The lifetime assessment of polymeric products is complicated, and if the methodology utilized leads to inaccurate predictions, the mistakes could lead to financial loss as well as potential loss of life, depending on the service application of the product. This article provides information on the common aging mechanisms of polymeric materials and the common accelerated testing methods used to obtain relevant data that are used with the prediction models that enable service life assessment. Beginning with a discussion of what constitutes a product failure, this article then reviews four of the eight major aging mechanisms, namely environmental stress cracking, chemical degradation, creep, and fatigue, as well as the methods used in product service lifetime assessment for them. Later, several methods of service lifetime prediction that have gained industry-wide acceptance, namely the hydrostatic design basis approach, Miner's rule, the Arrhenius model, and the Paris Law for fatigue crack propagation, are discussed.

Neural networks permit the discovery of fundamental relationships and quantitative structure within vast arrays of ill-understood data. This article provides an overview of neural network modeling method, describing its overfitting nature. It discusses the use of neural networks in modeling noise and uncertainties in conducting experiments. The article also presents examples of the application of neural-network modeling to the behavior of metals.

Understanding fatigue crack growth is critical for the safe operation of many structural components. This article reviews the standard fracture mechanics and methods to determine the crack growth rate for a material and loading condition experimentally. It also addresses the two most important aspects of crack-growth modeling: loading environment and crack geometry.

In the design of composite structures for durability and damage tolerance, the primary concerns are out-of-plane failures, such as delamination, material degradation associated with environment, stability under compression loading, large degree of scatter in fatigue life, and bearing failure of joints. This article presents an introductory discussion on the fatigue damage process, methodologies assessing fatigue behavior, and life prediction models. It describes the damage mechanisms introduced for a quasi-isotropic laminate under tension-compression fatigue loading. Delamination is a critical issue in fatigue and generally results from high interlaminar normal and shear stresses. The article schematically illustrates the structural elements in which high interlaminar stresses are common. It concludes with a discussion on the classification of fatigue models such as mechanistic or phenomenological, for composite materials under cyclic loading.

Brittle materials, such as ceramics, intermetallics, and graphites, are increasingly being used in the fabrication of lightweight components. This article focuses on the design methodologies and characterization of certain material properties. It describes the fundamental concepts and models associated with performing time-independent and time-dependent reliability analyses for brittle materials exhibiting scatter in ultimate strength. The article discusses the two-parameter and three-parameter Weibull distribution for representing the underlying probability density function for tensile strength. It reviews life prediction reliability models used for predicting the life of a component with complex geometry and loading. The article outlines reliability algorithms and presents several applications to illustrate the utilization of these reliability algorithms in structural applications.

Delamination is one of the most commonly observed failure modes in composite materials. This article describes the three fundamental fracture failure modes of composite delamination, namely, opening, in-plane shearing, and tearing or scissoring shearing modes. It discusses the characterization and analysis of delamination. The article also reviews the prediction of delamination factors, such as flexbeam fatigue life, and skin/stiffener pull-off strength and life.

This article provides an overview of the safety aspects and integrity concept for pressure vessels, piping, and tubing. It focuses on the fracture mechanics approaches used to validate components with longitudinal cracks and circumferential cracks and to analyze crack growth behavior under cyclic loading. Full-scale testing facilities and the typical test results required for various applications are discussed. The article also presents information on the transferability of mechanical properties of materials.

This article describes the fatigue properties of particle-reinforced metal-matrix composites (PR-MMCs) in terms of mechanisms of crack initiation, fatigue life, and fatigue crack growth. It reviews specimen preparation and microscopic procedures that are used in fatigue testing of MMCs. It also describes the evaluation of the long fatigue crack growth behavior of MMCs by using the test methods and specimens that are used for unreinforced metallic alloys. Fractography of MMCs under plane-strain conditions is also described with information on the observed features of MMC fatigue fracture surfaces and their observation methods.

This article reviews the basic processes of fracture and fatigue and shows how these processes occur in materials. It presents an overview of the fatigue mechanisms and some related models for appropriate classes of materials, such as carbon and alloy steels, aluminum alloys, and titanium alloys. Microstructural factors that affect the fracture toughness of these materials, are discussed. The article describes fatigue crack propagation (FCP) mechanisms and related models. It also analyzes FCP behavior in these materials, with an emphasis on general microstructural factors.

Fitness-for-service assessment procedures can be used to assess the integrity, or remaining life, of components in service. Depending on the operating environment and the nature of the applied loading, a structure can fail by a number of different modes: brittle fracture, ductile fracture, plastic collapse, fatigue, creep, corrosion, and buckling. This article focuses on the broad categories of these failure modes: fracture, fatigue, environmental cracking, and high-temperature creep. It also discusses the benefits of a fitness-for-service approach.

This article provides an overview of fractography and explains how it is used in failure analysis. It reviews the basic types of fracture processes, namely, ductile, brittle, fatigue, and creep, principally in terms of fracture appearances, such as microstructure. The article also describes the general features of fatigue fractures in terms of crack initiation and fatigue crack propagation.

Failure of structural polymeric materials under cyclic application of stress or strain is a subject of industrial importance. The understanding of fatigue mechanisms (damage) and the development of constitutive equations for damage evolution, leading to crack initiation and propagation as a function of loading or displacement history, represent a fundamental problem for scientists and engineers. This article describes the approaches to predict fatigue life and discusses the difference between thermal and mechanical fatigue failure of polymers.

Engineering component and structure failures manifest through many mechanisms but are most often associated with fracture in one or more forms. This article introduces the subject of fractography and aspects of how it is used in failure analysis. The basic types of fracture processes (ductile, brittle, fatigue, and creep) are described briefly, principally in terms of fracture appearances. A description of the surface, structure, and behavior of each fracture process is also included. The article provides a framework from which a prospective analyst can begin to study the fracture of a component of interest in a failure investigation. Details on the mechanisms of deformation, brittle transgranular fracture, intergranular fracture, fatigue fracture, and environmentally affected fracture are also provided.