SPE Library
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 and Prevention
Thermal Analysis of Plastics
Thermal analysis is an important group of tests used in the analysis of plastics and other polymeric materials. It consists of a family of well-established techniques that evaluate material properties as they change with temperature, time, and ambient environment under conditions of thermal programming. The results of thermal analysis tests provide qualitative and quantitative information about the material being evaluated. In particular, this information is important to address plastic failures or in characterization of the material composition and physical properties.
The upcoming webinar on thermal analysis will introduce the four primary techniques:
Environmental Stress Cracking
Environmental stress cracking (ESC) is the leading cause of plastic component failure, and a recent study suggests that 25% of plastic part failures are related to ESC. If you deal with plastic components, then “Environmental Stress Cracking of Plastics” will provide you with information that will enhance your understanding of the interaction between chemicals and plastic resins, with the goal of preventing part failure. ESC is a solvent-induced failure mode in which a plastics crack through contact with a chemical agent while under stress.
The webinar will be presented from a practical viewpoint with actual case studies to illustrate the ESC mechanism and explain plastic performance. Topics covered during this session include:
The Consequences of Ductile-To-Brittle Transitions in Plastics
Thermoplastic resins are utilized in many applications because of their unique property set, including their ductile response to applied stress. This ductility is associated with the viscoelastic nature of polymers and is attributed to their unique molecular structure. In spite of that inherent ductility, most plastic components fail through one of the many brittle fracture modes. Experience through conducting thousands of plastic component failure analyses has shown that less than 5% were associated with ductile overload. The remainder represent brittle fractures of normally ductile materials. Thus, within evaluations of plastic component failures, the focus of the investigation frequently turns to identifying the nature of the ductile to brittle transition. This relatively brittle response to stress is evident through the examination and characterization of the fracture surface morphology. There are numerous factors, associated with material, processing, design, and service conditions that influence a ductile-to-brittle transition within plastic materials. These include:
Navigating Plastic Material Selection
Material selection is one of the fundamental aspects that will determine the success or failure of a product. With so many choices available today regarding plastic materials, it is imperative that anyone involved in product design or material selection understand resin properties and how they will affect end product performance as well as part design and manufacturability. While plastic material selection is a frequent topic of discussion, it is not as simple as it may first appear. A thorough understanding of the short-term and long-term properties of the potential plastic resins is essential. To help make the best plastic resin choice, is also essential to have a basic knowledge of polymer chemistry.
This webinar will address some of the considerations that need to be made when selecting a plastic resin, and outline the challenges and benefits of selecting an appropriate material. The presentation will introduce a method of systematic selection that will optimize the plastics material selection process.
Understanding Wear of Plastics
Wear can be defined as damage to a solid surface caused by the removal or displacement of material through mechanical action associated with contact with a mating surface. Plastic components are used in a wide range of demanding applications in which they are subjected to surface damage and wear. These commonly include:
Fractography in Plastics Failures
The goal of a failure analysis is to discern the mechanism and cause of the component failure - essentially to identify how and why the part broke. Fractography plays critical role in this, particularly in identifying the failure mode. Cracking occurs as a result of the exertion of stresses, both external and internal, on a component. Cracking is simply a stress relief mechanism in which the material is attempting to reach a lower energy state. Plastics fail through a disentanglement mechanism in which polymer chains slide past each other.
The features on the fracture surface are created based upon a number of parameters:
Impact Failure of Plastics
While in service, plastic materials are subjected to many different types of mechanical stress. One common type of stress that is typically severe on plastics is rapid impact loading. The rate at which loading is applied, otherwise known as the strain rate, is a very important factor in the performance of a plastic component. Impact, together with snap fit assembly, and rapid pressurization are the most common forms of rapid loading or high strain rate mechanisms. The response of plastics to impact and the ability of a plastic part to withstand the stress through absorption of the applied energy is dependent on many aspects, including the material, design, processing and the service conditions. Topics covered as part of this presentation will include:
Impact loads are among the most challenging stresses that plastic component designers and manufactures must deal with. In many cases impact stress is not adequately accounted for. In may cases this leads to unnecessary premature or unexpected failure.
Plastic Failures Associated with Metal Fasteners
The need to secure plastic components is prevalent in the manufacture of assemblies in many industries. Joining plastic components to other plastic parts or metal parts often involves the use of mechanical fasteners, such as screws, inserts, or rivets. The joining of plastic parts is inherently more complicated than assembling two metal components because of the fundamental differences in physical properties, including strength, chemical resistance and susceptibility to creep and stress relaxation. Case Studies will be presented to illustrate failures associated with the interaction between plastic components and metal fasteners.
The presented cases will illustrate how the failure analysis process was used to identify the failure mechanism as well as the primary factors responsible for the failures. The cases depict representative failures involving varied designs and service conditions.
Failure Analysis of an Outdoor Instrument Housing
Cracking occurred within the housing for a piece of weather monitoring instrumentation being used as part of field service trial. The cracking was observed within the bosses used to secure the housing section to the mounting hardware. The focus of this investigation was the determination of the nature and cause of the failure. The results obtained during the evaluation of the failed housing indicated that the cracking occurred through three separate mechanisms. Significant factors in the failure included aspects of design, manufacturing, and the service conditions. This paper will review the testing performed to characterize the failure modes and identify the causes of the cracking, while demonstrating the analytical procedures used in the investigation.
Failure Analysis of Polymer Coating Systems
Failure analysis of polymer coating systems can be challenging due to the fact that coating systems typically involve multiple and generally very thin layered components. The root-cause for the failure of a polymer coating can be attributed to many factors. Thus, it cannot be easily determined by inspection or observations, and significant amount of testing is often required to determine the root cause for the failure. Typically, failures can be caused by selection of improper coating system, or it can be caused by insufficient surface preparation, or it can be caused by application related issues.
This paper attempts to provide a guide to performing failure analyses of polymer coatings by discussing two separate coating systems that utilized a polyvinylidene fluoride (PVDF) top coat and evaluates the fundamental root causes of failure. The importance of reviewing background information, performing site-inspections, conducting relevant laboratory and field testing, and utilizing published literature to reach a root-cause for the failure is high-lighted. In both cases, laboratory examinations revealed that while high performance coatings were utilized, their compatibility within the system and their susceptibility to hazards within their respective applications, were not accounted for, leading to poorly designed coating systems that eventually failed.
How Poor Selection of Materials, Design, Tooling and Design Errors Affect the Aesthetics of Plastic Parts and What Designers Need to Know About the Science of Color and Appearance - Part 2
Most engineers and designers come from the metal world. Therefore, many of them make assumptions on the predicted performance of plastic properties based on their metals background.
Unlike metals, the knowledge of color and appearance is extremely important in the case of plastics. Most plastic parts have dual functions— physical performance and aesthetics. Aesthetics are important since very few of the parts need to be painted or otherwise decorated if designed and manufactured with due diligence.
On the other hand, even if we are designing the most aesthetically critical metal components such as exterior automotive parts, we mostly choose the metals and alloys based on the physical properties, weight, and cost. The aesthetics are left to the paint specialist, who will in most cases find a paint system (primer, paint, and application method) that will meet the cost, durability, and cosmetic requirements. In other words, aesthetics and physical properties are quite independent of each other. A vast majority of metal parts meet their aesthetic and environmental requirements just by getting brushed, plated, chromate conversion coated or anodized.
Plastic parts not only need to meet the short-term color and appearance requirements, but also need to be resistant to long term color shift and fading.
This paper is in two parts.
Part 1 - Appearance and Color Factors
- Material
- Design
- Tooling and Processing
Part 2 –The fundamentals of Color and Appearance, Specifications, Measurement and Tolerances
Transition Metal-Catalyzed Degradation of Polymers: Review and Future Perspectives
In many instances, failure of polymer-based articles is attributed to chemical interaction with metals or metallic compounds. Indeed, the stability of polymers is often modified by these species; however, their effects on the degradation of polymers are complex and influenced by many factors. This paper reviews known polymer degradation mechanisms and how metals may influence them, discusses deactivators and their role use as stabilizers in polymer formulations, provides literature-based vignettes describing example scenarios where metal-accelerated degradation of plastics may contribute to failures, and provides commentary regarding potential future areas of work in the field.
Validation of the Virtual Lifetime Prediction Method for Elastomer Components
In the field of mechanical engineering technical elastomers are indispensable due to their material properties. They are often used to avoid load peaks and to influence the vibration behavior of dynamically loaded systems, because of their damping characteristics. Therefore, one field of research constitutes the damage accumulation and lifetime prediction.
This paper presents the validation of the virtual lifetime prediction model method, which was developed at the institute of product engineering at the University of Duisburg-Essen. The lifetime is defined as the number of load cycles till the global damage reaches the value 1. This damage is calculated by a failure criterion based on the change of a characteristic value like the dynamic stiffness degradation from a finite-element (FE) simulation. The virtual lifetime prediction method uses a combination of a damage-dependent material model (Yeoh-Model) and a nonlinear damage accumulation model (nlSAM). Both models are calibrated by means of experimental data from dynamically loaded elastomer components. The nlSAM computes the local damage for each finite element depending on material stresses and pre-damage. The dynamic stiffness degradation is a result of locally changed material properties in the FE simulation due to the damage of each element.
Finally, the lifetime prediction for unknown loads and different component geometries of the elastomer is carried out, which shows good agreement with the experimental data of the same material batch.
UV Effects on Plastics
If you work with plastic components that include outdoor exposure, then "Ultraviolet (UV) Effects on Plastic Materials" will provide you with information that will enhance your understanding of the interaction between UV radiation-based weathering and plastic resins, and help prevent premature failure. Topics covered during this session include an introduction to UV degradation and an explanation of the failure mechanism characteristic of UV radiation/plastic interaction. Case studies associated with UV radiation exposure will be presented.
You will learn…
Introduction to Plastics
Plastics are the most versatile materials ever invented, and have become a universal material, used for everything from water bottles to wings on combat aircraft. Plastic materials display properties that are unique when compared to other materials and have contributed greatly to quality of our everyday life. At this moment, you are almost certain to be touching plastic. Yet, while plastics play such an important role, we do not always understand the fundamental concepts of their production, compounding, end properties, and use. If words such as polymer, thermoplastic, creep, amorphous, and modulus are outside your normal vocabulary, this presentation is for you. This webinar will provide people not extensively familiar with plastics an understanding of the basics. The usefulness of plastics is attributed to the fact that they provide a wide range of properties and can be changed into and products by relatively simple and inexpensive fabrication means. In order to take full advantage of these materials, it is important to have a clear understanding of their composition and elementary properties.
Fourier Transform Infrared Spectroscopy in Failure & Compositional Analysis
Fourier transform infrared spectroscopy (FTIR) is a fundamental analytical technique for the analysis of organic materials. It provides critical information in the evaluation of polymeric materials, including material identification, contamination, and degradation. The webinar will present a fundamental understanding of the technique and the following topics will be covered:
Failure Associated With Injection Molding
The injection molding process is one of the key characteristics that determines how a plastic part will perform in service. Manufacturers certainly attempt to avoid failure, but often unanticipated factors result in unexpected problems.
The chances for a successful application can be significantly increased through preventative measures, including appropriate material selection, proper mold design, and process development. Even when appropriate actions are taken, failures can still occur. The evaluation of these failures provides an opportunity for learning. By understanding how and why a plastic component is failed, steps can be taken to prevent future occurrences. Case Studies will be presented to illustrate failures associated with the deficiencies from the injection molding process.
The presented cases will illustrate how the failure analysis process was used to identify the failure mechanism as well as the primary factors responsible for the failures.
Degradation Failure of Plastics
Plastic materials offer a unique balance of strength and ductility associated with their inherent viscoelastic nature. However, they are susceptible to molecular degradation through a variety of exposures. Molecular degradation is a permanent change in molecular weight that reduces the mechanical properties and integrity of the plastic material. This degradation can occur during compounding, processing, storage, or while in service. Such degradation mechanisms include:
The various forms of molecular degradation account for approximately 20% of plastic part failure, and an understanding of the nature of degradation can help to prevent failure. Topics covered during this session will include:
Understanding Failure Rate in Plastic Components
When a plastic part fails, a tough question is often asked, “Why are a limited number of parts failing?”. This is particularly true with seemingly random failures at significant, but low, failure rates. Two aspects are generally linked to such low failure rates, multiple factor concurrency and the statistical nature of plastic failures. Failure often only takes place when two or more factors take effect concurrently. Absent one of these factors, failure will not occur. Plastic resins and the associated forming processes produce parts with a statistical distribution of performance properties, such as strength and ductility. Likewise, environmental conditions, including stress and temperature, to which the resin is exposed through its life cycle is also a statistical distribution. Failure occurs when a portion of the distribution of stress on the parts exceeds a portion of the distribution of strength of the parts. This webinar will illustrate how the combination of multiple factor concurrency and the inherent statistical nature of plastic materials can result in seemingly random failures.
Dynamic Mechanical Analysis
Dynamic Mechanical Analysis (DMA) is a thermoanalytical technique that measures the stiffness (modulus) and damping (tan delta) of polymeric materials to assess the viscoelastic properties as a function of time, temperature, and frequency. Polymeric materials display both elastic and viscous behavior simultaneously, and DMA can separate these responses. Polymers, composed of long molecular chains, have unique viscoelastic properties, which combine the characteristics of elastic solids and Newtonian fluids.
As part of the DMA evaluation, a small deformation is applied to a sample in a cyclic manner. This allows the material’s response to stress, temperature, and frequency to be studied. The analysis can be in several modes, including tension, shear, compression, torsion, and flexure. DMA is a very powerful tool for the analysis of plastics and can provide information regarding:
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