Search Results for measurement accuracy

Electrode potential is a key parameter in the thermodynamic and kinetic processes that drive aqueous corrosion. This article discusses the complexities associated with measuring electrode potential and explains where and how to use reference electrodes to improve measurement accuracy. It describes a three-electrode approach that compensates for measurement error stemming from nonequilibrium conditions. It also examines electrode materials and behaviors and offers insights on selection and operating conditions.

This article provides an overview of the relationships between torque, angle-of-turn, tension, and friction and explains how they are measured and evaluated. It focuses on the principle, test equipment, procedure, evaluation, and test report of various testing methods, namely, friction coefficient testing, torque tension testing, locknut testing, and angular ductility and rotational capacity tests. The article reviews the basic methods and fundamental principles for mechanical testing of externally and internally threaded fasteners and bolted joints. The test methods for externally threaded fasteners include product hardness, proof load, axial and wedge tension testing of full-sized products, tension testing of machined test specimens, and total extension at fracture testing. Product hardness, proof load, and cone proof-load test are the test methods for internally threaded fasteners. The article concludes with a description of torque-angle signature analysis and the specification of measurement accuracy for torque and clamp force.

Quantifying microstructural parameters has received considerable attention and success in developing procedures and using such data to develop structure/property relationships has been achieved. This article reviews many of the simple stereological counting measurements of volume fraction, grain structure (two-phase grain structures, and nonequiaxed grain structures), grain size, and inclusion content. It also reviews simple relationships between number of grains per unit area, number of intersections of a line of known length with particle or grain, and number of interceptions of particles or grains by a line of known length.

The article provides an overview of the various types of testing machines: gear-driven or screw-driven machines and servohydraulic machines. It examines force application systems, force measurement, and strain measurement. The article discusses important instrument considerations and describes gripping techniques of test specimens. It analyzes test diagnostics and reviews the use of computers for gathering and reducing data. Emphasis is placed on universal testing machines with separate discussions of equipment factors for tensile testing and compressing testing. The influence of the machine stiffness on the test results is also described, along with a general assessment of test accuracy, precision, and repeatability of modern equipment.

Temperature control in heat treating is of paramount importance in maintaining the quality and achieving the desired metallurgical results. This article provides a detailed account of the factors affecting temperature control in heat treating furnaces, with information on temperature control systems, including contact sensors, noncontact sensors, controllers, energy-flow regulators, measurement instruments, and set-point programmers. Common contact sensors include temperature scales, thermocouples, and resistance temperature detectors, whereas optical pyrometers and on-line radiation thermometers fall under the noncontact type. The article describes two types of instrumentation used in heat treating: field test instruments for temperature-uniformity surveys and system-accuracy tests; and controlling, monitoring, and recording instruments for digital instrumentation.

This article describes the various steps involved in image analysis, including sample selection and preparation, image preprocessing, measurement, and data analysis and output. It reviews various types of image analyzers and explains how operator bias and poor sample selection and preparation practices can lead to measurement error. It also examines several applications, illustrating how microstructural measurements can be used to assess quality control and better understand how processing changes affect microstructure and, in turn, material properties and behavior.

This article discusses various control processes carried out in powder feeding, thermal spraying, and gas flow of the thermal spray process to standardize the coating quality. Quality of the entire powder feeding process can be achieved by controlling the processing of feeding equipment as well as the characteristics of the powder being fed. Gas flow control can be achieved by using rotameters, critical orifices, and thermal mass flowmeters, whose ability to provide useful information is defined by their resolution, accuracy, linearity, and repeatability. The commercial thermal spray controls discussed here include the open-loop input-based, open-loop output-based, closed-loop input-based, and closed-loop output-based or adaptive controls. The article discusses the common causes and practical solutions for arc starting problems. It also outlines certain important developments in measuring individual and collective particle velocities, temperature, and trajectories as well as other plume characteristics for the plasma spray process.

Forgings are classified in various ways, beginning with the general classifications open die and closed die. They are also classified according to how they are made; such as hammer upset forgings, ring-rolled forgings, and multiple-ram press forgings; and in terms of the close-to-finish factor or amount of stock that must be removed to satisfy the dimensional and detail requirements of the finished part. In addition to types and classifications, the article discusses critical design factors and ways to ensure that the resulting forgings measure up to metallurgical, mechanical property, and dimensional accuracy requirements. The responsibility for design verification is vested in material control, which depends on the proper application of drawings, specifications, manufacturing process controls, and quality assurance programs. The article addresses each of these areas as well as related topics; including stress-induced fatigue failure, tolerances, machining allowances; and the fundamentals of hammer and press forgings, hot upset forgings, and hot extrusion forgings.

This article provides information on metals that can be cast in permanent molds. It describes the advantages, disadvantages, applications, and design of permanent castings. Following a discussion on the factors considered in mold design and material selection, the article details the application of mold coatings and examines the effects of major processing variables on mold life. The variables that determine mold temperature and measures for controlling it are reviewed, and the effects of short-term and long-term variables on the dimensional accuracy of permanent mold castings are explained. The article concludes with a discussion on the factors influencing the surface finish on permanent mold castings.

Thermocouple devices are the most widely used devices for measurement of temperature in the metals industry. Favorable characteristics of these devices include good accuracy, suitability over a wide temperature range, fast thermal response, ruggedness, high reliability, low cost, and great versatility of application. Thermocouples are grouped into two broad categories, namely, standard thermocouples, including five base-metal thermocouples and three noble-metal thermocouples that have been given letter designations, and nonstandard thermocouples, including iridium-rhodium, platinum-molybdenum, platinel, and tungsten-rhenium thermocouples. This article discusses the basic principles, classification, and properties of thermocouples, and the techniques for insulating and protecting thermocouple wires from the operating environment.

This article is a detailed account of the principles of electron-excited X-ray microanalysis. It begins by discussing the physical basis of electron-excited X-ray microanalysis and the advantages and limitations of energy dispersive spectrometry (EDS) and wavelength dispersive spectrometry for electron probe microanalysis. Key concepts for performing qualitative analysis and quantitative analysis by electron-excited X-ray spectrometry are then presented. Several sources that lead to measurement uncertainties in the k-ratio/matrix corrections protocol are provided, along with the significance of the raw analytical total. Sections on accuracy of the standards-based k-ratio/matrix corrections protocol with EDS and processes of analysis when severe peak overlap occurs are also included. The article provides information on low-atomic-number elements, iterative qualitative-quantitative analysis for complex compositions, and significance of standardless analysis in the EDS software. It ends with a section on the processes involved in elemental mapping for major and minor constituents.

This article focuses on laboratory atomic force microscopes (AFMs) used in ambient air and liquid environments. It begins with a discussion on the origin of AFM and development trends occurring in AFM. This is followed by a section on the general principles of AFM and a comprehensive list of AFM scanning modes. There is a brief description of how each mode works and what types of applications can be made with each mode. Some of the processes involved in preparation of samples (bulk materials and those placed on a substrate) scanned in an AFM are then presented. The article provides information on the factors applicable to the accuracy and precision of AFM measurements. It ends by discussing the applications for AFMs in the fields of science, technology, and engineering.

This article focuses on the principles and applications of X-ray photoelectron spectroscopy (XPS) for the analysis of elemental and chemical composition. The discussion covers the nomenclature, instruments, and specimen preparation process of XPS. Some of the factors pertinent to the calibration of materials for accurate measurements using XPS are provided, along with some aspects of the accuracy in quantitative analysis by XPS. In addition, the article presents examples of how XPS data can be used to solve problems with surface interactions.

This article provides an overview of the studies on computational modeling of the vacuum arc remelting (VAR) and electroslag remelting (ESR) processes. These models involve the axisymmetric analysis of the electromagnetic, flow, heat-transfer, and phase-change phenomena to predict the pool shape and thermal history of an ingot using two-dimensional axisymmetric models for VAR and ESR. Analysis of segregation of alloying elements during solidification that gives rise to macrolevel compositional nonuniformity in titanium alloy ingots is also described. The article discusses the important features of the control-volume-based computational method to review the unique aspects of the processes. Measurement of the properties of alloys and slags is explained and an analysis of the process variants for improving the predictive accuracy of the models is presented.

Modeling will help reduce machining problems and thereby enable more rapid introduction of high-performance materials and components. This article discusses the technical needs of aircraft engine and airframe structural components and modeling of heat-treat-induced residual stress by finite-element residual-stress analysis. It describes the two-dimensional (2-D) and three-dimensional (3-D) procedures involved in finite-element residual-stress analysis. The article deals with the 2-D and 3-D machining distortion validation on engine-disk-type components. It describes methods for obtaining machining-induced residual stresses, including detailed finite-element analysis of the cutting process, the simple fast-acting mechanistic model, and the semi-empirical linear stress model. The article concludes with information on the modeling benefits and implementation of modeling in a production environment.

This article provides guidelines for the assessment of model quality in materials science and engineering. It discusses the fundamentals of model quality assessment and the calibration of mechanistic material models. The article reviews the considerations for the model verification during software implementation planning to identify suitable programs, software components, and programming languages. It describes the validity tests used in model validation, including boundary-value tests, degenerate problem tests, sensitivity tests, and benchmarking. The article also presents an example of model calibration, verification, and validation for the prediction of martensite start temperature of steels.

As additive manufacturing (AM) gains maturity as a manufacturing technique for production in many industrial sectors, inspection as a tool for quality control gains importance. This article is focused on the field of dimensional metrology, which is typically concerned with the verification of size, location, form, and surface topography of geometric features. This is split into two categories: geometric (size, location, form) and surface measurement (topography). The article also focuses on applicable inspection technologies, and it discusses the context within digital thread manufacturing. A case study on the Digital Inspection Requirements Enhancing Coverage and Traceability (DIRECT) is also presented.

Precision forging is defined as a closed-die forging process in which the accuracy of the shape, dimensional tolerances, and surface finish exceed normal expectations to the extent that some of the postforge operations can be eliminated. This article provides an overview of the key factors that impact the precision forging process. It provides information on the achievable tolerances and presents examples of precision forging. A discussion on forging of bevel gears/spiral bevel gears is also presented.