bluuebunny/crossref_metadata_2025 huggingface dataset:
Airflow through Polyurethane Foams with Near-Circular Cell-Face Holes
Authors: Fitzgerald C. , Lyn I. , Mills N. J.
Published: April 2004

A range of open-cell slow-recovery polyurethane (PU) foams were found to have roughly circular cell-face holes, which are small compared with the face area. The pressure gradient through the foam was measured for airflow velocities in the range 0.5–5ms 1, and the permeabilities K and inertial flow coefficients B calculated. Computational Fluid Dynamics (CFD) was used for laminar airflow through both an axisymmetric model and a regular Kelvin foam model. The predicted foam permeabilities from the latter were close to the experimental values. Finite Element Analysis (FEA) was used to predict cell-face shape changes under a pressure gradient. The distorted face shapes were then used in the CFD model to explain why the B values were negative for some foams.
Foaming Poly(methyl methacrylate) with an Equilibrium Mixture of Carbon Dioxide and Isopropanol
Authors: Gendron Richard , Moulinie Pierre
Published: April 2004

In this study we examine the mixture carbon dioxide (CO2) and 2-propanol (PrOH) as foaming agents for poly(methyl methacrylate). Gaseous CO2 was dissolved in liquid PrOH, allowing for injection of a homogenous liquid mixture into the extruder. The advantage of such a system is that the CO2/PrOH ratio remains stable, and the mixture can easily be metered with a suitable pump. While the PMMA foamed with this equilibrium mixture was similar to foams prepared with separately injected CO2 and PrOH, there appears to be synergistic effects on the plasticization of PMMA. Furthermore, a delay in the onset of cell nucleation for the PFA mixtures in which CO2 was the main component was also observed.
Continuous Process for Recycling of Polyurethane Foam
Authors: Ghose Sayata , Isayev A. I.
Published: April 2004

The investigation deals with the recycling of high resiliency polyurethane (PU) foam by the application of high-power ultrasound in a continuous ultrasonic reactor. The foam has been decrosslinked at various screw speeds and various amplitudes, then blended at different ratios with the virgin polyurethane rubber (PUR) and cured. The die pressure and the total power consumption have been recorded as a function of processing conditions. Rheological and mechanical properties, hardness as well as gel fraction and crosslink density of the decrosslinked foam and cured blends have been measured and compared in an attempt to find out the optimum condition for decrosslinking. Blends have also been prepared using different proportions of ground samples and virgin rubber, and a comparison of the properties between these blends and the blends of the decrosslinked foam has been carried out. The results show that compared to the ground samples, the blends of the decrosslinked samples are easier to mix and exhibit enhanced properties.
Deformation of Polypropylene Foam Neopolen® P in Compression
Authors: Beverte Ilze
Published: April 2004

Neopolen® P is a two-phase cellular composite foam material produced by BASF AG, Germany. In most of the practical applications, Neopolen® P works under a range of small and compressive deformations. Therefore it is necessary to determine the moduli in compression and compressive strength in the most effective way for a wide range of foam densities: 22≤ρ84≤kg/m3. Several experimental methods of different precision for deformation properties of Neopolen® P were compared. The direct measurements performed by a universal testing machine were used for the main part of the experiments. They were compared with results obtained by a more precise and time-consuming method, using an inductive extensiometer HBW5K.

Experimental data were obtained for structural, elastic, and strength properties. It was proved that the foam exhibited a slight monotropy for the highest density of the investigated range. The observed anisotropy of mechanical properties was correlated to the structure and the manufacturing technology of the foam. Influence of the interaction of the two main factors: the electrostatic forces and the Earth gravity on the final anisotropy mode of the foam was analyzed.
Supercritical CO2 Processed Polystyrene Nanocomposite Foams
Authors: Strauss Will , D’Souza Nandika Anne
Published: April 2004

Polystyerene (PS) nanocomposite foams were prepared using CO2 supercritical fluid (SCF) as a solvent and blowing agent. PS was first in situ polymerized with 0, 1, and 3% Montmorillonite-Layered Silicate (MLS) mixtures, which were then compression-molded into thin laminates. The laminates were foamed in a batch process at temperatures and pressures within the range of 60–85 C and 7.6–12 MPa. Characterization was accomplished with scanning electron microscopy (SEM), Differential Scanning Calorimetry (DSC), and X-ray Diffraction (XRD). SEM images revealed the effects of different processing parameters on the foam’s cellular morphology, and also showed that the MLS layers were arranged in alignment with the foam cell walls. DSC data indicated that different concentrations of MLS have a notable effect on the glass transition temperature (Tg) of the composite, and that the foaming process itself alters the endothermic behavior of the material. XRD spectra suggested that the PS–MLS composite had an intercalated structure at both the 1 and 3% mixtures, and that the intercalation may be enhanced by the foaming process.
The Effect of Si and Mg on Age Hardening Behavior of Al-SiCp Composites
Authors: Tekmen C. , Cocen U.
Published: April 2004

An investigation was carried out to determine the effect of Si and Mg on ageing behavior of Al-7%Si-0.7%Mg matrix composites reinforced with SiC particles of 10 and 20 vol.% and unreinforced matrix alloy. The samples were produced by compocasting technique and extruded. The produced samples were characterized by optical microscope, image analyzer, scanning electron microscope and X-ray mapping. The obtained results were compared with the previous study, which was studied on Al-5%Si-0.2%Mg matrix alloy and composites. It has been found that, the formation of some reaction products, mechanical properties and age hardening behavior of the composites strongly depend on Si and Mg content of the matrix alloy. In addition, increasing the Mg and Si content from 0.2 and 5 wt.% to 0.7 and 7 wt.% respectively, increase the critical temperature and hardening efficiency values.
Reduction in the Number of Independent Parameters for the Tsai—Wu Tensor Polynomial Theory of Strength for Composite Materials
Authors: DeTeresa Steven J. , Larsen Gregory J.
Published: April 2004

It is shown that the number of required parameters for the Tsai-Wu tensor polynomial strength criterion for fiber composites can be reduced from seven to five for composite materials that do not fail under practical levels of either hydrostatic or transverse pressure. For these materials, the interactive strength parameters can be defined in terms of their commonly measured uniaxial or noninteracting strength parameters, thereby eliminating the need to conduct combined stress tests. The derived parameters are given by F12 = − F11/4 F23 = − F22 These parameters fall within the stability limits of the theory, yet they lead to open failure surfaces in the compressive stress quadrant. The assumptions used to derive the interactive parameters were supported by measurements that showed typical carbon fiber composites did not fail under significant levels of hydrostatic pressure or unequal transverse compression. Comparison with previous work where the interactive parameters had been determined from combined stress experiments showed that predictions based on the derived parameters were generally in good agreement with test results. In evaluating the tensor polynomial failure theory, the behaviors under hydrostatic and transverse pressure were shown to be more discerning than other multiaxial stress states. It is therefore proposed that these two stress states be used in assessing other proposed three-dimensional failure models for fiber composites.
Cured Shape of Cross-Ply Composite Thin Shells
Authors: Ren Libo , Parvizi-Majidi Azar , Li Zhengneng
Published: April 2004

For a composite laminated plate, it has been found that classical laminate theory (CLT) can not always predict the final cured shape correctly and geometric nonlinearity must be considered. For composite laminated shells, experiments show that the cured shape depends on stacking sequence, radius, thickness, and size. This paper investigates the cured shape of several cross-ply composite shells. The cured shape of a cross-ply shell is generally cylindrical. A model is established to predict the cured shape. The model is based on the Rayleigh-Ritz energy method and considers geometric nonlinearity. Modeling and experiment show that, for certain stacking sequences, the generator of the cured shape may be orthogonal to the original generator, while other stacking sequences can lead to deeper or shallower cured shapes. The predictions of the model are very close to the results of FEM analysis and experiment. This model can be used as a guide in the manufacture of unsymmetric cross-ply laminates.
S2-Glass/Epoxy Polymer Nanocomposites: Manufacturing, Structures, Thermal and Mechanical Properties
Authors: Haque A. , Shamsuzzoha M. , Hussain F. , Dean D.
Published: April 2004

This paper is primarily focused in studying the effects of nanoclay particles such as montmorillonite on improving mechanical and thermal properties of fiber reinforced polymer matrix composite materials. Basic correlations between polymer morphology, strength, modulus, toughness, and thermal stability of thermoset nanocomposites were investigated as a function of layered silicate content. S2-glass/epoxy-clay nanocomposites were manufactured through an affordable vacuum assisted resin infusion method (VARIM). The nanocomposites are formed during polymerization when the adsorbing monomer separates the clay particles into nanometer scales. Transmission electron microscopy (TEM) and wide angle X-ray diffraction(WAXD) were used to characterize the morphology of the dispersed clay particles. The thermal properties such as onset of decomposition and glass transition temperatures were determined by Thermo Gravimetric Analysis (TGA) and Dynamic Modulus Analyzer (DMA). Mechanical properties such as interlaminar shear strength, flexural properties and fracture toughness are also determined for both conventional S2-glass/epoxy composites and S2-glass fiber reinforced nanocomposites.

The results show significant improvements in mechanical and thermal properties of conventional fiber reinforced composites with low loading of organo silicate nanoparticles. By dispersing 1% by weight nanosilicates, S2-glass/epoxy-clay nanocomposites attributed to almost 44, 24 and 23% improvement in interlaminar shear strength, flexural strength and fracture toughness in comparison to conventional S2-glass/epoxy composites. Similarly, the nanocomposites exhibit approximately 26 C higher decomposition temperatures than that of conventional composites. This improved properties of fiber reinforced polymer nanocomposites are achieved mostly due to increased interfacial surface areas, improved bond characteristics and intercalated/exfoliated morphology of the epoxy-clay nanocomposites. The TEM observations provide evidence of detailed morphology of the polymer layered-clay nanocomposites.
Predicting Failure in Composite Laminates Using Dissipated Energy
Authors: Huang Hansong , Springer George S. , Christensen Richard M.
Published: April 2004

We present a method for evaluating the damage in and failure of fiber reinforced composite materials. The method is based on dissipated energy and has three major components: (i) a relationship between the strain in the material and the magnitude of the dissipated energy density, (ii) a model that relates the dissipated energy density to matrix damage and fiber failure inside the material, and, accordingly, reduces the elastic properties of the material, and (iii) a nonlinear finite element code for calculating the strain at each point in the material taking into account the degradation of the stiffness as damage occurs. The method provides the parameters of interest, namely, the regions of matrix damage and fiber failure, the load-displacement curve, the failure load, and the failure displacement. Tensile, shear, and four point bend tests were performed with S-glass/epoxy solid coupons as well as with coupons containing a central hole. The load-displacement curves, failure loads, and failure displacements were measured and compared to the results computed by the method. The data and the results of the method are in good agreement.
Rigorous Dynamic Model-Based Economic Design of the Injected Pultrusion Process with Controllability Considerations
Authors: Srinivasagupta Deepak , Kardos John L. , Joseph Babu
Published: April 2004

The current industrial practice in design of the injected pultrusion (IP) process involves costly trial and error procedures, hitherto unavoidable in the absence of established process models. Even for well understood processes, economic design has traditionally used steady-state physical models, separately followed by control system synthesis using simpler dynamic models. This work describes the development of a rigorous model-based design algorithm for the IP process by integration of economics, operability, and environmental considerations. In our previous work, a 3D dynamic physical model of the IP process was experimentally validated on a bench-scale setup. Using this validated model, we can now reduce the time and expenses associated with a purely experimental approach. An understanding of processing economics leads to throughput rate maximization as the desired economic objective. We develop a multiobjective optimization algorithm that maximizes this objective function, using a response surface methodology with iterative meshing to determine optimal equipment specifications (die dimensions, puller ratings) and processing condition parameters (heating zone temperatures, resin injection pressure).

Retrofit design of the bench-scale setup promised a tenfold increase in throughput rate. Calculation of theoretical limit on throughput rates from intrinsic resin cure kinetics supported this finding. Various metrics were proposed to evaluate quality of design in a distributed-parameter sense. Sensitivity studies verified that the economic optimum is also robust to a wide range of expected process disturbances. An analysis of process instrumentation revealed the need for additional measurements. We propose resin flow-rate and cutting force measurements for void and cure sensing respectively. This research is a first step to the integration of design and control for a complex multiphase process using a single dynamic physical model. The integration offers several benefits over current design practices, and highlights the potential for increased productivity in polymer composites manufacturing.
Hydroxyapatite Toughened by Silver Inclusions
Authors: Asmus S. M. F. , Sakakura S. , Pezzotti G.
Published: April 2004

Three kinds of processing procedure, including conventional sintering, hot-isostatic pressing, and their combination, were explored to prepare hydroxyapatite-silver composites with high density and improved ceramic-metal interface properties. Optimizing the densification procedure, which allowed the desired fraction of Ag to remain within the apatite matrix after densification, has solved a problem related to the low wettability of Ag on hydroxyapatite. The major outcome of this study is that hot-isostatic pressing enables to reinforce the interface between hydroxyapatite and silver, thus improving the structural consistency of the prepared composite. Results are supported by investigations on microscopic fracture mechanisms. It is shown, that a toughening effect arose from the microscopic crack-bridging mechanism operated by the elasto-plastic stretching of unbroken Ag ligaments along the crack wake. A Raman piezo-spectroscopic technique enabled the in situ quantitative assessment of this bridging toughening mechanism.
An Investigation of Al-SiCp Composites Under Thermal Cycling
Authors: Ozdemir I. , Toparli M.
Published: April 2004

The effect of thermal cycling on the behavior of the aluminum-silicon matrix alloy Al-7%Si-0.7%Mg (AlSi7) reinforced with 10% volume SiC particles has been investigated experimentally and theoretically. Cast ingots of the matrix alloy and composite samples were extruded at 773 K at an extrusion ratio of 10:1. The extruded microstructures exhibit a more uniform distribution of the SiC particles. In this study, for determining the thermal stress and deformation on the composite materials ABAQUS finite element software package was used. Thermal residual stresses developed during and after thermal cycling were also investigated. Thermal cycling tests were performed between 373 and 703 K under a constant tensile load (150 N) and without external load. The stress distributions in the composite during heating and cooling were revealed. The axial displacement under constant external load after one thermal cycling was 0.01672 mm and kept increasing considerably. The maximum residual stresses were generated at the interfacial region during thermal cycling. SEM micrographs showed that cracks were present in the composite structure under repeated action of thermal cycling process (100 cycles).
Nondestructive Evaluation Technique Utilizing Embedded Thermal Fiber Optic Sensors
Authors: Stewart Anna , Carman Greg , Richards Lance
Published: April 2004

We investigated a thermal nondestructive evaluation (NDE) technique based on thermography that uses optical fiber thermal sensors to detect damage within a laminated graphite epoxy composite specimen. Two sets of composite samples were used for testing, one set had fiber optic sensors embedded between the layers while the other relied on thermocouple sensors attached to the exterior. A simulated impact system was used to induce damage of varying degrees into the samples. The damage was confirmed either with X-ray or C-scan imaging. The test apparatus in addition to the test data obtained from both sets of samples are presented. The data confirms that the fiber optic thermal sensors can not only detect the presence of damage, but can measure the severity of damage as well. This is the first known attempt to use in situ fiber optic point sensors with thermography to detect damage.
Method to Evaluate Winding Trajectories in Robotized Filament Winding
Authors: Carrino L. , Polini W. , Sorrentino L.
Published: April 2004

Robotized filament winding technology involves the deposition of a tape according to a planned robot trajectory and its polymerisation in a furnace for thermoset resin matrix. In this way it is possible to wind asymmetric or complex parts. The winding trajectory is a critical aspect of the robotized filament winding process, since the mechanical performances and the winding time of the manufactured composite part change according to winding trajectory geometry. This work presents an original method to optimize and to compare alternative winding trajectories for robotized filament winding. The proposed method uses a set of geometric parameters that characterize the winding process and, in the same time, that are easy to measure. Therefore, the implemented method is quick and user friendly. The designed method has been implemented and tested on two different trajectories that have been planned to wind a same composite part.
Effect of Powder Characteristic on Al Internal Oxidation to Prepare Al2O3- Cu Composite
Authors: Liang Shuhua , Fan Zhikang , Fang Liang
Published: April 2004

Effects of powder characteristics on the internal oxidation of Cu-Al prealloyed powders were discussed. The results show that the internal oxidation of Al was occurred during sintering not in ball milling when the content of Al in Cu-Al prealloyed powders was 0.8wt.%, the mechanism of Al internal oxidation was different with the milling time, when the milling time was short, the internal oxidation of Al during sintering were mainly the unsolved Al and absolute Cu-Al solid solution resulted in coarse Al2O3 and fine Al2O3 particles respectively. When the mixed powders were milling for time long enough, the internal oxidation of Al during sintering was all the metastable Cu-Al prealloyed. A good quality Al2O3-Cu composite was prepared. The Al2O3 particles with an average size 2-5 mm in diameter and about 5-10 mm in particle spacing have been observed uniformly dispersed in the composite prepared by prealloyed powders after milling 96 h.
Determination of Material Constants for Nonlinear Viscoelastic Predictive Model
Authors: Lin W. S. , Pramanick A. K. , Sain M.
Published: April 2004

Creep in the nonlinear zone of wood plastic composite can be described by a few material constants. The purpose of this study was to determine these creep related material constants for 60% wood flour reinforced extruded HDPE samples. Creep and recovery data in flexural bending mode were analyzed. Schapery's theory was used to simulate creep data. The creep related material constants varied according to the stress level. The experiment was short term and the values of these constants will be used to characterize, simulate, and model long-term creep under varying temperature and moisture in our ongoing project.
The Design, Matching and Manufacture of Auxetic Carbon Fibre Laminates
Authors: Evans K. E. , Donoghue J. P. , Alderson K. L.
Published: April 2004

Either an in-plane or out-of-plane negative Poisson’s ratio,, in continuous carbon fibre/epoxy resin composites can be achieved, providing the fibre volume fraction and anisotropy are high enough, by selecting suitable stacking sequences. This paper examines the use of specially designed software which allows the designer to match the mechanical properties of laminates with predicted negative to those with similar mechanical properties but positive. This has allowed auxetic and matched carbon fibre/epoxy resin laminates to be specifically designed. These laminates were then fabricated and tested, with good agreement found to theoretical predictions. This study, then, provides a route to evaluating the effect of a negative alone on properties such as fracture toughness and impact resistance.
Measurements of Thermal Properties of Carbon/Epoxy and Glass/Epoxy using Modulated Temperature Differential Scanning Calorimetry
Authors: Kalogiannakis Georgios , Van Hemelrijck Danny , Van Assche Guy
Published: April 2004

Major potential of composite materials relies in the nonlinear behavior triggered by their inhomogeneous nature. Particularly in heat diffusion, composite materials present a high variation of thermal properties as a function of temperature. Therefore, the spectrum of a propagating thermal wave can contain higher harmonics of the excitation frequency. The amplitude of these harmonics depends on the range of temperatures developed inside the material. This study is focused on the mathematical formulation of the relationship between thermal properties and temperature. To this end, the heat capacity and the thermal conductivity of Carbon/Epoxy and Glass/Epoxy cross-ply laminates were determined in a temperature range of interest for the aircraft industry using an ASTM method based on Modulated Temperature Differential Scanning Calorimetry. The results are indispensable toward a nonlinear treatment of heat diffusion phenomena and the respective exploitation for nondestructive testing.
Thermal Effects on the Compressive Behavior of IM7/PETI5 Laminates
Authors: Walker Sandra Polesky
Published: April 2004

The effect of changing operating temperature on the compressive response of IM7/PETI5 composite laminates is investigated within this paper. The three temperatures evaluated for this study were 129, 21, and 177 °C, a spectrum from cryogenic to an elevated operating temperature. Laminate compressivestrength property testing was conducted to generate strength data at the three operating temperatures of interest for several lay-ups. The Wyoming Combined-Load Compression fixture was chosen for the compression testing. The current investigation determined that the torque applied with utilizing the fixture needs to be adjusted for changing operating temperature. A three-dimensional finite element analysis model of a [90/0]8s composite laminate subject to compressive loading is developed. The model is used to study the key attributes of the laminate that significantly influence the state of stress in the laminate. Both the resin-rich layer located between lamina and the thermal residual stresses present in the laminate due to curing are included in the analysis model. For the laminate modeled, conducting nonlinear analyses using temperature-dependent material properties was determined to be unnecessary for the operating temperatures studied. Simply using the temperature-dependent material properties measured at the operating temperature of interest while conducting a more expeditious linear analysis was sufficient for predicting stresses accurately for the current problem. The unique three-dimensional analysis results revealed that the application of an applied compressive axial load in the 0-degree direction decreased the interlaminar stresses present in the laminate initially due to curing. Therefore, failure was concluded not be attributable to the interlaminar stresses in the composite laminate being studied when a compressive load is applied. The measured laminate strength increase with a decrease in temperature is determined to be due to the increase in the lamina compressive axial strength with a decrease in temperature.
Delamination Detection of Composite Beams Using Piezoelectric Sensors with Evenly Distributed Electrode Strips
Authors: Tan Ping , Tong Liyong
Published: April 2004

In this paper, a new analytical model is presented to detect the presence, size, and location of a delamination embedded in a laminated composite beam. The sensors bonded on the top and bottom surfaces of a host beam are made from PZT piezoelectric layers. By employing this analytical model, the first three natural frequencies and sensor charge output distribution for the beams with different delamination length, axial and through-the-thickness delamination location, and delamination gap can be predicted, when a beam is excited by an external force. An approach is also proposed to obtain the sensor charge output distribution along the beam length using evenly distributed electrode strips. Subsequently, the present model is applied to a laminated plain weave composite beam with an embedded and through-width delamination, followed by an extensive numerical study. An investigation is carried out on the influence of the boundary condition, delamination length, axial delamination location, through-the-thickness delamination location, delamination gap on the first three natural frequency change and sensor charge output distribution along the beam length. The effects of number and size of electrode strips on the sensor charge output distribution is also studied. A comparison of the first three natural frequencies between the present predicted and finite element analysis results reveals that there is a good agreement between these two models.
Elastic-Plastic Model of Adhesive-Bonded Single-Lap Composite Joints
Authors: Yang Chihdar , Huang Hai , Tomblin John S. , Sun Wenjun
Published: April 2004

An analytical model for determining adhesive stress distributions within the adhesive-bonded single-lap composite joints was developed. ASTM D3165 ‘‘Strength Properties of Adhesives in Shear by Tension Loading of Single-Lap-Joint Laminated Assemblies’’ test specimen geometry was followed in the model derivation. In the model derivation, the composite adherends were assumed linear elastic while the adhesive was assumed elastic-perfectly plastic following von Mises yield criterion. Laminated Anisotropic Plate Theory was applied in the derivation of the governing equations of the bonded laminates. The adhesive was assumed to be very thin and the adhesive stresses are assumed constant through the bondline thickness. The entire coupled system of equations was determined through the kinematics relations and force equilibrium of the adhesive and the adherends. The overall system of governing equations was solved analytically with appropriate boundary conditions. Computer software Maple V was used as the solution tool. The developed stress model was verified with finite element analysis using ABAQUS by comparing the adhesive stress distributions.
Finite Element Micromechanics for Stiffness and Strength of Wavy Fiber Composites
Authors: Garnich Mark R. , Karami Ghodrat
Published: April 2004

In this paper, a micromechanical model of a composite lamina material with fiber waviness is described. Results are presented and discussed with regard to stiffness and strength predictions for composite lamina. A micromechanical model of a unit cell from periodically distributed unidirectional waved cylindrical fibers embedded within matrix is proposed to withdraw the different material stiffness parameters. Finite element analysis of the periodic unit cell characterizing the structural stiffness of the composite material is carried out to determine the average stress and strain components. The composite stress-strain relations are then employed to determine the stiffness parameters. Numerical results for a typical composite constituted of polymer matrix and carbon fibers in the form of periodically hexagonal packing and initially sinusoidal waviness are presented for different amplitude to wavelength ratios and a range of fiber volume fractions. The results reveal the presence of local periodic-antisymmetric stresses that are usually unaccounted for in conventional structural analysis. The potential influence of these stresses on failure prediction is discussed.
Hygrothermal Modeling of Thick Thermoset Resin during Electron-Beam-Cure – Part I: Methodology and Modeling Cure Kinetics
Authors: Moon Sung-Won , Morgan Roger J. , Lau Sai C.
Published: April 2004

The hygrothermal model has been developed to predict the temperature evolution, epoxy conversion ratio, the glass transition temperature increase and associated resin yield stress rise, and absorbed moisture vapor pressure in ISbF 6 -catalyzed DGEBA epoxy resin systems during e-beam-induced polymerization on the effects of four different initiator concentrations: 0.1,1,3, and 10 phr. This paper summarizes the modeling procedure of e-beam-induced cure kinetics, and the results of local temperature and degree of cure rise within the sample as a function of dose. Dynamic characteristics of Tg y Pv rise and their modeling procedures together with an attempt at optimizing e-beam cure process will be presented in a subsequent paper.

These papers provide a methodology to generate the overall integrated model for the e-beam, fast cure process of composites and the consequences upon process control in terms of thermal control, moisture-induced void elimination, and minimization of inherent composite processing stresses that had not been previously addressed by composite process model studies.

An autocatalytic model was chosen to describe the cure kinetics for this study and provided excellent agreement with experimental results. The numerical results showed that the cure reaction of ISbF 6 –DGEBA epoxy resin is diffusion controlled, but long lived reactive species allowed for measurable increase in conversion after e-beam irradiation (postcure effects). Higher initiator concentration results in higher degree of cure at a specific dose, causing higher temperature rise and larger temperature and conversion ratio gradients within the sample under given experimental conditions.
Hygrothermal Modeling of Thick Thermoset Resin during Electron-Beam-Cure – Part II: Tg ry Pv Variations and Optimization
Authors: Moon Sung-Won , Morgan Roger J. , Lau Sai C.
Published: April 2004

A hygrothermal thermoset resin-cure model has been developed, in conjunction with experimental data, for the e-beam processing of composites in terms of e-beam dose-time sequences in order to achieve full resin cure, minimum residual stresses and avoidance of moisture-induced cavitation within the resin system. This paper, as Part II of this study, summarizes dynamic characteristics of Tg y Pv rise and their modeling procedures together with an attempt at optimizing the e-beam-cure process. The modeling procedure of e-beam-induced cure kinetics, and the results of local temperature and degree of cure rise within the sample as a function of dose were presented in Part I.
Design and Stress State of Tensions in Multilayer Bars
Authors: Bareisis Jonas
Published: April 2004

There is a proposed analytical method for calculation of normal stresses x and deformation of multilayer bars in this paper. Application possibilities of this method and the accuracy of the results was checked by FEM. It was ascertained that accuracy of the proposed method was sufficiently precise and it is very convenient for engineering calculations and scientific research. Using FEM it was established that when we have axial deformation of three-layer bars, stress state is spatial. Break-up of bars determines x stresses because the magnitude of stresses in other directions are very small compared to x stresses.
Stress Concentrations in Graphite/Epoxy Model Composites during Creep at Room Temperature and Elevated Temperatures
Authors: Zhou C. H. , Schadler L. S. , Beyerlein I. J.
Published: April 2004

Micro Raman spectroscopy (MRS) was used to monitor the change in the local stress concentrations surrounding a single fiber break in 2-dimensional graphite fiber/epoxy composites during creep at room temperature and elevated temperatures up to 80 C. The experimental results were compared with a few shearlagbased multifiber composite models: Hedgepeth, which assumes perfect bonding between the linear elastic fiber and shear-only matrix; MSSL, which additionally accounts for the axial stiffness of the matrix; and VBI, which assumes a viscoelastic shear-only matrix. Instead of assuming time-independent stress concentrations around a fiber break as in previous models, this work investigated the change in the stress concentrations due to the local matrix creep. The VBI model uses parameters measured from unreinforced matrix creep tests to predict the time dependent strain– stress evolution in the composite around fiber breaks. The stress concentrations of the nearby intact fibers were found to change due to the combined effects of temperature sensitive matrix creep and creep-driven inelastic zone growth emanating from the fiber break, which were in good agreement with the VBI predictions in the absence of significant inelastic zones.
Compressive Failure of Impacted NCF Composite Sandwich Panels - Characterisation of the Failure Process
Authors: Edgren Fredrik , Asp Leif E. , Bull Peter H.
Published: April 2004

In the present study, non-crimp fabric (NCF) composite face sheet sandwich panels have been tested in compression after impact (CAI). Damage in the face sheets was characterised by fractography.

Compression after impact loaded panels were found to fail by plastic fibre microbuckling (kinking) in the damaged face sheet. Studies of panels for which loading was interrupted prior to failure revealed extensive stable kink band formation at several positions and in numerous plies. Kink bands initiated and propagated within a wide region close to the point of impact. In addition, kink bands initiated in zones with high shear stresses, away from the impact centre line. Consequently, the fractographic results from this investigation do not support the assumption of modelling the impact damage as an equivalent hole. To achieve accurate predictions of kink band initiation, the stress field must be known. The results from this study imply that bending effects caused by remaining dent or material eccentricities in the damaged region must be considered.
Bending Natural Frequencies of Circular CFRP Shafts with a Metal Core or Casing
Authors: Kim W. , Argento A. , Mohanty P. S.
Published: April 2004

It has recently been shown that some carbon fiber-reinforced composite shafts with a metal core or casing are superior to all carbon fiber reinforced plastics (CFRP) or metal shafts from the viewpoint of the natural frequencies. However, it has not been reported whether or not the benefit of the metal/CFRP hybrid shafts exists in the general cases of various fiber angles, length-to-diameter ratios, material properties, and thicknesses of metal layers. In this study, the effects of a steel core or casing on the bending natural frequencies of CFRP shafts are analytically investigated. In order to calculate the frequencies, the equations of motion are obtained for metal/CFRP hybrid shafts. Several beam theories are evaluated, and differences between these theories in the prediction of the frequencies are also presented. It is found that, in certain cases, an optimum thickness of steel exists to maximize the frequencies of the steel/CFRP shafts. Parametric studies are also carried out over wide ranges of design factors, and design guidelines for the hybrid shafts are finally distilled.
Mode-II Fatigue Fracture of Wood-Composite Bonded Interfaces
Authors: Qiao Pizhong , Hu Guanyu
Published: April 2004

In this paper, the shear mode (mode-II) fatigue fracture of wood-FRP bonded interfaces using a unique linear tapered end-notched flexure (TENF) specimen is presented. A tapered beam on elastic foundation (TBEF) model developed for design and analysis of the TENF specimens is first reviewed. A combined analytical and experimental fracture mechanics method is developed to evaluate the fatigue fracture behavior of wood-FRP bonded interfaces under mode-II constant cyclic loading conditions. By applying the compliance method with the unique feature of TENF specimen (i.e., a constant compliance rate change) and modifying the original Paris Law equation, the fatigue fracture behavior of wood- FRP interface under Mode-II loading is effectively evaluated. The possible effects of loading variables (i.e., load ratio, waveform, and frequency) on crack propagation rate are investigated. Both the load ratio and frequency have shown pronounced influences on crack propagation rate; while the waveform has negligible effect. A modified Paris Law equation is proposed to include both the frequency and load ratio effects. The present method can be used for other similar studies of interface fracture of dissimilar materials, and the finding of this study can eventually lead to the development of design guidelines for hybrid material bonded interface.
Dynamic Compression of Sandwich Composites at Sub-ambient Temperatures
Authors: Thomas Tonnia , Mahfuz Hassan , Kanny Krishnan , Jeelani Shaik
Published: April 2004

The objective of this study is to investigate the dynamic response of S2-glass–vinylester foam core sandwich specimens at low temperatures. Sub-ambient testing condition was achieved using liquid nitrogen. The effect of the sandwich core density as well as microstructure was explored. Results from the stress–strain curves suggested that the energy absorption of the sandwich specimen was predominantly through progressive failure. Although a nominal increase in compressive strength was observed at sub-ambient temperature in respect to its room temperature, the effect of low temperature on the failure modes was severe. Each category of sandwich specimen portrayed its own unique mode of failure.
Through-Thickness Mechanical Characterization of Woven Fabric Composites
Authors: Abot J. L. , Daniel I. M.
Published: April 2004

The objective of this study was to investigate the interlaminar orthrough-thickness deformation and failure of woven fabric composites subjected toquasi-static loading and develop testing methods and specimens that would provideboth elastic properties and strengths for moderately thick composites. This study wasperformed on a thick composite consisting of a satin weave carbon fabricimpregnated with an amine-cured epoxy resin. All through-thickness mechanicalproperties under compressive, tensile, and shear loading with their correspondingfailure mechanisms were determined. These properties were also correlated with thecorresponding ones for a unidirectional composite having the same fiber and matrix.
Effect of Platelet Dispersion on the Load Transfer Efficiency in Nanoclay Composites
Authors: Tsai Jialin , Sun C. T.
Published: April 2004

Load transfer efficiency of nanoclay platelets in a polymer matrix wasinvestigated. Both tactoid nanocomposites and uniformly dispersed nanocompositeswere considered. The unit cell suitable for modeling the load transfer from thesurrounding matrix to nanoclay platelets using a shear lag model was discussed. Theload transfer efficiency in the nanocomposite was characterized by the effectivelength of the platelet carrying the saturated stress. For tactoid nanocomposites theplatelets were held together in clusters by the ionic bond which was simulated usingan elastic interphase with a low shear stiffness. It was demonstrated thatwelldispersed platelets in the polymer matrix can significantly enhance the load transferefficiency.
The Effects of Through-thickness Compression on the Interlaminar Shear Response of Laminated Fiber Composites
Authors: DeTeresa Steven J. , Freeman Dennis C. , Groves Scott E.
Published: April 2004

The effects of through-thickness compression on the interlaminar shear response of laminated fiber composites were studied. The combined stresses were generated using a hollow cylindrical specimen that was subjected to axial compression and torsion. For both glass- and carbon-fiber composites, through-thickness compression resulted in a significant enhancement in the interlaminar shear stress and strain at failure. Under moderate compression levels, the failure mode changed from elastic to plastic. An attempt was made to predict the observed increase in shear strength for carbon fiber epoxy laminates using three-dimensional lamina failure criteria. Although all the failure theories correctly predicted the trend of increasing shear strength with compression, none were able to predict the full extent of the observed strength increase. These results indicate that improved models are needed for determining failure under a combined state of interlaminar stress. The experimental results demonstrate that there are significant gains to be made in improving interlaminar strengths of composite structures by applying through-thickness compression. This effect could be exploited for improved strength and possibly improved fatigue life of composite joints and other regions in structures where interlaminar stress states are critical.
Modeling and Simulation of the Central Nervous System Control with Generic Fuzzy Models
Authors: Nebot Angela , Mugica Francisco , Cellier François E. , Vallverdú Montserrat
Published: April 2004

The analysis of the human cardiovascular system by means of modeling and simulation methodologies is of relevance from a medical point of view because it allows doctors to acquire a better understanding of cardiovascular physiology, offer more accurate diagnostics, and select better suited therapies. The cardiovascular system is composed of the hemodynamical system and the central nervous system (CNS). In this work, two generic models of the CNS for patients with coronary diseases are identified by means of the fuzzy inductive reasoning (FIR) methodology. One of the models is generic only in its structure, whereas the other one is a fully generic model. It is very useful for doctors to have available a generic CNS model for a group of patients with common characteristics because this model can be used to predict the future behavior of new patients with the same characteristics.
Modeling an Asynchronous Microprocessor
Authors: Theodoropoulos Georgios
Published: April 2004

Synchronous very large-scale integration (VLSI) design is approaching a critical point, with clock distribution becoming an increasingly costly and complicated issue and power consumption rapidly emerging as a major concern. Recently, there has been a resurgence of interest in asynchronous design techniques due to the significant potential benefits that the elimination of global synchronization may offer to issues such as clock distribution, power consumption, performance, and modularity. Modeling and simulation may perform a catalytic role in the quest for the realization of the potential offered by asynchronous logic. Hence, the recurrence of interest in asynchronous design has been accompanied by intense research activity aimed at developing notations and techniques appropriate for modeling and simulating asynchronous systems. Communication sequential processes and its executable counterpart, occam, are increasingly advocated as particularly suitable for this purpose. This article discusses the modeling of an asynchronous microprocessor using occam.
Timing Issues and Experiment Scheduling in Faster-Than-Real-Time Simulation
Authors: Anagnostopoulosa Dimosthenis , Nikolaidoua Mara
Published: April 2004

Faster-than-real-time simulation (FRTS) can be used for the performance evaluation of systems behavior in real time, providing significant capabilities for studying systems with a time-varying behavior. FRTS enables model validation through comparing simulation results with the corresponding system observations. However, experimentation proves to be rather demanding because delivering output results and ensuring their reliability must be accomplished within a predetermined time frame. Output analysis of system observations and model results and relevant timing issues are discussed. A method is introduced for determining the “optimal” faster-than-real-time experiment, in terms of the number of replications that may be scheduled for execution and whether a compromise is required between the ability to predict for the long future and the degree of reliability achieved for predictions. Experimental results are presented to validate and demonstrate the effectiveness of the proposed method. A case study in which this method is applied is also discussed.
A Framework for Remote Execution and Visualization of Cell-DEVS Models
Authors: Wainer Gabriel A. , Chena Wenhong
Published: April 2004

Simulation is becoming increasingly important in the analysis and design of complex systems with natural and artificial components. CD++ is a modeling and simulation tool that was created to study these kinds of systems by using a discrete event cell-based approach. It was successfully employed to define a variety of models for complex applications. Here, the authors present different extensions done to the tool using a client-server architecture. Users can create models in local workstations, execute them in a remote high-performance simulation engine, and then receive, visualize, and analyze the results locally with easy-to-use 2D and 3D interfaces. The 3D interface was built using the virtual reality markup language (VRML) to facilitate Web-based visualization. The tool now enables running several models simultaneously and supports multiview outputs.
Derivative Estimation with Finite Differences
Authors: Chen E. Jack
Published: April 2004

This article discusses the implementation of using finite differences to construct a confidence interval for a simulation estimator of the derivative of the steady-state distribution of a stochastic process. The quasi-independent procedure increases the simulation run length progressively until a certain number of essentially independent and identically distributed systematic samples are obtained. The author computes sample quantiles at certain grid points and constructs a histogram from those grid points. The derivative estimate is then computed from the histogram (i.e., the empirical distribution). An experimental performance evaluation demonstrates the validity of using this procedure to estimate the derivatives.