bluuebunny/crossref_metadata_2025_split huggingface dataset:
Three‐dimensional finite element computations for frictional contact problems with non‐associated sliding rule
Authors: Hjiaj M. , Feng Z‐Q , de Saxcé G. , Mróz Z. 
Published: June 2004

AbstractThis paper presents an algorithm for solving anisotropic frictional contact problems where the sliding rule is non‐associated.The algorithm is based on a variational formulation of the complex interface model that combine the classical unilateral contact law and an anisotropic friction model with a non‐associated slip rule. Both the friction condition and the sliding potential are elliptical and have the same principal axes but with different semi‐axes ratio. The frictional contact law and its inverse are derived from a single non‐differentiable scalar‐valued function, called a bi‐potential. The convexity properties of the bi‐potential permit to associate stationary principles with initial/boundary value problems. With the present formulation, the time‐integration of the frictional contact law takes the form of a projection onto a convex set and only one predictor–corrector step addresses all cases (sticking, sliding, no‐contact). A solution algorithm is presented and tested on a simple example that shows the strong influence of the slip rule on the frictional behaviour. Copyright 2004 John Wiley & Sons, Ltd.
Numerical integration in Natural Neighbour Galerkin methods
Authors: González D. , Cueto E. , Martínez M. A. , Doblaré M. 
Published: June 2004

AbstractIn this paper, issues regarding numerical integration of the discrete system of equations arising from natural neighbour (natural element) Galerkin methods are addressed. The sources of error in the traditional Delaunay triangle‐based numerical integration are investigated. Two alternative numerical integration schemes are analysed. First, a ‘local’ approach in which nodal shape function supports are exactly decomposed into triangles and circle segments is shown not to give accurate enough results. Second, a stabilized nodal quadrature scheme is shown to render high levels of accuracy, while resulting specially appropriate in a Natural Neighbour Galerkin approximation method. The paper is completed with several examples showing the performance of the proposed techniques. Copyright © 2004 John Wiley & Sons, Ltd.
Rayleigh wave correction for the BEM analysis of two‐dimensional elastodynamic problems in a half‐space
Authors: Arias I. , Achenbach J. D. 
Published: June 2004

AbstractA simple, elegant approach is proposed to correct the error introduced by the truncation of the infinite boundary in the BEM modelling of two‐dimensional wave propagation problems in elastic half‐spaces. The proposed method exploits the knowledge of the far‐field asymptotic behaviour of the solution to adequately correct the BEM displacement system matrix for the truncated problem to account for the contribution of the omitted part of the boundary. The reciprocal theorem of elastodynamics is used for a convenient computation of this contribution involving the same boundary integrals that form the original BEM system. The method is formulated for a two‐dimensional homogeneous, isotropic, linearly elastic half‐space and its implementation in a frequency domain boundary element scheme is discussed in some detail. The formulation is then validated for a free Rayleigh pulse travelling on a half‐space and successfully tested for a benchmark problem with a known approximation to the analytical solution. Copyright © 2004 John Wiley & Sons, Ltd.
Fiber orientation structures and mechanical properties of injection molded short glass fiber reinforced ribbed plates
Authors: Hine P. J. , Duckett R. A. 
Published: June 2004

AbstractIn this paper we describe a study of the fiber orientation structures present within a model ribbed injection molded plate. The details of the fiber orientation at each chosen location on the injection molded parts were measured using an in‐house developed image analysis system, which enabled large areas to be scanned (up to 200 mm2) up to a limit of 1 million fiber images. Two materials were used for these experiments, short glass fiber filled PBT and short glass fiber filled nylon 66. First, a comparison was made between the fiber orientation at an identical position, 28 mm from the injection gate on a transverse rib, on two plates made from glass fiber filled PBT. It was found that the fiber orientation in these two separately manufactured components was virtually identical when comparing the whole scanned area, but the differences became more significant when comparing areas on the length scale of an individual fiber (∼ 200 μm). Second, the fiber orientation at the same position was compared for two plates made using the glass/PBT and glass/nylon 66 materials. The differences for the complete scanned areas were small, confirming that mold geometry plays a crucial role in determining fiber orientation structures, and that matrix properties are secondary. Third, the fiber orientation structures at various positions across one of the glass/PBT plates were examined in greater detail, in particular across a number of the transverse ribs: the chosen ribs were of various widths and heights. Differences in structure were found depending on the local rib geometry. Finally, the effect of the measured fiber orientation structures in determining the mechanical properties of the ribbed plate was investigated using simple modeling schemes. While the stiffness of the rib/web assembly was found to depend on the average fiber orientation of the two parts, the different thermal expansions of the web and the rib, caused by the different fiber orientation in the two regions, led to significant warpage of the rib/web assembly. Polym. Compos. 25:237–254, 2004. © 2004 Society of Plastics Engineers.
A new kinetic and viscosity model for liquid composite molding simulations in an industrial environment
Authors: Henne Markus , Breyer Christian , Niedermeier Michael , Ermanni Paolo 
Published: June 2004

AbstractLiquid composite molding is broadly used for manufacturing composite parts. Apart from the preforming of the dry fibrous material, mold filling and curing of the resin are the main steps in the manufacturing process. For process simulation numerical methods, like finite element methods are applied. Flow models describing the flow behavior through a porous medium are well established. The ability to predict and monitor the curing process in liquid composite molding is crucial for manufacturing process optimization in case of application of rapid curing resin systems. Based on differential scanning calorimetry and rheological experiments, cure kinetics and viscosity of a resin system were characterized. A new kinetic and complex viscosity model is proposed to predict epoxy resin properties in numerical modeling of liquid composite molding. The semi‐empirical models are simple to use and therefore suitable for process optimization in an industrial environment. Both models were validated by a fitting to the experimental data by the Levenberg‐Marquardt method. A process to determine the initial values for the fitting procedure is also proposed. The predictions of the validated models were in good agreement with the measured data, and are therefore applicable for numerical process optimization. Polym. Compos. 25:255–269, 2004. © 2004 Society of Plastics Engineers.
Thermally induced performance decay in conductive polymer composites
Authors: Hou Yan Hui , Zhang Ming Qiu , Rong Min Zhi 
Published: June 2004

AbstractIn the course of long‐term service, electrically conductive polymer composites acting as positive temperature coefficient (PTC) materials are faced with performance decay characterized by gradually increased room temperature resistivity and decreased PTC intensity. To reveal the influencing factors and to find appropriate ways for solving the problems, thermal‐cold cycling experiments (which simulate the extreme operating conditions of PTC type materials in a laboratory environment) and electrification tests are carried out in the current work. The results demonstrate that irreversible damage of partial conductive networks and, in particular, oxidation degradation induced crystallizability deterioration of the matrix polymer are responsible for the electrical performance decay. Additionally, an increase in the contact resistance formed at the metallic electrode/composite contacts exerts a negative influence on the service life of the composites. Polym. Compos. 25:270–279, 2004. © 2004 Society of Plastics Engineers.
Creep behavior of biocomposites based on sisal fiber reinforced cellulose derivatives/starch blends
Authors: Alvarez Vera A. , Kenny José M. , Vázquez Analía 
Published: June 2004

AbstractBiodegradable composites based on cellulose derivatives/starch blends reinforced with sisal short fibers were fabricated by injection molding. Results of short‐term flexural creep tests are reported to investigate the time‐dependence behavior of the composites. Fiber content and temperature effects are also considered, taking into account various methods and equations. At short times, a creep power law is employed. A master curve with the Arrhenius model is used to determine the creep resistance at longer times and different temperatures. Good fitting of the experimental results with the four‐parameter model is reported, leading to a relationship between the observed creep behavior and the composite morphology. The addition of sisal fibers to the polymeric matrix promotes a significant improvement of the composite creep resistance. Polym. Compos. 25:280–288, 2004. © 2004 Society of Plastics Engineers.
Long‐term behavior of partially cured epoxy prepreg systems under tensile loading
Authors: Wolfrum J. , Stang C. , Ehrenstein G. W. 
Published: June 2004

AbstractFor the determination of the influence of processing conditions on the long‐term behavior of high performance thermoset composites, two different glass fiber laminate systems with varying degrees of cure were examined. The laminates were conditioned in both moist and dry environments, and characterized via thermoanalytical and mechanical investigations. During the progression of moisture conditioning, both systems exhibited a reduction in the measured glass transition temperature as a result of the plasticization of the matrix. Tensile tests revealed that a direct correlation exists between the processing conditions and the long‐term performance. Employing a linear model, the long‐term mechanical behavior as a function of processing and moisture absorption can be described. Thus, the manufacturer has access to a tool for calculating the mechanical and thermomechanical properties depending on the processing and environmental conditions. Polym. Compos. 25:289–297, 2004. © 2004 Society of Plastics Engineers.
Fast joining of composite pipes using UV curing FRP composites
Authors: Pang Su‐Seng , Li Guoqiang , Jerro H. Dwayne , Peck Jerry A. , Stubblefield Michael A. 
Published: June 2004

AbstractIn this paper, twelve butt‐weld composite pipe joints were prepared. Among them, six were prepared using ultraviolet (UV) curing fiber reinforced plastics (FRPs) and six were prepared using ambient environment curing FRPs as controls. Filament wound composite pipes were used. Each section of pipe was 304.8 mm long with a 101.6 mm inner diameter. The wet lay‐up technique was used to prepare the test samples. The curing time for the UV curing samples was 40 minutes, while the curing time was 24 hours for the control samples. Both internal pressure tests and four‐point bending tests were conducted on the prepared samples. The test results show that the UV curing FRP wrapped composite pipe joints achieved nearly the same bending strength as the control samples. However, the internal pressure rating achieved by the UV curing FRP coupled joints was lower than that achieved by the control samples. A finite element analysis was conducted to understand the mechanism for the lowered internal pressure rating. Based on the test and the finite element analysis results, the UV curing FRP can be used in joining composite truss structures and composite frame structures. Suggestions were made to increase the internal pressure rating of UV curing FRP coupled composite pipes. Polym. Compos. 25:298–306, 2004. © 2004 Society of Plastics Engineers.
Processing‐properties relationship of sandwich panels with polypropylene‐core and polypropylene‐matrix composite skins
Authors: Passaro Alessandra , Corvaglia Paolo , Manni Orazio , Barone Luigi , Maffezzoli Alfonso 
Published: June 2004

AbstractThis paper reports on the development and the optimization of a thermoforming process (compression molding) for thermoplastic sandwich panels. The skins of the panels are fabricated from polypropylene (PP)/continuous glass fibers dry prepregs in the form of a commingled fabric. The use of two different types of core material has been used, a PP foam and a PP honeycomb. Additionally, two alternative methods for the thermoforming process have been analyzed, using either a one‐stage or a two‐stage process. In the one‐step process, skin molding and skin‐core bonding are carried out simultaneously. In the two‐stage process, the skins are first thermoformed and then bonded to the core as the second stage. The influence of the selected process parameters on the mechanical properties of the panels has been experimentally investigated, leading to the identification of the preferred processing conditions. Polym. Compos. 25:307–318, 2004. © 2004 Society of Plastics Engineers.
A comparative study on the influence of epoxy sizings on the mechanical performance of woven carbon fiber‐epoxy composites
Authors: Fernández B. , Arbelaiz A. , Valea A. , Mujika F. , Mondragon I. 
Published: June 2004

AbstractIn the present work the effect of epoxy sizings on the fracture behavior of woven carbon fiber tetrafunctional epoxy composites has been investigated. Three‐point flexural, short beam shear (SBS) and Mode‐II interlaminar fracture toughness (ENF) tests have been carried out. Wettability and Atomic Force Microscopy (AFM) studies have been performed on commercial sized, desized and 0.7 wt% TGDDM and 0.7 wt% DGEBA sized carbon fibers. Dynamic mechanical thermal analysis and Scanning Electron Microscopy (SEM) studies were also carried out on the different carbon fiber/epoxy composites. The used sizing treatments provided composites with improved mechanical properties due to the enhancement achieved in the fiber‐matrix adhesion. Polym. Compos. 25:319–330, 2004. © 2004 Society of Plastics Engineers.
Fiber orientation in multilayer tubes processed by a conical extruder
Authors: Sarioglu Alp , Hagstrand Per‐Ola , Månson Jan‐Anders E. 
Published: June 2004

AbstractA new extruder design has been developed for the coextrusion of two‐layer annular sections. The extruder consists of a conical stator‐rotor‐stator assembly, which performs extrusion from each side of the rotor. Flow within this assembly is fully three‐dimensional, with helicoidal streamlines in the vicinity of the rotor and the die entry region. Fiber orientation is created in a circumferential direction by these helicoidal streamlines; close to the inner and outer surfaces of the tube, the fibers are parallel to the main extrusion direction, whereas in the mid‐thickness, they are oriented in the circumferential direction. It is demonstrated that the amount of orientation depends on rotor speed and die design. When using a short die and high rotor speed, an increased fraction of fibers are oriented in the circumferential direction. Polym. Compos. 25:331–341, 2004. © 2004 Society of Plastics Engineers.
Sterculia striata exudate polysaccharide: characterization, rheological properties and comparison with Sterculia urens (karaya) polysaccharide
Authors: Brito Ana Cristina F , Silva Durcilene A , de Paula Regina CM , Feitosa Judith PA 
Published: June 2004

AbstractThe exudate polysaccharide from Sterculia striata trees was investigated regarding its composition, structure and rheological properties and metal ion interactions. This polysaccharide contains galactose, rhamnose galacturonic and glucuronic acids as the main monosaccharide components. 13C NMR spectroscopy revealed that the anomeric composition is similar to that of Sterculia urens exudates, except for the presence of xylose, not identified in the latter polysaccharide. The empirical stiffness parameter B was determined for S striata (B = 0.043), suggesting that the polysaccharide exists in a semi‐rigid chain conformation, with no conformational change being demonstrated. Deacetylation led to a more flexible polymer chain (B = 0.058). The counter ion affinity of the polysaccharide aqueous solution was determined by intrinsic viscosity measurements, resulting in Al3+ > Ca2+ > Na+. Copyright © 2004 Society of Chemical Industry
Preparation and characterization of core–shell polystyrene–polydimethylsiloxane particles by seeded polymerization
Authors: Zou Mingxuan , Zhang Zhicheng , He Weidong , Ge Xuewu , Fan Fei 
Published: June 2004

AbstractNanometer scale particles of seed latex were successfully prepared by polymerization induced by gamma rays. By modification of the coupling agent 3‐methacryloxylpropyltrimethoxylsilane (MPS) at the surface of polystyrene (PSt) particles, polydimethylsiloxane (PDMS) was introduced outside the PSt particles and composite latex particles with a core–shell (PSt–PDMS) structure were successfully prepared. Because of the chemical bond linkage between the core and the shell, such a structure is stable. Direct evidence of the core–shell structure was observed by transmission electron microscopy (TEM). In addition the chemical bond linkage was confirmed by Fourier‐transfer infrared (FT‐IR) spectroscopy. An indirect proof of the core–shell structure was given by water absorption ratio determination of the different samples. Copyright © 2004 Society of Chemical Industry
Synthesis of poly(propylene glycol)‐grafted polyimide precursors and preparation of nanoporous polyimides
Authors: Do Jin‐Sek , Zhu Baoku , Han Sang Hyup , Nah Changwoon , Lee Myong‐Hoon 
Published: June 2004

AbstractA novel approach to prepare a polyimide nanofoam was explored by using a polyimide precursor grafted with a labile poly(propylene glycol) (PPG) oligomer. The PPG‐grafted polyimide precursor, poly((amic acid)‐co‐(amic ester)), was synthesized via partial esterification of poly(amic acid) derived from pyromellitic dianhydride (PMDA) and 4,4′‐oxydianiline (ODA) with bromo‐terminated poly(propylene glycol) in the presence of K2CO3 in hexamethylphosphoramide and N‐methylpyrrolidone. The precursor polymer film was spin‐coated onto a glass substrate, then imidized at 200 °C under nitrogen, and subsequently the PPG graft was decomposed by heating the film at 300 °C for 9 h in air, resulting in the PMDA/ODA polyimide nanofoam. The precursor polymers, polyimides and foamed polyimides were characterized by a variety of techniques including 1H‐NMR spectroscopy, Fourier‐transform infrared (FT‐IR) spectroscopy, differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). The homogeneously distributed nano‐sized pores of 20–40 nm were observed by transmission electron microscopy (TEM) of the foamed polyimide. Copyright © 2004 Society of Chemical Industry
Fibre reinforcement of elastomers: nanocomposites based on sepiolite and poly(hydroxyethyl acrylate)
Authors: Bokobza L , Burr A , Garnaud G , Perrin MY , Pagnotta S 
Published: June 2004

AbstractThe reinforcement of poly(hydroxyethyl acrylate) provided by sepiolite particles has been analysed. Stress–strain measurements at equilibrium, as well as swelling experiments, were carried out on the unfilled and filled polymers. The state of dispersion of the filler was characterized by transmission electron microscopy. Moreover, an evaluation of chain orientation by infrared dichroism reveals a high orientation level in the filled system. The strong interaction between the two phases, combined with a good dispersion and a high shape factor of these clay particles, explain the improvement of the mechanical properties of the composites with respect to the pure polymer. Copyright © 2004 Society of Chemical Industry
Synthesis of new open‐chain alkoxyamines and their evaluation for nitroxide‐mediated radical polymerization
Authors: Nesvadba Peter , Bugnon Lucienne , Sift Rosemarie 
Published: June 2004

AbstractNew readily available open‐chain alkoxyamines have been synthesized and evaluated as unimolecular initiators for nitroxide‐mediated radical polymerization of styrene and n‐butyl acrylate. The observed moderate control of polymerization is explained by the low thermostability of the parent nitroxide. Copyright © 2004 Society of Chemical Industry
Mechanical and dynamic mechanical properties of nylon 66/montmorillonite nanocomposites fabricated by melt compounding
Authors: Yu Zhong‐Zhen , Yan Cheng , Yang Mingshu , Mai Yiu‐Wing 
Published: June 2004

AbstractNylon 66 nanocomposites were prepared by melt compounding of nylon 66 with organically modified montmorillonite (MMT). The organic MMT was pre‐modified with about 14 wt% of ammonium surfactant, much lower than the 35–46 wt% in most commercial organic MMT powders. Transmission electron microscope observation indicated that the MMT layers were well exfoliated in nylon 66 matrix. Dynamic mechanical analysis confirmed the constraint effect of exfoliated MMT layers on nylon 66 chains, which benefited the increased storage modulus, increased glass transition temperature and reduced magnitude of alpha relaxation peak. The effects of organic MMT loading levels on reinforcement and fracture behaviour of the nanocomposites were evaluated using tensile and three‐point bending tests. The addition of the organic MMT clearly increased Young's modulus and tensile strength but decreased ductility and fracture toughness of nylon 66. Copyright © 2004 Society of Chemical Industry
Effects of shearing and comonomer content on the crystallization behavior of poly(butylene succinate‐co‐butylene 2‐ethyl‐2‐methyl succinate)
Authors: Chae Dong Wook , Kim Byoung Chul , Kim Dong Kook 
Published: June 2004

AbstractPoly(butylene succinate‐co‐butylene 2‐ethyl‐2‐methyl succinate) (PBSEMS) random copolymers were prepared with different comonomer compositions. The effects of shearing and comonomer content on the crystallization behavior of these copolymers were investigated at 80 °C. The thermal and morphological properties of the resulting samples were also discussed. The copolymers showed a longer induction time and a slower crystallization rate with increasing comonomer content. The promoting effect of shear on the overall crystallization behavior was more notable for those copolymers containing more 2‐ethyl‐2‐methyl succinic acid (EMSA) units. The melting temperature of ‘as‐prepared’ poly(butylene succinate) (PBS) was ca. 115 °C, while that of the copolymers varied from 112 to 102 °C. Higher comonomer contents in the copolymers gave rise to lower melting temperatures and broader melting peaks. In addition, the isothermally crystallized samples showed multiple melting endothermic behavior, the extent of which depended on the comonomer content. The copolymers showed different wide‐angle X‐ray diffraction (WAXD) patterns from that of neat PBS, depending on the comonomer content and shear applied during crystallization. With increasing comonomer content, the copolymers crystallized without shearing, showing the shifting of a diffraction peak to a higher angle, while those crystallized under shear did not show any peak shift. Copyright © 2004 Society of Chemical Industry