bluuebunny/crossref_metadata_2025_split huggingface dataset:
Plane strain and plane stress analysis of fatigue crack propagation in medium density polyethylene pipe materials
Authors: Strebel J. J. , Moet A. 
Published: May 2005

AbstractUsing the Crack Layer Theory, differences in damage formation under different stress states during fatigue crack propagation in an ethylene‐butene copolymer were quantified and compared. Despite having vastly different stress states and crack propagation behaviors, arc specimens (28 mm thick) and single edge notched (SEN) specimens (2 mm thick) were shown to have the same specific enthalpy of damage, ∼300 J/g, a parameter in the Crack Layer Theory that is a measure of the material's intrinsic toughness. Damage in the SEN specimen consisted of crazing the significant material yielding; the latter damage type is associated with plane stress conditions. In the predominantly plane strain arc specimen, material yielding was minimal compared to crazing, the dominant damage form. After measuring these damage forms and applying the Crack Layer Theory, the constancy of the specific enthalpy of damage was established. Also the dissipation coefficient, β, a second parameter of the Crack Layer Theory, was shown to be a process‐dependent parameter, which was inversely proportional to the lifetime of the specimen: βSEN = 4.6 × 10−5, βarc = 1.1 × 10−4, which corresponds to lifetimes of 140,000 and 30,000 cycles to failure, respectively.
Development of high performance, waterborne coatings. Part I: Emulsification of epoxy resin
Authors: Kojima Shunji , Watanabe Yoshiki 
Published: May 2005

AbstractA new manufacturing process of high performance, waterborne coatings for can coating applications is developed, which includes emulsification of an epoxy resin with or without its hardener by incorporation of an acrylic resin. It becomes possible by this new process to emulsify a variety of resins with minimum effects of the surfactant acrylic resin. Thus, latitude to design formulations is widened and the performance of epoxy resin and its hardener can be fully developed.
Computer modeling of polymeric materials: Single chains and multiple‐chain systems
Authors: Galiatsatos Vassilios 
Published: May 2005

AbstractApplications of molecular modeling techniques to the prediction of the properties of polymers are presented. First, a brief overview of the various polymer modeling techniques is presented with a focus on which technique is suitable for which properties. Recent results from current research are shown. The first set of results is from work on the statistical correlation of two physical properties (end‐to‐end distance and dipole moment) of single polymer chains with independent rotational potentials. It is shown that the correlation depends on the orientation of the dipole moment vector. The second set of results reviews work on computer simulation of the irradiation cure of polyethylene. Structural information regarding the crosslinks formed is presented.
Analysis of the coupling between the apparent time scale of thermal degradation and sample size
Authors: Cohen Arie , Carriere Craig J. , Pasztor Andrew J. 
Published: May 2005

AbstractSample size sensitivity of thermal gravimetric analysis (TGA) presents a serious handicap in the obtaining of reliable thermal stability data for high‐temperature applications. For example, predictions of the apparent time for degradation during an isothermal experiment based on the results obtained using a 10 μm thick specimen can be off by an order of magnitude when applied to a product with a thickness of 10 cm. To address this effect, TGA experiments studying the thermal degradation of poly(methyl methacrylate) were conducted. Analysis of the experimental data resulted in the development of a relationship between the apparent time scale of the thermal degradation and the specimen thickness. Origins of the new dependence were traced to the change of the diffusivity resulting from material volatilization. Implications of the coupling between these two events for the analysis of thermal stability for new polymeric materials are discussed, and required changes in the current methodology are outlined.
Percolation in electrical conductive polymer / filler systems. I: Density/ filler curves according to a new thermodynamic percolation model
Authors: Lux F. 
Published: May 2005

AbstractThis work deals with the conductivity of polymer/filler‐mixtures, with the conductive filler particles of colloid size. For the interpretation of the conductivity course in such systems Wessling recently proposed a new thermodynamical percolation model, the so‐called “dynamic boundary model.” A consequence of the dynamic boundary model is a fixed picture for some properties of the mixtures, i.e., the density should vary in a defined manner according to the theoretical assumptions of the model. The current paper first gives a short description of the percolation process according to the dynamic boundary model. Second, the derivation of the density/filler concentration curves according to the assumption of this model is given. Third, a comparison is made between calculated and experimentally determined density/filler concentration curves. It is shown that the dynamic boundary model cannot account for the experimentally observed density curves.
Filling of a complex‐shaped mold with a viscoelastic polymer. Part I: The mathematical model
Authors: Papathanasiou Thanasis D. , Kamal M. R. 
Published: May 2005

AbstractA model for the filling stage of injection molding of viscoelastic thermoplastics in cavities of complex shape is presented. The model considers two‐dimensional melt flow, with converging and diverging flow patterns induced by complex boundary shape and by the presence of an obstacle. The model is non‐isothermal (with the melt loosing heat to the mold walls as it travels into the cavity) and handles a viscoelastic (following the White‐Metzner model) material with properties that vary with temperature, shear rate, and pressure. The numerical method is based on finite differences, with boundary fitted curvilinear coordinates used in the mapping of the flow field (which has an arbitrary shape that evolves with time) into a time invariant rectangle. The numerical results reveal geometry‐induced asymmetries in the flow and thermal fields as well as the effect of various process parameters on the pressure and temperature profiles in the cavity. The model admits variable cavity thickness, thus allowing for a treatment of the cavity thickness as a process parameter in the simulations.
Free radical degradation of polypropylene: Random chain scission
Authors: Triacca V. J. , Gloor P. E. , Zhu S. , Hrymak A. N. , Hamielec A. E. 
Published: May 2005

AbstractFree‐radical reactions, which are relevant in the chemical modification of polymeric materials, are discussed in relationship to their influence on random chain scission. A mathematical model is developed to calculate the entire molecular weight distribution (MWD) with the degree of chain scission as the sole parameter. This expression is identical to the one derived by Saito for the case of scission initiated by irradiation. An expression for the variation of molecular weight averages with the degree of chain scission is derived and compared with those calculated with the methods of moments found in the literature. The validity of empirical closure conditions used with moment methods is discussed. Experimental data for polypropylene (PP), degraded with organic peroxides in a single screw extruder, are compared with predictions when fitting the degree of chain scission. For a specific degradation process, the degree of chain scission is found to be proportional to the initiator level.
Investigation of polymeric materials using the cone calorimeter
Authors: Goff Leslie J. 
Published: May 2005

AbstractThe use of polymeric materials in building or construction applications is steadily increasing. Therefore, the potential for these materials to be exposed to fire is also increased. The understanding of the pyrolysis characteristics of these materials is thus a necessity. There are many standard tests used to evaluate materials. Unfortunately, the correlation between these tests and large scale fire is less than desirable. A new bench scale rate of heat release apparatus, the Cone Calorimeter, is now being used more frequently in pyrolysis testing of polymeric materials. This apparatus has been shown to correlate much better between room scale testing and large scale fire testing. The cone Calorimeter provides a pyrolysis profile of a material under ambient oxygen conditions. Characteristics such as ignition time, total heat release, maximum rate of heat release, mass loss during pyrolysis, CO2, CO, and smoke production are determined. In this work several almost neat polymers are examined and the general pyrolysis characteristics of these polymers are discussed. The objective of this work is to provide information of basic polymeric pyrolysis properties of these materials. Variations in the material, i.e., molecular weight, polydispersity, and residual catalysis, along with changes in testing procedures, can have dramatic effects on results. Obviously the addition of flame retardant and flame retardant packages to any of these materials will have dramatic effects on results.
The origin of β relaxations in segmented rigid‐rod polyimide and copolyimide films
Authors: Arnold Fred E. , Bruno Katie R. , Shen Dexing , Eashoo Mark , Lee Chul Joo , Harris Frank W. , Cheng Stephen Z. D. 
Published: May 2005

AbstractMost aromatic polyimides and copolyimides show a β relaxation process below their α relaxation processes in dynamic mechanical and dielectric measurements. The origin of this β relaxation has been under active discussion. In order to gain a better understanding of the origin of the β relaxation process, the dynamic mechanical behavior of a series of segmented rigid‐rod polyimide and copolyimide films with different dianhydrides and diamines has been systematically studied. For some of the polymers, crystallinity and orientation effects on the β relaxation process were also investigated. It is found that the β relaxation process in the unoriented films can mainly be attributed to a relatively noncooperative motion in uncrystallized diamines. However, this noncooperative nature may be gradually lost by increasing the crystallinity and orientation. Molecular modeling and computation have led to a discussion of possible diamine motion in the β relaxation process.
Creep‐based characterization of nonlinear relaxation behavior of plastics
Authors: Brueller O. S. , Steiner H. 
Published: May 2005

AbstractIt is a matter of fact that creep experiments can be conducted more easily and accurately than stress relaxation experiments, since it is easier to maintain a stress constant (for instance by a “dead weight”) than a strain constant. Nevertheless, in practice, structural parts made of plastics (which are nonlinear viscoelastic materials) are very often loaded under stress‐relaxation conditions. The present paper presents an approach to predict the behavior of a nonlinear viscoelastic material under stress‐relaxation‐type loading, based on data obtained from creep‐type experiments. The nonlinear creep compliance is described mathematically by an exponential series with a limited number of terms and a single nonlinearity function depicting the transient behavior. The nonlinear behavior of the material under constant strain (i.e., stress relaxation) is then obtained by dividing the considered time range into very short time intervals in which constant stresses are acting, while the different values of the applied stresses are chosen in a manner that guarantees the same stain at the end of each interval. In this way, one performs a numerical nonlinear superposition of the effects of the loadings in the various intervals, leading to the desired results under stress relaxation. A comparison of theoretical results with experiments conducted on some thermoplastic materials shows good agreement.
The anisotropy of slow crack growth in polyethylene pipes
Authors: Lu Xici , Zhou Zhiqiang , Brown Norman 
Published: May 2005

AbstractSlow crack growth was measured in the perpendicular and parallel directions relative to the extrusion direction of the pipe. For five pipes from different manufacturers, the anisotropy factor, the lifetime to fracture in the perpendicular direction divided by lifetime in the parallel direction, varied from 1.2 to 4.7 for complete fracture and 1.4 to 4.0 for crack initiation. The degree of molecular orientation was determined by measuring the shrinkage that occured when a pipe specimen was heated near its melting point. The amount of shrinkage correlated with the anisotropy factor for slow crack growth. The shape change after shrinkage was related to the flow pattern of the resin during extrusion and the cooling rate after extrusion.
Analysis of the temperature rise in the projectile and extended chain polyethylene fiber composite armor during ballistic impact and penetration
Authors: Prevorsek Dusan C. , Kwon Young D. , Chin Hong B. 
Published: May 2005

AbstractThe ultra‐high strength/modulus, extended chain polyethylene fiber (Spectra® fiber) composite has shown great potential as a lightweight armor material with its extraordinary capability of absorbing the kinetic energy of projectiles. But the relatively low melting point of this fiber (∼ 145°C) has caused concerns regarding the effect of temperature rise during the impact/penetration process on the performance as armor material. In this article, an analysis of temperature rise in projectile and the fiber composite during the impact/penetration process is described. Combining the simulation of impact deformation by finite element analysis and the simulation of temperature rise by a finite difference approximation of the related dynamic equations, the temperature rise caused by the projectile/composite interaction was estimated. Results show that there is a significant temperature rise at the projectile/composite interface due to the friction but that the short length of time involved in the process and the low thermal conductivity of Spectra fiber composite keep the temperature rise in a very small region (in the order of 0.001 cm) around the interface during the impact/penetration process. Consequently, the volume that is affected by the temperature rise is very small, in the order of total 0.001 cm3 around the projectile, and this is too small to generate any detectable effect on the armor performance. After the projectile is stopped, however, substantial heating of fiber composite can occur under specific conditions as the result of heat flow from the hot projectile embedded in the composite. This heating of fibers, however, is a postmortem effect and hence inconsequential to the ballistic performance of the composite armor.
A model for the unfoamed skin on microcellular foams
Authors: Kumar Vipin , Weller John E. 
Published: May 2005

AbstractIn microcellular plastics, an unfoamed skin that is integral with the foamed core can be created by allowing the nucleating gas to diffuse from the surfaces of a gas saturated specimen prior to foaming. In this paper, a semi‐empirical model is proposed that predicts the skin thickness variation in microcellular foams as a function of gas desorption time. The model shows good agreement with experimental results on the polycarbonate–carbon dioxide system.
Two‐dimensional multilayer coextrusion flow in a flat coat‐hanger die. Part I: Modeling
Authors: Puissant S. , Demay Y. , Vergnes B. , Agassant J. F. 
Published: May 2005

AbstractThe multilayer stratified flow of several polymers in a flat coat‐hanger die was modeled using a finite element method. The problem was formulated using the lubrication approximation theory. A solution procedure in decoupling pressure and streamlines was developed. This new method is very powerful in comparison with more classical approaches, permitting the solution of flow problems involving a great number of layers in a complex industrial geometry. It allows us to obtain, among other things, pressure field, streamlines, residence times, and the values of the interface positions in the whole die.
Crack propagation in biaxially oriented polypropylene at low temperature
Authors: Snyder J. , Hiltner A. , Baer E. 
Published: May 2005

AbstractThe crack growth behavior of polypropylene biaxially oriented by cross‐rolling was studied at low temperature. Single edge notch testing produced a stable tearing type of crack growth in both 50% and 80% biaxially oriented polypropylene at −40°C, in contrast to the brittle fracture of unoriented polypropylene. The crack growth in the two oriented materials began slowly and accelerated to a constant rate that was higher in the 80% oriented material than in the 50% oriented material. The main difference between the crack growth behavior of the two was the longer period of initial slow growth in the case of 80% orientation. This period of slow growth corresponded to crack growth through the notch tip damage zone. Residual strength diagrams were used to present the crack growth data obtained when the stress state was intermediate between plane stress and plane strain. Fractography revealed large differences among the fracture surfaces of the three materials with the unoriented polypropylene showing a grainy appearance from the brittle fracture. The two oriented materials showed considerable ductility. The 50% oriented material showed many voids in the fracture surface, indicating that voiding during the fracture process contributed significantly to the toughness improvement. The 80% oriented polypropylene showed delamination crazing on the fracture surface with layered material and fibrils bridging the crazes.
The influence of inclusion geometry on the elastic properties of discontinuous fiber composites
Authors: Eduljee R. F. , McCullough R. L. , Gillespie J. W. 
Published: May 2005

AbstractSimplifying assumptions are used to reduce micromechanical treatments to compact expressions which directly reveal the role of the inclusion shape and aspect ratio in establishing the elastic behavior of heterogeneous materials. Attention is directed to the comparison of aligned ellipsoidal and cylindrical inclusions that exhibit transversely isotropic behavior characterized by five independent elastic constants. These comparisons show that the effective transverse in‐plane moduli (E,k* andG) are essentially independent of inclusion shape for aspect ratio greater than ∼ 20; ellipsoidal inclusions provide higher longitudinal reinforcement than cylindrical inclusions of equivalent aspect ratio. Comparison of predictions with measured elastic moduli shows that both the cylindrical and ellipsoidal shape models for isolated inclusions overpredict longitudinal elastic constants for systems which exhibit evidence of inclusion agglomeration. The notion of an effective aspect ratio based on clusters of filaments responding as a coherent unit appears to provide a means for reconciling a wide range of experimental observations.
Start‐up pressure transients in a capillary rheometer
Authors: Hatzikiriakos Savvas G. , Dealy John M. 
Published: May 2005

AbstractThe “rise time” required to achieve a steady pressure reading in a capillary rheometer operated at constant piston speed can be very long, up to several hours under certain circumstances. This phenomenon can pose a serious problem in the measurement of melt viscosity, and it would be useful to be able to estimate the rise time in the planning of experiments. Based on experiments involving several types of polyethylene, we found that the rise time increases with L/D and the amount of polymer initially in the reservoir and decreases with diameter and piston speed. When the rise time is short, melt viscoelasticity contributes to the rise time, but when it is long, melt compressibility is the dominant factor. A model was developed for the latter case, and this was found to give an accurate prediction of the rise time, given the viscosity and compressibility. The model can also be used to determine the power‐law parameters from the start‐up pressure trace, P(t), for a single experiment. Alternatively, if the viscosity is known, the compressibility can be inferred from a single pressure trace.
A unified lubrication approach for the design of a coat‐hanger die
Authors: Liu Ta‐Jo , Liu Li‐Dah , Tsou Jenq‐Der 
Published: May 2005

AbstractA simple unified lubrication approach has been proposed to design a coat‐hanger die that can deliver wide and uniform liquid sheets. This approach requires that the wall stress in the manifold be constant. With this constraint, any inelastic non‐Newtonian fluid model can be used to describe the liquid motion inside the die. Fluid models that can represent the pseudoplastic or viscoplastic behavior of polymeric liquids have been selected for illustration. A general equation that can be solved to determine the effect of production variations on flow uniformity inside the die has also been derived.
The large strain compression, tension, and simple shear of polycarbonate
Authors: Boyce Mary C. , Arruda Ellen M. , Jayachandran R. 
Published: May 2005

AbstractPolymeric materials subjected to large strains undergo an evolution in molecular orientation. The developing orientation and corresponding strengthening are highly dependent on the state of strain. In this paper, we examine and compare the very different stress‐strain results of polycarbonate produced from four types of mechanical testing: uniaxial compression, plane strain compression, uniaxial tension, and simple shear. These tests produce different states of orientation within the material and, in the case of simple shear, the principle axes of orientation rotate during the deformation. The ability of the recent constitutive model of Arruda and Boyce (1992) to predict the to predict the observed behavior is evaluated. The model has been incoporated into a finite element code in order to properly simulate the material behavior during the inhomogenous deformations of tension (cold drawing) and simple shear. The material properties of the model are obtained from the uniaxial compression test and the model is then found to be truly predictive of the other states of deformation demonstrating its fully three dimensional capability. The disadvantages of the tensile and simple shear tests for obtaining the data needed to accurately quantify the large strain material behavior of polymers are shown and discussed.
Entrance pressure drop studies of corn meal dough during extrusion cooking
Authors: Bhattacharya M. , Seethamraju K. , Padmanabhan M. 
Published: May 2005

AbstractThe entrance pressure drop during extrusion cooking of corn grits was measured using a cylindrical die viscometer attached to a single screw extruder and compared with results obtained using low‐density polyethylene (LDPE). The cylindrical die viscometer had a length to diameter ratio of 40 with half‐entry angles of 30, 37.5, 45 and 90° with the horizontal. The entrance pressure drop at the die was measured as a function of extrusion temperature, product moisture content and the die entry angle. Results indicate that the flow behavior of corn grits and the entrance pressure drop were affected by product moisture content, process temperature and the shear history in the extruder. Entrance pressure drop also increased with wall shear stress for plastic melt, but for food biopolymer, the increase was observed provided shear history effects were minimized. Entrance correction increased with apparent shear rate for LDPE, but the reverse was true for corn meal. Using Cogswell's analysis, corn grits exhibit severe extension thinning behavior in entry flow.