bluuebunny/crossref_metadata_2025_split huggingface dataset:
Estimation of kinetic parameters associated with the curing of thermoset resins. Part II: Experimental results
Authors: Scott Elaine P. , Saad Zoubeir 
Published: December 2004

AbstractThis is a two‐part theoretical and experimental study on the estimation of the kinetic parameters associated with the curing of a thermoset epoxy resin. In Part II, the kinetic parameters associated with the curing of the bisphenol‐A‐diglycidylether/meta‐phenylenediamine (BADGE/mPDA) resin were estimated from both differential scanning calorimetry (DSC) and dielectric experimental data using a new estimation procedure described in Part I. The kinetic parameters estimated were the Arrhenius constants associated with a kinetic model used to describe the degree of cure. Isothermal experiments were performed using both experimental techniques at four different curing temperatures. The resulting estimates of the kinetic parameters were compared with results obtained from the same data using a linear regression method. The magnitude of the confidence intervals of the estimated parameters and the standard deviation of the model (based on the residual errors between predicted values of the degree of cure and experimental values) were used as criteria in the comparison of the results. From this comparison, it was concluded that the parameters estimated from DSC data using the new estimation procedure provided the estimates with the least variability and, consequently, the smallest errors associated with the kinetic model.
Effects of moisture and other contaminants in friction composites
Authors: Subramaniam N. , Blum Frank D. , Dharani L. R. 
Published: December 2004

AbstractThe role of water and other contaminants like salt water, iso‐octane, and ethylene glycol on neat resin, composites, and friction materials have been investigated. The maximum solvent uptake and the diffusion coefficient of the solvent in these systems were determined and the experimental data was fitted to a Fickian model. The nature of the diffusion process was determined in each case and deviations from Fickian behavior were accounted for. For the neat resin and the composites, the diffusion coefficients of the liquids were of the order of 10−10 cm2/s. After exposure to these contaminants, mechanical properties of all the systems were determined and a general degradation in properties was found. The flexural strength and fracture toughness showed reduction in values while the flexural modulus was not affected.
Relating blow moldability to large amplitude oscillatory shear behavior
Authors: Giacomin A. J. , Jeyaseelan R. S. , Stanfill K. O. 
Published: December 2004

AbstractThe large amplitude oscillatory shear test has been used to discriminate subtle differences in nonlinear viscoelasticity between two high density polyethyene blow molding resins with different processability. Structural network theory was used to explain the subtle differences in terms of entanglement kinetics with remarkable accuracy. The resin with better shape retention characteristics in programmed parison blow molding was found to have a higher kinetic rate constant for molecular re‐entanglement.
Moldability studies for the reaction injection molding of polydicyclopentadiene
Authors: Ng Hendra , Manas‐Zloczower Ica , Shmorhun Mark 
Published: December 2004

AbstractMoldability diagrams for the filling and curing stages of a dicyclopentadiene (DCPD) based reaction injection molding (RIM) system were established based on a simplified engineering approach. Initial monomer temperature and filling time are the critical parameters for the filling stage whereas in the curing stage, mold wall temperature and demold time proved to be the main processing variables. The physical and thermal properties of the molded samples were examined and the results indicate that such simplified moldability diagrams are sufficiently accurate to establish the processing conditions for the system under investigation.
Numerical simulation of fluid flow and heat transfer in a single‐screw extruder with different dies
Authors: Chiruvella Raman V. , Jaluria Y. , Abib A. H. 
Published: December 2004

AbstractIn a plasticating screw extruder, a polymer melt forms in the melting zone of the extruder. Pressurization of the molten polymer takes place in the melting and the metering sections so that the melt can flow through the restricted passage of the die and assume a desired shape. In a melt fed extruder, the throughput is governed by the pressure rise over the entire length of the extruder. The pressure developed in the screw channel may also be employed in rapid filling of molds, such as those in injection molding. When the geometry of the screw, the barrel temperature, and the die are selected, a unique set of operating parameters arise for a particular flow rate or screw speed. In the present study, numerical and analytical methods are used to calculate the transport in the extruder and the pressure drop in the die. An iterative numerical method based on solving the equations of motion and energy in the screw channel and a correction scheme to couple the die with the screw channel is discussed. The numerical algorithm is capable of handling an arbitrary variation of the viscosity of the polymeric fluid with the shear rate and temperature. The results obtained by simulating the fluid flow in the screw channel are compared with available numerical and experimental results in the literature, indicating good agreement. The performance characteristics of the extruder, for chosen thermal boundary conditions and screw geometry, are presented for different die geometries and different fluids. The important considerations that arise in the numerical simulation of the extrusion process are also discussed.
Cold‐drawing (necking) behavior of polycarbonate as a double glass transition
Authors: Zhou Z. , Chudnovsky A. , Bosnyak C. P. , Sehanobish K. 
Published: December 2004

AbstractThe thermomechanical behavior of poly(bisphenol A carbonate) (PC) undergoing cold‐drawing (necking) over a large range of temperature and strain rate has been studied. The cold‐drawing of PC has been described from a material particle perspective in terms of true stress and strain relationships. The isothermal draw stress is shown to be a material parameter, and the true stress‐strain behavior of necked material above the true drawing stress follows conventional treatment by rubber elasticity. Cold‐drawing is described as a double glass transition: first, a transition from an isotropic glass to an isotropic rubber at the yield point, then, on unloading after stretching of a rubbery mesophase, a transition from an oriented rubber to an oriented glass.
Solidification of thermoviscoelastic melts. Part I: Formulation of model problem
Authors: Bushko Wit C. , Stokes Vijay K. 
Published: December 2004

AbstractThe solidification of a molten layer of amorphous thermoplastic between cooled parallel plates is used to model the mechanics of part shrinkage and warpage and the buildup of residual stresses in the injection molding process. Flow effects are neglected, and a thermorheologically simple thermoviscoelastic material model is assumed. The equilibrium thermomechanical properties of the material and the shift function can be temperature‐ and pressure‐dependent. The model allows material to be added to fill the space created by the packing pressure applied during solidification; therefore, this model can be used to assess packing‐pressure effects in injection molding. The model also accounts for freeze‐off effects in which the cavity pressure is controlled by the solidification process and must therefore be determined as a part of the solution.
Effects of variable viscosity on the steady melting of thermoplastics during spin welding
Authors: Stokes V. K. , Poslinski A. J. 
Published: December 2004

AbstractThe steady melting of several amorphous and semicrystalline polymers during spin welding is analyzed by solving a simplified set of momentum and energy balance equations, assuming a shear‐rate and temperature‐dependent viscosity. A numerical model is developed for predicting the flow field and the temperature distribution in the molten film. It is shown that the steady melting rate of the thermoplastic solid is affected by the variable viscosity, by the pressure applied on the parts to be joined, and by a balance between the viscous heat generation in the melt and the convection of colder material into the molten film. The convection of heat in the outflow direction is shown to have a much smaller effect on the melting process.
A process model for nonisothermal photopolymerization with a laser light source. I: Basic model development
Authors: Flach Lawrance , Chartoff Richard P. 
Published: December 2004

AbstractA mathematical model for a laser‐induced photopolymerization process has been developed. This model simulates important aspects of stereolithography, a rapid prototyping process used for the production of three‐dimensional plastic parts. The model consists of a set of coupled partial differential equations and considers irradiation, chemical reaction, and heat transfer in a small zone of material exposed to a stationary UV laser source. Numerical techniques are used for an approximate solution of the model equations, and the output includes spatial and temporal variations in the conversion of monomer to polymer, depletion of photoinitiator, and local variations of temperature in and around the region contacted by the laser light. Maximum conversions of approximately 60% and peak temperature rises of approximately 35° C were calculated for the cylindrical exposed region. Results have provided insights concerning laser dwell time, depth penetration, and the uniformity of polymer formed during the stereolithography process.
A process model for nonisothermal photopolymerization with a laser light source. II: Behavior in the vicinity of a moving exposed region
Authors: Flach Lawrance , Chartoff Richard P. 
Published: December 2004

AbstractA mathematical process model that stimulates important aspects of stereolithography, a rapid prototyping technique used for the production of three‐dimensional plastic parts, has been developed. The model consists of a set of coupled partial differential equations and considers irradiation, chemical reaction, and heat transfer in a vat of photomonomer exposed to a moving UV laser source. Laser motion occurs in a straight line (vector path), and the model thus simulates the production of a single strand of plastic. Numerical techniques are used for approximate solution of the model equations, and output includes spatial and temporal variations in conversion of monomer to polymer, depletion of photoinitiator, and variations of temperature along the line of exposed material. The formation of a temperature wave that moves along the line of plastic is observed, together with the fact that the leading edge of the wave is steeper than the trailing edge, i.e., the material heats considerably faster than it cools. The maximum temperature of the wave reaches a pseudo–steady state after a short time. The results have provided useful information concerning the temperature at which the majority of the polymerization occurs; provided information on overall transient temperature behavior; allowed computer prediction of stereolithography working curves (cure depth and cure width vs. laser scan rate); and afforded a means for evaluating the amount of reaction that occurs in the dark period after light exposure.
Correlations between relaxation time spectrum and melt spinning behavior of polypropylene. 1: Calculation of the relaxation spectrum as a log‐normal distribution and influence of the molecular parameters
Authors: Fulchiron R. , Michel A. , Verney V. , Roustant J. C. 
Published: December 2004

AbstractThe linear viscoelastic behavior of commercial broad‐distribution polypropylenes is studied. The samples underwent different controlled peroxide degradation rates, so they exhibit different molecular distributions. The relaxation spectrum is obtained by assuming that it takes the shape of a Log‐Normal distribution. It is in agreement with the linear viscoelasticity theory by providing limiting values, contrary to other models. Moreover, the ratio τw/τn which takes place in this law is very useful to distinguish the synthesis differences of the samples when the Melt Flow Index alone cannot.
A study of creep and creep rupture of polycarbonate
Authors: Challa Sudarsana R. , Progelhof Richard C. 
Published: December 2004

AbstractThe creep characteristics of polycarbonate at elevated temperatures are investigated. The onset of glass transition temperature of polycarbonate is determined. An Arrhenius type relationship is used to describe the creep process and the concept of property retention index as applied to creep is discussed. An attempt is made to construct the master rupture curves for polycarbonate. The onset of glass transition temperature of polycarbonate was placed at around 110°C. It is concluded that the Arrhenius theory and the concept of property retention index are extremely useful in the construction of master rupture curves and that they require further investigation.
A flow model for non‐newtonian liquids inside a slot die
Authors: Yuan Sinh‐Luh 
Published: December 2004

AbstractA one‐dimensional flow model for non‐Newtonian liquids inside a dual‐cavity slot die is presented. The model is capable of analyzing slot dies of any cavity shape, cavity taper, slot‐length variations, and slot‐gap variations. The proposed model incorporates a truncated‐power‐law model for the viscosity of non‐Newtonian liquids. According to flow models with power‐law approximation for liquid viscosity, the distribution of non‐Newtonian liquid through a slot die depends on the slot Reynolds number only. With our model, we find that the zero shear viscosity and the relaxation time of a non‐Newtonian liquid have large effects on its distribution. For non‐Newtonian liquids which are expected to experience shear‐thinning over portion of a slot die, it is concluded that a flow model with a truncated‐power‐law approximation for liquid viscosity be used to predict the liquid distribution from the die.
A polytetrafluoroethylene filled ultra‐high molecular weight polyethylene composite: Mechanical and wear property relationships
Authors: Silverstein M. S. , Breitner J. 
Published: December 2004

AbstractThis research addresses the wear properties and processes of 10 vol% polytetrafluoroethylene (PTFE) filled ultra‐high molecular weight polyethylene (UHMWPE) composites and their relationship to mechanical properties. The addition of the PTFE micropowder results in a slight increase in modulus and a significantly lower strain at break. This is due to a quasi‐brittle failure mechanism. Crosslinking the UHMWPE reduces both the modulus and the ultimate properties. Polymer wear studies against SiC abrasive paper can be divided into initial and steady‐state processes. The initial wear, polymer‐SiC wear, is dominated by microcutting and the formation of a transfer film. A single‐pass wear rate (R1) can be derived from a power‐law description of the initial wear. The steady‐state wear eventually achieved, called polymer‐film wear, is dominated by sliding against a self‐generated. A steady‐state multiple‐pass wear rate (Rx) can be derived from a linear description of steady‐state wear. The relationships between the wear of UHMWPE and the wear of PTFE can be predicted through their ultimate and deformation properties and through an understanding of the wear mechanisms. These relationships cannot be used to relate composite and UHMWPE wear due to their different failure mechanisms. The lower Rx and coefficient of friction of the composite may be related to the PTFE flakes found on the worn and wearing surface. Crosslinking the UHMWPE yields little change in the worn and wearing surfaces and in Rx. The increase in R1 on addition of PTFE and decrease in R1 on crosslinking may be related to the respective increase and decrease in modulus.
Compatibility of poly(ethylene 2,6‐naphthalate) and poly(butylene 2,6‐naphthalate) blends
Authors: Yoon Kwan Han , Lee Sang Cheol , Park O Ok 
Published: December 2004

AbstractBlends prepared from poly(ethylene 2,6‐naphthalate) (PEN) and poly(butylene 2,6‐naphthalate) (PBN) show only partial miscibility judged from their glass transition temperatures. Two distinct mechanical behaviors are observed: brittle for the blends < 20 wt% of PBN, while ductile > 20 wt% of PBN. The experimental modulus and strength values of the blends are within the predicted values according to Kleiner and Paul models, respectively. This means that PEN/PBN blends are somewhat compatible based on their tensile properties. Especially for 20 wt% of PBN blend, the high modulus and strength are observed. The viscosity of the blend is high, which may imply a somewhat entangled morphology in the amorphous state.
Multilayer rheology: A comparison of experimental data with modeling of multilayer shear flow
Authors: Carriere C. J. , Ramanathan R. 
Published: December 2004

AbstractThe rheological behavior of multilayer polyjeric structures has been investigated Measurements of the bulk viscoelastic properties via small‐amplitude oscilatory rheometry indicated that the shear viscosity is independent of both the numbe of layers (83 vs. 165) and the composition (30/70, 50/50, and 70/30 PC/PMMA by weight) within the limits of the data obtained. It is also apparent tha tthe shear viscosity is influenced strongly by the skin layer material. In additon, a model has been developed tha tcan be used to proedict the shear viscosity and shear stress ofa multilayer structure experiencing shear flow. The model predicts tha thte shear viscosity of a multilayer structure should be independent of the number of layers and strongly dependent on the material in the skin layer. These predictions are in agreement with experimental data.
Characterization of Synthetic‐Coal Char Particles using fractal dimension analysis
Authors: Ludlow Douglas K. , Vosen Wendy M. 
Published: December 2004

AbstractThe development and change of surface ruggedness in chars was studied at conditions typical in a pulverized coal furnace. The fractal dimension, a measure of surface ruggedness, of chars was measured using physisorption techniques. By adjusting the temperature encountered (1173 to 1773 K) and residence time (0.1 to 1.5 s) of the synthetic coal (sized to 46–106 μm diameter), chars at different stages of combustion were prepared in a laminar flow (drop‐tube) furnace. The particles were quickly cooled and quenched in an inert atmosphere. The samples were examined using a scanning electron microprobe, and their fractal dimensions were determined using gas physisorption. The adsorption data were used to test if the char surface was fractal on a molecular scale, to determine the fractal dimension, and to quantify changes in the fractal dimension during combustion. The fractal dimension of the unburned synthetic coal was approximately 2. The fractal dimension increased as high as 2.85 as the carbon matrix burned away and exposed mineral moieties. However, as combustion continued the carbon burned completely away leaving a mineral fly ash particle with a fractal dimension as low as 2.47.
Development of Agglomerate Size and Structure during spherical agglomeration in suspension
Authors: Müller Martina , Löffler Friedrich 
Published: December 2004

AbstractDuring the spherical agglomeration process, a suspended solid is agglomerated by adding a binding liquid. First, mircoagglomerates or flocs are produced, which are compacted in the course of the process. Agglomerate size was evaluated by laser diffraction spectrometry, image analysis was used to determine the size and some adequately defined shape parameters calculated by Fourier analysis of the particle contour.The shape analysis confirms the visual observations; the compaction of the flocs is expressed by the corresponding change of the shape parameters. The influence of several process parameters on changes in agglomerate shape can be described quantitatively and help to gain an insight into agglomeration mechanisms. The particle size distributions determined by image analysis and laser diffraction spectrometry hardly differ for fairly spherical flocs or agglomerates. Concerning the size distribution of the irregular flocs, laser diffraction spectrometry measures larger particles than image analysis.
Estimation of Analytical Procedures through Evaluation of analysis models
Authors: Barth P. , Zierath J. 
Published: December 2004

AbstractThe principles of the statistical valuation for the comparison of analytical procedures by evaluating model analyses are described. A computer program in FORTRAN I1 was developed and used for the evaluation of two process examples from the analytic field of explosives, i.e. determination of nitroglycerin and nitroglycol by means of gas chromatography.
Determining the Shelflife of Solid Propellants
Authors: Volk F. 
Published: December 2004

AbstractWhile stored at various temperatures between 65°C and 90°C, several double base propellants with the Same composition differing only in the stabilizer, were aged artificially to the onset of autocatalytic decomposition. A correlation between the temperature and the storage period has been established for the results obtained at the respective temperatures.Moreover, studies were carried out on the chromatographic analysis of stabilizer reaction products of the type occurring in particular in propellants with diphenylamine, 2‐nitrodiphenylamine, acardite I, acardite 11, and ethylcentralite as a result of storage at elevated temperatures due to reactions with the decomposition products of nitric acid esters.It has been shown that continuing aging of the propellant gives rise to stabilizer reaction products which are quite characteristic of the respective aging condition. These reaction products may be used as a criterion for different stages of aging within the shelflife of solid propellants.
“Swedish Base Bleed” – increasing the range of artillery projectiles through base flow
Authors: Andersson K. , Gunners N. E. , Hellgren R. 
Published: December 2004

AbstractThe following article summarizes the development of the base flow technique in Sweden. Extensive theoretical and experimental studies have been made in cooperation between the Research Institute of National Defence (FOA) and the Swedish Naval Materiel Department (FMV‐M). Base Bleed gives a significant increase in range and reduces the dispersion. The increase in range is obviously depending on the volume made available for the unit. At firing tests an increase in range of 25% has been achieved due to the base flow effect.
Thermochemical Computations on Propellant Powder Gases at interior ballistic pressures and temperatures
Authors: Dürschner M. G. 
Published: December 2004

AbstractThe interaction of powder gas molecules in the interior ballistic pressure and temperature range does not allow the application of the Nobel‐Abel equation of state. An equation of state which correlates the thermodynamic variables pressure, specific volume, and temperature, and which meets to a high extent the physical facts, is the virial equation. Using an additive combined theorem for the virial coefficients, the equations for equilibrium in a chemically reacting gas composition without solid phase are derived by virtue of the virial equation as an equation of state. The internal energy and the enthalpy of the powder gases are given for the computation of the explosion temperature and the adiabatic flame temperature. For a numerical solution of this non‐linear system of equations, a combination of the gradient process and the Newton‐Raphson process (Such‐Weg‐Verfahren) is applied. Furthermore, the numerical results for different propellant powders are stated and discussed.