bluuebunny/crossref_metadata_2025_split huggingface dataset:
Modeling of the dynamic mechanical properties of semicrystalline thermoplastic matrix composites
Authors: Kenny José M. , Maffezzoli Alfonso , Nicolais Luigi 
Published: May 2005

AbstractThe modeling of the viscoelastic properties of semicrystalline polymeric matrix composites is discussed. Different mathematical models are applied to describe the development of the storage modulus, measured by dynamic mechanical analysis, as a function of the crystalline content during isothermal crystallization experiments. Best results are obtained with an empirical power law model developed in this work. The application of the Halpin‐Tsai equation and of a theoretical model, based on a combination of parallel‐series arrangements of viscoelastic elements representing the crystalline and amorphous phases, is also discussed. The main objective of this research is the comparison between experimental results obtained by differential scanning calorimetry and dynamic mechanical analysis during crystallization processes.
The effect of high pressure on the mechanical behavior of short fiber composites
Authors: Yuan J. , Hiltner A. , Baer E. , Rahrig D. 
Published: May 2005

AbstractThree types of pressure dependent deformation processes have been observed for the short glass fiber reinforced composites of poly(vinyl chloride) (PVC). A unique deformation behavior, observed for the first time, features a sharp drop in stress followed by shear yielding in the matrix. Competitive pressure dependent failure processes in the composites are strongly affected by “debonding” at the fiber‐matrix interface. A new general pressure dependent yield criterion for PVC and its composites was elucidated.
A novel technique for the determination of high frequency equibiaxial stress‐deformation behavior of viscoelastic elastomers
Authors: Bhate A. P. , Kardos J. L. 
Published: May 2005

AbstractSynthetic elastomers and elastormeric‐like copolymers are now being utilized for a wide spectrum of biomaterial uses including primary structural applications such as pump bladders in artificial hearts and left ventricular assist devices (LVAD), leaflets in prosthetic heart valves, and vascular prostheses. In making fatigue lifetime measurements, as well as for predicting durability, it is essential to know the biaxial stress‐deformation behavior at high strain rates (high frequencies) and at extension ratios at least as high as those encountered under performance conditions. This paper describes a technique for determining the high frequency equibiaxial stress‐deformation behavior of elastomers. Measurements of material parameters are made at the high strain rates (or frequencies) at which accelerated biaxial flaw growth and fatigue experiments are performed and hence do not require correction for strain‐rate dependence of material properties. Furthermore, the plastic deformation (creep) which occurs in the case of viscoelastic membranes is incorporated in the calculations; yielding the “true” values of the extension ratios. Experimental measurements were performed on urethane‐based biomaterials using a tuned fluid oscillator which produces cyclic biaxial inflation of the elastomeric membranes clamped around the circumference. Up to moderately large equibiaxial deformations, the form of strain energy function derived from the Gaussian, network theory (or the first approximation to Rivlin's formulation of strain energy function) was found to adequately describe the stress‐deformation data. This in turn permits accurate calculation of the tearing energy under biaxial conditions, which is a prime requisite for predicting biaxial fatigue lifetime distributions.
Plastic deformation and tearing in high density polyethylene blown films
Authors: Sherman Edward S. 
Published: May 2005

AbstractPolymer films produced by tubular film blowing have a unique morphology that results from the large elongational flow in melt draw down and biaxial orientation due to bubble blow‐up. Three high density polyethylene (HDPE) blown films were produced under similar processing conditions from resins which varied principally in molecular weight (MW) and molecular weight distribution (MWD). Scanning electron microscopy (SEM) showed that the lower MW and narrower MWD resin produced film which had a uniaxial orientation of stacked lamellar crystals. The higher MW (HMW) and broad MWD resins produced films consisting of a network of nearly orthotropically oriented lamellar stacks. Greater high molecular weight fraction (MW > 106) in the resin resulted in more random orientation. The influence of these different structures on properties was studied by examining the plastic zone formation at crack tips and uniaxial tensile deformation with the SEM and comparing them to the macroscopic stress‐strain behavior. A continuous deformation of the network structure was observed in the HMW films. Lamellar deformation occurred primarily in regions of stacks oriented parallel to the tensile axis. Macroscopic yield occurred at 6 to 10 percent strain via a shearing and opening the lamellar crystals. Irreversible deformation occurred from ≃50 to 400 percent strain by transformation of the oriented lamellae to microfibrils. Eventually all the lamellar stacks in the network become aligned with the tensile axis. This process was found to improve the tear resistance in the crack propagation experiments. The lamellar stacks in the network orient perpendicular to the crack independent of crack propagation direction, insuring a more uniform transmission of stress and preventing local yielding. The tensile modulus, yield stress, and ultimate strength were highest in the film containing more high molecular weight polymer.
Kevlar 49 composite performance: Dependence on thermoset resin microstructure
Authors: Timm D. C. , Ayorinde A. J. , Lee C. H. , Steele L. F. , Plass N. C. 
Published: May 2005

AbstractMolecular structures for cured, thermoset resins have been examined by analyses of resin extracts by gel permeation chromatography. Numerical interpretation of leached oligomeric fractions coupled with kinetic reaction theory yields microscopic estimates of the network's structure, including crosslink average molecular weight. Leached monomeric fractions describe extent of cure. Analyses of test data incorporate irreversible, mechanical deformations for neat resin castings and for filament wound, Kevlar 49 composites. Heat distortion temperatures correlate with crosslink architecture. Short beam shear strength data for naval ordinance laboratory rings and pressure vessel burst performance are examined in terms of the resin's molecular structure. Variations in resin cure observed by positive feedback via chromatography indicate fluctuations in extent of crosslink development. Test specimen performance correlates with these microscopic, molecular distributions. Resin applications include filament wound composites for the aerospace industry, anhydride cured epoxies, and amine cured epoxies. The former resin is an elastic body at ambient test conditions. A third resin, a crosslinked resin of 1,2 polybutadiene/t‐butylstyrene, is in final developmental stages and may exhibit a higher degree of viscoelastic behavior.
Concentrated solution and melt rheology of poly(vinylidene fluoride)
Authors: Auyeung Kim Fung 
Published: May 2005

AbstractThe concentrated solution and melt rheology of poly(vinylidene fluoride) [PVDF] were studied by using a falling needle solution viscometer, a Brookfield viscometer, and a Kayeness capillary rheometer. It was found that the concentrated solution (15 wt% in N‐dimethyl acetamide) rheology exhibited a different behavior for various grades of PVDF produced by different types of polymerization. While Newtonian behavior was found in one type of PVDF, shear thinning was found in another type. The power law model was used to describe the general solution behavior of these materials. Zero shear rate viscosity correlated well with the molecular weight (Mw) of the material. Melt viscosity of PVDF exhibited continuous shear thinning behavior throughout the whole range of shear rates. The data were best fitted by a second‐degree polynomial curve. Correlations were established between the molecular weight, molecular weight distribution, and the parameters of the polynomial curve. These correlations are useful for the prediction of various grades of PVDF designated for specific engineering applications. The correlations obtained from solution provided better and more accurate correlations to Mw parameters than those of melt rheology.
Bubble‐free devolatilization in counterrotating nonintermeshing twin‐screw extruder
Authors: Foster R. W. , Lindt J. T. 
Published: May 2005

AbstractA theoretical analysis of the diffusion‐controlled, essentially bubble‐free, mass transfer regime of polymer solution devolatilization has been performed for a counterrotating, nonintermeshing twin‐screw extruder (1). The commonly used penetration diffusion approach is applied specifically to this geometry. Mass transfer from the recirculating pool and barrel film in the closed channel and the pool only in the open channel is taken into account. Use is made in this study of the recently determined pumping characteristics of this geometry (2), which allow the estimation of the length of the extraction section. Mass transfer rate measurements have been taken on a 20‐mm extruder using the model system polystyrene/ethylbenzene. The agreement between the mass transfer calculations and the experimental results is very good.
Viscoelastic response of epoxy glasses subjected to different thermal treatments
Authors: Lee Andre , McKenna Gregory B. 
Published: May 2005

AbstractIsothermal aging after a quench from above the glass‐transition temperature (Tg) to below it was studied as a function of cross‐link density for model epoxy networks using small deformation stress relaxation experiments. We found that time‐aging time and time‐cross‐link density superposition principles described the changes observed in the Viscoelastic behavior of the epoxy networks. The aging response in the nonlinear Viscoelastic regime was also studied using creep experiments for one of the networks. It was found that upon aging near to the conventional glass‐transition temperature, the time required for the glass to age into structural equilibrium was independent of the magnitude of the applied stress. This result suggests that large stresses do not erase physical aging (or cause rejuvenation of the glasses).
Effect of emulsifier type on the copolymerization of styrene and acrylic acid
Authors: Corona‐Galvan S. , Martinez‐Gomez A. , Castañeda‐Perez J. , Puig J. E. , Schulz P. C. , Dominguez J. M. , Ruano A. 
Published: May 2005

AbstractIn this work we report the emulsion copolymerization of styrene and acrylic acid using a cationic (cetyltrimethylammonium bromide or CTAB) or an anionic (sodium dodecylsulfate or SDS) emulsifier. Latexes were stable and monodisperse with spherical particles of ∼100 nm for the CTAB latex and of ∼70 nm for the SDS latex. However, a random copolymer was produced with CTAB whereas a “blocky” copolymer was obtained with SDS. Here we propose a mechanism to explain these structural differences in terms of the relative reactivities of styrene and acrylic acid and of their initial location and distribution in the SDS and CTAB emulsions.
A nonlinear mechanical model for solid‐filled rubbers
Authors: So H. , Chen U. D. 
Published: May 2005

AbstractA nonlinear mechanical model has been proposed for application to nonlinear viscoelastic elastomers. The model consists of four nonlinear elements similar to the Burgers model. Based on the theory of reaction rate proposed by Eyring and the statistic concept of entropy‐spring developed in rubber elasticity, four relevant nonlinear elements are used to construct the model. The deformation, or the time rate of deformation of each element is described by a nonlinear stretch parameter A. According to the model and the parameter A, two groups of equations are derived to describe the creep or relaxation behavior of solid‐filled and pure rubbers, respectively. In order to examine the applicability of the model as well as the nonlinear stretch parameter, a series of experiments for solid‐filled polybutadiene rubbers has been carried out, which include constant rate of tensile tests, creep and relaxation tests with and without aging effects. It is found that the nonlinear stretch parameter satisfies the Eyring equation and that the model agrees the experiments extremely well.
Dopant anion controlled ion transport behavior of polypyrrole
Authors: Qiu Yong‐Jian , Reynolds John R. 
Published: May 2005

AbstractA combination of electrochemical and microgravimetric techniques, utilizing the electrochemical quartz crystal microbalance (EQCM), has been employed to study the ion transport behavior of polypyrrole films, prepared with a variety of electrolytes, during redox switching. Systems investigated include poly(pyrrole chloride), poly(pyrrole dodecylsulfate), poly{pyrrole‐co‐[3‐(pyrrol‐1‐y1)propanesulfonate]}, and polypyrrole/Nafion composites. It has been demonstrated that controlled ion transport properties of polypyrrole can be achieved by incorporating properly selected dopant anions into the polypyrrole film during electrosynthesis.
Structure and properties of molded polyblends containing liquid crystalline polymers
Authors: Beery D. , Kenig S. , Siegmann A. 
Published: May 2005

AbstractThe relationship between the microstructure developed during injection molding of liquid crystalline polymers (LCPs) containing blends and their mechanical properties, was studied. A wholly aromatic copolyester LCP was melt blended in various levels with polycarbonate (PC), poly(butylene terephthalate) (PBT), Nylon 6 (N‐6), and amorphous nylon (AN). In all cases the LCP was the minor component. The resulting injection molded structure had a distinct skin core morphology, where elongated fibrous LCP particles comprised the skin layer and spherical and ellipsoidal ones composed the core section. The highest elongation and the finest diameter LCP fibrils were obtained with AN/LCP system, followed by PC/LCP. PBT/LCP blends showed a coarser morphology, while N‐6/LCP system did not correlate with the tensile moduli of the injection molded specimens. AN/LCP blends demonstrated the highest moduli values, consistent with the highest orientations observed using electron microscopy, followed by PC/LCP, PBT/LCP, and N‐6/LCP. Finally, tensile strength levels were correlated with both orientation levels and interfacial adhesion between the polyblend components. AN/LCP that exhibited the highest orientation and good adhesion appearance gave the highest tensile strength values followed by PC/LCP, PBT/LCP, and N‐6/LCP polyblends.
A robust, streamlined, and reproducible method for proteomic analysis of serum by delipidation, albumin and IgG depletion, and two‐dimensional gel electrophoresis
Authors: Fu Qin , Garnham Christopher P. , Elliott Steven T. , Bovenkamp Diane E. , Van Eyk Jennifer E. 
Published: May 2005

AbstractSerum is a readily available source for diagnostic assays, but the identification of disease‐specific serum biomarkers has been impeded by the dominance of human serum albumin and immunoglobulins (Igs) in the serum proteome. There is a need to reduce the technical variation in serum processing and analysis to allow for a reproducible analysis of large cohorts. To this end, we have developed a rapid and reproducible procedure for sample preparation and high‐resolution two‐dimensional gel electrophoresis to analyze human serum. Serum is centrifuged at high speed to remove lipids and aggregated proteins, incubated with protein G resin to remove IgG, precipitated with NaCl/ethanol to deplete albumin, and slowly resolubilized in a sodium dodecyl sulfate (SDS)/N‐(2‐hydroxyethyl)piperazine‐2’‐(2‐ethanesulfonic acid) (HEPES) buffer. The delipidated and IgG/albumin depleted serum proteins are focused on pH 4–7 linear large immobilized pH gradient strips, and then resolved by Bis‐Tris SDS‐polyacrylamide gel electrophoresis. The robustness and reproducibility of the optimized procedure was determined for three individual serum samples on three consecutive days. An image analysis of the nine silver‐stained gels demonstrated that the intensity and localization of protein spots are highly reproducible. Our IgG and albumin depletion procedure will aid in screening the patient sera for normal biological variation and disease‐specific biomarkers.
Controlling the Plasma‐Polymerization Process of N‐Vinyl‐2‐pyrrolidone
Authors: Norrman Kion , Winther‐Jensen Bjørn 
Published: May 2005

AbstractSummary: N‐vinyl‐2‐pyrrolidone was plasma‐polymerized on glass substrates using a pulsed AC plasma. Pulsed AC plasma produces a chemical surface structure different from that produced by conventional RF plasma; this is ascribed to the different power regimes used. A high degree of control over the structure of the chemical surface was obtained using pulsed AC plasma, as shown by ToF‐SIMS. It is demonstrated how the experimental conditions to some extent control the chemical structure of the plasma‐polymerized film, e.g., film thickness, density of post‐plasma‐polymerized oligomeric chains, and the density of intact pyrrolidone rings.Electrode configuration and gas flow in the two‐phase AC plasma chamber.magnified imageElectrode configuration and gas flow in the two‐phase AC plasma chamber.
Flow Pattern in an Indoor Rocket Test Stand during static rocket motor firing
Authors: Korting P. A. O. G. , Reitsma H. J. 
Published: May 2005

AbstractExperiments to determine the flow pattern in an indoor rocket test stand during static rocket motor firing are described. After a theoretical treatment of the flow properties, a description is given of the experimental set‐up. Tests were performed with short burning (1.8 s), low thrust (2,8 kN) rockets as well as with a long burning (40 s) rocket motor with higher thrust (9.5 kN). With the short burning rocket motors flow velocities obtained were between 3.3 m/s and 7.9 m/s. The stationary flow velocities of the long burning rocket motor amounted up to 24 m/s, while the increase in temperature of the flow was appr. 200 K. Experimental flow velocity appeared to be lower while the experimental flow temperature appeared to be higher than the theoretical values, mainly due to after burning of the fuel‐rich combustion gases.
Determination of the Decomposition Behavior of Double‐Base Propellants at Low Temperatures
Authors: Volk F. , Wunsch G. 
Published: May 2005

AbstractThermal and mechanical stability are very important characteristics of energetic materials used as ingredients of propellants compositions. For the determination of the thermal decomposition behavior of solid double base propellants, usually gravimetric, calorimetric, and chemical methods are being employed. At ICT, the decreasing rates of stabilizers determined by high‐performance chromatography at different temperatures are successfully used as a mean to forecast the chemical life time of propellants containing nitric esters. On the other hand, the mechanical properties are evaluated by measuring the tensile strength with a more or less accuracy.In the last years, the increasing performance of the gel‐permeation chromatography enabled the determination of the molecular weight and the molecular weight distribution of nitrocellulose in different propellants. In this connection a linear relationship between temperature and depolymerization rate was obtained. This relationship corresponds fairly well with the stabilizer depletion rate and the drop in the mechanical properties.
Corner Turning Research Test
Authors: Held Manfred 
Published: May 2005

AbstractThe so‐called corner turning research test according to Cox and Campbell gives beside of the corner turning distance — short CTD — also the area of the not fully detonating zone — the so‐called dark or dead zone — around the initiation axis. This is achieved by cutting the charge parallel and near to the booster axis and by observing this surface with multiple streak lines. With the help of a computer program the digitized data can be quickly analyzed.
The Kinetic Parameters and Parameter Effect Factors Calculation of multicomponent energetic materials decomposition reaction from a single differential thermal analysis curve
Authors: Luo Kuo‐Ming 
Published: May 2005

AbstractThe kinetic parameter of energetic materials with four components, i.e. lead thiocyanate, antimony sulfide, potassium chlorate, and trinitrotoluene, (PSKT), was analyzed with differential thermal analysis (DTA) technique. Kinetic parameter equations were derived for estimating a general nth‐order decomposition reaction from a single DTA curve. Three categories, for n < 1, n = 1, and n ≠ 1 were derived. Three kinetic parameters, namely, activation energy E, reaction order n, and pre‐exponential factor A can be calculated directly without any iteration from the characteristic temperatures To, Til, Tm, and Te that are the decomposition starting point, first inflection point, peak maximum point and end point on the DTA curve, respectively. The stability and compatibility of PSKT energetic material can be judged from experimental characteristic temperatures and calculated kinetic parameters. The effect factors of characteristic temperature and kinetic parameters were evaluated by means of Yates' algorithm.
Electrostatic calculations and model‐building suggest that DNA bound to CAP is sharply bent
Authors: Warwicker J. , Engelman B.P. , Steitz T.A. 
Published: May 2005

AbstractTwo observations suggest that DNA, upon binding to E. coli catabolite gene activator protein (CAP), is sharply bent by a total angle of at least 100–150 degrees: (1) The electrostatic protential field of CAP shows regions of positive potential that from a ramp on 3 sides of the protein. (2) The DNA binding site size as determined by DNA ethylation interference with binding, (Majors: “Control of the E. coli Lac Operon at the Molecular Level.” Ph.D. Thesis, Harvard University, Cambridge, 1977) and by relative affinities of DNA fragments of various lengths (Liu‐Johnson et al.: Cell 47:995–1005, 1986) requires severe bending of the DNA to maintain its favorable electrostatic contact with the protein.
Accommodation of single amino acid insertions by the native state of staphylococcal nuclease
Authors: Sondek John , Shortle David 
Published: May 2005

AbstractSingle alanine and glycine insertions were introduced at 20 randomly selected positions in staphylococcal nuclease. The resulting changes in catalytic activity and in stability to guanidine hydrochloride denaturation indicate that the native state structure is frequently able to accommodate the extra residue without great difficulty, even insertions within secondary structural elements such as alpha helices and beta sheets. On average, an inserted residue reduces the free energy of denaturation (ΔG) by an amount roughly comparable to an alanine or glycine substitution for one of the residues flanking the site of insertion. Several positions outside of the enzyme active site were found where insertions, but not substitutions, lead to structural changes that modify catalytic activity and the circular dichroism spectrum. Amino acid insertions represent a virtually unexplored class of genetic mutation that may prove complementary to amino acid substitutions for engineering proteins with altered functional and structural properties.