Search Results for fatigue

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.

Thermomechanical fatigue (TMF) refers to the process of fatigue damage under simultaneous changes in temperature and mechanical strain. This article reviews the process of TMF with a practical example of life assessment. It describes TMF damages caused due to two possible types of loading: in-phase and out-of-phase cycling. The article illustrates the ways in which damage can interact at high and low temperatures and the development of microstructurally based models in parametric form. It presents a case study of the prediction of residual life in a turbine casing of a ship through stress analysis and fracture mechanics analyses of the casing.

A major cause of failure in components subjected to rolling or rolling/sliding contacts is contact fatigue. This article focuses on the rolling contact fatigue (RCF) performance and failure modes of overlay coatings such as those deposited by physical vapor deposition, chemical vapor deposition, and thermal spraying (TS). It provides a background to RCF in bearing steels in order to develop an understanding of failure modes in overlay coatings. The article describes the underpinning failure mechanisms of TiN and diamond-like carbon coatings. It presents an insight into the design considerations of coating-substrate material properties, coating thickness, and coating processes to combat RCF failure in TS coatings.

Rolling-contact fatigue (RCF) is a surface damage process due to the repeated application of stresses when the surfaces of two bodies roll on each other. This article briefly describes the various surface cracks caused by manufacturing processing faults or blunt impact loads on ceramic balls surfaces. It discusses the propagation of fatigue cracks involved in rolling contacts. The characteristics of various types of RCF test machines are summarized. The article concludes with a discussion on the various failure modes of silicon nitride in rolling contact. These include the spalling fatigue failure, the delamination failure, and the rolling-contact wear.

This article discusses the fundamental variables involved in fatigue-life assessment, which describe the effects and interaction of material behavior, geometry, and stress history on the life of a component. It compares the safe-life approach with the damage-tolerance approach, which employs the stress-life method of fatigue life assessment. The article examines the behavior of three different metallic materials used in the design and manufacture of structural components: steel, aluminum, and titanium. It also reviews the effects of retardation and spectrum load on component life. The article concludes with case studies of fatigue life assessment from the aerospace industry.

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 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 ASTM standard definitions for fatigue and describes the approaches that are used to design finite or infinite life, used in a complementary sense in fatigue design. It explains four distinct phases of fatigue: nucleation, structurally dependent crack propagation, crack propagation, and final instability. The article discusses the significant role that fatigue plays in industrial design applications.

There are two parts to deal with uncertainty in fatigue design: determining the distributions of possible values for all uncertain inputs and calculating the probability of failure due to all the uncertain inputs. This article discusses the sources of uncertainty in a fatigue analysis, such as the material properties, distribution of applied stress levels within a given environment, environments or loading intensities, and modeling or prediction. It presents a probabilistic approach for analyzing the uncertainties and determining the level of reliability (probability of failure).

This article provides information on the nominal compositions of high-carbon bearing steels and carburizing bearing steels. It discusses the bearing fundamentals with emphasis on surface contact, stresses, and fatigue life of bearings. The article describes bearing life prediction using three factors, namely, reliability, material, and application. It analyzes the bearing damage modes and concludes with information on fatigue failure considerations.

Copper alloys are classified by the International Unified Numbering System designations to identify alloy groups by major alloying element. This article presents the designations and compositions of various copper alloys, such as brasses, nickel silvers, bronzes, beryllium coppers, and spinodal alloys. It discusses the fatigue testing of the copper alloys and tabulates the tensile and fatigue strengths of the copper alloys. The article schematically illustrates S-N curves for the solid-solution (non-aging) strengthened alloys. It concludes with a discussion on the role of microstructure in the fatigue performance of beryllium copper alloys.

This article discusses the failure mechanism of springs. It describes the critical application factors that affect spring fatigue performance. These include: material type and strength; stress conditions; surface quality; manufacturing processes; rate of application of load; and embrittlement or cracking. The article summarizes the methods of statistical analysis of S-N data for general comparisons of fatigue strength of spring steels. The fatigue performance of springs is illustrated by Goodman diagrams. The article also exemplifies the examination of failed springs.

This article describes a scientific approach to the planning and evaluation of fatigue tests based on the determination of probabilities for detected fracture positions within the observed range of fatigue scatter. It schematically illustrates a constant-amplitude stress cycling about a possible mean load that leads to the fracture of a single part or specimen. The article discusses the evaluation of the range of transition and of the finite-endurance range for fatigue curves. It concludes with a discussion on extrapolation from the range of finite endurance into the range of transition.

This article presents an overview of fatigue crack nucleation from the point of view of the material microstructure and its evolution during cycling. It describes the sites of microcrack nucleation at the free surfaces. The article discusses the relation of dislocation structures and surface relief and reviews the mechanisms of crack nucleation. The damage of material due to crack nucleation, the extent (in terms of the number of cycles) of the nucleation stage, and the factors influencing crack nucleation are discussed.

This article focuses on the corrosion fatigue testing of steel in high-temperature water and discusses critical experimental issues associated with it. It provides information on the fundamental aspects of environmental crack advancement in general. The article explains the concepts and role of environmentally assisted crack growth in corrosion fatigue. It also discusses the fatigue test methods, including crack initiation testing and crack propagation testing. The article describes the specific types and influence rankings of experimental variables in corrosion fatigue.

This article presents an approach to characterize the effects of surface treatments to enhance fatigue properties, with particular concern for wear, corrosion, and thermal effects. It discusses the considerations in selecting fabrication or subsequent surface processing procedures to improve fatigue resistance in terms of their respective effects on fatigue performance. The article details the experimental data sets representing specific materials, typical test geometries, and a range of different processing methods used to enhance resistance as compared to results for laboratory tests.

This article summarizes the fatigue and fracture resistance of selected magnesium alloys. It reviews the effects of surface condition and test variables on fatigue strength. The article also provides an overview of the fatigue crack growth, fracture toughness, and stress-corrosion cracking of magnesium alloys.

This article discusses the various options for controlling fatigue and fractures in welded steel structures, with illustrations. It describes the factors that influence them the most. The article details some of the leading codes and standards for designing against failure mechanisms. Codes are presented for fitness-for-service and standards for fatigue and fracture control.

This article describes the test techniques that are available for monitoring crack initiation and crack growth and for obtaining information on fatigue damage in test specimens. These techniques include optical methods, the compliance method, electric potential measurement, and gel electrode imaging methods. The article discusses the magnetic techniques that are primarily used as inspection techniques for detecting fatigue cracks in structural components. It details the principles and operation procedures of the liquid penetrant methods, positron annihilation techniques, acoustic emission techniques, ultrasonic methods, eddy current techniques, infrared techniques, exoelectron methods, and gamma radiography. The article explains the microscopy methods used to determine fatigue crack initiation and propagation. These include electron microscopy, scanning tunneling microscopy, atomic force microscopy, and scanning acoustic microscopy. The article also reviews the X-ray diffraction technique used for determining the compositional changes, strain changes, and residual stress evaluation during the fatigue process.

Fretting is a special wear process that occurs at the contact area between two materials under load and subject to slight relative movement by vibration or some other force. This article focuses on measures to avoid or minimize crack initiation and fretting fatigue. It lists the factors that are known to influence the severity of fretting and discusses the variables that contribute to shear stresses. These variables include normal load, relative displacement (slip amplitude), and coefficient of friction. The article describes the general geometries and loading conditions for fretting fatigue. It presents the types of fretting fatigue tests and the effect of variables on fretting fatigue from different research test programs. The article also lists the general principles and practical methods for the abatement or elimination of fretting fatigue.