During autofrettage of a thick-wall steel pressure vessel, a crack developed through the wall of the component. Certain forged pressure vessels are subjected to autofrettage during their manufacture to induce residual compressive stresses at locations where fatigue cracks may initiate. The results of the autofrettage process, which creates a state of plastic strain in the material, is an increase in the fatigue life of the component. Analysis (visual inspection, 50x/500x unetched micrographs, and electron microprobe analysis) supports the conclusion that the fracture toughness of the steel was exceeded, and failure through the wall occurred because of the following reason: the high level of iron oxide found is highly abnormal in vacuum-degassed steels. Included matter of this nature (exogenous) most likely resulted from scale worked into the surface during forging. Therefore, it is understandable that failure occurred during autofrettage when the section containing these defects was subjected to plastic strains. Because the inclusions were sizable, hard, and extremely irregular, this region would effect substantial stress concentration. No recommendations were made.

A bracket which formed part of the carrier of a chain conveyor system used to transport components through a continuous oven fractured. A brittle crack originated on the inside of the right-angled bend, the surface having oxidized subsequently. The remaining portion of the fracture resulted from fatigue. Shallow oxidized regions adjacent to the inside surface of the bend indicated pre-existing cracks. A sulphur print on the edge of the bracket showed the material was rolled from a rimming steel ingot. The general appearance of the fracture, and the fact failure took place where embrittlement had developed following plastic straining and service at a temperature of 260 deg C (500 deg F) suggested that failure resulted from strain-age embrittlement.

Explosive cladding is a viable method for cladding different materials together, but the complicated behavior of materials under ballistic impacts raises the probability of interfacial shear failure. To better understand the relationship between impact energy and interfacial shear, investigators conducted an extensive study on the shear strength of explosively cladded Inconel 625 and plain carbon steel samples. They found that by increasing impact energy, the adhesion strength of the resulting cladding can be improved. Beyond a certain point, however, additional impact energy reduces shear strength significantly, causing the cladding process to fail. The findings reveal the decisive role of plastic strain localization and the associated development of microcracks in cladding failures. An attempt is thus made to determine the optimum cladding parameters for the materials of interest.

This article presents a failure analysis of an aluminum cylinder head on an automotive engine. During an endurance test, a crack initiated from the interior wall of a hole in the center of the cylinder head, then propagated through the entire thickness of the component. Metallurgical examination of the crack origin revealed that casting pores played a role in initiating the crack. Stress components, identified by finite element analysis, also played a role, particularly the stresses imposed by the bolt assembly leading to plastic strain. It was concluded that the failure can be prevented by eliminating the bolt hole, using a different type of bolt, or adjusting the fastening torque.

This article offers an overview of fatigue fundamentals, common fatigue terminology, and examples of damage morphology. It presents a summary of relevant engineering mechanics, cyclic plasticity principles, and perspective on the modern design by analysis (DBA) techniques. The article reviews fatigue assessment methods incorporated in international design and post construction codes and standards, with special emphasis on evaluating welds. Specifically, the stress-life approach, the strain-life approach, and the fracture mechanics (crack growth) approach are described. An overview of high-cycle welded fatigue methods, cycle-counting techniques, and a discussion on ratcheting are also offered. A historical synopsis of fatigue technology advancements and commentary on component design and fabrication strategies to mitigate fatigue damage and improve damage tolerance are provided. Finally, the article presents practical fatigue assessment case studies of in-service equipment (pressure vessels) that employ DBA methods.

Superelastic nitinol wires that fractured under various conditions were examined under a scanning electron microscope in order to characterize the fracture surfaces, produce reference data, and compare the findings with prior published work. The study revealed that nitinol fracture modes and morphologies are generally consistent with those of ductile metals, such as austenitic stainless steel, with one exception: Nitinol exhibits a unique damage mechanism under high bending strain, where damage occurs at the compression side of tight bends or kinks while the tensile side is unaffected. The damage begins as slip line formation due to plastic deformation, which progresses to cracking at high strain levels. The cracks appear to initiate from slip lines and extend in shear (mode II) manner.

The article commences with an overview of short-term and long-term mechanical properties of polymeric materials. It discusses plasticization, solvation, and swelling in rubber products. The article further describes environmental stress cracking and degradation of polymers. It illustrates how surface degradation of a plain strain tension specimen alters the ductile brittle transition in polyethylene creep rupture. The article concludes with information on the effects of temperature on polymer performance.

Microstructural examinations on transverse cross sections of a steam reformer tube, showed the presence of large macrovoids elongated in the radial direction and emanating from the internal surface of the tube. The macrovoids were located at the interdendritic regions, and were partially filled by a Mn-Fe bearing chromium oxide film. The areas adjacent to the oxide film were chemically depleted in C, Cr and Mn and rich in Fe and Ni. Associated with this depletion were a large concentration of microvoids. It was suggested that the dissolution of carbides in areas surrounding the macrovoids and the concentration of stresses at their tips, caused extensive localized plastic deformation which led to the formation of microvoids and subsequently to the spalling of the oxide film. The non-protective character of the film induced a progressive deterioration of the grain boundaries properties. Grain boundary sliding and dislocation motion were enhanced, causing a local increase in the steady state strain rate and the premature failure of the tube.

A gas-fired, ASTM A-106 Grade B carbon steel vaporizer failed on three different occasions during attempts to bring the vaporizer on line. Dye penetrant examination indicated the presence of multiple packets of ductile cracks on the inside of the coil radius at the bottom of the horizontal axis coils. Visual examination of the inside of the tubing indicated the presence of a carbonaceous deposit resulting from decomposition of the heat-exchanging fluid. Subsequent metallographic examination and microhardness testing indicated that the steel was heated to a temperature above the allowable operating temperature for the fluid. The probable cause for failure is thermal fatigue due to the localized overheating. Flow conditions inside the tubing should be reexamined to ensure suitable conditions for annular fluid flow.

Copper shortening has been found to occur in the rotor windings of turbo alternators and takes the form of a progressive reduction in the length of the coils leading to distortion of the end windings. The trouble results from the high loading which develops between successive layers of the strip conductor due to centrifugal force. This leads to a high frictional binding force between turns and prevents axial expansion under normal heating in service. Rotor trouble which proved to be due to copper shortening was found in a set rated at 27.5 MW. It was manufactured in 1934 at which time silver-bearing copper was not available. The use of hard-drawn silver-bearing copper for a rewind, in conjunction with special attention to blocking up the end windings, is confidently expected to effect a complete cure.

A 2–3 mm thick electroformed nickel mold showed early cracking under thermal load cycles. To determine the root cause, investigators obtained monotonic and cyclic properties of electroformed nickel at various temperatures and identified possible fatigue mechanisms. With the help of finite element modeling, they analyzed the material as well as the design and in-service application of the mold. They discovered that overconstraining the mold, while it was in service, caused excessive thermal stresses which accelerated crack initiation and propagation. Investigators also proposed remedies to prevent additional failures.

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.

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.

This article reviews the applied aspects of creep and stress-rupture failures. It discusses the microstructural changes and bulk mechanical behavior of classical and nonclassical creep behavior. The article provides a description of microstructural changes and damage from creep deformation, including stress-rupture fractures. It also describes metallurgical instabilities, such as aging and carbide reactions, and evaluates the complex effects of creep-fatigue interaction. The article concludes with a discussion on thermal fatigue and creep fatigue failures.

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.

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.

Distortion failure occurs when a structure or component is deformed so that it can no longer support the load it was intended to carry. Every structure has a load limit beyond which it is considered unsafe or unreliable. Estimation of load limits is an important aspect of design and is commonly computed by classical design or limit analysis. This article discusses the common aspects of failure by distortion with suitable examples. Analysis of a distortion failure often must be thorough and rigorous to determine the root cause of failure and to specify proper corrective action. The article summarizes the general process of distortion failure analysis. It also discusses three types of distortion failures that provide useful insights into the problems of analyzing unusual mechanisms of distortion. These include elastic distortion, ratcheting, and inelastic cyclic buckling.

Distortion often is observed in the analysis of other types of failures, and consideration of the distortion can be an important part of the analysis. This article first considers that true distortion occurs when it was unexpected and in which the distortion is associated with a functional failure. Then, a more general consideration of distortion in failure analysis is introduced. Several common aspects of failure by distortion are discussed and suitable examples of distortion failures are presented for illustration. The article provides information on methods to compute load limits, errors in the specification of the material, and faulty process and their corrective measures to meet specifications. It discusses the general process of material failure analysis and special types of distortion and deformation failure.

X-ray diffraction (XRD) residual-stress analysis is an essential tool for failure analysis. This article focuses primarily on what the analyst should know about applying XRD residual-stress measurement techniques to failure analysis. Discussions are extended to the description of ways in which XRD can be applied to the characterization of residual stresses in a component or assembly and to the subsequent evaluation of corrective actions that alter the residual-stress state of a component for the purposes of preventing, minimizing, or eradicating the contribution of residual stress to premature failures. The article presents a practical approach to sample selection and specimen preparation, measurement location selection, and measurement depth selection; measurement validation is outlined as well. A number of case studies and examples are cited. The article also briefly summarizes the theory of XRD analysis and describes advances in equipment capability.

A pipe in the lateral wall of a boiler powering an aircraft carrier flat-top boat failed during a test at sea. The pipe was made from ASTM 192 steel, an adequate material for the application. Microstructural analysis along with equipment operating records provided valuable insight into what caused the pipe to rupture. Although the pipe had been replaced just 50 h before the accident, the analysis revealed incrustations and corrosion pits on the inner walls and oxidation on the outer walls. Microstructural changes were also observed, indicating that the steel was exposed to high temperatures. The combined effect of pitting, incrustations, and phase transformations caused the pipe to rupture.