The design of components against fatigue failure may involve several considerations of irregular loading, variable temperature, and environment. This article focuses on design considerations against fatigue related to material performance under mechanical loading at constant temperature. It reviews the traditional methods of fatigue design on smooth and notched components. The article discusses high-cycle fatigue in terms of fatigue strength and tensile strength, mean stress effects, stress concentration, and multiaxial fatigue. It describes low-cycle fatigue in terms of deformation behavior and concludes with a discussion on lifetime analysis based on a strain approach.

Fatigue failures may occur in components subjected to fluctuating (time-dependent) loading as a result of progressive localized permanent damage described by the stages of crack initiation, cyclic crack propagation, and subsequent final fracture after a given number of load fluctuations. This article begins with an overview of fatigue properties and design life. This is followed by a description of the two approaches to fatigue, namely infinite-life criterion and finite-life criterion, along with information on damage tolerance criterion. The article then discusses the characteristics of fatigue fractures followed by a discussion on the effects of loading and stress distribution, and material condition on the microstructure of the material. In addition, general prevention and characteristics of corrosion fatigue, contact fatigue, and thermal fatigue are also presented.

This article describes the tests for the common types of fabricated components and modeling of metal deformation. It provides an overview of component testing and briefly reviews the relationship of mechanical properties in the process of mechanical design for static loads, cyclic loads, dynamic loads, and high-temperature materials. The article describes the general properties related to monotonic stress-strain behavior of steels. It also discusses materials properties and operating stresses as well as other factors, such as part shape and environmental effects, which play significant roles in the design process of components.

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.

The principal types of elevated-temperature mechanical failure are creep and stress rupture, stress relaxation, low- and high-cycle fatigue, thermal fatigue, tension overload, and combinations of these, as modified by environment. This article briefly reviews the applied aspects of creep-related failures, where the mechanical strength of a material becomes limited by creep rather than by its elastic limit. The majority of information provided is applicable to metallic materials, and only general information regarding creep-related failures of polymeric materials is given. The article also reviews various factors related to creep behavior and associated failures of materials used in high-temperature applications. The complex effects of creep-fatigue interaction, microstructural changes during classical creep, and nondestructive creep damage assessment of metallic materials are also discussed. The article describes the fracture characteristics of stress rupture. Information on various metallurgical instabilities is also provided. The article presents a description of thermal-fatigue cracks, as distinguished from creep-rupture cracks.

This article describes the phenomena of crack initiation and early growth. It examines specimen design and preparation as well as the apparatus used in crack initiation testing. The article provides descriptions of the various commercially available fatigue testing machines: axial fatigue testing machines and bending fatigue machines. Load cells, grips and alignment devices, extensometry and strain measuring devices, environmental chambers, graphic recorders, furnaces, and heating systems of ancillary equipment are discussed. The article presents technologies available to accomplish closed loop control of materials testing systems in performing standard materials tests and for the development of custom testing applications. It explores the advanced software tools for materials testing. The article includes a description of baseline isothermal fatigue testing, creep-fatigue interaction, and thermomechanical fatigue. The effects of various variables on fatigue resistance and guidelines for fatigue testing are also presented.

This article discusses stress relaxation testing on metallic materials, as covered by ASTM E 328. It reviews the two types of stress relaxation tests performed in tension, long-term and accelerated testing. The article illustrates load characteristics and data representation for stress relaxation testing used for the most convenient and common uniaxial tensile test. It concludes with information on compression testing, bend testing, torsion testing, and tests on springs.

An integral aspect of designing and material selection is the use of mechanical properties derived from various mechanical testing. This article introduces the basic concepts of mechanical design and its relation with the properties derived from various mechanical testings, namely, tensile, compressive, hardness, torsion and bend, shear load, shock, and fatigue and creep testings. It describes the design criteria for combined properties derived from each of the mechanical testing. The article concludes with a discussion on the effect of environment on the mechanical properties.

This article provides information on the typical experimental observations of formation and propagation of small fatigue cracks under various stress states and explores the relation to long crack fracture mixed-mode fracture mechanics. It discusses state I crystallographic and stage II normal stress-dominated growth, along with some observations regarding the influence of combined stress state on the propagation of small cracks. The article discusses the differences between low-cycle fatigue and high-cycle fatigue (HCF) behaviors. Several other features of multiaxial fatigue are also explained, including mean stress effects, sequences of stress/strain amplitude or stress state, nonproportional loading and cycle counting, and HCF fatigue limits. In addition, the article covers the formation and propagation of cracks on the order of several grain sizes in diameter in initially isotropic and ductile structural alloys.

The process of fatigue failure consists of three stages: initial fatigue damage leading to crack initiation; crack propagation to some critical size; and final, sudden fracture of the remaining cross section. Variations in mechanical properties, composition, microstructure, and macrostructure, along with their subsequent effects on fatigue life, have been studied extensively to aid in the appropriate selection of steel to meet specific end-use requirements. The metallurgical variables having the most pronounced effects on the fatigue behavior of carbon and low-alloy steels are strength, ductility, cleanliness, residual stresses, surface conditions, and aggressive environments. The article discusses the stress-based and strain-based approach to fatigue. The application of fatigue data in engineering design is complicated by the characteristic scatter of fatigue data; variations in surface conditions of actual parts; variations in manufacturing processes such as bending, forming, and welding; and the uncertainty of environmental and loading conditions in service.

Life assessment of structural components is used to avoid catastrophic failures and to maintain safe and reliable functioning of equipment. The failure investigator's input is essential for the meaningful life assessment of structural components. This article provides an overview of the structural design process, the failure analysis process, the failure investigator's role, and how failure analysis of structural components integrates into the determination of remaining life, fitness-for-service, and other life assessment concerns. The topics discussed include industry perspectives on failure and life assessment of components, structural design philosophies, the role of the failure analyst in life assessment, and the role of nondestructive inspection. They also cover fatigue life assessment, elevated-temperature life assessment, fitness-for-service life assessment, brittle fracture assessments, corrosion assessments, and blast, fire, and heat damage assessments.

This article describes three design-life methods or philosophies of fatigue, namely, infinite-life, finite-life, and damage tolerant. It outlines the three stages in the process of fatigue fracture: the initial fatigue damage leading to crack initiation, progressive cyclic growth of crack, and the sudden fracture of the remaining cross section. The article discusses the effects of loading and stress distribution on fatigue cracks, and reviews the fatigue behavior of materials when subjected to different loading conditions such as bending and loading. The article examines the effects of load frequency and temperature, material condition, and manufacturing practices on fatigue strength. It provides information on subsurface discontinuities, including gas porosity, inclusions, and internal bursts as well as on corrosion fatigue testing to measure rates of fatigue-crack propagation in different environments. The article concludes with a discussion on rolling-contact fatigue, macropitting, micropitting, and subcase fatigue.

This article provides an overview of the structural design process and discusses the life-limiting factors, including material defects, fabrication practices, and stress. It details the role of a failure investigator in performing nondestructive inspection. The article provides information on fatigue life assessment, elevated-temperature life assessment, and fitness-for-service life assessment.

A wide range of mechanical properties can be obtained with a given composition of cast iron, depending on the microstructural constituents that form during solidification and subsequent solid-state processing. This article discusses the mechanical properties of gray iron and provides some general property comparisons with malleable, ductile (nodular), and compacted graphite irons. The mechanical properties of gray iron are determined by the combined effects of its chemical composition, processing technique in the foundry, and cooling rates during solidification. The article provides information on the classification of gray irons based on ASTM International specification A48/A48M. It discusses the loading effect, surface effect, notch sensitivity, and environmental effect on the mechanical properties of gray iron. The chemical composition ranges of some of the more widely used heat-resistant gray irons suitable for elevated-temperature service are presented in a table.

This article summarizes the general fatigue and fracture properties of cast steels, namely, toughness, fatigue, and component design factors such as section size and discontinuities. It describes the various factors that influence fatigue of cast steels. These factors include section size, defect size, stress modes, and waveform types. The article discusses various fracture mechanics in cast steels: cyclic stress-strain behavior and low- and high-cycle fatigue life behavior; plane-stress fracture toughness; plane-strain fracture toughness; constant-amplitude fatigue crack initiation and growth; and variable-amplitude fatigue crack initiation and growth.

In addition to failures in shafts, this article discusses failures in connecting rods, which translate rotary motion to linear motion (and conversely), and in piston rods, which translate the action of fluid power to linear motion. It begins by discussing the origins of fracture. Next, the article describes the background information about the shaft used for examination. Then, it focuses on various failures in shafts, namely bending fatigue, torsional fatigue, axial fatigue, contact fatigue, wear, brittle fracture, and ductile fracture. Further, the article discusses the effects of distortion and corrosion on shafts. Finally, it discusses the types of stress raisers and the influence of changes in shaft diameter.

This article focuses on the isothermal fatigue of solder materials. It discusses the effect of strain range, frequency, hold time, temperature, and environment on isothermal fatigue life. The article provides information on various isothermal fatigue testing methods used to assess solder joint reliability. These include the accelerated thermal cycling test and isothermal mechanical deflection system test.

Analysis of the failure of a metal structure or part usually requires identification of the type of failure. Failure can occur by one or more of several mechanisms, including surface damage (such as corrosion or wear), elastic or plastic distortion, and fracture. This leads to a wide range of failures, including fatigue failure, distortion failure, wear failure, corrosion failure, stress-corrosion cracking, liquid-metal embrittlement, hydrogen-damage failure, corrosion-fatigue failure, and elevated-temperature failure. This article describes the classification of fractures on a macroscopic scale as ductile fractures, brittle fractures, fatigue fractures, and fractures resulting from the combined effects of stress and environment.

This article discusses failures in shafts such as connecting rods, which translate rotary motion to linear motion, and in piston rods, which translate the action of fluid power to linear motion. It describes the process of examining a failed shaft to guide the direction of failure investigation and corrective action. Fatigue failures in shafts, such as bending fatigue, torsional fatigue, contact fatigue, and axial fatigue, are reviewed. The article provides information on the brittle fracture, ductile fracture, distortion, and corrosion of shafts. Abrasive wear and adhesive wear of metal parts are also discussed. The article concludes with a discussion on the influence of metallurgical factors and fabrication practices on the fatigue properties of materials, as well as the effects of surface coatings.