bluuebunny/crossref_metadata_2025_split huggingface dataset:
Strain rate effect in the single‐fiber‐fragmentation test
Authors: Gong X. J. , Arthur J. A. , Penn L. S. 
Published: April 2004

AbstractThe single fiber fragmentation test (SFVU) has been widely used to characterize the interface it fiber‐reinforced polymers. The purpose of the work reported here was to determine the effect of strain rate on the fiber fragment lengths obtained in the SFFT. Three materials systems were used to make single‐fiber‐composite specimens: E‐glass fiber/polycarbonate matrix, AS4‐carbon fiber/polycarbonate matrix, and AS4‐carbon fiber/polycarbonate matrix. The fiber‐matrix adhesion in all three systems is based on physisorption rather than chemisorption. Each system was tested at strain rates ranging over four orders of magnitude. Results are reported in terms of fragment length, the dependent variable in this study, which is inversely related to the quality of the Interface. It was expected that the fragment length would show a systematic decrease with Increasing strain rate, but the expected trend was not found. Although the polycarbonate matrix exhibited rate‐dependent viscoelastic behavior typical of amorphous polymers below Tg, the fragment length at saturation did not show a statistically significant variation with strain rate for any of the three materials systems. A major contributor to the lack of observed effect was the inherent random variability associated with the SFFT; random variability in average fragment length was equal or greater than the 19% effect of rate predicted for ideal elastic systems with no debonding at the interface. In addition, considerable interfacial debonding occurred during the SFFT, not surprising for Interfaces based on physisorption alone. Debonding Interferes with transfer of applied load from matrix to fiber, and would thus interfere with transfer of the effect of rate from matrix to fiber. A tensile Impact test developed previously was also performed on single‐fiber composite specimens made from the same three materials systems. The results of the Impact tests differed from those obtained at controlled strain‐rates for only two of the materials systems.
Estimating the residual fatigue lifetimes of impact‐damaged composites using thermoelastic stress analysis
Authors: Horn Gavin P. , Mackin Thomas J. , Kurath Peter 
Published: April 2004

AbstractA new experimental method is presented for quantifying impact damage and estimating the remaining fatigue lifetime of impact damaged polymer matrix composite materials. The procedure is demonstrated using composites of glass fiber reinforced polyurethane produced by injection molding and structural reaction injection molding. Thermoelastic stress analysis (TSA) was used to quantify the stress concentration associated with impact‐damage in test samples of each composite. Following impact and TSA imaging, the samples were fatigued to failure over a range of stress amplitudes. The TSA‐derived stress concentration factors were used to determine a modified stress amplitude that collapsed the impact‐fatigue data onto a master stress‐life curve. This approach provides a quantitative measure of impact damage and a practical methodology for estimating the residual fatigue lifetime of impact; damaged composites.
A model for the consolidation of warp‐knitted reinforced laminates
Authors: Rozant O. , Michaud V. , Bourban P.‐E. , Månson J.‐A. E. 
Published: April 2004

AbstractA model for the consolidation of thermoplastic composites reinforced with a warp‐knitted fabric was developed. The evolution of void content during composite consolidation achieved via film stacking was related to the processing parameters and the material properties. Since the knitting process results in local variations of fiber volume fractions even within a tow, the flow mechanisms are not identical to those occurring in homogeneously dispersed fibers. Two different types of micro‐scale porosities were determined and a unit cell geometry was proposed for modeling. The reduction of the effective pressure due to the gas entrapment was also accounted for. Predictions of the variation of the void content as a function of time, pressure and temperature were compared to experimental data. As a good correlation was found between experiments and predictions, this approach can thus be applied to the consolidation of textile reinforcements in which the tows are locally compressed.
Effect of compatibilizer on the structure‐property relationships of kenaf‐fiber/polypropylene composites
Authors: Feng Daan , Caulfield D. F. , Sanadi A. R. 
Published: April 2004

AbstractAlthough lignocellulosic, fiber‐thermoplastics composites have been used for several decades, recent economic and environmental advantages have resulted in significant commercial interest in the use of these fibers for several applications. Kenaf is a fast growing annual growth plant that is harvested for its bast fibers. These fibers have excellent specific properties and have potential to be outstanding reinforcing fillers in plastics. This paper reports the structure‐property relationships of kenaf fiber reinforced polypropylene (PP) and its impact copolymers. The use of maleated polypropylenes (MAPP) is important to improve the compatibility between the fiber and matrix. A significant improvement in impact strengths was observed when the MAPP was used in the composites. Results also indicate that the impact copolymer blends with coupling agent have better high temperature moduli and lower creep compliance than the uncoupled systems. The coupling agent also changes the crystallization and melting behavior of these blends. Because of the better adhesion between the polymer molecules and kenaf fibers, the coupled samples have more restricted molecules than the uncoupled blends. As a result, the crystallization of the coupled high molecular weight blends is slower than the uncoupled blends, resulting in a lower crystallization temperature (Tc) and reduced crystallinity. For the lower molecular weight blends, the coupling agent enhances the crystallization of polymer matrix and results in a higher crystallization temperature and increased crystallinity of the coupled blend. The coupled blends also have more defects in the polymer crystals, and the crystallinity of coupled blends is also lower than the uncoupled blends. This could explain the lower melting temperatures of the coupled samples as compared to uncoupled samples.
Jute felt composite from lignin modified phenolic resin
Authors: Sarkar Sanjay , Adhikari Basudam 
Published: April 2004

AbstractRaw and dewaxed jute felt composites were prepared with resol and lignin modified phenol formaldehyde resin. Four different types of lignin modified resins were used by replacing phenol with lignin. The lignin modified resins were prepared from purified lignin obtained from paper industry waste black liquor. To investigate bonding between jute and resin, IR spectroscopy of jute felts and composites was carried out. The thermal stability of the composites was assessed by DSC and TGA. It was found that the lignin resin jute composite is thermally more stable than resol composite. XRD of jute felt and composite shows that the crystallinity of the jute fiber increases after composite preparation. The lignin resin composites were tested for water absorption and thickness swelling, and it was found that the results are comparable with those of resol jute composite. Composites prepared from lignin phenol formaldehyde resin with 50% phenol replacement has shown 75% tensile strength retention to that of pure resol jute composite.
Improved model of orthotropic closure approximation for flow induced fiber orientation
Authors: Chung Du Hwan , Kwon Tai Hun 
Published: April 2004

AbstractWe developed improved models (called ORW and ORW3) of existing “orthotropic fitted” closure approximations (ORF or ORL) for use with a wide range of fiber‐fiber interaction coefficients. Closure approximation refers to the approximation of a higher order tensor in terms of a lower order tensor. Principal values of the 4th order tensor are assumed in terms of polynomial expansions of the eigenvalues of the 2nd order tensor. Unknown parameters are determined by a least‐square fitting technique with assumed exact solutions. Flow data for the optimal fitting were designed to cover the entire domain of the orientation triangle as uniformly as possible to eliminate non‐physical oscillation. Shear/biaxial stretching combined flow turns out to play an important role in covering the orientation triangle, thereby increasing the accuracy of fiber orientation prediction. When tested for a variety of flow cases, neither ORW nor ORW3 shows any of the non‐physical oscillatory behaviors that ORF and ORL frequently suffer from.
Role of vacuum pressure and port locations on flow front control for liquid composite molding process
Authors: Hsiao Kuang‐Ting , Gillespie John W. , Advani Suresh G. , Fink Bruce K. 
Published: April 2004

AbstractIn this paper, the influence of air pressure gradients at the flow front, due to presence of two air vents under different vacuum pressures, is investigated for Liquid Composites Molding (LCM) Processes such as Resin Transfer Molding (RTM) and Vacuum Assisted Resin Transfer Molding (VARTM). An analytical mode introduced to predict the pressure distribution. It is suggested that the air press variation along the flow front can be used to control the flow front progress during the injection molding processes. The parametric studies identify a simple relationship that captures the most important process physics, which in prat can be implemented for flow front control.
A process performance index and its application to optimization of the rtm process
Authors: Jiang Shunliang , Zhang Chuck , Wang Ben 
Published: April 2004

AbstractResin transfer molding (RTM) is a promising manufacturing process for hig formance composite materials. However, the fact that RTM process design has traditionally been an expensive, time‐consuming trial‐and‐error procedure has p ited its wide application base. This paper proposes a solution to that problem—a simulation‐based optimum process design scheme for RTM. This scheme ei engineers to determine the optimum locations of injection gates and vents so both process efficiency and high part quality can be ensured. Essential to this mum process design scheme is a process performance index, which is defined respect to the major factors influencing RTM process efficiency and part quality This index is then used as the objective function for the RTM process design optimization model. Gate and vent locations are the process design parameters optimized. All data is obtained by running an RTM simulation program, and th netic algorithm (GA) is employed to carry out the optimization procedure for design parameters. It is found that constant pressure optimization will yi process with a short flow path, whereas constant flow optimization will yield process with smooth and vent‐oriented flow pattern. Although there is no dry factor in the objective function, it is interesting to note that both constant pres and constant flow optimization procedures result in process designs with a mil mum probability of dry spot formation. This study finds that, in general, cons flow optimization should be employed if injection pressure is not a major cone otherwise, constant pressure optimization should be used. Two case studies presented to illustrate the efficacy of this approach.
Delamination characteristics of multi‐directional carbon fiber/epoxy composites under high pressure
Authors: Rhee Kyong Yop , Oh Hwan Sup , Jang Seung Ho , Park Soo‐Jin 
Published: April 2004

AbstractIt was shown in a previous study that for unidirectional (0‐deg) graphite/epoxy composites, the fracture toughness under hydrostatic pressure increased 38% as hydrostatic pressure increased from 0.1 MPa to 200 MPa. This work investigates the compressive delamination behavior of multi‐directional graphite/epoxy laminated composites subjected to various hydrostatic pressures. Compressive delamination tests were performed under four hydrostatic pressure levels: 0.1, 100, 200, and 300 MPa Eighty‐eight‐ply dog‐bone type specimens with a single delamination at the center of the specimen were used. The stacking sequence applied was [0°/±45°/90°]lls. The compliance and fracture load were determined from load‐displacement curves as a function of hydrostatic pressure.The results show that the compliance decreases with increasing pressure while fracture load increases with increasing pressure. The compressive delamination toughness, Gc, was determined from the compliance method as a function of applied hydrostatic pressure. The results also show that Gc is significantly affected by hydrostatic pressure and increases from 2.11 kJ/m2 to 3.04 kJ/m2 (44% increase) as hydrostatic pressure increased from 0.1 MPa to 300 MPa. Visual examination of the fractured surface revealed that the increase of Gc is due to the suppression of micro‐cracks With increasing pressure. It was also found from SEM examination of delaminated surface that the Gc increase is due to more epoxy adhering to the fibers and more plastic deformation of epoxy material as applied hydrostatic pressure increases.
Interfacial adhesion in jute‐polyolefin composites
Authors: Tripathy S. S. , Levita G. , Di Landro L. 
Published: April 2004

AbstractThe interfacial adhesion between four different forms of jute fibers (sliver, bleached, mercerized and untreated) and polyolefinic matrices (LDPE and PP) was studied, as a critical factor affecting the mechanical behavior of these composites. The fiber‐matrix adhesion was estimated by means of the critical fiber length (lc) and the stress transfer ability parameter (τ); such parameters were obtained by Single Fiber Composite (SFC) tests. Tests were carried out to evaluate the mean tensile strength of the fibers, the mean critical fiber lengths and the stress transfer ability parameter for every fiber‐matrix combination, according to Weibull's statistical method. Thermal‐mechanical characterization of the fibers was also carried out to evaluate the resistance to processing conditions. A limited degradation of strength was observed, which, however, does not preclude the use of jute fibers as reinforcing means in polyolefin based composites. It was found that the adhesion was better in PP‐jute composites than in LDPE‐jute composites. In both cases the results showed that the sliver jute and the untreated jute had better adhesion to both matrices than had the bleached and the mercerized fibers. With both matrices the interface adhesion was in the order: mercerized < bleached < untreated = sliver.
Dynamics of binder displacement in liquid molding
Authors: Chen Jinglei , Backes Douglas , Jayaraman K. 
Published: April 2004

AbstractThis paper provides experimental data and an analytical description for mass transfer of soluble thermoplastic binder from a fiber preform to the resin during nonisothermal filling in liquid molding processes. The variation of binder concentration in resin during fill and the viscosity variation must be determined and controlled. This is because of the consequences for wet‐out, preform deformation, development of “fingering” flow patterns and nonuniformities in molded parts. Experimental binder washout curves have been obtained from random continuous glass mat preforms with a range of flow lengths, into a vinyl ester resin. An experimental method developed in this work was then used to estimate from such washout curves the binder concentration profiles within resin at the end of fill for the entire preform. Thus binder concentrations in the resin at the end of fill are seen to vary from 1 to 5 wt%. This range of binder concentrations yields a viscosity increase of more than two‐fold within the mold. A model has been developed and tested for the resin viscosity that takes into account three factors—binder dissolution, temperature variations, and a small amount of cure. This relation has been incorporated into a process model for one‐dimensional flow in a heated mold. Two parameters for the mass transfer coefficient relation were estimated from a run at a reference mold wall temperature. The model then provided good estimates over a range of mold wall temperatures, for binder concentration profiles as well as temperature profiles during filling, that match with experimental data to within 10%. Hence the model describes the interaction between nonisothermal effects and binder dissolution effects well. Calculations with this model thus provide quick estimates of viscosity variation under various process conditions. Design guidelines based on the predicted viscosity variation have also been developed for operating conditions in resin transfer molding.
In‐plane permeability determination for simulation of liquid composite molding of complex shapes
Authors: Rudd C. D. , Long A. C. , McGeehin P. , Smith P. 
Published: April 2004

AbstractProcess simulation forms an important part of the design loop for parts manufactured by liquid composite molding. Critical to this is the determination of accurate permeability data. While constitutive models and test methods for determination of in‐plane permeability of mats and fabrics exist, these do not take account of the effects of changes in fiber architecture during preform manufacture. The deformation behavior of mats and fabrics is reviewed, leading to fiber architecture predictions based upon deformed geometry. Existing models are applied to estimate the distribution of in‐plane permeabilities within the preform based upon the predicted fiber architecture. The predictions are compared with test results for pre‐stretched and pre‐sheared reinforcements, and the method is demonstrated for two prototype automotive parts.
Heat transfer and reaction issues in liquid composite molding
Authors: Tucker Charles L. 
Published: April 2004

AbstractThis paper surveys current issues in the modeling of heat transfer and chemical reaction in resin transfer molding and structural reaction injection molding. The discussion is organized around four steps of modeling: incorporating the physical phenomena into a model, gathering material data, analyzing the model to provide physical understanding, and solving the model for relevant cases. The local volume averaging approach is summarized as a method for deriving appropriate balance equations. The resulting equations are analyzed using dimensional analysis, and analytical solutions are presented for several special cases. These include steady heat transfer for small and large Graetz numbers, and a transient solution for heat transfer during filling at large Graetz numbers. This latter solution explains why preheating the fibers does not heat the resin uniformly. Numerical solution methods are discussed, with emphasis on upwinding techniques for hyperbolic problems. The paper concludes with a summary of research achievements and needs.
Consolidation and cure simulations for laminated composites
Authors: Young Wen‐Bin 
Published: April 2004

AbstractFiber reinforced polymer composites have been increasingly used in various structural components. One of the important processes for fabricating high performance laminated composites is autoclave assisted prepreg lay‐up. Since the quality of laminated composites is largely affected by the cure cycle, selection of the cure cycle for each particular application is important and must be optimized. Thus, some fundamental model of the consolidation and cure processes is necessary to properly select the suitable parameters for each application. This study used the viscoelastic solid model for the consolidation of the laminate. In addition, variations of permeability and thermal properties caused by the change of the fiber volume content during the consolidation process were also included. Simulated thickness variations of epoxy continuous carbon fiber prepreg (AS4/3501‐6 from Hercules) laminate under consolidation were compared to the experimental results to test the model. Based on the model analysis, one can predict the pressure, velocity, and laminate thickness during the consolidation process, which can be used to properly select the cure cycle for applications of laminated composites.
A new curvature‐driven delamination test for measuring the mode II toughness of composites
Authors: Matsumoto D. S. , Vallance M. A. , Gifford S. K. 
Published: April 2004

AbstractThe measurement of the delamination toughness of composites requires fracture tests with well‐characterized geometries. Because the delamination toughness is frequently used as a material selection parameter, it is necessary to differentiate between experimental artifacts, data scatter, and changes in the mechanism of delamination. This new Curvature‐Driven Delamination (CDD) test for Mode II provides a direct, steady‐state measurement of the pure Mode II delamination toughness without the compliance calculations inherent in other delamination test protocols. Like the Wedge‐Driven Delamination (WDD) test for Mode I, the CDD Mode II test measures the toughness at controlled crack growth rates. The CDD Mode II test correlates well with the results of the established End‐Notch Flexure (ENF) Mode II test but is not subject to the geometric instabilities of that test. Changes in the delamination mechanism are easily observed by the direct, continuous measurement of the toughness in the CDD Mode II test.
Experimental verification of models for induction heating of continuous‐carbon‐fiber composites
Authors: Fink Bruce K. , McCullough Roy L. , Gillespie John W. 
Published: April 2004

AbstractHeating of continuous‐carbon‐fiber‐reinforced polymers (CFRPs) by the application of an alternating magnetic field has been shown to be due to dielectric losses in the polymer. Models that predict thermal generation in these composites are input to a finite element heat transfer analysis, providing the predicted transient thermal profile in the plane of the laminate. The validity of the global thermal generation model is established through an experimental test matrix in which various specimen configurations are evaluated and compared with theoretical predictions of transient surface temperatures.
Mold filling analysis in resin transfer molding
Authors: Calhoun Daryl R. , Yalvaç Selim , Wetters Derrick G. , Wu Cheng‐Hsien , Wang T. James , Tsai J. Stephen , Lee L. James 
Published: April 2004

AbstractThis study is a comparison of independently designed mold flow experiments performed at The Dow Chemical Company with simulations from a computer code developed at The Ohio State University. The experiments used in the validation study included isothermal 1‐dimensional flow with line gating and end venting, isothermal 2‐dimensional flow with converging flow and center venting, and two different resin systems. The simulation results were compared with experimental pressure and temperature readings and fill times. It was found that simulated fill times could be predicted within experimental error and pressure distributions could be predicted with the application of a scaling factor.
Sensor system for monitoring impregnation and cure during resin transfer molding
Authors: Schwab Scott D. , Levy Ram L. , Glover Gregg G. 
Published: April 2004

AbstractIn the resin transfer molding (RTM) fabrication of composites, knowledge of the position of a moving resin front during impregnation is important for process optimization. We describe here a simple, inexpensive, multi‐point sensor system based on DC conductometry for determination of resin position in an RTM mold. This Resin Position Sensor (RPS) system consists of a matrix of small sensors embedded in the RTM tool, whose combined output can be used to produce a resin flow pattern at any given time after the start of impregnation. As it cures, the resin resistance increases and the sensor can then function as a cure monitor. A large, 24‐sensor RTM tool was fabricated for demonstration of the RPS. Flow contour maps generated from sensor data during impregnation of both E‐glass and carbon fiber preforms are shown.