The SPE Library contains thousands of papers, presentations, journal briefs and recorded webinars from the best minds in the Plastics Industry. Spanning almost two decades, this collection of published research and development work in polymer science and plastics technology is a wealth of knowledge and information for anyone involved in plastics.
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The reliability of a commercially available injection molding simulation program for part designers, Moldflow Part Advisor, is examined with a set of molding trials. Break-outs and thin tab features, part geometries typically seen with electrical applications, are studied. An instrumented test mold is built to model the geometric features of break-outs and thin tabs. Molding trials are conducted with two resins. The molding trial results are used to validate the melt front advancement predicted by the simulation. Process conditions are varied to yield short shot moldings as well as completely filled parts. Results show that the filling patterns in parts with thin tabs are fairly well predicted. Filling patterns through break-out features are not well predicted. Molding situations that yield short shots are seen to be predicted in some cases.
The heating and melting phenomena in co-rotating twin screw extruders is quite complex and awfully difficult to analyze it. The main difficulties are not only complexity in the rotor geometry but also the variation of operating conditions. It has been observed the variation of both screw configuration and the operating conditions gave rise to the different melting phenomena and the processing values such as percent torque and melt temperature. In the recent years, some attention has been paid to the research of polymer melting in co-rotating twin-screw extrusion in systematic way(1,2,3). The vehicle to understand and analyze these complex phenomena was invented. In this study, based on the previous experimental results(1,2,4,5,6) and the systematic experiments to illuminate each distinct heat generation terms (1,2,3) were used to elucidate the complex polymer melting progressing in co-rotating twin-screw extrusion.
In this paper, the main emphasis and focus will be to study and illuminate the nature of Plastic Energy Dissipation (PED) in a variety of polymers and relate it to the relevant polymer solid state material properties. This PED term represents the heat generated during deforming a polymer solid. Polymer solids are viscoelastic and their viscous nature generates heat. A series of experiments for various polymers have been conducted in 'direct measurement method' and 'indirect evaluation method'. The experimental evidence to relate the stress relaxation and the sensible temperature rise were revealed by the series of direct method experiments. A number of PED experiments were conducted as functions of strain rate, strain and temp erature and the iso-temperature rise plots were obtained in temperature-strain space for commercial amorphous and semicrystalline polymers.
Many in-service structural components (underwater piles, railroad ties, utility posts, guardrail posts, and others) require strength and stiffness increases either to overcome structural defects, or to enhance the inherent material structural properties. The objective for this research is to develop procedures to wrap structural components using fiber/fabric-reinforced composites to enhance strength, serviceability, and durability. To accomplish the above objective, research will include the following aspects: • Selection of primer and resin combination that is compatible to the original substrate. • Type of fiber/fabric-reinforced composite that enhances mechanical, thermal, and chemical resistance. • Type of manufacturing/installation process to develop a FRP composite stiffened base material resulting in higher strength and stiffness ratios compared to the original substrate.
Joung Gul Ryu1, Pil Soo Lee, Hyung Soo Kim, Jae Wook Lee, May 2001
Thermoplastic nanocomposites based on the copolymers of polypropylene (PP) - polystyrene (PS) and organically-modified montmorillonite (org-MMT) were produced by using power ultrasonic wave in an intensive mixer. Owing to the unique action of the ultrasonic wave, free radicals of styrene monomers and macroradicals of PP were generated, by which copolymers of PP and PS were polymerized. Another important aspect of using ultrasonic wave during the mixing process was to enhance nano-scale dispersion of org-MMT by destructing the agglomerates of org-MMT in the polymer matrix. Optimum conditions for the in-situ copolymerization and melt intercalation were studied with various concentrations of styrene monomer, sonication time and different kinds of clay. It was found that a novel attempt carried out in this study yielded further improvement in the mechanical performance of the nanocomposites compared to those produced by the conventional melt mixing process.
A.B. Hassan, A.H. Yahaya, P.R. Hornsby, M.J. Folkes, May 2001
Injection molding the dry blend of fibers and matrix granules usually results in composite materials with poor surface finishes, high mould shrinkage and variable strength. Therefore, the process usually involved two stages, i.e. compounding and molding. This process however, is associated with the problem of fiber breakage. In this work, short and long carbon fiber reinforced polyamide 6,6 composites, prepared by extrusion and pultrusion compounding respectively, were injection molded. Test pieces were then subjected to the fiber length distribution characterization and mechanical test. It was found that pultrusion compounded composites showed superior fiber characteristics compared to the extrusion compounded composites counterpart. Number average fiber length (Ln) and weight average fiber length (Lw) supports this behavior. These fiber length characteristics were also in agreement with the improved tensile strength and tensile modulus of long fiber composites over the short fiber composites, despite the reduction in their fracture strain.
S. Walker, G.M. Mc Nally, P.J. Martin, M. Murphy, May 2001
A number of metallocene catalysed linear low density polyethylenes and a conventional LDPE, of different material properties, were injection moulded over different mould cooling conditions. An assessment of the effect of the cooling rate, density and the co-monomer type on the mechanical performance and crystallinity was then conducted in order to establish any underlying trends. The results obtained from this report show a direct correlation between the density and co-monomer type of the materials with the mechanical properties, and a less significant relationship with the mould temperatures.
P. Slobodian, V. Pelíšek, J. Kubát, P. Sáha, May 2001
Sudden temperature change stimulated process of physical aging has been studied through enthalpy and volume relaxation. The investigated polymers were a-PMMA and its amorphous blends containing 6 and 14vol.% of PEO. Differential scanning calorimetry and mercury-in-glass dilatometry were employed. Based on , where Kubát at al. suggested the possibility of correlation of enthalpy and volume relaxation data, apparent bulk moduli, Ka, were calculated and compared with the moduli determined by direct compression. The correlation between computed and measured data was reasonably good.
Adhesion properties were determined on five-layer coextruded cast films that consisted of two high density polyethylene (HDPE) cap layers, two tie layers, and an ethylene-vinyl alcohol copolymer (EVOH) barrier layer (ABCBA configuration). The tie layers consisted of varying amounts of maleic anhydride-modified polyethylene-containing concentrates and various diluting resins. The extrusion temperature was also varied. Adhesion increased fairly uniformly as the film thickness and the concentrate level were increased. Adhesion was also affected by the choice of diluent and the ethylene content of the EVOH. Adhesion did not vary over our experimental temperature range.
In this paper, the morphology distribution of injection molded ZMA 6170 polypropylene observed using polarized optical microscopy is reported. A three-region- multi-layer model is sufficient to describe the skin-core morphology of these injection-molded parts. In the fully developed flow regions, a clear three-layer structure composed of a surface skin layer, a transition layer, and an inner core layer is observed. The simulation software package Moldflow MPI is used to identify the thermal and shear histories of the polymer melt during injection molding process. The characterization of each layer and its dependence on the thermal and shear histories are discussed.
Daisuke Watanabe, Hiroyuki Hamada, Kiyotaka Tomari, May 2001
The sandwich injection molding technique can be used in wide range of engineering applications. In this study, the developing behavior of core materials and break through phenomenon in the sandwich injection molding was investigated. The samples were preferred using a spiral-flow mold by changing the viscosity ratio and the melt temperature of skin and core materials. Developing behavior of the materials in sandwich injection moldings divided four regions, and it is noted that core material tends not to completely penetrate through the skin material at a stretch point, and it resulted in break through phenomenon. It is considered that break through phenomenon depends on the melt strength of the freezing layer of the skin material at flow front.
Interface construction is very important in the design of composite materials. Composites that consist of same materials but different shape such as fiber shape and matrix phase can create high interfacial strength. Call this composite Interface-less Composites". In this study knitted fabric was chosen as reinforcement configuration which has good drapability expandability and high productivity. Knitted polyethylene (PE) fiber reinforced PE film (PE/PE composite film) by film stacking method was prepared. Injection molding specimens were prepared by inserting this PE/PE composite film and PE was injected as matrix. Tensile properties of Interface-less composites by using injection-molding method were investigated."
Chao Li, Xiaodong Tang, Hung-Jue Sue, John D. Whitcomb, May 2001
The damage mechanisms in uni-weave/satin-weave hybrid IM7/BMI composites under uniaxial static tension loading have been investigated. The results reveal that hybridization effects on the damage mechanisms largely depend on the degree of waviness. For low waviness composites, the damage process is not affected significantly by hybridization. The damage patterns in the woven and hybrid composites are similar to those found in tape laminate. However, the large waviness composites exhibit complex damage behavior. Hybridization has a significant effect on the damage process.
The interfacial structure and mechanical properties of polypropylene (PP/PP) composites consisting of homo-PP fiber and propylene-ethylene random copolymer matrix were investigated. In PP/PP composites, the transcrystalline structure grows on PP fiber, which influences the mechanical properties. The two types of unidirectional PP/PP composite with different impregnating system were fabricated. In the well impregnated PP/PP composites, there were many transcrystalline layers, and the tensile modulus and strength were higher than those of badly impregnated PP/PP composite. Particularly in the transverse direction, well impregnated PP/PP composites had good adhesive properties. Therefore, it is supposed that the mechanical properties of PP/PP composites are influenced by trenscrystalline.
A. Nakai, M. Kamaya, E. Fukui, Y. Uetsuji, H. Hamada, May 2001
'Micro-braided yarn' has been proposed as a means of overcoming the difficulty of manufacturing long fiber reinforced thermoplastic composites. Micro-braided yarn is intermediate material for long-fiber reinforced thermoplastic composite. In the Micro-braided yarn a reinforcement fiber is covered by a matrix fiber. In this study, unidirectional carbon-fiber/ PA6-Nylon composites manufactured from micro-braided yarn with different strand diameter were molded in order to investigate the effect of the molding conditions on impregnation mechanism. Through this the mechanical properties of micro-braided composites were understood. A microscopic observation was performed with optical microscopy to understand the impregnation mechanism of thermoplastic resin into the fiber bundle. A parameter for the impregnation property was proposed based on the impregnation volume. 3-point bending test was carried out to investigate the effects of diameter of reinforcements strand in micro-braided yarn and molding condition on the mechanical properties.
The fiber/resin interface can be considered to have three-dimensional region, so that technical term of interphase has been often used instead of interface. Interphase should be considered as the third component in fiber reinforced composite materials, and is generated during composite manufacturing. The authors have tried to apply a new function to interphase and called Affordable Interphase". As an example of affordable interphase we have developed the composites with more flexible interphase than matrix resin. In this study we applied the concept of flexible interphase to the woven fabric composites. As a result it was cleared that tensile strength was improved because flexible interphase restrained generation of cracks at interphase inside of fiber bundles."
Violet Stefanovski, Edward Kosior, Syed Masood, Pio Iovenitti, Igor Sbarski, May 2001
Dairy and fruit juice bottles are a major source of post consumer recycled high density polyethylene (PCR HDPE). The recycled HDPE has limited post-consumer applications due to its poor stress crack resistance (SCR). This paper presents a review of a test method for SCR and some preliminary results of the development of recycled HDPE blends with improved SCR. The improvement has been achieved with the addition of a modifier, and results indicate that there is a potential to incorporate the use of recycled HDPE in non-pressure pipe applications. These customised blends have been tested for SCR according to the Notched Constant Ligament Stress (NCLS) test. The NCLS test is a new test method (ASTM F17.40) which is currently under development. The NCLS test will be used to determine the susceptibility of HDPE resins to slow crack growth (SCG) under a constant ligament stress in an accelerated environment. The results from the test will subsequently be correlated with field performance results.
Previous product quality models based on cavity pressure suffer from being geometry and polymer specific and requiring large amounts of data to develop. The present study focuses on the development of geometry/polymer independent models to predict part weight with a minimum of experimental data. Several product geometries were created using inserts in a standard ASTM tensile specimen cavity. Both amorphous and semi-crystalline polymers were utilized. Real-time cavity pressure data was collected, quantified via pressure curve attributes" and used to develop predictive models through multivariate linear regression. Future work will apply the model results to the molding of a typical commercial electrical connector."
The injection molding process has several inherent problems associated with the constant temperature mold. A basic solution is the rapid thermal response molding process that facilitates rapid temperature change of the mold surface thereby improving quality of molded parts without compromising cycle time. Rapid heating and cooling systems consisting of one metallic heating layer and one oxide insulation layer were investigated in this paper. Design issues towards developing a mold capable of raising surface temperature from 25°C to 250°C in 2 seconds and cooling to 50°C within 10 seconds were discussed. To reduce thermal stresses in the layers during heating and cooling, materials with closely matched low thermal expansion coefficient were used for both layers. Effects of various design parameters, such as layer thickness and material properties, on the performance of the mold were studied in detail with the aid of heat transfer simulation and thermal stress simulation. Several rapid thermal response mold inserts were constructed on the basis of the simulation results. The experimental heating and cooling response agrees with the simulation and also satisfies the target heating and cooling requirement.
Marie-Claude Heuzey, Paula Wood-Adams, André Fortin, May 2001
The simulation of polymer viscoelastic flows is a complicated problem and until now it is not possible to perform simulations that are relevant from an industrial perspective. One of the limiting factors is the degree to which elasticity plays an important role in the flow. For a given constitutive equation and numerical technique, a higher material relaxation time, will result in a lower maximum deformation rate for which convergence is possible. Since industrial processes typically involve very large deformation rates, a practical way to allow their simulation might be to truncate the longest relaxation times. In this work the Leonov constitutive equation was used to simulate flow through an abrupt contraction. The possibility of truncating the relaxation spectrum was explored and the impact of using truncated spectra on simulations is described. Finally we propose a technique for obtaining a truncated relaxation spectrum that will be useful for flow simulations.
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ANTEC 2016 - Indianapolis, Indiana, USA May 23-25, 2016. [On-line].
Society of Plastics Engineers
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