bluuebunny/crossref_metadata_2025_split huggingface dataset:
Review of failure criteria of fibrous composite materials
Authors: Echaabi Jamal , Trochu Françlois , Gauvin Raymond 
Published: April 2004

AbstractComposite materials exhibit various and complex failure behavior. Different formalisms have been used to predict failure. Improvement of old theories and new ones continue to be published. In this paper, the most recent and widely used models are presented. Failure criteria such as Tsai‐Wu, parametric formulations, maximal stress and strain, Hashin criterion, Hart‐Smith criterion, and the method based on kriging are presented. These failure theories may be classified in two categories, depending whether they integrate failure modes or not. The formalism of each theory is briefly described and their application to model failure of composite laminates is discussed by comparing the advantages and limitations of each method. The diversity of experimental failure envelopes, as reported in the literature on composites, is outlined and it is shown that most criteria permit modeling only particular failure properties of composite laminates.
Permeability model for a woven fabric
Authors: Šimáček Pavel , Advani Suresh G. 
Published: April 2004

AbstractThe resin transfer molding (RTM) method is used to manufacture composite parts. The reinforcing fibers are placed in a mold cavity and the resin is injected to fill up the empty spaces. After the resin cures, the mold is opened and the part ejected. To predict necessary pressures and filling times and the proper locations for the inlet ports for resin injection and vents for air ejection it is necessary to model the resin infiltration process. A key to this modeling is permeability which characterizes the resistance of fibers to the flow of infiltrating resin. A simplified model for in‐plane permeability of fabric reinforcement (preform) is developed here. This model uses lubrication theory for modeling the flow through open pores and Darcy's law for the transverse flow through the reinforcement. Scaling analysis is provided to justify the simplification and to estimate the range of validity for resulting expressions. Extension of the model to cover multi‐layered preforms is derived. Boundary conditions and the data necessary to specify the problem geometry are discussed. A numerical experiment is conducted to estimate the influence of the transverse permeability of the preform on the solution. A calculation is provided for the permeability of a plain weave fabric.
Liquid‐crystal polymer fiber production and reinforcing in ribbons of poly(ether imide)/vectra‐B blends
Authors: Bastida S. , Eguiazábal J. I. , Nazábal J. 
Published: April 2004

AbstractBlends of poly(ether imide) (PEI) with a liquid‐crystal polymer (Vectra‐B950) were extruded into ribbon. Two PEI‐rich compositions at three different draw ratios were obtained, and the miscibility and morphology of the blends analyzed. The tensile properties of the ribbons were determined, both in the processing and in the perpendicular direction and were compared with those of the pure PEI. Results showed that PEI/Vectra blends are immiscible and that complex structures were obtained as a consequence of extrusion. The blend composition and the draw ratio determined to a great extent the mechanical properties of the blends. The interfacial adhesion between blend components is low, but enough to break the LCP fibers when significant aspect ratios are attained.
Impact fracture behavior of injection molded long glass fiber reinforced polypropylene
Authors: Skourlis T. P. , Mehta S. R. , Chassapis C. , Manoochehri S. 
Published: April 2004

AbstractIn this work the variation in Izod impact strength with spatial location was examined for injection molded long glass fiber polypropylene composite plaques. These plaques were fabricated at different sets of processing conditions, with injection speed and melt temperature being varied. By carefully machining test specimens, fifteen different plaque locations both in the in‐flow and cross‐flow directions were tested. The part morphology was described with the use of characteristic layer thickness ratios, i.e., the shell and the core to part thickness ratios, which were measured experimentally. It was shown that the variation in impact strength with sample location strongly correlates to shell to part thickness ratio. In addition, it was observed that different failure mechanisms exist for different fiber orientations, i.e., for fibers oriented transversely to the crack plane or on the crack plane itself. Scanning electron microscopy (SEM) of the fracture surface was conducted and the results supported our findings on the microstructural level.
Performance of multilayer films using maleated linear low‐density polyethylene blends
Authors: Sánchez‐Valdes S. , Orona‐Villarreal F. , Lopez‐Quintanilla M. , Yañez‐Flores I. , De Valle L. F. Ramos , Guerrero‐Salazar C. 
Published: April 2004

AbstractBlends of linear low‐density polyethylene (LLDPE) and linear low‐density polyethylene grafted maleic anhydride (LLDPE‐gMA) were prepared by melt mixing and then coextruded as external layers, with a central layer of polyamide (PA) on three‐layer coextruded flat films. Blends with contents of 0% to 55 wt% of maleated LLDPE, on the external layers, were analyzed. The T‐peel strength and oxygen and water vapor transmission rate of the films were measured. The surfaces of the peeled films were characterized using attenuated total reflection infrared spectroscopy (FTIR‐ATR) and scanning electron microscopy (SEM). The observed increase in T‐peel strength of the films with 10% and higher levels of maleated LLDPE in the blend suggests good interfacial adhesion between layers. This sharp increase in peel strength appears to be associated, besides interdiffusion, with specific interactions between polymers, as the bond formation between maleic anhydride and the polyamide end groups by in situ block copolymer formation across the interface. No significant modifications in oxygen barrier properties of the films were observed; however, the use of higher contents of LLDPEgMA, even though it increases the adhesion performance, also increases the water vapor transmission rate by a reduction in the degree of crystallinity.
Properties and kinetics of thermally crystallized oriented poly(ethylene terephthalate) (PET). I: Kinetics of crystallization
Authors: Varma Pankaj , Lofgren E. A. , Jabarin S. A. 
Published: April 2004

AbstractThe crystallization kinetics of previously oriented poly(ethylene terephthalate) (PET) sheets have been studied under unconstrained conditions, as functions of stretch ratio, mode of extension, and crystallization temperature. Isothermal and dynamic crystallization conditions have been utilized for the determination of half‐times of crystallization and activation energies, respectively. Results indicate that rates of crystallization of pre‐oriented PET increase substantially, with increasing stretch ratios. Half‐times of crystallization, at a given isothermal temperature, were found to decrease from a few minutes to fractions of seconds. Similarly, the activation energies of thermal crystallization have been shown to decrease from 75 kcal/mol for unoriented PET, to less than 20 kcal/mol for highly oriented material. These changes are most apparent among samples with low to moderate levels of orientation. Highly oriented samples have proven to be less sensitive, yielding similar extents of thermal crystallization, regardless of specific initial extension ratios. These samples have also shown less sensitivity to temperature of crystallization, exhibiting only slightly higher levels of crystallinity as a result of exposure to increasing temperatures in the range from 100°C to 120°C.
Study on the surface tensions of polymer melts using axisymmetric drop shape analysis
Authors: Kwok D. Y. , Cheung L. K. , Park C. B. , Neumann A. W. 
Published: April 2004

AbstractIt is shown that Axisymmetric Drop Shape Analysis (ADSA) is well‐suited for the study of polymer melt surface tensions. The technique is not restricted to equilibrium surface (interfacial) tensions; it is also suitable for measuring the time dependence (or kinetics) of surface tension of polymer melts. Results for three polymers, polypropylene, polyethylene, and polystyrene, at temperatures above 170°C are reported. Contrary to the well‐known decrease of surface tension in low molecular weight surfactant solutions as a result of equilibration, an increase in the melt surface tension is observed under isothermal conditions.
Hot plate welding of polypropylene. Part I: Crystallization kinetics
Authors: Nieh Jenn‐Yeu , James Lee L. 
Published: April 2004

AbstractThe crystalline structure formation in the heat affected zone during hot plate welding has a great influence on the performance of the welded semi‐crystalline polymers. The quiescent and flow induced crystallization of polypropylene was investigated experimentally. A simplified, phenomenological crystallization model was developed, which can describe the crystal formation from completely melted and partially melted polymer. Predictions obtained from the model were compared with experimental results.
Packing mechanics of fiber reinforcements
Authors: Toll Staffan 
Published: April 2004

AbstractTheories of fiber packing, of use in manufacturing composite materials, are developed. The maximum packing fraction of force free fibers is estimated based on a statistical analysis of the distribution of fiber‐fiber contact points. The new expressions are more general than previous ones by allowing for a distribution in fiber length and orientation. The forced packing beyond this limit is governed by the bending of fiber segments between contact points. A micromechanical theory is developed for this, again based on the contact point statistics, and equations relating the force response per unit area of a fiber bed to the fiber volume fraction are derived for three basic types of assembly: a general 3D wad, a planar mat of dispersed fibers, and a bundle of almost parallel fibers. Other types of reinforcement structure, such as woven fabrics, and the effect of lubrication are also treated briefly.
Filamentary extrusion of microcellular polymers using a rapid decompressive element
Authors: Park Chul B. , Suh Nam P. 
Published: April 2004

AbstractAn extrusion process for manufacturing microcellular plastics is presented. In the past, microcellular structures have been produced in batch processes by using a thermodynamic instability of a polymer/gas system. In order to utilize such a thermodynamic instability in a continuous extrusion process, a large amount of gas must be dissolved quickly in a molten plastic flowing in the machine, and a rapid drop in the gas solubility must be induced in the flowing polymer/gas solution. Since the solubility of a gas in a polymer is a sensitive function of pressure, a thermodynamic instability for producing a microcellular structure can be induced by rapidly lowering the pressure. This paper presents a means for continuously forming the polymer/gas solution at an industrial processing rate and a means of nucleating microcells in the polymer/gas solution using a nozzle. Finally, a process model for controlling the cell morphology is presented by identifying the key parameters that control microcellular foaming in a continuous process. The experimental results agree with theoretical analyses, confirming the fact that the processing pressure strongly affects the microcellular foaming process through its effects on the amount of gas dissolved in the polymer and the magnitude of the pressure drop in the nucleation device.
Selection of adhesive system for radio‐frequency heating of structural sheet molding compound components
Authors: Malaczynski Gerard W. , Cinpinski Gerald J. 
Published: April 2004

AbstractA series of laboratory tests and computer simulations of adhesive curing enhanced by radio‐frequency heating indicated that not all adhesive systems can be effectively used for RF‐based curing because of the danger of thermal runaway. Our investigation of the process mechanism also resulted in several other findings that could lead to further improvement of the processing cycle. Both experimental and theoretical results indicated a high sensitivity of the adhesive exothermal reaction kinetics to the thickness of the bond line, which varies with changes of the thickness of the processed sheet molding compound (SMC) components. Thus, regardless of the type of adhesive system employed, tighter dimensional tolerance would ensure better quality of the bond. Finally, we proved that the initial surface temperature of the SMC members substantially affects the process effectiveness and joint quality, and should be strictly monitored.
Effects of additives on molecular weight correlations to dynamic viscosity of polypropylenes
Authors: Tollefson Norris M. , Roy Suresh , Shepard Thomas A. , Long William J. 
Published: April 2004

AbstractThe relationship between weight averaged molecular weight and zero‐shear viscosity (commonly known as the Mark‐Houwink equation) as determined by dynamic oscillatory rheometry was found to depend upon the absence or presence of viscosity‐modifying additives such as a plasticizing oil. An empirical expression was derived to estimate molecular weights from zero‐shear viscosities and compensated for the presence of plasticizing OIL or nucleating agent and their influence on the viscosity measurement. The model was verified by calculation of weight‐averaged molecular weights of irradiated polypropylenes, and comparison to molecular weight determined by gel permeation chromatography. In the process of derivation, it was found that superposition principles and interpretations of viscosity curves based on pure polymer systems were equally valid when applied to viscosity‐modified polymer systems.
Curing, compatibility, and fracture toughness for blends of bismaleimide and a tetrafunctional epoxy resin
Authors: Lin King‐Fu , Chen Jyh‐Chien 
Published: April 2004

AbstractThe curing, compatibility, and fracture toughness of blends of 4,4 ′‐bismaleimidodiphenylmethane (BDM)/tetraglycidyl diamino‐diphenyl methane (TGDDM) were investigated. Diamino‐diphenyl sulfone (DDS) was used as a curing agent. BDM alone could be both homopolymerized (at a lower temperature) and could also undergo Michael addition reactions with the primary amine of DDS. The secondary amine of DDS did not react with BDM. However, the network produced by homopolymerization was not miscible with that produced by the latter reactions. Curing of TGDDM with DDS took place almost at the same temperature as that of the homopolymerization of BDM, but well below the temperature of the Michael addition reaction. When a BDM/TGDDM mixture was cured with DDS in the stoichiometric ratio, the miscibility of the cured system increased with the amount of TGDDM. This was attributed to the fact that the network produced by Michael addition reactions was diminished. When DDS reacted entirely with TGDDM, the BDM/TGDDM/DDS cure yielded only a TGDDM/DDS network and a BDM homopolymerized network, which were not only miscible, but are also interpenetrating. The superior interpenetrated network, as indicated by the highest fracture toughness, was found at BDM/TGDDM = 40/60 weight ratio in the BDM/TGDDM/DDS curing systems.
Post extrusion hot drawing of polycarbonate/liquid crystalline polymer blends
Authors: Beery D. , Kenig S. , Siegmann A. , Narkis M. 
Published: April 2004

AbstractThe post extrusion hot drawing of polycarbonate/liquid crystalline polymer (PC/LCP) blends, over the entire composition range, was studied. The extruded filament morphology and elastic modulus were followed as a function of blends composition, initial phase morphology, and draw ratio (DR). Hot drawing was found to cause further orientation to the already existing partially oriented LCP phase at the die exit, as reflected by the increased blends modulus. The additional orientation depends on the initial filaments structure, the blend composition, and the DR. Moreover, the orientability of the LCP phase is much higher, similar to that of neat LCP, for blends in which the LCP forms the continuous phase. In low LCP content blends, a critical DR was identified, beyond which the LCP fibrils undergo fragmentation and voids at the fibrils/matrix interface are formed, resulting in a decrease in the drawn filament modulus.
Comparative X‐ray scattering, microscopical, and mechanical studies on rectangular plates injection molded from different types of isotactic polypropylene
Authors: Zipper Peter , Jánosi András , Geymayer Wolfgang , Ingolic Elisabeth , Fleischmann Ernst 
Published: April 2004

AbstractRectangular plates were injection molded from two grades of commercial polypropylene (PP) differing in the molar mass distribution. The mold was mechanically sealed when a desired pressure pi,max (up to 1560 bar) was reached. Samples were taken from each plate at different distances from the gate and were investigated by applying various methods. In spatially resolved wide‐angle X‐ray studies, the cross section of the sample was scanned with a fine X‐ray beam (collimated by a Kratky small‐angle camera) and the intensity of scattering was registered by a linear detector as a function of position in the cross section. The evaluation of the scattering data delivered profiles of several parameters, describing the distribution of crystallite modification β‐PP and γ‐PP, the degree of orientation, the size of crystallites, and interplanar spacing, depending on the distance from surface. These results and those from measurements of birefringence and elongation at break, and from polarization microscopy and transmission electron microscopy, provided details of the layered structures in the plates, at different flow lengths, and allowed far‐reaching statements about the influence of molecular properties and processing conditions on the development of texture in the plates.
Blends and thermoplastic interpenetrating polymer networks of polypropylene and polystyrene‐block‐poly(ethylene‐stat‐butylene)‐block‐polystyrene triblock copolymer. 1: Morphology and structure‐related properties
Authors: Ohlsson Bertil , Hassander Helen , Törnell Bertil 
Published: April 2004

AbstractBlends of polypropylene (PP), the triblock copolymer polystyrene‐block‐poly(ethylene‐stat‐butylene)‐block‐polystyrene (SEBS), and processing oil were found to form thermoplastic interpenetrating polymer network (IPN) structures in a composition range from about 10 to 55% by weight polypropylene. The IPN structure was confirmed by electron microscopy and by solvent extraction. At high elongations, the cocontinuous blends showed a stress‐strain behavior similar to rubber and no signs of the typical necking phenomenon normally associated with polypropylene at large deformations. The processing oil used to improve the processing properties of SEBS was found to partly dissolve in the polypropylene phase, causing a marked lowering of the polypropylene glass‐transition temperature. The distribution coefficient for oil between polypropylene and SEBS was estimated to be 0.35. While the degree of crystallinity of polypropylene did not vary with blend composition, the melting temperature decreased from 162.7°C in the pure polypropylene to 149.3°C in the blend with lowest polypropylene content. The large melting point depression suggests that polypropylene, the EB fraction of SEBS, and the oil may form a homogeneous melt phase. This probably explains the formation of an IPN structure on cooling.
Chemorheology of thermosets—an overview
Authors: Halley Peter J. , Mackay Michael E. 
Published: April 2004

AbstractA review of current chemorheological techniques and measurement systems is presented for unfilled and filled thermoset resins. The specific measurement techniques for the kinetics, chemorheology, and modeling of these systems are presented, with particular emphasis on the chemorheological techniques and measuring systems. These techniques and measurement systems provide a greater understanding of traditionally complex thermoset processes, provide effective quality control measures for these processes, and will reduce design and operating costs in associated industries.
Improvement of mechanical properties of composites through polyamide grafting onto kevlar fibers
Authors: Salehi‐Mobarakeh Hamid , Ait‐Kadi Abdellatif , Brisson Josée 
Published: April 2004

AbstractChemical modifications of the surface of Kevlar fiber were investigated as a means of improving fiber‐matrix adhesion. The fiber surface was used as a polymerization support for interfacial polycondensation. Nylon‐6,6 was successfully polymerized in this way. The grafted nylon was characterized by ESCA (electron spectroscopy for chemical analysis), DSC (differential scanning calorimetry), and extraction procedures. An increase of the transcrystalline layer thickness was observed through optical microscopy, indicating better fiber‐matrix adhesion. Both plasma treated fibers having been submitted or not to chemical treatments were used as reinforcements for nylon‐6,6 unidirectional composites. Improvement of the mechanical properties were related to better interfacial interactions due to grafted nylon chains.
On the use of PET‐LCP copolymers as compatibilizers for PET/LCP blends
Authors: Poli Giovanna , Paci Massimo , Magagnini Pierluigi , Scaffaro Roberto , La Mantia Francesco P. 
Published: April 2004

AbstractCopolyesters of poly(ethylene terephthalate) (PET) with a liquid crystalline polymer (LCP), SBH 1:1:2, have been synthesized by the polycondensation, carried out in the melt at temperatures up to 300°C of sebacic acid (S), 4,4′‐dihydroxybiphenyl (B), and 4‐hydroxybenzoic acid (H) in the presence of PET. The PET‐SBH copolyesters have been characterized by differential scanning calorimetry, scanning electron microscopy, X‐ray diffraction, etc., and the relationships between properties and preparation conditions are discussed. The copolyesters show a biphasic nature, which is more evident for the products synthesized with a thermal profile comprising relatively lower temperatures (220–230°C) in the initial stages of the polycondensation. Another procedure, whereby the addition of PET to the monomer charge was made at a later stage of the reaction, has also been devised to prepare copolyesters with enhanced blockiness. The compatibilizing effect of the PET‐SBH copolymers toward PET/SBH blends has been investigated. PET/SBH blends (75/25, w/w) have been prepared in a Brabender mixer at 270°C and 30 rpm, with and without the addition of appropriate amounts (2.5, 5, and 10%, w/w) of 50‐50 PET‐SBH copolyesters. Different blending techniques have been used according to whether the three components were fed into the mixer at the same time, or one of them was added at a later stage. The effect of the type and the amount of added copolyester has been studied through morphological, thermal, and mechanical characterizations. The results show that the addition of small amounts ∼5 wt% of copolyesters leads to improved dispersion and adhesion of the minor SBH phase. Moreover, while the tensile modulus of the blends is practically unaffected by the addition of the copolymer, a substantial increase of both tensile strength and elongation to break is found for a concentration of added copolyester of ∼5wt%. Slightly better results were apparently obtained by the use of a block copolyester.