bluuebunny/crossref_metadata_2025_split huggingface dataset:
Numerical simulation of the post‐filling stage in injection molding with a two‐phase model
Authors: Chen B. S. , Liu W. H. 
Published: May 2005

AbstractA two‐phase model is presented for simulating the post‐filling stage of injection molding of amorphous and semicrystalline materials. A finite‐element scheme with quadratic shape function for the pressure is proposed. The melt is considered in terms of Hele‐Shaw flow for a non‐Newtonian fluid using a modified‐Cross model with either an Arrhenius‐type or WLF‐type functional form to describe the viscosity under nonisothermal conditions; the compressible behavior of the polymer is assumed to obey either a double‐domain Tait or single‐domain Spencer Gilmore equation of state. The interfacial energy balance equation including the latent‐heat effect for semicrystalline materials is coupled with the transient energy equation for the solid and melt phases in order to predict the solidified layer and temperature profile. Two well‐characterized materials, namely a commercial‐grade PP and PS, were used in the present work. Good agreement is obtained between the present simulation and experimental pressure traces from this study and from previous investigation in the literature. The effects of compressibility, viscosity model, and thermal properties upon the predicted pressure field are also considered.
Deformation and energy absorption of polymer foams as a function of 2‐D indenter and absorber geometries
Authors: Stupak P. R. , Donovan J. A. 
Published: May 2005

AbstractTwo‐dimensional indenters (flat plate and cylinder) were used to compress rectangular and trapezoidal foam energy absorbers as a function of polymer, foam density, and thickness. An increased deformation volume formed when the indenter contact area was less than the foam absorber area, resulting in both increased energy absorption and stress transmitted to the indenter (i.e., “load spreading”). The deformation volume was trapezoidal, not prismatic, and was characterized by the indenter geometry, dimensions, and foam thickness. Conservative energy absorber design can be achieved by using “energy absorption diagrams” that account for the indenter (i.e., product) and absorber geometry and degree of load spreading.
Rheological and mechanical properties of thermotropic polyesters with long flexible spacers in the main chain
Authors: Shin Boo Young , Chung In Jae , Kim Bong Shik 
Published: May 2005

AbstractLinear thermotropic liquid crystalline polymers based on two bisphenol monomers and terephthaloyldichloride were prepared via melt polymerization. Fibers from liquid crystalline polymers were spun above the mesophase transition temperature. In this work, the mechanical and morphological properties of fibers based on such polymers were studied. High values of tensile strength and tensile modulus were obtained, and we tried to prove these high mechanical properties quantitavely by using rheological properties of these polymers and morphology of their fibers. These values were varied by the take‐up speed.
The morphology of rigid‐rod polymers and molecular composites resulting from coagulation processing
Authors: Nelson Donald S. , Soane David S. 
Published: May 2005

AbstractThe effects of processing conditions on the morphology of molecular composite films are examined by optical and electron microscopy. During coagulation processing from solutions in methanesulfonic acid (MSA), rigid‐rod polymer, such as poly(p‐phenylenebenzobisoxazole) (PBO), phase separates into undesirable aggregates. The coagulant and the method of its introduction have been found to exert a strong impact on the final film morphology. A quench of a PBO solution in MSA into a water bath results in a three dimensional interconnected network of PBO, while a slower introduction of water results in a more amorphous material. A computer simulation program of the coagulation process has been developed to better understand the different structures emerging from coagulation processing of molecular composites. The simulation results are in qualitative agreement with the experimental observations.
The production and properties of oriented polypropylene laminates
Authors: Chen H. J. , Kortschot M. T. , Leewis K. G. 
Published: May 2005

AbstractThe mechanical properties of isotactic polypropylene can be enhanced in one direction by a combination of rolling and drawing in a rolling mill. The longitudinal strength and modulus of the oriented polypropylene (OPP) increases with an increase in draw ratio; however, the transverse properties remain relatively unchanged. In this study, multidirectional OPP laminates [with (0)2, (0/90)s and (0/±45)s lay‐ups] were made to obtain sheet materials with improved properties in more than one direction in the plane. A hot‐plate welding technique was used to produce these translucent and recyclable laminates. The in‐plane properties of the laminates were successfully predicted with classical laminate theory (CLT), which is commonly used to predict the properties of fiber reinforced materials. These laminates can be quasi‐isotropic and were found to have improved modulus [up to 6 GPa for (0/90)s laminates] and strength [up to 150 MPa for (0/90)s laminates] as well as exceptionally good impact toughness.
Fiberoptic intrinsic fluorescence for in‐situ cure monitoring of amine cured epoxy and composites
Authors: Paik Hyung‐Joon , Sung Nak‐Ho 
Published: May 2005

AbstractThe cure reactions of epoxy‐diamine and its composites are monitored in‐situ using the intrinsic fluorescence of the aromatic diamine, diaminodiphenyl sulfone (DDS). With a fiberoptic fluorimeter, in‐situ cure monitoring was performed via a single fiber, distal‐end probe, in neat epoxy as well as in commercial grade prepregs containing graphite fibers and DDS curing agent. The prepregs were investigated during multiply lamination in an oven. The fluorescence excitation spectra were obtained by emitting at 420 nm with a scan range of 320 to 400 nm, and the DDS peak position was determined as a function of cure time and temperature. The DDS spectra show a progressive red shift up to 24 nm when the primary amine is reacted with epoxide to become the secondary and the tertiary amines. The spectral shift of the DDS is also correlated with the extent of epoxide reaction determined by the Fourier transform infrared (FTIR) spectroscopy. Both data exhibit a linear relation, consistent with the behavior of the DDS peak shift, which increases linearly with the amine reaction. The excitation spectra also show a temperature dependency such that the amount of red shift increases with the measurement temperature in a manner that can be described by an exponential function. The temperature effects also depend on the state of cure in the sample. The temperature correction can be made by the application of an empirically developed equation. Thus, a direct comparison can be made among the on‐line data obtained under varying conditions of cure, by reducing the spectral data to any reference temperature. This intrinsic fluorescence technique is much simpler than the previously reported extrinsic fluorophore technique, which requires the addition of an extrinsic fluorophore and an internal dye, and can be applied to any commercial prepregs containing DDS, thus making it a very powerful and widely applicable monitoring tool for composite processing.
Generation of microcellular polymeric foams using supercritical carbon dioxide. I: Effect of pressure and temperature on nucleation
Authors: Goel Satish K. , Beckman Eric J. 
Published: May 2005

AbstractSupercritical carbon dioxide is known to swell and plasticize poly(methyl methacrylate), PMMA, dramatically. We have employed a pressure quench in a CO2‐swollen PMMA sample to generate a microcellular core structure encased by a nonporous skin. Further, we have demonstrated that classical nucleation theory can be used to model the effects of saturation pressure, temperature, and time on the cell density of the porous materials, provided that the effects of the CO2‐diluent on the surface tension of PMMA are adequately taken into account. This is because our system is in a homogeneous liquid state at our operating conditions because of the plasticization. Both model predictions and data indicate that cell density rises sharply at a saturation pressure of approximately 14 MPa (at 40°C), leveling out above 27 MPa. By contrast, the effect of temperature on cell density in the range 40°C to 80°C is minimal.
Weld lines and mechanical properties of injection molded polyethylene/polystyrene/copolymer blends
Authors: Brahimi B. , Ait‐Kadi A. , Ajji A. 
Published: May 2005

AbstractIn this article, we investigate the effect of weld lines on the tensile mechanical properties of unmodified and copolymer modified high density polyethylene (HDPE) and polystyrene (PS) blends. The homopolymers were melt blended in the proportion of 20 wt% HDPE and 80 wt% PS using a twin screw extruder at a temperature of 200°C. The results show that the mechanical properties are generally lower when weld lines are present. The decrease of the mechanical properties is much more pronounced for the blends. The addition of small amounts of a commercial styrene/butadiene copolymer significantly improves the strength and the elongation at break of this blend. An optimum copolymer concentration was observed at 3 wt%. This value coincides with the interphase saturation concentration of the copolymer obtained from the analysis of the DMTA (dynamic mechanical and thermal) properties of the blends. The copolymer was also found to induce important changes in the morphology of the blend. The interdiffusion of the polymer fronts in the weld region was also improved by the presence of the copolymer. It is believed that these two aspects contribute to the enhanced properties obtained with copolymer modified blends in presence of weld lines. An important effect of the injection temperature on the tensile strength and the elongation at break of welded samples with copolymer modified blends was observed. The effect of mold temperature on these properties was less important mainly at low injection temperatures. Only a slight effect of these two parameters was observed for the tensile modulus in the range of mold and injection temperatures considered in this study.
Crystallinities of poly(chlorotrifluoroethylene) and its copolymers by differential scanning calorimetry, X‐ray diffraction, and density measurements
Authors: Murthy N. S. , Khanna Y. P. , Signorelli A. J. 
Published: May 2005

AbstractCrystallinities of films of copolymers of chlorotrifluoroethylene with 0 to 4% vinylidene fluoride, different molecular weights and thermal histories were calculated from differential scanning calorimetry (DSC), X‐ray diffraction (XRD), and density measurements. The crystallinities for these films range between 16 to 58%, 11 to 71%, and 13 to 77% as determined by DSC, XRD, and density, respectively. Although the numerical value of the DSC, XRD, and density crystallinities obtained by each of the techniques are different, they correlate well with each other. The primary source of error in DSC is the uncertainty in drawing the baseline for separating the heat of fusion and heat of crystallization. In XRD, the ambiguities in the separation of the amorphous and crystalline peaks reduce the precision of the results. Calculation of crystallinity from density values requires that the distribution of the VF2 between the amorphous and crystalline regions be known. In addition, the density technique is not sensitive to variations in the crystalline and amorphous densities.
An extension of the Painter‐Coleman miscibility guide to ternary polymer blends
Authors: Espi E. , Fernandez‐Berridi M. J. , Iruin J. J. 
Published: May 2005

AbstractThe idea of separating the free energy of mixing into two contributions (corresponding to the “physical” or “nonspecific” and to the “specific” interactions, respectively) proposed by Painter and Coleman has been extended to ternary polymer/polymer/polymer blends. In this paper experimental phase diagrams of three ternary blends have been reproduced by estimating both contributions for the interaction energy density (Bij) which characterizes each polymer pair. In contrast to the Painter‐Coleman Miscibility Guide rules, we have found that, in some cases, “specific” contributions positive and unfavorable to the mixing, due to the self‐association of one of the components, can describe more adequately the experimental trends.
Water soluble copolymers. 55: N‐isopropylacrylamide‐co‐acrylamide copolymers in drag reduction: Effect of molecular structure, hydration, and flow geometry on drag reduction performance
Authors: Mumick Pavneet S. , Hester Roger D. , McCormick Charles L. 
Published: May 2005

AbstractNon‐ionic, hydrophobically associating, water soluble N‐isopropylacrylamide‐co‐acrylamide (IPAM) copolymers have been synthesized and characterized specifically for the study of drag reduction. The drag reduction (DR) performance has been measured with a rotating disk rheometer and a capillary flow apparatus. The DR studies were performed in deionized water, 0.514 M NaCl and 1 M urea. DR efficiency is dependent on copolymer structure, composition, and solvation. Copolymers showing intermediate values of hydrophobic character are found to be the most effective drag reducers. For this copolymer series, IPAM‐70 (the copolymer synthesized with 70 mole% N‐isopropylacrylamide in the feed) is the most efficient drag reducer. The DR properties of the IPAM copolymers are influenced by hydrophobic associations as well as hydrogen bonding. The effects of salts from the Hofmeister series, cosolvents such as dioxane, and temperature are also examined. Drag reduction performance of the various copolymers is correlated to empirical relationships involving degree of polymerization, second virial coefficient or other solvation parameters, and concentration.
Shear and elongational behavior of linear low‐density and low‐density polyethylene blends from capillary rheometry
Authors: Müller A. J. , Balsamo V. , Silva F. Da , Rosales C. M. , Sáez A. E. 
Published: May 2005

AbstractIn this work we present an experimental study of shear and apparent elongational behavior of linear low‐density (LLDPE) and low‐density (LDPE) polyethylene blends by means of capillary rheometry. The characterization of these rheological properties is crucial in the design of a blend that combines the ease of processing of LDPE with the mechanical advantages of the LLDPE. Two different low‐density polyethylenes and one common linear low‐density polyethylene were used to prepare the blends. The results obtained indicate a strong sensitivity of the rheology of the blend to changes in the molecular weight of the LDPE employed. For the higher molecular weight LDPE, the shear viscosity of the blend was essentially equal to that of the LDPE homopolymer up to a concentration of 25% of LLDPE, whereas the apparent extensional viscosity was appreciably lower. For the lower molecular weight LDPE, the same trend was obtained regarding the shear viscosity, but in this case the apparent extensional viscosity of the blend was somewhat higher than that of the LDPE homopolymer.
Dynamic rheological properties of polyetherimide/polyetheretherketone/liquid crystalline polymer ternary blends
Authors: Bretas R. E. S. , Collias D. , Baird D. G. 
Published: May 2005

AbstractThe dynamic rheological properties of poly(etherimide)/poly(etheretherketone)/liquid crystalline polymer (LCP) ternary blends were measured in order to correlate these properties with the morphology obtained after extrusion. The viscosity radio, ηd/ηm, where ηd = disperse phase viscosity and ηm = matrix viscosity, had to be redefined. Below 50 wt% LCP, ηd = ηLCP, ηm = ηPEEK+PEI and ηd/ηm < 1. Above 50 wt% LCP, ηd = ηPEEK+PEI, ηm = ηLCP and ηd/ηm > 1. Fibrillar morphologies were obtained in both cases, except below a concentration of 20 wt% LCP. At low concentrations of LCP the ternary blends had lower viscosities than the component polymers, showing a flow promotion effect of the LCP on the PEI‐ and PEEK‐rich phases.
Design of electrofusion joints and evaluation of fusion strength using fusion simulation technology
Authors: Nishimura Hiroyuki , Inoue Fumio , Nakashiba Akio , Ishikawa Testuo 
Published: May 2005

AbstractFusion simulation is one of the key techniques in designing and producing electrofusion (EF) joints for gas distribution and in evaluating fusion joint integrity. This paper describes the result of a numerical simulation of a thermal fusion process, using the finite element method. A nonlinear heat transfer computer program was used to obtain the temperature profile of a large electrofusion joint at fusion. The effects of applied voltage, heating time, wire pitch, and ambient temperature were examined for designing a 150‐mm EF joint. A method to shorten the cooling time was also investigated. The fusion condition range suitable for a 150‐mm EF joint was found to be slightly narrower than that suitable for a 50‐mm EF joint. Examination of the effect of wire pitch revealed that if the pitch is extremely large, thermal degradation starts in the resin close to the wire before the fusion‐interface strength reaches the maximum value. We have developed a program to simulate the process of closing the gap between the pipe and the joint due to resin expansion and melting after the power is supplied.
Rubber toughening of poly(lactide) by blending and block copolymerization
Authors: Grijpma D. W. , Van Hofslot R. D. A. , Supèr H. , Nijenhuis A. J. , Pennings A. J. 
Published: May 2005

AbstractCopolymers of L‐lactide with 15 or more mole % D‐lactide are amorphous, noncrystallizable hydrolytically degradable materials. These glassy materials are brittle in tension and bending. To make these materials suitable for use as load‐bearing devices in biomedical applications, toughness has to be enhanced. This is effectively accomplished by introducing a separate degradable rubber phase in the amorphous matrix. Several approaches have been explored: solution blending and coprecipitation of trimethylene carbonate and ϵ‐caprolactone rubbers and poly(lactide), preparation of ABA triblock copolymers and blending of ABA block copolymers with the amorphous poly(lactide) matrix. In all cases very tough materials could be prepared. These materials are easily processable by compression molding at relatively low temperatures.
The effect of particles on failure modes of filled polymers
Authors: Bazhenov S. 
Published: May 2005

AbstractThe effect of rigid particles on the fracture mode of polymers that yield with necking was analyzed theoretically with a model of regularly arrayed spherical particles. The adhesion between a polymer and particles was assumed to be weak, and particles were assumed to debond from the polymer before necking. A linear decrease in engineering draw stress with an increase in the filler content was derived. An increase in filler content leads to a transition in deformation mechanism. The transition depends on the ability of the polymer to strain‐harden. If the ability to strain‐harden is insignificant and the engineering fracture stress (strenght) of the polymer is lower than its yield stress, the transition is from ductile to brittle fracture. If the ability to strain‐harden is essential and the strength of the unfilled polymer is higher than its yield stress, the transition (ductile‐to‐ductile) is from neck propagation to uniform ductile yield. The critical filler contents were determined for both transitions from the properties of an unfilled polymer. The ductile‐to‐ductile transition without embrittlement is possible if the strength of the unfilled polymer is higher than its yield stress. Results for polymers filled by weakly bonded particles were compared with polymers filled by particles that debond after the yield stress.
Weldline strength in glass fiber reinforced polyamide 66
Authors: Meddad A. , Fisa B. 
Published: May 2005

AbstractPresence of weldlines introduces an element of uncertainty to the performance of injection molded parts. Weldlines are particularly problematic in reinforced plastics because, unlike molecular orientation in neat polymers, the flow induced fiber orientation does not relax. This paper deals with the structure and mechanical behavior of weldlines in glass fiber reinforced nylon 66, a plastic known for excellent fiber‐matrix adhesion. Two molds were used to generate weldlines: a double gated tensile sample shaped cavity in which the weldline is formed by a head‐on collision of melt fronts flowing in opposite directions and a film gated rectangular plaque with a circular insert in which the weldline formation behind the insert is followed by additional flow. In both cases the weldline zone is several millimetres wide: in the plane where the melts fronts have met fibers are oriented parallel to this plane (random‐in‐plane in the double‐gated cavity and unidirectional in the cavity with insert). The transition zone between the weldline plane and the rest of the sample is characterized by an increased presence of microvoids. Weldline tensile depends little on the fiber concentration and on the sample shape or thickness: values close to the matrix strength are found: in samples without weldlines strength increases with the fiber content. However, in instrumented impact penetration test during which the material is subjected to multiaxial loading, the weldline effect appears negligible.
Wall thickness uniformity in plastic pipes: Computer simulations of the effectiveness of die mandrel offsetting and pipe rotation in combatting sag
Authors: Pittman J. F. T. , Whitham G. P. , Farah I. A. 
Published: May 2005

AbstractA computer simulation, based on a thermoviscous model of cooling and gravity induced flow (sag) in plastic pipe manufacture, which has previously been described in detail and validated against experimental results, is here used to investigate the effectiveness of die mandrel offsetting and pipe rotation in combatting sag. SDR11 MDPE pipes of 315, 560, 800, and 1000 mm diameter are considered. Results are examined in terms of a waste percentage, representing polymer used in excess of that corresponding to the minimum wall thickness. With a concentric mandrel, waste is predicted to be 4.3, 14.0, 17.9, and 18.7% for the four sizes, respectively. Optimum offsets and minimum waste percentages are found to be: 2 mm, 0.8%; 15 mm, 4.6%; 42 m, 9.8%; 63 mm, 12.7%, respectively. For the largest pipe this corresponds to a wall thickness variation of 19.6 mm. Simulations of rotation of the 800 mm pipe show waste falling rapidly to 5% at 1 revolution/4800s, then a slower decrease, reaching 1.6% at 1 revolution/600s. The simulation is equally applicable to all grades and sizes of pipe, and provides a valuable computer aid for the design and operation of pipe cooling lines.
Chaotic mixing in the enhanced mixing simulator
Authors: Ling F. H. 
Published: May 2005

AbstractThe mixing performance of an experimental device—the enhanced mixing simulator (EMS)—is studied in this paper. In this device, the Couette flow is perturbed laterally, so that uniform and quick mixing can be achieved. Numerical simulation of the mixing in EMS flows is performed, which shows good agreement with the experimental results. Spline interpolation and advanced integration techniques are used in particle tracking, so that accurate results are obtained at low costs. Poincaré sections are used to study the long‐term mixing behavior. The uniformity of the simulated mixture is evaluated using statistical approaches—the variation coefficient and the Kolmogorov test. The Kolmogorov test is adequately implemented for our purpose and incorporated with efficient sorting algorithms. The mixing rate is determined from the time evolution of uniformity during mixing. It is also shown that although the Lyapunov exponent can identify chaos, it does not measure the mixing rate. Optimal design of the EMS is discussed.