The truck beam of the left main landing gear (MGL) of a Boeing 707 airplane collapsed on the ground just after the aircraft was unloaded and refueled. The investigation revealed that failure was caused by the propagation of an intergranular crack originating from the bottom of the pit. The crack reached the critical size and caused failure by stress-corrosion cracking (SCC) under static loading conditions in service. The failed beam was protected by a well adhering paint system. However, the presence of adequate amounts of corrosion preventive compound films (CPC) on the surfaces of the failed beam could not be conclusively established because of the long term service exposure and presence of lubricants.

This article provides an overview of the electrochemical nature of corrosion and analyzes corrosion-related failures. It describes corrosion failure analysis and discusses corrective and preventive approaches to mitigate corrosion-related failures of metals. These include: change in the environment; change in the alloy or heat treatment; change in design; use of galvanic protection; use of inhibitors; use of nonmetallic coatings and liners; application of metallic coatings; use of surface treatments, thermal spray, or other surface modifications; corrosion monitoring; and preventive maintenance.

Corrosion is the deterioration of a material by a reaction of that material with its environment. The realization that corrosion control can be profitable has been acknowledged repeatedly by industry, typically following costly business interruptions. This article describes the electrochemical nature of corrosion and provides the typical analysis of environmental- and corrosion-related failures. It presents common methods of testing of laboratory corrosion and discusses the processes involved in the prevention of environmental- and corrosion-related failures of metals and nonmetals.

Hydrogen damage is a term used to designate a number of processes in metals by which the load-carrying capacity of the metal is reduced due to the presence of hydrogen. This article introduces the general forms of hydrogen damage and provides an overview of the different types of hydrogen damage in all the major commercial alloy systems. It covers the broader topic of hydrogen damage, which can be quite complex and technical in nature. The article focuses on failure analysis where hydrogen embrittlement of a steel component is suspected. It provides practical advice for the failure analysis practitioner or for someone who is contemplating procurement of a cost-effective failure analysis of commodity-grade components suspected of hydrogen embrittlement. Some prevention strategies for design and manufacturing problem-induced hydrogen embrittlement are also provided.

This article provides an overview of the classification of hydrogen damage. Some specific types of the damage are hydrogen embrittlement, hydrogen-induced blistering, cracking from precipitation of internal hydrogen, hydrogen attack, and cracking from hydride formation. The article focuses on the types of hydrogen embrittlement that occur in all the major commercial metal and alloy systems, including stainless steels, nickel-base alloys, aluminum and aluminum alloys, titanium and titanium alloys, copper and copper alloys, and transition and refractory metals. The specific types of hydrogen embrittlement discussed include internal reversible hydrogen embrittlement, hydrogen environment embrittlement, and hydrogen reaction embrittlement. The article describes preservice and early-service fractures of commodity-grade steel components suspected of hydrogen embrittlement. Some prevention strategies for design and manufacturing problem-induced hydrogen embrittlement are also reviewed.

The phenomenon of on-load corrosion is directly associated with the production of magnetite on the water-side surface of boiler tubes. On-load corrosion may first be manifested by the sudden, violent rupture of a boiler tube, such failures being found to occur predominantly on the fire-side surface of tubes situated in zones exposed to radiant heat where high rates of heat transfer pertain. In most instances, a large number of adjacent tubes are found to have suffered, the affected zone frequently extending in a horizontal band across the boiler. In some instances, pronounced local attack has taken place at butt welds in water-wall tubes, particularly those situated in zones of high heat flux. To prevent on-load corrosion an adequate flow of water must occur within the tubes in the susceptible regions of a boiler. Corrosion products and suspended matter from the pre-boiler equipment should be prevented from entering the boiler itself. Also, it is good practice to reduce as far as possible the intrusion of weld flash and other impedances to smooth flow within the boiler tubes.

This article describes the two critical goals in a failure investigation: damage mechanisms and damage modes. It explains the determination of primary and secondary damage mechanisms and discusses the methodology used to classify the damage mechanisms.

The principal task of a failure analyst during a physical-cause investigation is to identify the sequence of events involved in the failure. Technical skills and tools are required for such identification, but the analyst also needs a mental organizational framework that helps evaluate the significance of observations. This article discusses the processes involved in the characterization and identification of damage and damage mechanisms. It describes the relationships between damage causes, mechanisms, and modes with examples. In addition, some of the more prevalent and encompassing characterization approaches and categorization methods of damage mechanism are also covered.

Polymer materials are key building blocks of the modern world, commonly used in packaging, automobiles, building materials, electronics, telecommunications, and many other industries. These commercial applications of polymeric materials would not be possible without the use of additives. This article is divided into five sections: mechanical property modifiers, physical property modifiers, biological function modifiers, processing aids, and colorants. It describes three classes of additives that are used to inhibit biological activity, six classes of mechanical property modifiers, three classes of physical property modifiers, and two classes of both colorants and processing aids.

Erosion occurs as the result of a number of different mechanisms, depending on the composition, size, and shape of the eroding particles; their velocity and angle of impact; and the composition of the surface being eroded. This article describes the erosion of ductile and brittle materials with the aid of models and equations. It presents three examples of erosive wear failures, namely, abrasive erosion, erosion-corrosion, and cavitation erosion.

Failures in boilers and other equipment taking place in power plants that use steam as the working fluid are discussed in this article. The discussion is mainly concerned with failures in Rankine cycle systems that use fossil fuels as the primary heat source. The general procedure and techniques followed in failure investigation of boilers and related equipment are discussed. The article is framed with an objective to provide systematic information on various damage mechanisms leading to the failure of boiler tubes, headers, and drums, supplemented by representative case studies for a greater understanding of the respective damage mechanism.

This article first provides an overview of the types of mechanical fasteners. This is followed by sections providing information on fastener quality and counterfeit fasteners, as well as fastener loads. Then, the article discusses common causes of fastener failures, namely environmental effects, manufacturing discrepancies, improper use, or incorrect installation. Next, it describes fastener failure origins and fretting. Types of corrosion in threaded fasteners and their preventive measures are then covered. The performance of fasteners at elevated temperatures is addressed. Further, the article discusses the types of rivet, blind fastener, and pin fastener failures. Finally, it provides information on the mechanism of fastener failures in composites.

Erosion is the progressive loss of original material from a solid surface due to mechanical interaction between that surface and a fluid, a multicomponent fluid, an impinging liquid, or impinging solid particles. The detrimental effects of erosion have caused problems in a number of industries. This article describes the processes involved in erosion of ductile materials, brittle materials, and elastomers. Some examples of erosive wear failures are given on abrasive erosion, liquid impingement erosion, cavitation, and erosion-corrosion. In addition, the article provides information on the selection of materials for applications in which erosive wear failures can occur.

This article discusses different types of mechanical fasteners, including threaded fasteners, rivets, blind fasteners, pin fasteners, special-purpose fasteners, and fasteners used with composite materials. It describes the origins and causes of fastener failures and with illustrative examples. Fatigue fracture in threaded fasteners and fretting in bolted machine parts are also discussed. The article provides a description of the different types of corrosion, such as atmospheric corrosion and liquid-immersion corrosion, in threaded fasteners. It also provides information on stress-corrosion cracking, hydrogen embrittlement, and liquid-metal embrittlement of bolts and nuts. The article explains the most commonly used protective metal coatings for ferrous metal fasteners. Zinc, cadmium, and aluminum are commonly used for such coatings. The article also illustrates the performance of the fasteners at elevated temperatures and concludes with a discussion on fastener failures in composites.

Fretting is a wear phenomenon that occurs between two mating surfaces; initially, it is adhesive in nature, and vibration or small-amplitude oscillation is an essential causative factor. Fretting generates wear debris, which oxidizes, leading to a corrosion-like morphology. This article focuses on fretting wear related to debris formation and ejection. It reviews the general characteristics of fretting wear, with an emphasis on steel. The review covers fretting wear in mechanical components, various parameters that affect fretting; quantification of wear induced by fretting; and the experimental results, map approach, measurement, mechanism, and prevention of fretting wear. This review is followed by several examples of failures related to fretting wear.

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.

This article reviews the general characteristics of fretting wear in mechanical components with an emphasis on steel. It focuses on the effects of physical variables and the environment on fretting wear. The variables include the amplitude of slip, normal load, frequency of vibration, type of contact and vibration, impact fretting, surface finish, and residual stresses. The form, composition, and role of the debris are briefly discussed. The article also describes the measurement, mechanism, and prevention of fretting wear. It concludes with several examples of failures related to fretting wear.

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 explains the main types and characteristic causes of failures in boilers and other equipment in stationary and marine power plants that use steam as the working fluid with examples. It focuses on the distinctive features of each type that enable the failure analyst to determine the cause and suggest corrective action. The causes of failures include tube rupture, corrosion or scaling, fatigue, erosion, and stress-corrosion cracking. The article also describes the procedures for conducting a failure analysis.