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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Mechanical Properties of Plastics Used in Finite Element Method Calculations
Finite Element Method (FEM) calculations are suitable for predicting the mechanical behavior of plastic products with complex geometries. The problem is to obtain to the relevant material data in particular for thin walled sections. Results from laboratory tensile specimens are not very reliable, because they are relatively thick and have little orientation.To determine the influence of thickness and orientation, creep and recovery experiments have been carried out. The specimens had different thicknesses and different flow directions. The results from tests have been used for FEM-calculations to determine the influence of thickness and orientation on the mechanical behavior of a beam shaped product.
Reducing Paint Particle Size for Painted TPO Regrind
Many industries, such as the automotive industry, are faced with a high volume of plastics scrap associated with painted plastic parts. Ideally, the paint is removed prior to reuse of the painted regrind. Paint removal methods include differential thermal expansion, chemical attack and abrasion. If not removed, paint flakes in the regrind material influence the mechanical properties and aesthetics of the product molded from the painted regrind. The size of the paint flakes will likely have an influence on the mechanical properties of the molded part.A reground painted thermoplastic olefin (TPO) will be extruded using a general purpose and a “grater” screw being developed at UML. The grater section design will then be modified to implement a progressive grating technique. The effect of the design change on paint flake size, output, melt temperature and mechanical properties will be monitored.
An Investigation into the Gate Location and its Effects on Product Quality in Injection Molding
Gate location is an important aspect of thermoplastic part design, and injection mold design. A proper gate location will facilitate high quality parts, whereas poor gate location may cause the quality of the part to suffer. There are many different factors that affect the gate location. These factors that may affect gate location include: flow properties of the plastic, gating into the approximate center of the part, wall thickness, gating into an obstacle, style of the gate, separation of the runner system from the part, aesthetic properties, and ease of manufacturing. Computer simulations may help to facilitate the proper gate location and decrease the lead-time in producing a mold.The focus of this research project is to determine the ideal gate location given the previously mentioned factors for a single gated thermoplastic part, comparing both the experience of previous engineers through research of current materials, and the analysis of computer simulation software. The first portion of this project consists of research compiled from accredited individuals within the plastics industry; their perspectives and experiences have been combined to discuss the various possibilities in placing an ideal gate location. Following the research, these ideas were tested through the use of Mold Flow (Mold Flow Inc.) in various part designs. The last portion of this project compares and contrasts the industry experience to the results of the simulation software.
The Use of Sub-Micron Particle Size Calcium Carbonate Filler and Ester Modified Processing Lubricant Systems to Add Value or Performance to Rigid PVC Formulations
Formulators are constantly being asked to lower cost, improve performance, or both. This paper addresses this problem by reporting on the evaluation of an old standard calcium stearate paraffin lube system and one micron filler, vs. sub-micron fillers with ester modified lube systems.In the past this approach has been successful in allowing the use of lower modifier levels, or higher filler levels, without loss of properties, with modifier levels lowered from 4.5 to 3.0phr. This paper answers the question, “Is there any merit to using this approach when the modifier ranges from 2 to 0phr?” with the goal of eliminating the modifier altogether.
Strength, Toughness, Lifetime and Reliability of Plastics in Engineering Applications
Major factors affecting short term and longterm performance of plastics in engineering applications include a) chemical makeup and molecular architecture, additives etc; b) material and parts manufacturing conditions; c) installation and service conditions that include load, loading rate, temperature and other environmental conditions. Successful design of plastic components for intended application requires an understanding of the role of the above factors together with economic considerations that account for a cost of fabrication as well as for a price of failure. Material characterization and ranking with respect to strength, toughness and durability provide a basis for rational design with plastics. There are industrial standards and regulations develop to assist in product selection. Advantages and limitations of widely publicized standards and methods for durability and lifetime of engineering thermoplastics will be illustrated by examples of field failure analysis. Methodology of material durability and structural reliability assessment will be discussed.
Aspects of Yield and Fracture of Polymers and Their Nanocomposites
The physical and mechanical behavior of nano-scale reinforced polymers is currently receiving a significant amount of interest in the scientific arena. One of the more controversial aspects discussed is associated with the role the interface has on the physical state and bulk properties of the resulting composite. Another aspect is that associated with length scale effects necessary for energy dissipation in polymer matrix composites and the role of nanocomposites in this arena. These issues are discussed in contrast to reinforcements evaluated over a range of length scales ranging between micron and molecular length scases.
Applicability and Limitations of Fracture Mechanics Concepts for Lifetime Prediction of Polyethylene Pipes
The traditional method to compare different types and grades of plastics as to their performance potential for pressurised plastics pipes consists of stress rupture experiments with pipes under constant internal pressure. Based upon the observation that long-term pipe failure generally is governed by a two stage process consisting of a crack initiation stage and a period of stable, slow crack growth (SCG), various methods of fracture mechanics have been applied in the last two decades to study and characterise the SCG resistance of PE pipe grade materials.The paper will provide an overview of the various approaches including concepts of linear elastic fracture mechanics (LEFM) and elastic-plastic fracture mechanics (EPFM), with a particular focus on their applicability and limitations in terms of lifetime prediction, on the one hand, and their potential for quick material comparisons and material rankings, on the other. From an experimental point of view the characterisation methods include monotonic fracture tests over a wide loading rate range, creep crack growth and fatigue crack growth tests, and full notch creep tests (FNCT) with square and round bar specimens in air and liquid surfactant environments.
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.
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