This article presents fractographs that show evidence of overload and fatigue in gray cast irons. The overload failure section illustrates a fractured motor housing, valve body, and bracket with microvoid coalescence (dimpled rupture) in the metal matrix between graphite flakes. The fractographs of fatigue failures illustrate a gearbox housing with fatigue striations and pearlitic microstructure.

This article describes some of the underlying factors of tool steel and bearing steel fractures and appearances. It also briefly introduces the general types of cold work and hot work tool steels and their typical performance requirements. This includes the importance of microstructural conditions achieved with powder metallurgy (PM) tool steels and the need for steel “cleanliness,” especially in preventing contact fatigue in bearings or bending fatigue in gears.

The role of a mixer/agitator in quenching applications is to control the mixing environment in order to meet the process criteria. This article provides the basic fundamentals of the sizing of agitators, tank geometry importance, and other considerations for the application of agitators in quench tanks. It also discusses the differing methods for the sizing and selection of agitators for quench tank applications.

Computational fluid dynamics (CFD) provides an efficient, alternate, virtual approach for simulating and analyzing quenching processes with an impact on component design, manufacturing process, and quality. This article provides domain insights for quenching researchers and CFD practitioners for the modeling of the industrial quenching process and for supporting the diverse multifunctional needs in an industry, ranging from primary metallurgical companies (steel, aluminum, and other alloys), original equipment manufacturers, engineering companies, captive and commercial heat treating facilities, quench system manufacturers, and quench fluid suppliers. It describes the governing differential equations for the fluid flow and heat-transfer phenomena during quenching. The article also discusses different modeling categories to determine a CFD methodology for quenching.

Flow visualization is an important characterization process to not only understand uniformity of the interfacial cooling mechanisms, but also to characterize the overall impact of agitation on the uniformity of the overall cooling process. This article focuses on thermal flow simulation and visualization in the quenching process. The study presents the effect of bubbling, boiling, and breaking the steam film on the heat-transfer coefficient during the agitated quenching process.

This article details investigations on the characterization of various nanofluids as quenchants for industrial heat treatment. It provides a discussion on the preparation, stability, thermophysical properties, and wetting characteristics of nanofluids. The article explains the mechanism of heat transfer in nanofluids and discusses the effect of the deposition of nanoparticles on the probe surface. The article also presents the microstructure and mechanical properties of steel quenched in nanofluids.

This article provides a detailed discussion on nanoindentation hardness, high-strain-rate behavior and strain-rate sensitivity, and corrosion response of additively manufactured (AM) metals. It summarizes the most commonly used AM alloys for applications in harsh environments and their respective corrosion responses in various service environments. It also provides several case studies on location-dependent properties, microstructural evolution, and indentation strain-rate sensitivity of various additively manufactured alloys.

Additive manufacturing (AM) is a highly desired layer-by-layer fabrication process capable of creating near-net-shaped three-dimensional components for a wide range of industries, such as the automotive and aerospace industries. This article focuses on aluminum, titanium, and stainless steel alloys that are commonly used or highly desired for use with AM due to their widespread applicability and favorable mechanical properties. It presents an overview of two of the major AM processes: powder-bed and powder-fed. The article discusses processability using AM. It also provides an overview of material microstructures, defects, and the impact on mechanical behaviors.

Structure-property relationships for metal additive manufacturing (AM) using solidification-based AM processes (e.g., powder-bed fusion and directed-energy deposition) are the focus of this article. Static strength and ductility properties in AM materials are impacted heavily by the microstructure but are also affected by porosity and surface roughness. Fatigue failure in AM materials is also influenced by porosity, surface roughness, microstructure, and residual stress due to applied manufacturing processing parameters. Post-processing treatments can further influence fatigue failure in AM materials.

Fatigue failure is a critical performance metric for additively manufactured (AM) metal parts, especially those intended for safety-critical structural applications (i.e., applications where part failure causes system failure and injury to users). This article discusses some of the common defects that occur in laser powder bed fusion (L-PBF) components, mitigation strategies, and their impact on fatigue failure. It summarizes the fatigue properties of three commonly studied structural alloys, namely aluminum alloy, titanium alloy, and nickel-base superalloy.

This article summarizes how the tensile properties of several key metal alloy systems commonly used in additive manufacturing (AM) compare against their traditionally manufactured counterparts, which process parameters can be manipulated to enable more optimized performance, the role that process-induced artifacts play in influencing tensile behavior, and how postprocessing can be employed to overcome any anomalies induced during manufacture. Popular specific grades include type 316L and 17-4PH stainless steels, AlSi10Mg, Scalmalloy, Inconel 625 and 718, H13 tool steel, Ti-6Al-4V, and cobalt-chromium.

The field of bioprinting is a subset of additive manufacturing (AM) that is rapidly expanding to meet the needs of regenerative medicine and tissue engineering. Bioprinting encompasses a broad spectrum of issues, from cell expansion and novel bioink development to cell/stem cell printing, from organoid-based tissue organization to bioprinting of human-scale tissue structures, and from building cell/tissue/organ-on-a-chip to biomanufacturing of multicellular engineered living systems. This article focuses on two challenges regarding bioprinting: bioinks and crosslinking. It describes the methods for characterizing the performance of bioink formulations and the effectiveness of crosslinking strategies. The topics covered include modalities of bioprinting, characteristics of bioink, rheological properties of bioink sols, rheological measurements, mathematical models of bioink rheology, postfabrication polymer network mechanics, mechanical properties of crosslinked bioinks, and printability of bioinks. Finally, specific strategies used for crosslinking bioinks, as well as some emerging strategies to further improve bioinks and their crosslinking, are summarized.

An ankle-foot orthosis (AFO) is a support designed to regulate the ankle's position and mobility, compensate for weakness, or rectify abnormalities. This article focuses on the biomechanical affects and mechanical properties of custom-made 3D-printed AFOs and compares them to traditionally created AFOs. Investigations in the fields of 3D scanning, 3D printing, and computer-aided design and analysis for the production of custom-made AFOs are also covered.

This article addresses some established protocols for characterizing thermoplastics and whether they are homogeneous resins, alloyed, or blended compositions or highly modified thermoplastic composites. It begins with a discussion on characterizing mechanical, rheological, and thermal properties of polymer. This is followed by a section describing molecular weight determination using viscosity measurements. Next, the article discusses the use of cone and plate and parallel plate geometries in melt rheology. It then reviews the processes involved in the analysis of thermoplastic resins by chromatography. Finally, the article covers three operations of thermoanalysis, namely differential scanning calorimetry, thermogravimetric analysis, and thermomechanical testing.

This article presents the mechanisms of polymer wear and quantifies wear in terms of wear rate (rate of removal of the material). Interfacial and bulk wear are discussed as well as a discussion on the wear study of "elastomers," "thermosets," "glassy thermoplastics," and "semicrystalline thermoplastics." The article also discusses the effects of environment and lubricant on the wear failures of polymers. It presents a case study on considering nylon as a tribological material and failure examples, explaining wear resistance of polyurethane elastomeric coatings and failure of an acetal gear wheel.

This article discusses the most common thermal analysis methods for thermosetting resins. These include differential scanning calorimetry, thermomechanical analysis, thermogravimetric analysis, and dynamic mechanical analysis. The article also discusses the characterization of uncured thermosetting resins as well as the curing process. Then, the techniques to characterize the physical properties of cured thermosets and composites are presented. Several examples of stress-strain curves are shown for thermosets and thermoplastic polymers.