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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Failure Analysis of Automotive Assemblies - Part I
Failures occurred within assemblies used in a transportation application. The cracking was observed in a relatively high number of parts immediately after cyclic thermal shock testing of the components. The cracking was found at several locations within the overmolded resin in areas immediately adjacent to underlying metal components. The focus of this investigation was a determination of the nature and cause of the failures. The results obtained during the evaluation of the failed components indicated that the cracking was the direct result of severe molecular degradation which occurred during the resin drying and molding operations, in conjunction with stresses induced through thermal shock testing of the parts. This paper will review some of the testing performed to characterize the failure mode and identify the cause of the cracking, while demonstrating the analytical procedure used in a failure investigation.
Failure Analysis of Automotive Assemblies - Part II
Failures occurred within assemblies used in a transportation application. The cracking was observed in a relatively high number of parts immediately after cyclic thermal shock testing of the components. The cracking was found at several locations within the overmolded resin in areas immediately adjacent to underlying metal components. The focus of the investigation was a determination of the nature and cause of the failures. The results obtained during the evaluation of the field samples indicated that the cracking was the direct result of molecular degradation that occurred during resin drying and molding operations, in conjunction with stresses induced through thermal shock testing of the parts. This part of the paper reviews the various methods that were used to evaluate viscosity changes in the material during drying and molding. This study illustrates the various strengths and weaknesses of the methods available to determine the molecular weight of a polymer.
Failure Behavior of Fiber-Reinforced Toughened Polymers
In fiber-reinforced toughened polymers, the influence of matrix deformation needs to be properly considered in their failure processes. There is a transition from failure dominated by massive matrix plasticity to that dominated by fiber-related mechanisms as the fiber content increases. This paper addresses some experimental observations and physical rationalization of the complex events that lead to failure of short fiber reinforced toughened nylon 6,6. The toughening behavior was studied using fracture mechanics techniques. The essential work of fracture analysis shows that the inclusions of short glass fibers not only provided a stiffening effect but also a toughening influence.
Failure of TPE Washers in Central Heating Systems
Widespread failure of TPE washers in central heating systems led to a large claim against the manufacturers and suppliers. Initial blame had been placed on plumbers who fitted the washers, either for under - or over-tightening the joints to the radiators. The material had been chosen for its ease of manufacture by injection moulding and replaced fibre washers. Inspection of failed washers showed numerous radial brittle cracks suggesting a different explanation for the failures. Trial experiments with new washers exposed to water at 85°C for three weeks stiffened, with 90% permanent set, the polyester elastomer changing dramatically in properties at short exposure times. The washers could not seal the system and extensive leakage occurred.
Failures Due to Stress Concentrations
The majority of plastic products fail due to stress concentrations. This is often due to insufficient radii of curvature, but also due to manufacturing and the condition of moulds.The stress concentration factor (SCF) can easily be determined from Peterson's book of SCF and they give about the same values as linear Finite Element Method calculations.For plastic products the values of the SCF is not sufficient to predict failure. The temperature and the strain rate are very important. The manufacturing method of the stress concentration by mechanical machining or by injection moulding gives significant differences in failure behaviour.In fatigue the stress concentration will determine the crack initiation and because of that stress concentrations are more dangerous in fatigue then in static loading.
Fatigue - Temperature Resistance of Continuous Glass Fiber/Polypropylene Composites
The flexural fatigue resistance of a continuous fiber composite (CFC) of glass and polypropylene (PP) under a fabric form has been investigated. Stress-life curves at a temperature of -40°C, 23°C and 50°C were obtained. These S-N curves show that the very high fatigue resistance of the PP/CFC composite at 23°C, in terms of normalized maximum flexural stress in fatigue (with respect to the flexural strength), remains relatively high at a testing temperature of 50°C. These curves also show that the fatigue resistance is actually improved at -40°C, i.e. at a temperature below than the glass transition temperature of the PP matrix. Comparison with a thermoset composite of similar flexural strength indicates that the intrinsic toughness and ductility of the thermoplastic PP matrix provides improved fatigue resistance, especially below the glass transition temperature.
Fatigue and Creep Crack Propagation Kinetics in PVC Pipe Material
The kinetics and mechanisms of creep and fatigue crack growth in PVC pipe material were studied in order to develop a methodology for prediction of creep fracture. In this study, fatigue crack propagation was resolved into fatigue and creep components. The creep component became more prominent with increasing temperature or decreasing loading rate. By studying the dependence of fatigue crack growth rate on loading rate and temperature, the contributions of fatigue and creep components to the overall crack growth rate were determined. The creep crack growth rate of PVC was predicted at ambient temperature by taking the ratio of the fatigue and creep contributions.
Fatigue Evaluation of Derakane* Vinylester/Glass Fiber Composites (Nabi Bus Program)
Information regarding the long-term durability of fiber reinforced structural composites is lacking in the community, but this information plays an extremely important role in the design and performance of the structure.This study is an out come of discussions that took place between TPI and Dow regarding the differentiation of the mechanical performance of composites made with DERAKANE* 8084 and XU1 MOMENTUM* 411-200. Based on clear casting data, the DERAKANE 8084 system appears to be a tougher resin however in order to obtain the same correlation on a composite, fatigue (durability) was suggested. The present document therefore details the experimental set-up, procedure and data obtained on flexure fatigue tests that were performed on the two composite systems. The data shows very clearly that whilst quasi-static flexure tests are not effective in differentiating the products that the fatigue (stress versus number of cycles) plot is able to bring out the differences. These tests were performed at 2 Hz and an R (ratio of minimum to maximum stress) = 0.2.Whilst the intent of this paper is not to generate durability data that could be used for designing the actual bus structure (as the test conditions mentioned above are far from those that exist in the field in terms of both stress level as well as frequency), it serves to present a framework for carefully obtaining and understanding data pertaining to the long-term fatigue performance of these composites. In doing so it also reinforces the importance of designing and carefully executing experiments that would provide time for damage to initiate and propagate in the composite in order to differentiate resins with varying toughness and durability.
Fatigue Resistance of Polyamide-6 and Polyamide-6/Clay Nanocomposite
Axial fatigue tests were carried out on polyamide- 6/clay nanocomposite and non-filled polyamide-6 (PA6). The results indicate that for these materials the evolution of the strain amplitude is better compared at the same maximum cyclic stress, while the accumulated strain at fracture is better compared at the same strain amplitude. The evolution of the accumulated volume variation suggests a localization of the deformation early in the fatigue process. The nanocomposite and the non-filled matrix showed similar fatigue lifetimes in the mechanically dominated fatigue regime. However, microscopic observations indicate changes in the fatigue fracture mechanisms.
Fiber Contents Effect on the Fiber Orientation in Injection Molded GF/PP Composite Plates
Short glass fiber reinforced polymer composites are common materials used to produce parts for structural applications. The attractiveness of these materials is a result of the combined advantages of the fiber reinforcing effect and the high production rates achievable by technologies such as injection molding.In fiber reinforced thermoplastic injection moldings, complex patterns of fiber orientation are obtained through-thickness. Most of the properties of the composite depend on the fiber orientation pattern. Thus, the prediction of the final properties of those composites requires either the prediction or the measurement of the fiber orientation field. The measurement of the fiber orientation field is a cumbersome and uneconomic task; thus the option has been to explore the capabilities offered by new computer modeling tools.An experimental programme was launched to systematically study the effect of fiber contents on the fiber orientation and final properties of injection molded short glass fiber reinforced polypropylene edge gated rectangular plates.
Fiber Orientation in Multilayer Tubes from a Conical Extruder
A new extruder design has been developed for the coextrusion of bi-layer annular sections. The extruder consists of a conical stator-rotor-stator assembly, which performs extrusion from each side of the rotor. Flow within this assembly is fully three-dimensional, with helicoidal streamlines in the vicinity of the rotor and the die entry region. Fiber orientation is created in the circumferential direction by these helicoidal streamlines; close to the inner and outer surfaces of the tube, the fibers are parallel to the main extrusion direction, whereas in the mid-thickness, they are oriented in the circumferential direction. The degree of orientation depends on the die design and on the polymers used.
Filler Phase Distribution in Elastomer Blends
Carbon black (CB) filler phase distributions in filled BR/BIMS blends (poly(1,4-cis-butadiene)/brominated poly (isobutylene-co-paramethylstyrene)) were quantified by image processing their tapping phase AFM blend morphologies. Preferential CB filler partition into the BIMS phase was indicated where the preference is enhanced with an increase in BIMS content suggesting a kinetic controlled filler partition process in straight mixing. 3D finite element modeling based on randomly generated blend morphologies and experimentally determined filler phase distributions could accurately predict blend tensile properties. Preferential filler partition into the BIMS phase may account for the observed synergistic improvement in abrasion resistance of these blends.
Finite Element Analysis of Impact Durablity on Extruded Plastic-Wood Fiber Composite Lineals
The impact performance of hollow profile extruded plastic-wood fiber composites depends on the profile geometry, the material properties and the damping of the system. Finite Element Analysis was used to simulate the Rosenheim and Gardner impact tests for a number of profile designs tailored for a series of plastic-wood fiber composites known as Fibrex™. In general, the analysis investigates the influence of geometry and damping properties on the impact energy and stress for fixed material properties. This investigation presents a failure criterion based on the penetration of critical impact energy. The results provide valuable information for plastic-wood fiber profile extrusion designs.
Flammability and Mechanical Properties of Vinyl Ester/Clay Nanocomposites
Flammability and mechanical properties of vinyl ester containing organically-treated montmorillonite were examined. Structure determination, done using transmission electron microscopy, revealed partial exfoliation of clay platelets. The tensile modulus was found to increase with clay content but without adversely affecting tensile strength. In small burner tests, the nanocomposites were not self-extinguishing, but vertical samples behaved quite differently from horizontal ones. Heat-release rates were also measured in a microcalorimeter at a temperature of 70°C, and these showed that clay could be effective in the enhancement of fire resistance.
Flexible and Transparent Blends Based on Ethylene/Styrene/Propylene Terpolymers
Polymer blends are generally opaque due to lack of miscibility or to a refractive index mismatch between the components. Dependent upon comonomer composition, novel ethylene/styrene/propylene (ESP) terpolymers obtained with INSITE* technology offer flexibility in tailoring refractive index. Blends of these terpolymers with other polymers, such as polypropylene, ethylene/octene copolymer and poly(styrene-ethylene-butylene-styrene) (SEBS) block copolymer, are shown to have interesting combinations of optical transparency, processability and mechanical properties. The morphologies of the blends have been studied using microscopic techniques, and the results corroborate the synergistic optical properties. Potential applications for the blend systems include label stocks, removable signage, protective drapery and injection molded products.
Flow Behavior of Core Material in Sandwich Injection Molding with Sequential and Simultaneous Injection
The sandwich injection molding technique can be used in wide ranges of engineering applications for recycle. In this study, flow behavior of core material in sandwich injection molding with sequential and simultaneous injection was investigated. Flow behavior of materials in sandwich injection moldings revealed to divided into four regions (Primary injection region, core advance region, core expansion region and break region). The flow length of core expansion region was increased with increasing of simultaneous injection time of skin and core material. And it is revealed that the core layer was formed as wide and thin structure with increasing of simultaneous injection time.
The Formation and Properties of Plastic Electronic Devices
One of the advantages of conjugated polymers is the solution processing capability, which can significantly simplify the device fabrication process as well as the cost. Although conjugated polymer has often been considered as amorphous semiconductor, the bulk electronic and photonic characteristics are strongly influenced by the detail arrangement of polymer main chains and its side groups. In this presentation, various polymer thin film deposition techniques (such as spin-casting, inkjet printing, and continuous coating processes) will be discussed. It is realized that although polymer thin films can be processed by various coating techniques, the final polymer morphology plays an important role of determining the polymer electronic properties. We will report the physical properties of polymer thin films prepared by different deposition techniques, and corresponding characteristics of polymer light-emitting diodes.
Fracture Behavior of Weldline in Polystyrene Injection Moldings
Fracture behavior of weldline occurring behind an obstructive pin in injection-molded polystyrene plates was investigated using double torsion (DT) test. Alternate slow and rapid crack propagation was observed during the test. Ripple marks appeared on the fracture surface when crack propagated rapidly. It seemed that crack propagation was affected by the V-notch of the weldline surface. However, the marks could be observed where no V-notch existed on the surface. This indicated that a poor bonding area in the sub-layer of weldline, not V-notch, affected crack propagation. The fracture toughness of the weldline was also studied by varying the pre-notch length along the weldline. The fracture toughness of the weldline was affected by the flow behavior behind the pin and quite different between the upstream side and the downstream side of first collision point (FCP). This tendency is considered to be dependent on the relaxation behavior of molecular orientation.
Fracture of a Breast Tissue Expander
A silicone breast tissue expander failed suddenly after several infusions of saline solution, causing great distress to the patient. The device had fractured at the junction between the bag and the feed catheter. Examination of the dome attached to the catheter into which the saline is fed showed the number of infusions. The fracture surface when examined using ESEM showed a smooth crack path caused by growth of a single crack. The origin lay at the shoulder of the catheter where it met the bag, and numerous microcracks were found at all parts of the junction. Their presence suggested failure of the adhesive used to join the two parts, with slow crack growth under progressively increasing load leading to catastrophic rupture. Especial care is needed in the design of silicone implants to allow for all possible loading patterns.
Fracture Toughness Measurement of Ductile Polymeric Sheets and Films
Many engineering polymers and their blends are tough and the conventional fracture parameters, such as the critical potential energy release rate Gc and critical stress intensity factor Kc, are inapplicable as they are only valid for linear elastic fractures. Post-yield J-integral or crack-tip opening displacement (CTOD) characterization is problematical due to certain experimental difficulties. To overcome these problems, a review is given on the now accepted essential work of fracture approach, which was developed at Sydney University, to determine valid fracture toughness under these circumstances. The theoretical concept will be presented and examples in support of the theory will be taken from data obtained from a range of ductile polymer sheets and their blends covering the effects of temperature and loading rates under mode I crack opening. We will also extend our fracture analysis and experiments to the out-of- plane tearing mode III that is more relevant for failure of thin films.
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