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In a world contending with decades-old infrastructure and more frequent dire weather events while also seeking more energy-efficient building solutions--polymer-based materials are shouldering more of the burden. From bridges and [...]

Plastics blow molding has grown rapidly for the past couple of decades. Annular parison extrusion is a critical stage in extrusion blow molding. In this work, numerical simulations on the parison extrusion were performed using finite element (FE) method and the Kaye-Bernstein-Kearsley-Zapas type constitutive equation. A total of 100 simulations was carried out by changing the extrusion die inclination angle, die gap, and parison length. Then a back-propagation artificial neural network (ANN) was proposed as a tool for modeling the parison extrusion using the numerical simulation results. The network architecture determination and the training process of the ANN model were discussed. The predictive ability of the ANN model was examined through several sets of FE simulation results different from those utilized in the training stage. The effects of the die inclination angle, die gap, and parison length on the parison swells can be predicted using the ANN model. The results showed that the die gap has a smaller effect on the diameter swell but a greater effect on the thickness swell. Both diameter and thickness swells increase as the die inclination angle increases. The hybrid method combining the FE and ANN can shorten the time for the predictions drastically and help search out the processing conditions and/or die geometric parameters to obtain optimal parison thickness distributions. [DOI: 10.1115/1.2409357] Keywords: blow molding, parison extrusion, finite element simulation, neural network model

When contact problems are solved by numerical approaches, a surface profile is usually described by a series of discrete nodes with the same intervals along a coordinate axis. Contact computation based on roughness datum mesh may be time consuming. An adaptive-surface elasto-plastic asperity contact model is presented in this paper. Such a model is developed in order to reduce the computing time by removing the surface nodes that have little influence on the contact behavior of rough surfaces. The nodes to be removed are determined by a prescribed threshold. The adaptive-surface asperity contact model is solved by means of the element-free Galerkin-finite element coupling method because of its flexibility in domain discretization and versatility in node arrangements. The effects of different thresholds on contact pressure distribution, real contact area, and elasto-plastic stress fields in contacting bodies are investigated and discussed. The results show that this model can help reduce about 48% computational time when the relative errors are about 5%. [DOI: 10.1115/1.2345418] Keywords: elasto-plastic, contact, adaptive, rough surface, threshold

We demonstrate that mammalian cells can survive for 5 min within high-pressure C[O.sub.2]. Cell survival was investigated by exposing a range of mammalian cell types to supercritical C[O.sub.2] (scC[O.sub.2]) (35[degrees]C, 74 bar; 1 bar = 100 kPa) for increasing exposure and depressurization times. The myoblastic C2C12 cell line, 3T3 fibroblasts, chondrocytes, and hepatocytes all displayed appreciable but varying metabolic activity with exposure times up to 1 min. With depressurization times of 4 min, cell population metabolic activity was [greater than or equal to] 70% of the control population. Based on survival data, we developed a single-step scC[O.sub.2] technique for the rapid production of biodegradable poly(DL-lactic acid) scaffolds containing mammalian cells. By using optimum cell-survival conditions, scC[O.sub.2] was used to process poly(DL-lactic acid) containing a cell suspension, and, upon pressure release, a polymer sponge containing viable mammalian cells was formed. Cell functionality was demonstrated by retention of an osteogenic response to bone morphogenetic protein-2 in C2C12 cells. A gene microarray analysis showed no statistically significant changes in gene expression across 4,418 genes by a single-class t test. A significance analysis of microarrays revealed only eight genes that were down-regulated based on a [delta] value of 1.0125 and a false detection rate of 0. biodegradable polymer | bone | scaffolds

In this paper we report the experimental investigation to evaluate the published models for the contact of a deformable sphere against a hard flat in the fully plastic contact regime. A new measurement method has been used to measure the contact area. The behavior of the mean contact pressure and the contact area as a function of the contact load are presented. Substantial differences are found between the measurements and the model predictions. A constant value of the mean contact pressure as the load increases is observed, however, the value is lower than the hardness, as often reported. The contact area is found to be a simple truncation of the sphere by a hard flat. [DOI: 10.1115/1.2164470]

The nonlinear rheology of HDPE/maple melt in both shear and extensional flow was studied using a rotational parallel plate rheometer and the hyperbolic die technique, respectively. Nonlinear features were found in oscillatory shear tests at strain levels far below the values for neat polymer melt. The shear stress relaxation tests revealed the time-strain factorizability, and the damping function was found to follow the sigmoidal-type relation. The nonlinear nature of the shear flow was further observed as the shear stress growth function from step rate tests as compared to the prediction based on linear viscoelasticity. Extensional stress growth functions of the filled HDPE was build through the viscosity data based on hyperbolic dies with different Hencky strain. The comparison with prediction based on linear viscoelasticity and the Trouton's law further indicated significant damping owing to the particulate suspension nature of the wood plastics melts. POLYM. ENG. SCI., 46:114-121, 2006. © 2005 Society of Plastics Engineers, INTRODUCTION The past decade has seen a rapid expansion of the wood plastics industry [1-3]. Among the many factors for this rapid development, the economic competitiveness associated with high filler [...]

Montmorillonite is a promising substitute for aluminum trihydroxide in flame-retardant polypropylene/aluminum trihydroxide (PP/ATH) composites. Study was made of the partial substitution of organoclay for ATH in PP/ATH composites. The total concentration of filler was kept at 30 wt%. The composites were compatibilized with two types of compatibilizer: commercial maleic anhydride functionalized polypropylene (PP-g-MA) and hydroxyl-functionalized polypropylene (PP-co-OH) prepared with metallocene catalyst. The effect of compatibilization on the morphology was studied by the transmission electron microscopy and the scanning electron microscopy. Mechanical properties were characterized by tensile and impact measurements, and flammability properties with a cone calorimeter. Addition of compatibilizer and stearic acid (SA) treatment of the ATH particles contributed to the dispersion of the fillers. Both compatibilizers produced organoclay with exfoliated structure and improved adhesion between the fillers and the matrix. Toughness improved and decomposition and flammability were reduced. POLYM. ENG. SCI., 45:1568-1575, 2005. [c] 2005 Society of Plastics Engineers, INTRODUCTION Flame retardancy is commonly introduced to polymers by adding metal hydroxide filler, such as aluminum trihydroxide (ATH). Typically about 60 wt% of filler is required, however, and this creates [...]

To investigate the mechanical properties of pipeline subjected to plastic deformation, tensile tests and crack-tip-opening displacement (CTOD) tests were conducted on X60, X65, and X80 line pipe steels with uniaxial tensile or compressive prestrain, [[epsilon].sub.pr]. The tensile tests revealed that the Bauschinger effect and work hardening were dependent on the yield-to-tensile ratio (Y/T) of the steels; the change in yield stress due to prestrain linearly depended on the Y/T of the base metal. A critical CTOD for crack initiation decreased with increasing \[[epsilon].sub.pr]\. Compressive prestrain had a larger effect on the reduction of the critical CTOD than tensile prestrain. The test results showed that the reduction in the critical CTOD due to tensile prestrain was predictable with a simplified theoretical model employing a critical fracture strain of the base metal. [DOI: 10.1115/1.1894405]

Conform[TM] extrusion is a very versatile manufacturing process enabling the production of a wide range of extruded profiles. It is critical to maintain a precise predefined wheel-tooling gap for the efficient running of the Conform extrusion process and to maintain high product quality. However, this is a challenging task due to the hostile environment, high operating temperatures, and required accuracy. An accurate high-temperature gap measurement system for Conform extrusion machinery, using a capacitive sensing system, is developed in this study. The sensor is implemented in a copper Conform extrusion machine, and experimental results are presented, providing for the first time a detailed view of Conform Extrusion gap behavior during production. It is shown that the proposed gap-sensing and control system results in a number of advantages, including reduced machine setup times, reduced flash (waste) rates, and on-line monitoring and control of gap size. The research is carried out in collaboration with Holton Machinery Ltd., a leading manufacturer of Conform Extrusion machinery. [DOI: 10.1115/1.1870004] Keywords: Conform[TM] Extrusion, High Temperature Gap Measurement, Capacitive Sensors

To shorten the cycle time in conventional hot embossing, an infrared laser (laser/IR)-assisted microembossing process was investigated in this study. Since the laser/IR heats the substrate rapidly and locally, the heating and cooling time can be substantially reduced. Two different modes of IR embossing were tested. In one case, the polymer substrate was the IR-transparent poly(methyl methacrylate) (PMMA) and a carbon black-filled epoxy mold was used. In the second case, the polymer substrate was an IR-absorbent PMMA, and an IR transparent epoxy mold was used. The experimental results showed that both a shorter cycle time and good replication accuracy could be achieved. A commercially available finite element (FEM) code, DEFORM[TM], was used for process simulation. The relationship between the penetration of radiation energy flux from the laser/IR heating source and temperature distribution inside the polymer substrate was considered in the simulation. The flow pattern observed in the experiments agreed well with the numerical simulation. However, the displacement curve showed a discrepancy. POLYM. ENG. SCI., 45: 661-668, 2005. [c] 2005 Society of Plastics Engineers, INTRODUCTION Hot embossing is a relatively simple and low-cost process that is widely used for fabricating planar polymeric devices with micro-/nanofeatures [1-8]. However, in conventional hot embossing, both the mold [...]

This report describes the spontaneous folding of flat elastomeric sheets, patterned with magnetic dipoles, into free-standing, 3D objects that are the topological equivalents of spherical shells. The path of the self-assembly is determined by a competition between mechanical and magnetic interactions. The potential of this strategy for the fabrication of 3D electronic devices is demonstrated by generating a simple electrical circuit surrounding a spherical cavity. folding | microfabrication | 3D structure | soft lithography | soft electronics

The theoretical foundation of Youngdahl's correlation parameters, which have been used to eliminate pulse shape effects in the dynamic plastic response of two-dimensional structural members, is studied in the present paper with the aid of bounds obtained for a rigid-plastic material. It is shown that Youngdahl's empirical estimate for the structural response time is, in general, a lower bound on the actual response time. A lower bound expression is obtained for the maximum final displacement of a two-dimensional structural member when subjected to an axisymmetrically loaded transverse time-dependent pulse, which depends only on Youngdahl's correlation parameters, and offers a theoretical foundation for the validity of Youngdahl's correlation parameter method. [DOI: 10.1115/1.1839183]

The foaming process of poly([epsilon]-caprolactone) (PCL) with carbon dioxide and nitrogen has been investigated in this work from a theoretical and experimental point of view. C[O.sub.2] and [N.sub.2] showed very different behavior, as foaming agents for PCL. This was due to the different transport, chemical, and physical properties of the polymer/gas mixture that led to different foam morphology in terms of density, cell number density, and cell size. The lowest density (0.03 g/[cm.sup.3]) was obtained with C[O.sub.2], but the highest number of cells with [N.sub.2] (although with a higher density, (0.2 g/[cm.sup.3]). Foam with a low-density microcellular structure, was obtained when a mixture of the two gases was employed. POLYM. ENG. SCI., 45: 432-441, 2005. [c] 2005 Society of Plastics Engineers, INTRODUCTION Polymeric foams represent an important class of materials with important technological applications. Due to their peculiar properties, these materials find wide use when good mechanical properties and low weight [...]

Thermotropic liquid crystalline polymers (TLCPs) exhibit a number of mechanical and physical properties such as excellent chemical resistance, low permeability, low coefficient of thermal expansion, high tensile strength and modulus, and good impact resistance, which make them desirable as a rotationally molded storage vessel. However, there are no reports in the technical literature of the successful rotational molding of TLCPs. In this article, conditions are identified that lead to the successful rotational molding of a TLCP, Vectra B 950. First, a technique was developed to produce particles suitable for rotational molding because TLCPs cannot be ground into a free-flowing powder. Second, because the viscosity at low shear rates can be detrimental to the sintering process, coalescence experiments with isolated particles were carried out to determine the thermal and environmental conditions at which sintering should occur. These conditions were then applied to static sintering experiments to determine whether coalescence and densification of the bulk powder would occur. Finally, the powders were successfully rotationally molded into tubular structures in a single axis, lab-scale device. The density of the molded structure was essentially equivalent to the material density and the tensile strength and modulus were approximately 18 MPa and 2 GPa, respectively. POLYM. ENG. SCI., 45:410-423, 2005. [c] Society of Plastics Engineers, INTRODUCTION Thermotropic liquid crystalline polymers (TLCPs) exhibit a number of mechanical and physical properties that make them desirable for use in storage vessels for cryogenic or corrosive fluids. TLCPs have [...]

A three-dimensional flow simulation for epoxy casting has been developed. A control-volume-based finite-element method is employed, containing a conservative upwind formulation for the advection terms and equal order interpolations for all variables. This simulation predicts the non-isothermal and reactive flow behavior under the gravity. The viscosity and reaction-rate parameters were estimated by using a dynamic rheometer and a differential scanning calorimeter. The predicted flow front advancement and temperature profiles in the calculation domain similar to the mold cavity were in close agreement with the corresponding experimental results. The variation of epoxy surface configuration with flow rate also showed the same tendency between the prediction and the experiment. This simulation seems to be applicable not only to the epoxy casting, but also to other molding processes of various thermoset resins. POLYM. ENG. SCI., 45:364-374, 2005. [c] 2005 Society of Plastics Engineers, INTRODUCTION Epoxy casting is a widely used technique for the manufacturing of electric insulation parts, such as bushings, switchgear parts, and instrument transformers. During the process, a liquid epoxy resin [...]

An in-line method was applied to determine local residence time distribution (RTD) at two places in a completely filled corotating twin screw extruder. Axial mixing effects of different types of elements were evaluated. Paddles +90[degrees] induced flow patterns that appear to be circular, both upstream and downstream, whereas paddles -30[degrees] induced flow patterns that appear to be circular and mainly upstream. Transport and single-lead elements induced backflow. The results could be explained from pressure differences and direction of drag flow in the elements. All elements were characterized using an equivalent additional mixing length [lambda], dependent on the type of element and its position in the extruder, which may be practically useful for extrusion design. POLYM. ENG. SCI., 45:271-278, 2005. [c] 2005 Society of Plastics Engineers, INTRODUCTION In the last decades, interest has steadily grown in the use of corotating twin screw extruders in both food and nonfood applications [1-3]. The extruder is used for various [...]

A statically admissible solution for a perfectly plastic material in plane stress is presented for the mode I crack problem. The yield condition employed is an alternative type first proposed by von Mises in order to approximate his original yield condition for plane stress while eliminating most of the elliptic region as pertaining to partial differential equations. This yield condition is composed of two intersecting parabolas rather than a single ellipse in the principal stress space. The attributes of this particular solution of the mode I problem over that previously obtained are that it contains neither stress discontinuities nor compressive stresses anywhere in the field. [DOI: 10.1115/1.1828061]

This article investigates the radial extrudate swell and velocity profiles of polystyrene melt in a capillary die of a constant shear-rate extrusion rheometer, using a parallel coextrusion technique. An electro-magnetized capillary die was used to monitor the changes in the radial extrudate swell profiles of the melt, which is relatively novel in polymer processing. The magnetic flux density applied to the capillary die was varied in a parallel direction to the melt flow, and all tests were performed under the critical condition at which sharkskin and melt fracture did not occur in the normal die. The experimental results suggest that the overall extrudate swell for all shear rates increased with increasing magnetic flux density to a maximum value and then decreased at higher densities. The maximum swelling peak of the melt appeared to shift to higher magnetic flux density, and the value of the maximum swell decreased with increasing wall shear rate and die temperature. The effect of magnetic torque on the extrudate swell ratio of PS melt was more pronounced when extruding the melt at low shear rates and low die temperatures. For radial extrudate swell and velocity profiles, the radial swell ratio for a given shear rate decreased with increasing r/R position. There were two regions where the changes in the extrudate swell ratio across the die diameter were obvious with changing magnetic torque and shear rate, one around the duct center and the other around r/R of 0.65-0.85. The changes in the extrudate swell profiles across the die diameter were associated with, and can be explained using, the melt velocity profiles generated during the flow. In summary, the changes in the overall extrudate swell ratio of PS melt in a capillary die were influenced more by the swelling of the melt around the center of the die. Polym. Eng. Sci. 44:2298-2307, 2004. © 2004 Society of Plastics Englineers., INTRODUCTION The coextrusion of polymer products involves two or more melt streams flowing together along a die. Knowledge of the flow properties of each melt stream is essential in terms [...]

This study demonstrates the successful use of back-propagation artificial neural networks (BPANNs) in predicting the shrinkage and warpage of injection-molded thin-wall parts. The effects of structural parameters of a BPANN on the prediction accuracy and the capability of a BPANN in determining the optimal process condition are also discussed. The training and testing data are obtained experimentally based on a Taguchi [L.sub.27] ([3.sup.13]) test schedule. The results show that the trained BPANN can successfully predict the shrinkage and warpage of injection-molded thin-wall parts. Comparing the prediction accuracies of the trained BPANN and C-Mold software, it is noted that the trained BPANN predicts more accurately. In terms of determining the optimal process condition for minimizing the shrinkage and warpage of injected thin-wall parts, the trained BPANN is also shown to give a better optimal process condition than Taguchi's method. Polym. Eng. Sci. 44:2029-2040, 2004. [c] 2004 Society of Plastics Engineers., INTRODUCTION Because of the highly competitive nature of 3C (computers, communication devices and consumer electronics) industries, demands for shortening the research and development time, reduction in the size of the [...]

Die lines are annoying surface striations that can destroy extrudate aesthetics and compromise product properties. The available literature on die lines has been previously reviewed to explore how die lines arise and how to minimize them. Many factors have been found to influence die line formation. Some techniques are effective in suppressing die lines, mainly discovered through manufacturing experience. Here, we first briefly introduce how to measure and characterize die lines (die line metrology). Film blowing experiments are then conducted to study how various die defects, material properties and operating conditions affect die lines. The empirical relations between die lines and die defects, material properties and operating conditions are explored using dimensionless groups. We also investigate the fluid mechanics in die line formation. The free surface flow of polymer melt leaving the die lips is simulated. The qualitative relations between die defects and die lines are explored. The results are compared with film blowing experiments. Finally, new ways to suppress die lines and prospects for future studies are proposed., INTRODUCTION Extrusion is the most important unit operation in the plastics processing industry. It is a convenient way to continuously manufacture lengths of complex cross section to strict dimensional tolerances, [...]

We measured the basic electrical insulation characteristic of biodegradable polylactic acid (PLA), and the following results were obtained. The volume resistivity, dielectric constant, and dielectric loss tangent measured at room temperature were almost the same as those of crosslinked polyethylene (XLPE) currently used as insulating material for cables and electric wires. The mean impulse breakdown strength of PLA was about 1.3 times that of XLPE. Also, space charge accumulation in PLA and XLPE was measured. The amount of space charge accumulation in PLA was one-half that in XLPE when dc voltage was applied for a short time. Index Terms--Biodegradable polymer, electrical insulation characteristics, film, polylactic acid (PLA).

Ha, Young-Wook The microcellular plastics (MCPs) process is a foaming process that has been developed to reduce the weight of a product without significant changes to the mechanical properties. To [...]

A systematic approach was used to study the effect of the process variables that control bonding of the injected melt to the previously injected parts, in sequential injection molding of thermoplastic polymers. Three polymer pairs were sequentially injected in a mold with the same geometry, in a range of mold and injected melt temperatures, and packing pressure conditions. Standard Peel Tests were conducted on injected samples to measure the resulting bonding strength. The analysis of the experimental results allows the quantification of the relative importance of the processing parameters involved. A direct correlation is found between the calculated interface temperature and the packing pressure needed for bonding. A generalized procedure is proposed to establish the processing conditions, which allow polymer-polymer bonding to be optimized., INTRODUCTION Sequential injection molding of thermoplastic polymers has gained considerable importance in recent years (1). There is some literature on this subject (2) for vitreous polymers, but the bonding mechanisms, [...]

Synthetic polymers offer a wealth of opportunities to design responsive materials triggered by external stimuli. Changing the length, chemical composition, architecture, and topology of the chains allows response mechanisms and rates to be easily manipulated; and devices based on the entropy of the chains, surface energies, and specific segmental interactions can readily be made. Although numerous applications exist, intriguing possibilities are emerging that have tremendous potential to further developments in surface-responsive materials., A classic example of a responsive material is an elastic band. Within some finite limit, it can be stretched at a rapid rate of extension, and yet it is still [...]

An experimental investigation was conducted to evaluate the split tensile load-deformation strength and toughness properties of a granular soil chemically stabilized with cement and fly ash, and mechanically reinforced with recycled plastic strips [high-density polyethylene (HDPE)] obtained from postconsumer milk or water containers. The primary objective of this research was to evaluate if a modest amount of reinforcing fibers derived from recycled plastics can enhance the mechanical performance of a lean cementitious composite by improving the split tensile strength and the postpeak load carrying capacity. As an extension to the ASTM C 496 procedures for split tensile tests, two lateral linear variable differential transformers were attached to measure the tensile deformation of the horizontal diameter due to loading in the orthogonal direction; this method permitted an evaluation of the fiber toughening action under split tension. Two major groups of mixes were used for the study. The first group was stabilized with only 2-5% cement, while the second group contained 10% cement (by weight); several specimens also contained an additional 2-10% ASTM class C fly ash. Fiber-reinforced specimens contained 0.25% (by weight) to 0.80% (by weight) of recycled HDPE. A dimensionless toughness index and a fiber factor were defined in order to quantify the improvement in strength and toughness characteristics. It was found that the inclusion of HDPE fibers does not meaningfully improve the tensile strength, but significantly enhances the overall toughness of the composite. Results indicate that the test procedure, and the toughness index and fiber factor proposed in this study can be utilized to evaluate the performance of a fiber-reinforced stabilized soil for geotechnical and pavement applications. DOI: 10.1061/(ASCE)0899-1561 (2002) 14:2(177) CE Database keywords: Tensile strength; Fly ash; Plastics; Toughness.