Search Results for density measurements

The potential for introducing defects during processing becomes greater as the relative density of pressed and sintered powder metallurgy (PM) parts increases and more multilevel parts with complex geometric shapes are produced. This article discusses the potential defects in pressed and sintered PM parts: density variations, compaction and ejection cracks, microlaminations, poor degree of sintering, and voids from prior lubricant agglomerates. It describes the various methods applicable to green compacts: direct-current resistivity testing, radiographic techniques, computed tomography, and gamma-ray density determination. The article also discusses the methods for automated nondestructive testing of pressed and sintered PM parts: acoustic methods-resonance testing, eddy current testing, magnetic bridge comparator testing, ultrasonic techniques, radiographic techniques, gamma-ray density determination, and visual inspection.

Voids in fiber-reinforced composite materials are areas that are absent of the composite components: matrix (resin) and fibers. Voids have many causes but generally can be categorized as voids due to volatiles or as voids that result from entrapped air. This article describes the analysis of various types of voids. It reviews techniques for analysis of voids at ply-drops, voids due to high fiber packing, and voids that occur in honeycomb core composites. The final section of the article discusses void documentation through the use of nondestructive inspection techniques and density/specific gravity measurement methods.

This article describes testing and characterization methods of ceramics for chemical analysis, phase analysis, microstructural analysis, macroscopic property characterization, strength and proof testing, thermophysical property testing, and nondestructive evaluation techniques. Chemical analysis is carried out by X-ray fluorescence spectrometry, atomic absorption spectrophotometry, and plasma-emission spectrophotometry. Phase analysis is done by X-ray diffraction, spectroscopic methods, thermal analysis, and quantitative analysis. Techniques used for microstructural analysis include reflected light microscopy using polarized light, scanning electron microscopy, transmission electron microscopy, energy dispersive analysis of X-rays, and wavelength dispersive analysis of X-rays. Macroscopic property characterization involves measurement of porosity, density, and surface area. The article describes testing methods such as room and high-temperature strength test methods, proof testing, fracture toughness measurement, and hardness and wear testing. It also explains methods for determining thermal expansion, thermal conductivity, heat capacity, and emissivity of ceramics and glass and measurement of these properties as a function of temperature.

The interaction of an implant with the human body environment may result in degradation of the implant, called corrosion. This article discusses the corrosion testing of metallic implants and implant materials. The corrosion environments for medical implants are the extracellular human body fluids, very complex solutions containing electrolytes and nonelectrolytes, inorganic and organic constituents, and gases. The article describes the fundamentals of electrochemical corrosion testing and provides a brief discussion on various types of corrosion tests. It illustrates corrosion current density determination by Tafel extrapolation, potentiodynamic measurement of the polarization resistance, electrochemical impedance measurement, and potentiostatic deaeration. Tests combining corrosion and mechanical forces, such as fretting corrosion tests, environment-assisted cracking tests, and ion-leaching tests are also discussed.

This article focuses on the theory, advantages, and limitations of various methods used for the determination of surface area, density, and porosity of powder. These include gas adsorption, permeametry, pycnometry, and mercury porosimetry. Information on various equipment used in these processes are also provided.

The measurement of thermophysical properties of metal alloys, especially at high temperatures, is difficult because of the reactivity of some alloys. This article reviews the methods available for measurement of thermal and other physical properties for liquid, semi-solid, and solid commercial alloys, including adiabatic calorimetry, modulated calorimetry, Calvet calorimetry, single-pan calorimetry, and drop calorimetry. It describes differential scanning calorimetry and differential temperature analysis for measuring transition temperatures such as phase transformation or glass transition temperatures. The article schematically illustrates the laser flash apparatus for measuring the thermal diffusivity of solids and oscillation viscometer for measurements of the viscosity of metals. A summary of the measurement methods is presented in tables.

The primary goal of quality control in electron beam (EB) welding is to consistently produce defect-free and structurally sound welds. This article discusses the common procedures for controlling the EB welding process, the control of the essential machine parameters, and the introduction of closed-loop controls and diagnostic feedback systems in the EB welding systems. It reviews the beam diagnostic tools that interrogate the beam to produce a reconstruction of the power density distribution and provide additional information on the size and shape of the EB. Knowledge of these beam parameters can be used to improve process understanding and control. The article also describes the application areas of beam diagnostics: machine characterization, weld parameter transfer, and weld quality control.

This article describes the methods for determining the flow rate of metal powders. It examines the factors affecting flow rate, apparent density, and angle of repose of metal powders. The article reviews the frictional properties, cohesive strength, frictional properties, tap density, and compressibility of metal powders. It explains the mechanisms of powder segregation. The article provides information on green strength and springback value of rectangular test bar. It concludes with a discussion on the chemical composition of metal powders.

This article focuses on the testing and typical corrosion behavior of coating-substrate systems in aqueous solutions and humid aggressive atmospheres. It includes a short review of the fundamentals of corrosion, followed by a discussion of specific system behavior, electrochemical and laboratory accelerated tests, and simulated service tests. The article also contains examples of different types of corrosion damage and presents guidelines for improving corrosion resistance.

There are several main sources of thermophysical property data that provide the most authoritative and comprehensive compilations of critically and systematically evaluated data that are presently available. This article provides thermophysical property data to assist in the materials properties selection for the simulation of casting processes. The measurements of thermophysical property are difficult due to high temperatures and the reactivity of some alloys. The article discusses the strategies adopted to minimize the effects of high temperatures and reactivity of alloys. It presents the thermophysical properties of pure metals and some commercial alloys and tabulates the enthalpy of fusion and solidus and liquidus temperatures for various alloys of commercial interest. The article also lists the density, thermal conductivity, surface tension, and viscosity for some commercial alloys.