Search Results for ultraviolet resistance

This article presents a general overview of outdoor weather aging factors, their effects on the performance of polymeric materials, and the accelerated test methods that can be used to investigate those effects. These test methods are used to characterize material performance when subjected to specific, often controlled, and well-defined factors. The article also presents an overview of weathering instrument types that simulate outdoor stress factors.

This article describes the processes involved in photochemical aging and weathering of polymeric materials. It explains how solar radiation, especially in the UV range, combines with atmospheric oxygen, driving photooxidation and the development of unstable photoproducts that cause various types of damage when they decompose, including the scission of carbon bonds and polymer chains. The article illustrates some of the degradation reactions that occur in different polymers and presents an overview of the strategies used to prevent such reactions or otherwise mitigate their effects.

The failures of two aircraft components, one from a landing gear and the other from an ejector rack mechanism, were investigated. Both were made from PH 13-8 Mo (UNS S13800) precipitation-hardening stainless steel which had been heat treated to the H1000 and H950 tempers respectively and then chromium plated. The parts were characterized metallographically and mechanically and were found to be compliant. Detailed fractographic examination revealed that the first stage of both failures was similar: subsurface initiation of numerous cracks with a wide range of orientations and cleavage like features. The cracking was followed by fatigue in one case and catastrophic failure in the other. Hydrogen embrittlement was identified as the most likely mechanism of failure.

Plastic product failures are directly attributed to one of the following four reasons: omission of a critical performance requirement, improper materials specification, design error, and processing/manufacturing error. Therefore, product failures can be minimized or eliminated if all of these parameters are comprehensively examined during the design process. This article focuses on all of these factors, except processing-related failures, which are outside the design and engineering domain. It is dedicated to the identification and avoidance of common problems associated with the selection and designing of plastic parts. The article provides information on the material-related design criteria that depend on the applications, environmental conditions of use, and performance requirements. It discusses physical properties of plastics based on their relevance to real-world environmental conditions. The most-common design problems related to design considerations are also covered.

This article provides an overview of the electrochemical nature of corrosion and analyzes corrosion-related failures. It describes corrosion failure analysis and discusses corrective and preventive approaches to mitigate corrosion-related failures of metals. These include: change in the environment; change in the alloy or heat treatment; change in design; use of galvanic protection; use of inhibitors; use of nonmetallic coatings and liners; application of metallic coatings; use of surface treatments, thermal spray, or other surface modifications; corrosion monitoring; and preventive maintenance.

This introductory article describes the various aspects of chemical structure that are important to an understanding of polymer properties and thus their eventual effect on the end-use performance of engineering plastics. The polymers covered include hydrocarbon polymers, carbon-chain polymers, heterochain polymers, and polymers containing aromatic rings. The article also includes some general information on the classification and naming of polymers and plastics. The most important properties of polymers, namely, thermal, mechanical, chemical, electrical, and optical properties, and the most significant influences of structure on those properties are then discussed. A variety of engineering thermoplastics, including some that are regarded as high-performance thermoplastics, are covered in this article. In addition, a few examples of commodity thermoplastics and biodegradable thermoplastics are presented for comparison. Finally, the properties and applications of six common thermosets are briefly considered.

This article reviews the mechanical behavior and fracture characteristics that discriminate structural polymers from metals. It provides information on deformation, fracture, and crack propagation as well as the fractography involving the examination and interpretation of fracture surfaces, to determine the cause of failure. The fracture modes such as ductile fractures and brittle fractures are reviewed. The article also presents a detailed account of various fracture surface features. It concludes with several cases of field failure in various polymers that illustrate the applicability of available analytical tools in conjunction with an understanding of failure mechanisms.

Polymer materials are key building blocks of the modern world, commonly used in packaging, automobiles, building materials, electronics, telecommunications, and many other industries. These commercial applications of polymeric materials would not be possible without the use of additives. This article is divided into five sections: mechanical property modifiers, physical property modifiers, biological function modifiers, processing aids, and colorants. It describes three classes of additives that are used to inhibit biological activity, six classes of mechanical property modifiers, three classes of physical property modifiers, and two classes of both colorants and processing aids.

Accelerated life testing and aging methodologies are increasingly being used to generate engineering data for determining material property degradation and service life (or fitness for purpose) of plastic materials for hostile service conditions. This article presents an overview of accelerated life testing and aging of unreinforced and fiber-reinforced plastic materials for assessing long-term material properties and life expectancy in hostile service environments. It considers various environmental factors, such as temperature, humidity, pressure, weathering, liquid chemicals (i.e., alkalis and acids), ionizing radiation, and biological degradation, along with the combined effects of mechanical stress, temperature, and moisture (including environmental stress corrosion). The article also includes information on the use of accelerated testing for predicting material property degradation and long-term performance.

This article addresses electrical testing and characterization of plastics and presents a number of techniques for evaluating the electrical properties of insulating materials, with a special focus on plastics, accompanied by a list of the electrical properties of different types of plastics. It provides the reader with sufficient information to select the appropriate electrical test(s) for a specific application. The tests covered in this article are widely used in industry to determine the electrical properties of insulating materials, particularly plastics. The article lists and defines terms used in connection with testing and specification of plastics for electrical applications.

This article reviews the mechanical behavior and fracture characteristics that discriminate structural polymers from metals, including plastic deformation. It provides overviews of crack propagation and fractography. The article presents the distinction between ductile and brittle fracture modes. Several case studies of field failure in various polymers are also presented to illustrate the applicability of available analytical tools in conjunction with an understanding of failure mechanisms.

There are many reasons why plastic materials should not be considered for an application. It is the responsibility of the design/materials engineer to recognize when the expected demands are outside of what the plastic can provide during the expected life-time of the product. This article reviews the numerous considerations that are equally important to help ensure that part failure does not occur. It provides a quick review of thermoplastic and thermoset plastics. The article focuses primarily on thermoset materials that at room temperature are below their glass transition temperature. It describes the motivation for material selection and the goal of the material selection process. The use of material datasheets for material selection as well as the processes involved in plastic material selection and post material selection is also covered.

Corrosion is the deterioration of a material by a reaction of that material with its environment. The realization that corrosion control can be profitable has been acknowledged repeatedly by industry, typically following costly business interruptions. This article describes the electrochemical nature of corrosion and provides the typical analysis of environmental- and corrosion-related failures. It presents common methods of testing of laboratory corrosion and discusses the processes involved in the prevention of environmental- and corrosion-related failures of metals and nonmetals.

This article reviews analytical techniques that are most often used in plastic component failure analysis. The description of the techniques is intended to familiarize the reader with the general principles and benefits of the methodologies, namely Fourier transform infrared spectroscopy, energy-dispersive x-ray spectroscopy, differential scanning calorimetry, thermogravimetric analysis, and dynamic mechanical analysis. The article describes the methods for molecular weight assessment and mechanical testing to evaluate plastics and polymers. The descriptions of the analytical techniques are supplemented by a series of case studies to illustrate the significance of each method. The case studies also include pertinent visual examination results and the corresponding images that aided in the characterization of the failures.

While there are many fracture mechanisms that can lead to the failure of a plastic component, environmental stress cracking (ESC) is recognized as one of the leading causes of plastic failure. This article focuses on unpacking the basic concepts of ESC to provide the engineer with a better understanding of how to evaluate and prevent it. It then presents factors that affect and contribute to the susceptibility of plastic to ESC: material factors, chemical factors, stress, and environmental factors. The article includes the collection of background information to understand the circumstances surrounding the failure, a fractographic evaluation to assess the cracking, and analytical testing to evaluate the material, design, manufacturing, and environmental factors.

This article briefly introduces the concepts of failure analysis and root cause analysis (RCA), and the role of failure analysis as a general engineering tool for enhancing product quality and failure prevention. It reviews four fundamental categories of physical root causes, namely, design deficiencies, material defects, manufacturing/installation defects, and service life anomalies, with examples. The article describes several common charting methods that may be useful in performing an RCA. It also discusses other failure analysis tools, including review of all sources of input and information, people interviews, laboratory investigations, stress analysis, and fracture mechanics analysis. The article concludes with information on the categories of failure and failure prevention.

This article describes the preliminary stages and general procedures, techniques, and precautions employed in the investigation and analysis of metallurgical failures that occur in service. The most common causes of failure characteristics are described for fracture, corrosion, and wear failures. The article provides information on the synthesis and interpretation of results from the investigation. Finally, it presents key guidelines for conducting a failure analysis.

This article reviews generalized test methodologies for fatigue characterization of polymers and examines fatigue fracture mechanisms in different engineering plastics. It provides detailed micromechanistic images of crack-tip processes for a variety of semicrystalline and amorphous engineering polymers. The article describes fracture mechanics solutions and approaches to the fatigue characterization of engineering polymers when dealing with macroscale fatigue crack growth. It includes mechanistic images for high-density polyethylene, ultrahigh-molecular-weight polyethylene, nylon 6, 6, polycarbonate, and polypropylene. The article describes the micromechanisms of toughening of plastics and uses a macroscale approach of applying fracture mechanics to the fatigue life prediction of engineering polymers, building on the mechanistic concepts. It also describes the factors affecting fatigue performance of polymers.