The main objective for the study of combined-stress fatigue is to obtain fatigue data for axles and to find the criterion for fatigue limit under combined stress. This article begins with a description of the stress states of combined stress and stress fields near crack tips. It provides an account of the various biaxial and multiaxial fatigue testing methods, specimen geometries, and stress intensity factors important in the study multiaxial fatigue. Widely used test methods are the torsion-rotating bending fatigue test and biaxial and triaxial fatigue tests. Common specimen geometries include rectangular plate specimens, cruciform specimens, compact tension shear specimens, compact shear specimens, mode II crack growth specimen, circumferentially notched cylindrical specimens, tubular specimens containing a slit, and solid cylindrical specimens containing a small hole or initial crack.

This article is an atlas of fractographs that helps in understanding the causes and mechanisms of fracture of medium-carbon steels and in identifying and interpreting the morphology of fracture surfaces. The fractographs illustrate the torsional-fatigue fracture, cup and cone tensile fracture, brittle fracture, and in-service rotary bending fatigue fracture of fractured roof-truss angles, pressure-vessel shells, automotive axle shafts, broken keyed spindles, crane gears, blooming-mill spindles, automotive bolts, and crane wheels of these steels.

This article reviews the common methods of shear and multiaxial testing for the evaluation of engineering components such as fasteners and mill products. It discusses shear test methods, including through-thickness tests, in-plane shear tests, and double-notched shear test. The article provides information on torsional (rotational shear) tests as well as the basic equipment and setup of torsion testing. Motors, twist and torque transducers, torque sensors, and heating systems as well as the specimen preparation procedure are also discussed.

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 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 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.

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 common types of automotive and truck axle shafts. It provides information on steels used for induction-hardened shafts, and on the manufacturing and induction hardening methods of axle shafts. The article discusses the effects of case depth, shaft length, and carbon content on torsional properties of axle shafts, and the effect of changes in shaft diameter and those of splines on torsional shaft performance. It also provides useful information on straightening and tempering of induction-hardened axle shafts, and describes an effective technique to ensure quality of induction-hardened axle shafts.

Fatigue failure of engineering components and structures results from progressive fracture caused by cyclic or fluctuating loads. Fatigue is an important potential cause of mechanical failure, because most engineering components or structures are or can be subjected to cyclic loads during their lifetime. This article focuses on fractography of fatigue. It provides an abbreviated summary of fatigue processes and mechanisms: fatigue crack initiation, fatigue crack propagation, and final fracture,. Characteristic fatigue fracture features that can be discerned visually or under low magnification are then described. Typical microscopic features observed on structural metals are presented subsequently, followed by a brief discussion on fatigue in polymers and polymer-matrix composites.

This article commences with a summary of fatigue processes and mechanisms. It focuses on fractography of fatigue. Characteristic fatigue fracture features that can be discerned visually or under low magnification are described. Typical microscopic features observed on structural metals are presented subsequently, followed by a brief discussion of fatigue in nonmetals. The article reviews the various macroscopic and microscopic features to characterize the history and growth rate of fatigue in metals. It concludes with a description of fatigue of polymers and composites.

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.

This article discusses the common causes of failures of springs, with illustrations. Design deficiencies, material defects, processing errors or deficiencies, and unusual operating conditions are the common causes of spring failures. In most cases, these causes result in failure by fatigue. The article describes the operating conditions of springs, common failure mechanisms, and presents an examination of the failures that occur in springs.

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.

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.