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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Effect of Process Zone on Tear Resistance of Polymeric Films
Tear resistance is a critical requirement for polymeric film for applications such as packaging and imaging. Tear resistance is measured using the Elmendorf tear, trouser tear, and single edge notch tests. It was observed that in many cases the increase of tear resistance was results of crack curving. The mechanism of crack curving and the effect of process zone on crack curving are investigated in this paper. Crack curving during tear process is attributed to the process zone geometry, material orientation or damage orientation inside the process zone, and the large stretching or crack bluntness that create a mix mode fracture process. The effect of film orientation on process zone formation, crack curving, and the tear resistance is also investigated.
Accelerated Test for Stress Corrosion Crack Initiation in PB Tubing
The Stress Corrosion Cracking (also called Environmental Stress Cracking) process in Polybutylene (PB) tubing consists of three stages: 1) Crack initiation, 2) Slow crack growth, and 3) Dynamic crack propagation. The first two stages primarily determine the useful lifetime of PB tubing, since the third stage occurs in a relatively short time interval. In this paper, an examination of PB field failures, observation of crack initiation mechanisms, and evidences of chemical degradation as a primary cause of failure are presented. To evaluate crack initiation time in mechno-chemical conditions, a modification of ASTM standard environmental stress cracking technique is employed to accelerate the crack initiation process in PB and a simple extrapolation technique is proposed to estimate the time of crack initiation in service conditions.
Creep of Polyphthalamide (PPA) under Compression and Temperature
Polyphthalamide (PPA) with fiber reinforcement is widely used in electronics as connector housing materials. In high temperature applications, the material undergoes creep. Creep deformation is further amplified when the material is under mechanical loading. This paper addresses PPA creep under temperature and compression loading. A modified time hardening model is shown to fit the experimental data very well. All parameters for the modified time hardening model are provided in the paper. Creep strain as a function of temperature, stress and time is discussed in details. Finite element model is presented to analyze creep strain for application conditions. For a screw tightening mechanism where PPA is under compression, clamping retention is analyzed as a result of material creep. Final discussions also include interactions between creep and pressure relaxation caused by creep, and its effect on clamping retention.
Assessment of Polycarbonate Toughness by Creep Test
The problems associated with fracture toughness as a material parameter is addressed through studies of the crack and associated process zone developed under creep loading with polycarbonate. Fracture toughness, G1C, increased 40% with a 5% decrease in creep load, which shows it is not a material parameter. The time interval from steady crack growth to ultimate failure is even more sensitive to the creep stresses. It was found that a gradient of shear band density exists within the process zone which plays a strong role in the above measures of fracture toughness and lifetime. This finding is incorporated into a model for crack and process zone interaction, the crack-layer model.
Application of Acoustic Emission Technique for the Quality Control of Epoxy Coatings on Steel Substrate
The quality of epoxy coatings on steel substrate mainly depends on their cohesion and adhesion properties. In this study the application of acoustic emission (AE) technique in coating quality control was investigated for two coating formulations and three substrates with different surface treatments. Research results showed that AE method can effectively differentiate epoxy coatings based on their cohesion and adhesion properties. All available AE parameters were ranked according to their effectiveness in discriminating coating formulation and substrate surface treatment.
Micro-Deformation and Failure in Polymeric Materials as Studied by In-Situ Tensile Test in a Transmission Electron Microscope (Tem)
This report describes a method for the study of micro-deformation mechanisms of polymeric materials using tensile straining stages in transmission electron microscopy (TEM). The straining stages allow the in-situ observation of morphological changes while tensile strain is applied to a material over a temperature range - 165 °C up to 500 °C. The application of this technique to different polymeric materials will be described. Micro-deformation mechanisms observed in the in-situ deformation study will be correlated to macroscopic mechanical test results. Implication for materials designing and failure mechanisms will be discussed.
Applicability and Limitations of the FNCT-Methodology to Predict the Long Term Failure Behavior of Polyethylene-Pipe Materials
The Full Notch Creep Test (FNCT) is widely used to characterize slow crack growth (SCG) in polyethylene (PE) pipe materials, especially in Europe. The test is currently standardized in ISO 16770.3 and EN 12814-3 in order to establish uniform test conditions enabling the use of FNCT for material specifications. Some important questions concerning the test conditions (e.g. surface-active solution, notching procedure, etc.) remain to be answered. In the research project presented here, a detailed study of the influence of various test parameters was carried out. The applicability and limitations of the methodology are discussed.
Mechanical Properties and Behavior of Polymeric Materials Simulated by Molecular Dynamics
We have used computer simulations to investigate the behavior of polymeric materials under a uniaxial tensile force. The simulations allow us to follow the behavior of individual macromolecular chains at the molecular level during deformation and thus study the deformation mechanisms developing up to fracture under different loading conditions.The influence of micro-structural features on the mechanical properties has also been investigated. For this we simulate materials with varying skin-core ratio and orientation of the chains. Although we use simplified models for the structure of the skin and core regions, the behavior of the simulated materials is akin to that observed in real materials.From the simulations we have gained a better understanding of the structure-properties relationships in polymeric materials. This knowledge can be used to create materials with improved properties.
Thermal and Hydrolic Stability of DOW's PULSE*2000EZ High Flow Polycarbonate/Acrylonitrile-Butadiene-Styrene Blend
Engineering thermoplastics are important materials for use in vehicle interiors where energy management requirements are critical. PULSE*2000EZ, a polycarbonate/acrylonitrile-butadiene-styrene (PC/ABS) blend from The Dow Chemical Company, was introduced and discussed at ANTEC 2000 as a new high flow PC/ABS blend capable of lowering injection molding cycle times without compromising the physical and thermal characteristics of the material. An additional benefit and feature with this material is its ability to maintain its properties as indicated by accelerated thermal and humidity aging. This paper will discuss the retention of the key material properties after aging the material at 90°C (194F) and 95% relative humidity up to one thousand hours and compare it to other pre-high flow PC/ABS products from Dow.
Failure Analysis of an Acrylic Automotive Part
Cosmetic integrity is an extremely important property for automotive interior applications. Field returns or customer complaints are considered unacceptable from a supplier’s standpoint. The occurrence of one such failure in a painted acrylic part, prompted an investigation into the nature and potential origin of the observed cracking. The cracking occurred in a key slot location, resulting in delamination and ultimate loss of surface material. It was the conclusion of the analysis that several factors had played a role in the failure, including part design, residual stress, pre-existing flaws and chemical exposure. This paper will summarize the testing involved in determining the failure mode of the part as well as the potential source of the failure and proposed resolution of the situation.
Electrochemical Degradation of a Cooling System Component
Cracking and subsequent leakage occurred within a high power rectifier cooling system component. The leakage was observed after four years of rectifier service. The cracking was found at the bend of an elbow connector that joined two hoses. The investigation focused on the determination of the nature and cause of the failure. The results obtained during the evaluation indicated that the cracking was due to electrochemical polymer attack, which occurred as a consequence of an electrical potential present in the cooling system. This paper will focus on the testing used to characterize the failure mode and identify the cause of the cracking, thereby illustrating the failure analysis process.
Fractographic Characterization of Polycarbonate Failure Modes
Polycarbonate is an important plastic molding resin used to fabricate many engineered components. Because of its widespread usage, many different types of failures can result from various service conditions. Evaluating these failures through a systematic analysis program allows an assessment of how and why the parts failed. An essential portion of the failure analysis process is the fractographic examination, which provides information about the crack origin location, and the crack initiation and extension modes. The focus of this investigation was to characterize the surfaces of intentionally cracked laboratory samples in order to gain a more thorough understanding of polycarbonate fracture mechanisms. This paper will document some of the key fracture features associated with various polycarbonate failure modes.
Gas Moulding Problems
Injection of high pressure gas to assist moulding has developed quickly in the last decade, but there are problems in the technique. Foam moulded office chair arms are expensive and timeconsuming to make, while gas moulding appears to offer substantial saving in material costs and lowered cycle time. The case study shows how the project failed to address serious objections of structural integrity and process control, and so resulted in litigation. The case turned on demonstration samples, which on X-ray inspection, proved to be flawed internally. The case was resolved by negotiation before trial, with both parties compromising on costs and so saving goodwill.
Extension Ladder Failures
Accidents involving falls from a height are a common cause of death and serious injury in developed countries, coming second only to automobile accidents. One of our case studies shows how failure of one of the plastic tips fitted to an extension ladder misled the user into believing that the failure had caused the accident. However, examination of the trace evidence left showed that the tip fractured during the fall and did not cause the accident at all. The ladder had been leant at well below the recommended angle of 75°, practical reconstruction showing that the accident was probably caused by sideways movement by the user while at the top. It made the ladder unstable, and the tips slid down the wall by a stick-slip mechanism. The second case shows however, that accidents can be caused by poor maintenance of the elastomeric feet. Wear allowed them to swivel back into the aluminium stiles when erected, lowering the coefficient of friction with the floor. The severely injured workman was awarded substantial compensation.
Failure Analysis of Hinges: Application of Root Cause Analysis
Plastic hinges experience different types of stresses and end-use conditions that could lead to their failure. Root cause analysis (RCA) was used to investigate three different cases of the failure of hinges. An illustrative description of each case is stated followed by the suggestion of the potential causes and the investigation of the most probable cause(s). Some of the used investigation tools were macroscopy and finite element analysis (FEA). In these cases, the effects of the four common causes of failure (part design, material choice, processing factors, and end use) are discussed. Finally, some corrective actions are recommended to avoid future failures.
Materials and Processes Used in the Wright Brothers' Gliders and Flyer, 1900-1903
The first successful powered, controlled flights by Orville and Wilbur Wright in December 1903 were preceded by many designs and pre-flight experiments. Construction of their three gliders and the successful airplane followed a careful sequence of lessons learned from each trial. This paper discusses how they used many natural polymers and composites very effectively, to make aircraft built for impact resilience as much as for strength. Their testing of airfoils and the design of their propeller were major advances in aerodynamics. Their wise use of materials and assembly processes as well as their persevering innovations are a stimulation to present generations.
Novel Thermoplastic Elastomer Resulting from Physical Gelation of Telechelically Labeled Polydimethylsiloxane
Polydimethylsiloxane (PDMS) that has been labeled on both chain ends with a pyrene-based dye yields a novel thermoplastic elastomer. This behavior is due to thermoreversible physical gelation in the bulk state associated with nanocrystal formation of the pyrene dyes that are strongly insoluble in the PDMS. The gelation temperature, which is equal to the nanocrystal melting temperature, can be tuned by varying the PDMS molecular weight. At the nanocrystal melting temperature, a greater than three order of magnitude change in the value of tan ? is observed from oscillatory shear flow measurements. Significant hysteresis is observed upon heating and cooling due to the time needed to achieve equilibrium nanocrystal formation.
150°C Heat- and Oil-Resistant TPVs- Long-Term Fluid and Spike Temperature Comparison
New families of thermoplastic vulcanizates (TPVs) were commercially introduced in early 2003 offering 150°C heat and oil resistance in excess of 3000hrs. These TPVs are based on a continuous phase polyamide thermoplastic matrix and dynamically vulcanized polyacrylate (ACM) elastomer. Applications have a broad interest from underhood automotive to industrial applications.The heat and oil resistance of a commercialized TPV from this family will be compared at 150°C to conventional and silicone-based TPVs in addition to an ethylene-acrylate (AEM) thermoset elastomer, all of similar initial physical properties. Degradation after 175°C spike temperature exposure to air and an assortment of automotive fluids will also be compared. Finally, an overall comparison will be made to qualitatively measure the equivalency of these materials in manufacturing and end use application.
High Performance Thermoplastic Vulcanizates (TPVs) for Long Term High Temperature Application
New thermoplastic vulcanizates (TPVs) based on Hydrogenated Styrene Block Copolymer (HSBC) have been developed for long term high temperature applications. A comparative study using these new TPVs and conventional TPVs (Polypropylene(PP)/EPDM rubber) was performed. Standard factorial designs were used to evaluate material performance. The material characteristics under investigation were rheological properties, dynamic mechanical properties, tensile properties and morphology. These new TPV compounds showed increased solvent resistance and elastic recovery of approximately 20%, respectively relative to conventional TPVs.
A New TPV Technology Bringing Unique Features to the Market
A new TPV (EPDM/PP) product line has been commercialized by DSM Thermoplastic Elastomers. The new product line is based on a patented combination of a vulcanization system and compounding technology (WO 03068859) and is available in the Shore A 30 to 80 hardness ranges. It combines easy processing with excellent aesthetic appearance and a dry rubbery feel of the final products. The product line eliminates the gap between TPVs and SEBS compounds with respect to colorability and viscosity .Already, applications have been commercialized in the consumer market and in the automotive interior market in the EurAsia region.
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