This article commences with a brief introduction on the hardenability of carburized steels, and then reviews the factors used in the selection of carburizing steels and heat treatment methods. The factors include quench medium, stress considerations, case depth, and type of case. The article provides information on steels for carburized gears with emphasis on gear design requirements, selection process, selection of carbon content, case and core hardness, microstructure, and toughness and short-cycle fatigue.

Gears can fail in many different ways, and except for an increase in noise level and vibration, there is often no indication of difficulty until total failure occurs. This article reviews the major types of gears and the basic principles of gear-tooth contact. It discusses the loading conditions and stresses that effect gear strength and durability. The article provides information on different gear materials, the common types and causes of gear failures, and the procedures employed to analyze them. Finally, it presents a chosen few examples to illustrate a systematic approach to the failure examination.

Honeycomb-cored sandwich panels increase part stiffness at a lower weight than monolithic composite materials. This article illustrates an area of a honeycomb-cored sandwich structure composite cross section that is viewed using transmitted polarized light. This area shows the differences in the constituents and resin intermingling. The article discusses the factors that govern the honeycomb core movement and honeycomb core crush, with illustrations. Some common tests performed on honeycomb composites to characterize the skin-to-core bond strength are the climbing drum peel and flatwise tensile tests. The article concludes with a description on the reasons for core failure, which are analyzed after these tests.

This article discusses the various elements of thread grinding processes, including thread grinding machines, tolerances, wheel selection, grinding speed, and grinding fluids. It describes truing of grinding wheels and reviews the process applications. In addition, the article describes the five basic methods employed for cylindrical thread grinding, namely, single-rib wheel traverse grinding, multirib wheel traverse grinding, multirib wheel plunge grinding, multirib wheel skip-rib, or alternate-rib, grinding, and multirib wheel three-rib grinding. It also provides an overview of centerless grinding of threads and high-volume applications of thread grinding.

A sandwich structure is comprised of layered composite materials formed by bonding two or more thin facings or facesheets to a relatively thick core material. This article describes the sandwich panel failure modes. It tabulates the nomenclature and definitions for loads, geometry, and material properties. The article illustrates critical strength-check locations for a flat sandwich panel. It discusses the analysis methods formulated for flat rectangular honeycomb panels; curved sandwich panel; and for each of the various sandwich panel failure modes. The article concludes with a discussion on flat panel stability analysis methods.

Case hardening involves various methods and each method has unique characteristics and different considerations in the selection of steels This article reviews the various grades of carburizing steels, carbonitriding steels, nitriding steels, and steels for induction, or flame hardening. This review is based on their process characteristics, compositions, applications, and mechanical properties, which help in selecting steels for case hardening.

The mechanism of contact fatigue can be understood in terms of several sources of stress concentration, or stress raisers, within the macroscopic Hertzian stress field. This article focuses primarily on rolling contact fatigue of hardened bearing steels. It discusses Hertzian shear stresses at and below the contact surfaces and briefly summarizes bearings and gear characteristics. The article provides an overview of the key types of gear and bearing steels. It analyzes two types of macropitting that result from the subsurface growth of fatigue cracks, namely, subsurface-origin macropitting and surface-origin macropitting. The article describes the factors influencing contact fatigue life of hardened steel bearings and gears, including hardness, inclusions, carbides, and residual stresses.

This article describes the microstructure, properties, and performance of carburized steels, and elucidates the microstructural gradients associated with carbon and hardness gradients. It provides information on case depth measurement, the factors affecting case depth, and the formation and causes of microcracks. The article discusses the effects of alloying elements on hardenability, the effects of excessive retained austenite and massive carbides on fatigue resistance, the effects of residual stresses and internal oxidation on fatigue performance of carburized steels. In addition, the causes of intergranular fracture at austenite grain boundaries and their prevention methods are explored. The article also describes the major mechanisms of bending fatigue crack initiation in carburized steels.

Honeycomb is a product consisting of very thin sheets attached to form connecting cells. This article briefly explains the construction, core characteristics, properties, and testing methods of the honeycomb structures. It discusses the special processes carried out in customizing the shape of core to fit customer's specific needs. The article provides information on the basic concept of creating sandwich structures and its corresponding aspects like material selection, design guidelines, and structural efficiency.

Refractory metals are extracted from ore concentrates or scrap, processed into intermediate chemicals, and then reduced to metal, usually in powder form. This article discusses the raw materials needed and the processing steps for producing pure and alloyed refractory metal powders. The effects of processing conditions on the physical and chemical properties of tungsten, molybdenum, tantalum, niobium, and rhenium powders are reviewed.

Lightweight structural cores are used on aircrafts to reduce weight and increase payload and fight distance. This article discusses the classification of lightweight structural cores, namely, honeycomb, balsa, and foam. It reviews the four primary manufacturing methods used to produce honeycomb: adhesive bonding and expansion, corrugation and adhesive bonding, corrugation and braze welding, and extrusion. The article describes cell configuration and properties of honeycomb. It discusses the factors influencing specification of structural cores, including materials, size, density, mechanical properties, environmental compatibility, formability, durability, and thermal behavior. The article provides information on the benefits and concepts of a sandwich panel containing lightweight structural cores.

Engineered components fail predominantly in four major ways: fracture, corrosion, wear, and undesirable deformation (i.e., distortion). Typical fracture mechanisms feature rapid crack growth by ductile or brittle cracking; more progressive (subcritical) forms involve crack growth by fatigue, creep, or environmentally-assisted cracking. Corrosion and wear are another form of progressive material alteration or removal that can lead to failure or obsolescence. This article primarily covers the topic of abrasive wear failures, covering the general classification of wear. It also discusses methods that may apply to any form of wear mechanism, because it is important to identify all mechanisms or combinations of wear mechanisms during failure analysis. The article concludes by presenting several examples of abrasive wear.

Wear, a form of surface deterioration, is a factor in a majority of component failures. This article is primarily concerned with abrasive wear mechanisms such as plastic deformation, cutting, and fragmentation which, at their core, stem from a difference in hardness between contacting surfaces. Adhesive wear, the type of wear that occurs between two mutually soluble materials, is also discussed, as is erosive wear, liquid impingement, and cavitation wear. The article also presents a procedure for failure analysis and provides a number of detailed examples, including jaw-type rock crusher wear, electronic circuit board drill wear, grinding plate wear failure analysis, impact wear of disk cutters, and identification of abrasive wear modes in martensitic steels.

Induction hardening is a prominent method in the gear manufacturing industry due to its ability of selectively hardening portions of a gear such as the flanks, roots, and/or tips of teeth with desired hardness, wearing resistance, and contact fatigue strength without affecting the metallurgy of the core. This article provides an overview of gear technology and materials selection. It describes different gear-hardening patterns, namely, tooth-by-tooth hardening, tip-by-tip hardening, gap-by-gap hardening, spin hardening, single-frequency gear hardening, dual-frequency gear hardening, simultaneous dual-frequency gear hardening, and through heating for surface hardening. It provides information on the different inspection methods based on the American Gear Manufacturers Association, revealing metallurgical data, hardness, and dimensions of gears. In addition, the article presents a comparative study on the mechanical properties of contour-hardened and carburized gears. It concludes by describing typical failures of induction-hardened steels and the corresponding prevention methods.

Adhesive-bonded joints are extensively used in aircraft components and assemblies where structural integrity is critical. This article addresses the problem of how to inspect bonded assemblies so that all discrepancies are identified. It describes several inspection techniques and presents drawbacks and limitations of these techniques. Generic flaw types and flaw-producing mechanisms are listed in a table. The article discusses metal-to-metal defects, adherend defects, honeycomb sandwich defects, repair defects, and in-service defects. It reviews the methods applicable to the inspection of bonded structures, including visual inspection, ultrasonic inspection, X-ray radiography, and neutron radiography. The evaluation and correlation of inspection results are also discussed. The article concludes with information on the effects of ultrasonic wave interference in the ultrasonic inspection of adhesive-bonded joints.

Ores, which consist of the primary valuable mineral, predominant gangue content, valuable by-products, and detrimental impurities, are extracted and directed to mineral processing. This article describes the mineral processing facilities, such as crushers, grinders, concentrators, separators, and flotation devices that are used for particle size reduction, separation of particles according to their settling rates in fluids and dewatering of concentrate particles. It explains the basic principles, flow diagrams, ore concentrate preparation methods, and equipment of major types of metallurgical processes, including pyrometallurgical, hydrometallurgical, and electrometallurgical processes.

This article discusses Allenby's two streams for environmental aspects of design: generic and specific concerns. Generic concerns include guidelines that provide the structure in which specific techniques can be developed and used. Specific methods are environmentally responsible for design and specific information that engineers can use. These methods include life cycle assessment, environmental impact assessment, quality function deployment, design for “X”, failure modes and effects analysis, and design for disassembly.