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Conference Proceedings

Modeling of the Thermomechanical Behavior of Nonlinear Viscoelastic Materials under Multidimensional State of Stress
N.M. Yazici, E. Schmachtenberg, C. Bonten, May 2001

The thermomechanical behavior of nonlinear viscoelastic materials depends on time, temperature, loading rate and height of load. A model has been presented that allows the simulation of nonlinear viscoelastic materials under multidimensional state of stress. This 3-dimensional deformation model is built by parallel arrangement of a certain number of basic elements. Each basic element consists of an elastic Hookean element and a damper system (3D damper) to describe the viscous properties. The model is calibrated by isothermal strain rate controlled tensile tests at different temperatures. Along with suitable calculation algorithms, this model offers the ability to simulate any multidimensional load history caused by direct stresses and changing temperatures. The model allows the simulation both of quasi-static and dynamic loading at different temperatures [1]. Building up on this model, modifications on the calculation algorithms are done to enable the simulation of thermally induced stresses in constrained geometries. For this reason the calibration of the model has to be extended. The thermal expansion coefficient is determined from non-isothermal zero stress experiments. Furthermore modifications on the biaxial testing device are started to be able to carry out non-isothermal, biaxial tests.

Failure Analysis of a Cracked Construction Vehicle Grille
Jeffrey A. Jansen, Mary K. Kosarzycki, May 2001

Cracking occurred within grilles used on heavy construction equipment, without apparent cause. The cracking was observed to be sporadic and had initiated while the parts were being stored in a warehouse, prior to installation on the vehicles. The cracking was found adjacent to holes used to secure a logo nameplate in conjunction with metal bolts. The focus of this investigation was a timely determination as to the nature and cause of the failures. Of particular interest was whether the failure was primarily associated with material, design, processing, or environmental factors. This paper will document some of the testing performed to characterize the failure mode and identify the root cause of the cracking, in order to illustrate the failure analysis process.

A Study on the Processability of Polycarbonate in Solids Conveying Zone
Young-Cheol Ahn, Hyo-Jun Kim, May 2001

For several bisphenol-A polycarbonate resins, pressure distributions along the screw channel have been obtained according to the transport theory in the solids conveying zone. Structure and properties of those resins are related to the pressure distribution and the flow rate. When the chemical structures, mechanical properties, and number average molecular weights are equal, the polymer with broader molecular weight distribution (MWD) shows both a lower glass transition temperature and a lower pressure distribution in the solids conveying zone in spite of the increased flow rate. The polymer with broader MWD also shows shorter melting length than the others. The numerically determined length of the solids conveying zone is used to correct the pressure distribution.

The Influence of Red Phosphorous upon the Flame Properties and Dielectric Properties of Glass Fiber Reinforced Nylon-66
Wern-Shiarng Jou, Kan-Nan Chen, T.Y. Lin, Jen-Taut Yeh, May 2001

Incorporation of red phosphorous into glass fiber reinforced nylon-66 composites not only confers good fire retardancy but also retains good dielectric properties. The flame retardancy of the red phosphorous filled nylon-66 composites increase along with their red phosphorous contents. However, their arc resistance and dielectric strengths decrease along with the red phosphorous content. Flame retardant experiments were performed to understand these interesting behaviors. Possible mechanisms accounting for these behaviors are discussed.

The Effect of Pigment Type and Concentration on the Mechanical Performance of Injection Moulded Metallocene Catalysed Polyethylenes
M.J. Murphy, G.M. McNally, M.P. Kearns, May 2001

A linear Low density octene and hexene based metallocene catalysed poly(ethylene/? olefin) copolymer (mPE's) and conventional polyethylene of similar density were injection moulded using different pigment types and loading of 0.05% to 0.5%. The results for the metallocene polyethylenes show significant deterioration in impact properties by up to 14% at room temperature and up to 16% at -40°C, depending on pigment type and concentration. Increases in tensile and dynamic modulus were also found to be related to pigment concentration and metallocene alpha olefin co-monomer type. Differential scanning calorimetry studies also showed significant increase in the crystallinity in pigmented materials. Increases of over 500% in tensile elongation for metallocene PE resins over the conventional PE resins were recorded.

Numerical Calculation of Stresses in Film Blowing
V. Sidiropoulos, Z. Wahab, J. Vlachopoulos, May 2001

Film blowing is the major process for producing thin plastic film. In recent years, many researchers have noted the strong relation between the film stresses and orientation at the frost line and the final film properties. In the current work, using the bubble kinematics and material properties as inputs, numerical calculations have been performed to obtain the stress profiles in blown film bubbles using a viscoelastic constitutive equation (PTT) and focusing on stress variations in the thickness direction of the film. The results indicate that the film stresses are higher in the external surface of the film, which may explain experimentally observed differences in crystallinity and morphology between the two surfaces.

Environmentally Friendly Plasticizers for Polyvinyl Chloride (PVC) Resins
Bhima R. Vijayendran, Herman Benecke, Joel D. Elhard, Vincent D. McGinniss, Kim F. Ferris, May 2001

There has been increased interest in developing alternatives to phthalate plasticizers used in the processing of polyvinyl chloride (PVC). This paper describes research on modifying the composition of vegetables oils such as soybean oil for use as primary plasticizers for PVC. Advanced computational chemistry and modeling studies have been conducted to correlate structures of modified soybean oil with their compatibilities in PVC resin. The new soy oil derived plasticizers have excellent plasticizing efficiency with significantly reduced migration and volatility. Properties and performance of the new modified soy oil compositions as primary plasticizers in typical PVC formulations are summarized and compared to those of a standard phthalate PVC plasticizer.

Permeability Prediction from Non-Destructive Imaging of Composite Microstructure
Joy P. Dunkers, Frederick R. Phelan, Kathleen M. Flynn, Daniel P. Sanders, Richard S. Parnas, May 2001

Knowledge of the permeability tensor in liquid composite molding is important for process optimization. Unfortunately, experimental determination of permeability is difficult and time consuming. Numerical calculation of permeability from a model reinforcement can circumvent experimentation. However, permeability predictions often rely on a model reinforcement that does not accurately mimic the actual microstructure. A rapid, non-destructive technique called optical coherence tomography (OCT) can image the microstructure of a composite in minutes. Actual microstructure information can be then used to improve the accuracy of the model and therefore the predicted permeability. Additionally, the influence on fiber volume fraction and microstructural variability on permeability can be systematically studied. In this work, binary images of the microstructure of a unidirectional E-glass/epoxy composite were generated from the low contrast OCT data through image de-noising, contrast enhancement and feature recognition. The resulting data were input to a lattice Boltzmann model for permeability prediction. Results show that the image processing induced alterations in fiber volume fraction and tow surface area have an influence on the predicted permeability. Level-set methods for image analysis were then used to process the images to binary images. Level-set methods offer image de-noising and feature recognition while preserving fiber volume fraction and tow surface area. The calculated axial and transverse permeabilities from the level-set images shows excellent agreement with experimental values.

A Concept for a Applied Dryer Control by Prediction of the Moisture Content of Dried Material
T. Schroer, J. Wortberg, E.A. Siekmann, May 2001

To produce high quality parts from hygroscopic plastic materials like ABS, PA, PC, PET, PUR, etc. it is mandatory to keep the moisture content of the processed material below an upper limit for the specific product. Otherwise, the residual water causes problems during processing and probably decreases product quality. As a result of an increasing pricing pressure on the plastic processing industries the productivity of the manufacturing processes became more significant. One way to increase productivity is to reduce the energy consumption of the process. Drying requires a lot of energy. Process parameters are set after specifications from the producer of the raw material. These parameters are independent from the moisture of the raw material. Consequently, this leads to a higher energy consumption than is necessary and to fluctuations of the residual moisture. There is no closed loop control to keep the residual moisture behind the dryer at a constant level. The main reason is that there is no economic unit available to measure the moisture content that works for all materials independent from colour, apparent density, etc. This work presents a way to keep the level of the residual moisture at a constant level. For that a model of the drying process is used.

Meltdown-Time Profiles of Vibration Welded Nylon 66 Compounds
P.J. Bates, J. MacDonald, V. Sidiropoulos, H. Liang, May 2001

Meltdown is an important vibration welding process parameter. This research experimentally measured the meltdown-time profiles obtained from nylon 66 parts vibration welded on a Branson Mini II linear vibration welder. The study examined the effect of material (glass reinforced and unreinforced nylon 66), process parameters (weld pressures) and weld geometries (butt, T-shaped and cup welds) on meltdown-time profiles. Experimental meltdown-time profiles compare favorably with theoretical profiles obtained from existing models. Additionally, the presence of moisture in parts, and uneven or excessive welding are detectable by observing meltdown. This suggests its potential as an on-line quality control parameter.

The Influence of Different Processing Parameters on the Properties of Polypropylene for Rotational Moulding
J.P.F. Van Hooijdonk, M.P. Kearns, C.G. Armstrong, B. McCann, L. Coey, R.J. Crawford, May 2001

This paper presents an overview of an experimental investigation to determine the influence of various processing parameters on the properties of rotomoulded polypropylene. Polypropylene samples were rotationally moulded under different heating and cooling regimes and under a nitrogen blanket. Mechanical properties were determined and compared to those of injection moulded polypropylene. It is shown that with the correct processing parameters, mouldings with good mechanical properties are achieved. Moulding with a nitrogen blanket combined with fast heating and cooling reduces degradation to acceptable levels.

A New Concept in Coextrusion Dies
Rafael J. Castillo, May 2001

Producing coextruded product structures with more layers results in stronger more economic film structures enhancing the polymer's unique properties in combination with the reduction of the unfavorable attributes of some polymers. Coextrusion brings out the best properties of the individual polymers in the film structure. This paper will present the Dual Spiral System (DSS), a new patented concept in coextrusion blown film and blow molding. The DSS enables processors to take advantage of the improvements brought about from adding layers without adding additional equipment costs. By dividing each individual layer into two separate layers, the enhanced structural and physical properties of each layer material can be taken advantage of. This means that a five extruder DSS die would in fact be producing a 10 layer film sheet.

Flow Instabilities of Linear Polyethylenes in Capillary Experiments and Effect of Die Materials
Hector J. Larrazabal, Andrew N. Hrymak, May 2001

Flow instabilities of linear polyethylenes have been studied in capillary dies. The effects of shear stress, temperature, molecular weight and material of construction of the dies on the critical shear stress for the onset of slip have been evaluated. Flow curves were obtained using dies with constant L/D and different diameters. Slip velocities were calculated using the Mooney technique (1) as a function of shear stress. The onset of slip and slip velocity are affected by the material of construction of the capillary die. Stainless steel and copper alloys were used to determine the effectiveness of a dezincification hypothesis to explain observed slip phenomena.

The Rheological, Mechanical and Thermal Properties of Polypropylene/Polyethylene-Octene Copolymer Blends
P.M. McShane, G.M. Mc Nally, T. Mc Nally, W.R.M. Murphy, May 2001

Blends of ethylene-octene copolymer (EOC), Engage 8150, with Polypropylene (PP) were prepared using a Killion compounding extruder. The blends studied were in the range 1% - 30% EOC content. Rheological analysis of the various blends showed only slight increases in apparent viscosity with increasing EOC content. Mechanical analysis on injection moulded samples of these blends showed that tensile modulus and flexural modulus decreased and impact properties were improved significantly with increasing EOC content, especially at higher EOC concentrations. Dynamic mechanical thermal analysis (DMTA), and Differential Scanning Calorimetry analysis (DSC) would tend to indicate some degree of polymer miscibility especially at the higher EOC concentrations, with slight decreases in crystallinity and phase transition temperatures being recorded especially for the higher EOC concentrations.

Understanding the Source of Reduced Mechanical Properties in Reinforced Molded Products
Jason S. Trahan, Kurt Hayden, Paul Engelmann, Jay Shoemaker, Michael Monfore, May 2001

The movement to design plastic products with thinner walls has raised many issues for molders. Using a glass-reinforced resin in high-shear applications can decrease the resin's physical and mechanical properties. Understanding where the breakdown occurs in the molding system is fundamental in designing thin-walled plastic products. Changes in glass fiber lengths were measured at various locations in the delivery system to the part, over several material generations. This information was developed in conjunction with the data collection for the long-term wear study of copper alloy mold components. A procedure was developed for prediction, testing and measurement of fiber length in a thin-wall application.

New Product Development: The Effect of Speed and Role of Outsourcing
Amit Dharia, May 2001

Inventions and innovation process play critical role in long-term success of industry. New products promote growth and increase profitability - far more than added-on or derivative products. Higher costs, crowded market space, major acquisitions, and globalization in 1990s have forced industries to focus on supporting and sustaining core products and to avert risk involved with new products. This in turn has reduced corporate R&D budgets for developing new products. R & D and product managers are faced with managing new product development efforts with leaner staff and limited resources. Understanding how to stay in the game with limited resources is key. In this article, author reviews key factors for successful new product development process, with emphasis on effect of speed and role of outsourcing R & D early on.

Standard Test Method for Particle Size Analysis of Plastic Materials (Wet Analysis)
Jerome I. Paulson, Brian L. Keck, William F. Sahrhage III, May 2001

Standard test methods (ASTM D1921-96) have proven unreliable in determining percent passing" particle size analysis of plastic pellets on a given sieve size. Statically charged particles make dust collection and quantification difficult. Therefore dry sieve methods are unacceptable for particle sizes below 38 micron. We have developed a reliable method for quantifying a passing of plastic materials on a given particle size allowing for collection and quantification of particles above and below 38 micron. A liquid is used to wash particles through a sieve. The liquid is filtered and the filter papers dried and weighed to determine a passing Parts-Per-Million (PPM)."

Solid Conveying Model for Determining the Throughput for Ultra-Short Single Screw Extruders with Spiral-Groove Cylinder
H. Potente, F. Reckert, May 2001

Dimensioning conventional single screw extruders, axially grooved cylinders are utilised to achieve increased throughput and an operating performance being independent of the counter pressure by increasing the friction of the material on the cylinder wall. In contrast to this, the geometry of the grooves in an ultra-short single screw extruder [3] with combined conveying and plasticising areas serves to increase material friction and to realise a mass flow. For this reason, the models of the material throughput for conventional single screw extruders are not unconditionally applicable for this extruder type. It is not possible to consider only one volume element in the screw channel for formulating the model. Instead, a combined system of various volume elements that move at different speeds and in different directions must be taken into consideration.

Dynamic Mechanical Analysis of Aromatic Polyamide/Ethylene-Propylene-Diene Terpolymer Laminates
Geralda Severe, Donovan Harris, Christopher Macosko, May 2001

The dynamic mechanical analysis of aromatic polyamide, ethylene- propylene-diene terpolymer (EPDM) and 256-microlayer laminates of aromatic polyamide and ethylene-propylene-diene terpolymer have been investigated at different temperatures. Furthermore, microscopy was used to correlate the thermomechanical observations with the morphology. The aromatic polyamide studied is a random copolymer of isophthalic acid, 12-aminododecanoic acid and bis(4-amino-3- methylcyclohexyl)methane. The 256-microlayer laminates were prepared by using microlayer co-extrusion technology. Increasing compatibility between the aromatic polyamide and EPDM showed minor improvement on the dynamic response for the laminates.

On-Line Viscosity Control for the Injection Molding Process
G. Sherbelis, R.G. Speight, May 2001

Variation in material viscosity during production is a well-documented phenomenon. The variation can be caused by regrind usage, humidity level, factory temperature variation, and raw material batch to batch variation. Today's quality control systems react to viscosity changes by maintaining certain parameters of the process constant. These control systems operate without directly effecting the material viscosity, for example trying to maintain a reference peak cavity pressure profile. Direct control of material viscosity by means of melt temperature is one concept being explored. Compensation is required for the effect of temperature changes on density and material solidification times. The paper examines the ability to control part weight and dimensions in a production environment, as part of an on going research programme in the Moldflow laboratories.

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