplastic matrix composites has been developed. Based on a finite element formulation, the model accounts for the anisotropy, vis‐coelasticity and heterogeneity of the materials and represents mechanisms of both stress generation and stress relaxation. The viscoelastic properties are described by a linear thermoviscoelastic formulation. The model allows the buildup of stresses during processing to be monitored, in particular when the material is cooling through its transition temperatures, and enables the prediction of stress release and the resulting part waipage on demolding. Its use is demonstrated for unidirectional and crossply polyetherimide/glass fiber (PEI/GF) laminates processed by compression molding, and the influence of cooling conditions on stress levels is shown.
Extrusion conditions and properties of vapor grown carbon fiber reinforced polypropylene
Authors: Kuriger Rex J. , Alam M. Khairul 
Published: April 2004

AbstractVapor grown carbon fiber (VGCF) is a new and inexpensive carbon fiber produced by vapor deposition of hydrocarbons on metal catalysts. The ability to fabricate VGCF reinforced thermoplastic composites by extrusion provides the potential to exploit VGCF into new commercial markets. This study investigates the extrusion conditions and properties of VGCF reinforced polypropylene. Extrusion was carried out using a Leistritz twin‐screw extruder. Polypropylene reinforced with 0% to 12.5% volume fraction VGCF was extruded successfully at temperatures ranging from 215°C to 250°C. The extrusion pressure increased and the flow rate decreased as the percentage of fiber was increased. Increases in tensile strength and modulus were observed by the addition of VGCF. However, the void content of the composite samples increased with fiber content.
Dynamic stress/strain response of the interphase in polymer matrix composites
Authors: Tanoglu M. , McKnight S. H. , Palmese G. R. , Gillespie J. W. 
Published: April 2004

AbstractThe interphases of various sized E‐glass‐fiber/epoxy‐amine systems were tested at displacement rates in the range of 230 to 2450 fxm/sec using a new experimental technique (dynamic micro‐debonding technique). The fiber systems include unsized, epoxy‐amine compatible sized, and epoxy‐amine incompatible sized glass fibers. A data reduction scheme was developed to relate the force vs. displacement response obtained from the dynamic micro‐debonding technique to interphase shear stress/strain response. The stress/strain curves and interphase shear modulus values were obtained from these composite systems under average shear strain rates (ASSR) in the range of 215–3278 (1/s). The results showed that the magnitude of the interphase shear modulus was sizing and strain rate dependent. In all cases, the shear modulus was found to be more compliant than the bulk matrix. The two sized fiber systems exhibited the highest strain rate sensitivity, with modulus increasing about threefold over the range studied. In addition, the rate dependent behavior of the model interphase materials were determined using the dynamic mechanical analysis (DMA) technique. The model interphase materials closely resemble the interphase that forms on unsized and compatible sized fibers. Master curves relating the flexural storage modulus to strain rate were constructed based on the time‐temperature superposition principle from DMA frequency sweep measurements. The DMA measured results are consistent with the dynamic micro‐debonding test results, providing confidence in the test method as a reliable technique for characterizing the high strain rate properties of the interphase in composites.
Studies on the preparation and mechanical properties of esthetic polymeric dental restoratives using silane treated silica microfiller via freeze‐drying
Authors: Kim Ohyoung , Shim W. Jaewoo 
Published: April 2004

AbstractPolymeric dental restorative composites were prepared using silica filler where the surface was treated with γ‐methacryloxypropyltrimethoxysilane and decanted solvents by the freeze‐drying method. This treatment improved the miscibility of the filler with 2,2′‐bis‐[4‐(methacryloxy‐2‐hydrbxypropoxy)‐phenyl]‐propane/triethyl‐eneglycoldimethacrylate resin matrix and enhanced the esthetic properties of the composite. Diametral tensile strength (DTS) and flexural strength (FS) of the dental composite were measured, and the effect of drying methods in the surface treatment of filler on the mechanical properties of the composite was also investigated. Dental restorative composites prepared by the freeze‐drying method showed substantially higher DTS and FS values than those prepared by the conventional heat‐drying method. This resulted in increasing the loading percentage of filler in the resin matrix, and thereby, DTS values were increased dramatically. Dispersion of silica filler in the resin matrix and surface characteristics were examined by scanning electron microscopy. Various esthetic grades of dental composites were successfully prepared using iron oxide pigments, and its Hunter L. a. b. values of vita color‐shade were also investigated.