bluuebunny/crossref_metadata_2025_split huggingface dataset:
High‐Strain‐Rate Testing of Materials: The Split‐Hopkinson Pressure Bar
Authors: Gray George T. (Rusty) 
Published: May 2012

Abstract

Robust models that capture the physics of high‐rate material response are required for developing predictive capability for highly dynamic events. One develops a strength constitutive model for a particular material by measuring its mechanical properties over a range of temperatures, strain rates, and stress states. The samples of interest are loaded in compression, tension, or torsion over a range of loading rates and temperatures germane to the application of interest. Various mechanical testing frames are available that achieve nominally constant loading rates for limited plastic strains and, thereby, a constant strain rate. The standard screw‐driven or servohydraulic testing machines achieve strain rates of up to 5 s
−1
. Specially designed testing machines, typically equipped with high‐capacity servohydraulic valves and high‐speed control and data acquisition instrumentation, can achieve strain rates as high as 200 s
−1
during compression loading. To go even higher, we must employ projectile‐driven impacts that induce stress‐wave propagation in the sample materials. Chief among the techniques to measure the dynamic stress–strain response of materials is the split‐Hopkinson pressure bar. This technique is capable of achieving the highest uniform uniaxial stress loading of a specimen in compression at nominally constant strain rates of the order of 10
3
s
−1
and true strains of 0.3. Stress in the Hopkinson bar is measured by using an elastic element in series with the specimen of interest. Stress waves are generated via an impact event and the elastic elements utilized are long bars such that the duration of the loading pulse is less than the wave transit time in the bar. In this article the principles of the split‐Hopkinson pressure bar, its data reduction, sample preparation, and limitations are detailed.
Hardness Testing
Authors: Edwards Janice 
Published: May 2012

AbstractIndentation hardness tests such as Brinell, Rockwell, Vickers, Knoop, and instrumented indentation are frequently used methods for determining hardness. The basic concept utilized in all of these tests is that a set force is applied to an indenter in order to determine the resistance of the material to penetration. If the material is hard, a relatively small or shallow indentation will result, whereas if the material is soft, a fairly large or deep indentation will result.These tests are often classified in one of the following two ways: by the extent of the test force applied or the measurement method used. A “macro” test refers to a test where a load >1 kg is applied; similarly “micro” refers to a test where a load of ≤1 kg of force is applied. Additionally, some instruments are capable of conducting tests with loads as light as 0.01 g and are commonly referred to as ultralight or nanoindentation testers. Rockwell and Brinell testers fall into the macro category, whereas Knoop testers are used for microindentation tests. Vickers and instrumented indentation testers can be employed for both macro‐ and microindentation tests. The measurement methods available include a visual observation of the indentation or a depth measurement of the indentation. Rockwell and instrumented indentation testers are capable of determining the depth of the indentation, whereas Brinell, Knoop, and Vickers testers require an indentation diameter measurement. These visual measurements can be automated, as will be discussed later in this article.Hardness is not a fundamental property of a material, yet hardness testing is considered a useful quality‐control tool. Many properties are predicted from hardness values when combined with additional information such as alloy composition. The following is a list of such properties: resistance to abrasives or wear, resistance to plastic deformation, modulus of elasticity, yield strength, ductility, and fracture toughness. Some of these properties, such as yield strength, have numerical relationships with hardness values, whereas others such as fracture toughness are based on observations of cracks surrounding the indentations. Data analysis and conversions will be discussed in greater detail later in this article.
Tribological and Wear Testing
Authors: Bayer Raymond G. 
Published: May 2012

AbstractTribology is the science of friction, wear, and lubrication. More fundamentally, tribology is concerned with the interaction of contacting surfaces in relative motion. Friction is the resisting tangential force that occurs between two surfaces in contact when they move or tend to move relative to one another. For solid surfaces the magnitude of this force is characterized by the coefficient of friction, defined as the dimensionless ratio of the magnitude of the friction force to the magnitude of the normal force. In the absence of an externally applied normal force, this tangential force is sometimes referred to as sticktion. Wear is damage to a solid surface due to the relative motion between that surface and a contacting substance or substances. It involves the progressive loss of material. Lubrication is the ability of an interposing material to reduce either the friction between or the wear of surfaces.The tribological behavior that a material exhibits is dependent on both the properties of the material and the contact conditions. As a result, parameters used to characterize the friction, wear, and lubrication of a material are system properties of the material, not intrinsic properties such as an elastic modulus or coefficient of thermal expansion. The collection of all those elements that can influence tribological behavior is referred to as the tribosystem. The primary elements of a tribosystem are (1) materials, (2) shapes and contours, (3) surface roughness, (4) motions, (5) loading, (6) lubrication, and (7) environment.
Theory of Magnetic Phase Transitions
Authors: McHenry Michael E. , Laughlin David E. 
Published: May 2012

AbstractThis article discusses magnetic order and a class of physical phenomena that can be described as magnetic phase transitions. We describe the thermodynamics of magnetic ordering transitions, the order of the transitions, critical exponents, and thermodynamic variables. We further describe magnetic phase transitions within the framework of the mean field Landau theory of phase transitions with discussion of several magnetic equations of state. We end with an application to magnetocaloric materials.
Techniques to Measure Magnetic Domain Structures
Authors: Celotta R. J. , Unguris J. , Kelley M. H. , Pierce D. T. 
Published: May 2012

AbstractCritical to understanding the magnetic properties and the technological application of magnetic materials is the ability to observe and measure magnetic domain structure. The measurement challenge is quite varied. Magnetic fluids can be used to decorate and make simple domain structures visible while highly sophisticated electron microscopy‐based methods may be needed to explore and image nanometer‐scale magnetic phenomena. No one method will solve all of the domain imaging problems. For that reason, the bases of the important methods and the practical implications of each are discussed.For purposes of comparison, several important characteristics of each domain imaging technique are briefly summarized.There are several general comments that apply to every domain imaging method discussed in this article. First, each method is related either to a sample's magnetization or to the magnetic field generated by that magnetization. The former observation is of great usefulness in understanding or developing new materials, and the latter is of practical importance in devices. Second, all of the methods are limited to the topmost few micrometers of the sample, and are therefore dominated by magnetic structure related to the surface. None provide the domain structure of the interior of a thick sample where bulk magnetic microstructure is fully developed. Third, all of the methods require smooth, clean, damage‐free surfaces. In general, the surfaces need to have at least the equivalent of a mirror polish, otherwise, topography and surface stress will affect the measurement to varying degrees. Fourth, correlations exist between several of the parameters in each technique we describe. For example, it may not be possible to achieve the ultimate sensitivity specified at the highest resolution possible. Finally, almost all of the techniques use digital signal acquisition and can benefit from the use of modern image processing tools.Expanded discussions of the basis of each technique, its practical aspects, sample preparation required, possible sample modifications, and problems that are specific to the technique described are given. Each section contains references to more complete treatments of the technique and recent examples of its use.
The Quartz Crystal Microbalance in Electrochemistry
Authors: Arbuckle‐Keil Georgia A. 
Published: May 2012

Abstract

The quartz crystal microbalance (QCM) is based on the principle that a change in resonance frequency of a quartz crystal is directly proportional to a change in total mass (crystal and surface deposit). When one of the quartz crystal contacts is the working electrode of an electrochemical cell, the charge passed during an electrochemical process can be correlated with nanogram mass changes on the quartz crystal electrode. Other factors that influence overall frequency change include viscoelastic behavior of electrode deposit, surface roughness, entrapment of solvent or air in electrode deposit, nonuniform mass distribution, and ambient temperature changes. The ability to determine both the energy dissipation,
D
, and resonance frequency change,
f
r
, illustrates the use of QCM as both a gravimetric and viscoelastic probe of materials deposited onto the quartz crystal electrode surface.
Photoluminescence Spectroscopy
Authors: Aoki Takeshi 
Published: May 2012

AbstractThis article presents a brief introduction to photoluminescence (PL) spectroscopy in solid‐state physics and technology, known as fluorescence spectroscopy in chemistry and biology. Though PL spectroscopy is usually known as spectral‐resolved spectroscopy, time‐resolved PL spectroscopy containing information about recombination lifetime of photoexcited electrons and holes has now become essential to the PL study on various materials ranging from nanoparticles to living tissues. Since a variety of methods of PL spectroscopy exist, they are classified into three categories, namely, static or steady‐state PL spectroscopy, time‐resolved PL spectroscopy, and frequency‐resolved spectroscopy, each of which groups several methods, and, moreover, PL mapping and imaging are also addressed in the text.
Ultraviolet and Visible Absorption Spectroscopy
Authors: Tissue Brian M. 
Published: May 2012

Abstract
This article describes the principles and applications of absorption spectroscopy in the ultraviolet (UV), visible (Vis), and near‐infrared (NIR) regions of the electromagnetic spectrum. UV/Vis spectroscopy is used for (1) quantitative measurements of material components and precursors and (2) characterization of the optical and electronic properties of a material. Most measurements can be made with commercially available spectrophotometers and sampling accessories.
Cyclotron Resonance
Authors: Hilton, D. J. , Arikawa, T. , Kono J. 
Published: May 2012

AbstractThis article reviews the technique and phenomenon of cyclotron resonance (CR). CR is a method for measuring the effective masses of charge carriers in solids and is by far the most direct and accurate method for providing such information. In the 1950s, the first CR studies were carried out in germanium and silicon crystals, which, in conjunction with the effective mass theory, successfully determined the band‐edge parameters for these materials with unprecedented accuracy. Since then, CR has been investigated in a large number of elementary and compound materials and their alloys and heterostructures. Quantum mechanically, CR can be viewed as a transition between adjacent Landau levels. In real solids, Landau levels are generally not equally spaced since the energy dispersion relation is not generally given by a simple parabolic dispersion relation, and, thus, effective masses are energy dependent as well as direction dependent. A detailed comparison between theory and experiment on quantum CR can provide a critical test of the band theory of solids. As a secondary purpose, one can also use CR to study carrier scattering phenomena in solids by examining the scattering. As the frequency of scattering events increases, CR linewidth increases, and, eventually, CR becomes unobservable when scattering occurs too frequently. Temperature and magnetic field dependence of CR linewidth provides insight into dominant scattering mechanisms.
Mössbauer Spectrometry
Authors: Fultz Brent 
Published: May 2012

AbstractMössbauer spectrometry provides unique measurements of electronic, magnetic, and structural properties within materials. A Mössbauer spectrum is an intensity of γ‐ray absorption versus energy for a specific resonant nucleus such asor. Mössbauer spectrometry looks at materials from the “inside out,” where “inside” refers to the resonant nucleus. For one nucleus to emit a γ ray and a second nucleus to absorb it with efficiency, both nuclei must be embedded in solids, a phenomenon known as the “Mössbauer effect.”Mössbauer spectra give quantitative information on “hyperfine interactions,” which are small energies from the interaction between the nucleus and its neighboring electrons. The three important hyperfine interactions originate from the electron density at the nucleus (the isomer shift), the gradient of the electric field (the nuclear quadrupole splitting), and the unpaired electron density at the nucleus (the hyperfine magnetic field). Over the years, methods have been refined for using these three hyperfine interactions to determine valence and spin at the resonant atom. Even when the hyperfine interactions are not easily interpreted, they can often be used reliably as “fingerprints” to identify the different local chemical environments of the resonant atom, usually with a good estimate of their fractional abundances. Mössbauer spectrometry is useful for quantitative phase analyses or determinations of the concentrations of resonant element in different phases, even when the phases are nanostructured or amorphous.Most Mössbauer spectra are acquired with simple laboratory equipment and a radioisotope source, but the recent development of synchrotron instrumentation now allows for measurements on small 10‐μm samples, which may be exposed to extreme environments of pressure and temperature. Other capabilities include measurements of the vibrational spectra of resonant atoms, and coherent scattering and diffraction of nuclear radiation.This article is not a review of the field, but an instructional reference that explains principles and practices, and gives the working materials scientist a basis for evaluating whether or not Mössbauer spectrometry may be useful for a research problem. A few representative materials studies are presented.
XAFSSpectroscopy
Authors: Heald Steve 
Published: May 2012

AbstractThe x‐ray absorption fine structure (XAFS) that is present near x‐ray absorption edges contains detailed information about the local structure and bonding of the absorbing atoms. With the advent of intense tunable sources of x‐rays using synchrotron radiation facilities, the application of x‐ray absorption spectroscopy has become widespread and routine. The XAFS is a local probe sensitive to the location and type of atoms surrounding the absorbing atom. As a local probe, it can be applied to many materials where diffraction‐based techniques would be impractical such as resolving the structure near highly dilute components and determining the local structure of atoms in nanoparticles, liquids, metalloproteins in solution, amorphous solids, and poorly crystalline materials. In addition to the direct structural information, the absorption edge position and shape can be used to determine the site symmetry and valence of the absorbing atoms. This chapter describes the physical principles that result in the fine structure, basic experimental techniques, and basic principles for the extraction of the information present in the spectra. It also touches on some of the unique aspects of performing measurements at a synchrotron radiation facility.
Scanning Tunneling Microscopy
Authors: Park Jeong Y. 
Published: May 2012

Abstract
Scanning tunneling microscopy (STM) is an instrument in which a sharp metallic probe raster scanned across the sample is employed to detect changes in surface structure on the atomic scale. STM enabled us to study surface structure, electronic structure, atomic manipulation, dynamics of molecules and atoms, and chemical properties of the surface at the atomic scale. During the last three decades, the field of scanning tunneling microscopy has advanced explosively. New experimental modes and theoretical models have been developed. In this chapter, the principle and practical aspects of the new methods associated with STM techniques are outlined. Variation of STM and scanning tunneling spectroscopy (STS) and their principles and examples are also shown here. Data analysis, sample preparations, and problems of various STM experiments are introduced as well.
Magnetic Neutron Scattering
Authors: Lynn Jeffrey W. 
Published: May 2012

AbstractNeutron scattering is a powerful tool to investigate the magnetic structures and spin dynamics of materials. In this tutorial we provide examples of the application of magnetic neutron diffraction using polycrystalline materials, single crystals, thin films, and artificially grown multilayers, to determine the spatial arrangement and directions of the atomic magnetic moments, the atomic magnetization density of magnetic ions, and the ordered moments as a function of thermodynamic variables such as temperature, pressure, and applied magnetic field. We also present examples of the technique of inelastic scattering to determine the spin dynamics of systems. Both polarized and unpolarized neutron techniques are discussed.
Effect of Temperature on the Dynamic Mechanical Behaviors of Zr‐Based Metallic Glass Reinforced Porous Tungsten Matrix Composite
Authors: Chen Chen , Xue Yunfei , Wang Lu , Cheng Xingwang , Wang Fuchi , Wang Zhengbin , Zhang Haifeng , Wang Aiming 
Published: May 2012

AbstractThe dynamic mechanical behaviors of Zr‐based metallic glass reinforced porous tungsten matrix composite were investigated by a split Hopkinson pressure bar at different testing temperatures. The flow stress of the composite decreased, while the ductility increased with increasing testing temperature, which were attributed to that more microcracks were initiated in the tungsten phase as well as more microshear bands were induced in the metallic glass phase with increasing temperature. The failure mode of the composite is a mixture of shearing and axial splitting. The flow layer of the metallic glass phase in the shearing fracture surface at 473 K was longer and thinner than that at 223 K.
Epitaxial NiMnGa Films for Magnetic Shape Memory Alloy Microactuators
Authors: Backen Anja , Yeduru Srinivasa Reddy , Diestel Anett , Schultz Ludwig , Kohl Manfred , Fähler Sebastian 
Published: May 2012

AbstractActive materials such as piezoelectrics are established in the field of microsystems application despite their low achievable strains which often require the integration of additional gear mechanisms. The ongoing search for new active materials has focused on magnetic shape memory (MSM) alloys such as NiMnGa since they combine macroscopic strains of up to 10% with a cycling frequency well above the frequencies of conventional thermal shape memory alloys. The present review focuses on preparation and analysis of NiMnGa films that can eventually be integrated in microsystems. Single crystal like films are prepared by epitaxial growth on suitable substrate materials. Since the magnetically induced reorientation of variants is blocked by a rigid substrate, we present different methods for releasing films from the substrates. We show that the sacrificial layer technology is the most promising approach. Further processing of the freestanding film requires a microtechnology which is adjusted to the film laminate structure. The properties of the freestanding films are compared with films on a rigid substrate. Although we observe stress‐induced twin boundary motion, the twinning stress is too high to be overcome by an external magnetic field. Therefore, it is necessary to develop suitable training methods to reduce the twinning stress below 2 MPa to enable the activation of the material by means of an external magnetic field.
Principle Design of Actuators Driven by Magnetic Shape Memory Alloys
Authors: Schlüter Kathrin , Holz Benedikt , Raatz Annika 
Published: May 2012

AbstractMagnetic shape memory alloys (MSMA) are a promising material for actuation purposes as they provide relatively large strains and relatively high operation frequencies. In this paper three concepts of such actuators are introduced. The first part will describe a so called spring actuator, where the MSM element is working against a restore pre‐stress spring. The second concept uses two MSM elements working antagonistically to substitute the pre‐stress spring. A small sized actuator for valve or switching applications is shown in the third concept. Advantages and disadvantages are highlighted and show the potential of the comparatively new active material.
Revisited Storage and Dynamic Recovery of Dislocation Density Evolution Law: Toward a Generalized Kocks–Mecking Model of Strain‐Hardening
Authors: Bouaziz O. 
Published: May 2012

AbstractThe current work extends the well established approach of Kocks and Mecking by a more realistic description of strain‐hardening using an original dislocation density law with a revisited physical understanding of dynamic recovery, without new material parameters and keeping only one internal variable.
Efficient Synthesis of Heteroatom (N or S)‐Doped Graphene Based on Ultrathin Graphene Oxide‐Porous Silica Sheets for Oxygen Reduction Reactions
Authors: Yang Shubin , Zhi Linjie , Tang Kun , Feng Xinliang , Maier Joachim , Müllen Klaus 
Published: May 2012

AbstractHeteroatom (N or S)‐doped graphene with high surface area is successfully synthesized via thermal reaction between graphene oxide and guest gases (NH3 or H2S) on the basis of ultrathin graphene oxide‐porous silica sheets at high temperatures. It is found that both N and S‐doping can occur at annealing temperatures from 500 to 1000 °C to form the different binding configurations at the edges or on the planes of the graphene, such as pyridinic‐N, pyrrolic‐N, and graphitic‐N for N‐doped graphene, thiophene‐like S, and oxidized S for S‐doped graphene. Moreover, the resulting N and S‐doped graphene sheets exhibit good electrocatalytic activity, long durability, and high selectivity when they are employed as metal‐free catalysts for oxygen reduction reactions. This approach may provide an efficient platform for the synthesis of a series of heteroatom‐doped graphenes for different applications.