Flaring—An analytical approach

This paper deals with a metal forming process leading to a conical extension of circular cylindrical shells (tubes). This forming process is called ‘flaring’. Analytical expressions are derived for determining stress and strain fields as well as the force required for driving the expansion. The results are compared to finite element solutions and show reasonably good agreement.     

Surface crystallography via electron microscopy

The study of atomic structure of surfaces is fundamental to the understanding of electronic, chemical and mechanical properties of surfaces and numerous techniques have been developed to this end. Transmission Electron Microscopy techniques, namely transmission electron imaging (TEM) and diffraction (TED), due to their ability to provide structural information at very high resolutions, have emerged as powerful tools for the study of surface structure. In this article we review the experimental method alongside the various post-processing routines that are necessary to extract vital structural information from experimental data.     

An analytical reflection and emission UHV surface electron microscope

An UHV surface electron microscope is described which allows the study of surfaces under vacuum conditions common in surface science with the following techniques: LEERM; LEED; photo, thermionic, secondary emission microscopy; absolute micro area work function measurements. In particular, the first LEERM of Mo(110) and Si(111) surfaces are presented. They show monoatomic steps with high contrast due to Fresnel diffraction and structural differences, respectively. Condensed silver crystallites are imaged. Gold adsorption layers on Si(111) show strong contrast in photoemission; the layer thickness is deduced from LEED.     

An analytical approach for structural synthesis of substructures

A structure is broken down into a number of substructures by means of the finite element method and the substructures are synthesized for the complete structure. The divided substructures take two types : fixed-free and free-free elements. The flexibility and stiffness matrices of the free-free elements are the Moore-Penrose inverse of each other. Thus, it is not easy to determine the equilibrium equations of the complete structure composed of two mixed types of substructures. This study provides the general form of equilibrium equation of the entire structure through the process of assembling the equilibrium equations of substructures with end conditions of mixed types. Applications demonstrate that the proposed method is effective in the structural analysis of geometrically complicated structures.     

Assessment of resolution in biological electron crystallography.

The resolution of images or density maps produced by electron microscopy and electron crystallography can be objectively defined in terms of the spatial frequency of the highest resolution diffraction spot, or Fourier coefficient, included in the data processing. In practice, this objective definition of resolution is expected to be too optimistic if the amplitudes of the highest resolution structure factors are too weak, if the population of high resolution reflections is too sparse, or if the signal-to-noise ratio of the high resolution data is too low. Calculated examples are presented here which illustrate how the apparent resolution in images of a membrane protein, bacteriorhodopsin, can be reduced from a nominal value of 3.5 A by weak amplitudes, sparse data or high noise levels. These calculations provide concrete examples which can serve as a guide when estimating whether the objective definition of image resolution is likely to correspond to a practical, structurally useful estimate of image resolution.     

Soft x-ray continuum radiation transmitted through metallic filters: an analytical approach to fast electron temperature measurements

A new set of analytic formulas describes the transmission of soft x-ray continuum radiation through a metallic foil for its application to fast electron temperature measurements in fusion plasmas. This novel approach shows good agreement with numerical calculations over a wide range of plasma temperatures in contrast with the solutions obtained when using a transmission approximated by a single-Heaviside function [S. von Goeler et al., Rev. Sci. Instrum. 70, 599 (1999)]. The new analytic formulas can improve the interpretation of the experimental results and thus contribute in obtaining fast temperature measurements in between intermittent Thomson scattering data.     

基于压电悬臂梁的驱动器与传感器性能分析的精确解析模型

三层压电梁结构在电场作用下发生变形后会产生诱发电势,进而改变材料整体电势分布,本文考虑此变形和电势耦合效应,基于欧拉-伯努利梁变形理论,推导出能够准确预测压电智能悬臂梁传感器与驱动器性能的解析表达式。考虑压电梁结构弯曲变形后产生的电场影响,建立了三层压电梁结构的控制方程;建立了压电梁作为驱动器时端部输出位移、驱动力矩与输入电压之间联系的解析表达式,以及作为传感器时输出电压与端部作用力之间联系的解析表达式。通过与ANSYS有限元模拟结果以及传统的驱动器和传感器性能表达式的对比,验证了所推导的解析表达式的准确性。     

An analytical approach to cutting force prediction in milling of carbon fiber reinforced polymer laminates

ABSTRACT

A prediction model of cutting force for milling multidirectional laminate of carbon fiber reinforced polymer (CFRP) composites was developed in this article by using an analytical approach. In the predictive model, an equivalent uniform chip thickness was used in the case of orthogonal plane cutting, and the average specific cutting energy was taken as an empirical function of equivalent chip thickness and fiber orientation angle. The parameters in the model were determined by the experimental data. Then, the analytical model of cutting force prediction was validated by the experimental data of multidirectional CFRP laminates, which shows the good reliability of the model established. Furthermore, the cutting force component of flank contact force was correlated with the surface roughness of workpiece and the flank wear of tool in milling UD-CFRP composites. It was found that surface quality as well as flank wear has a co-incident varying trend with the flank contact force, as confirmed by the observations of the machined surfaces and tool wear at different fiber orientations. So, it can be known that low flank contact force be required to reduce surface damage and flank wear.     

An analytical approach for the prediction of forming limit curves subjected to combined strain paths

In the present work, an analytical approach for the prediction of forming limit curves is proposed to incorporate the effect of combined strain paths. The effect of combined strain paths (considering the directional dependency of pre-straining and further straining) is addressed by integrating the incremental equivalent strain expression in two stages i.e., pre-strain and subsequent loading. In each stage, the strain path is assumed to be linear and different combinations of pre-strain (uniaxial, plane-strain and equi-biaxial) are considered. Material anisotropy is taken into account in each stage. The predictions of the present model are compared with the experimental results on forming limit curves under combined strain paths for Al6111-T4 [24] and are found to be in good agreement with each other.     

Contribution of electron energy loss spectroscopy to the development of analytical electron microscopy.

The combined use of an electron energy loss spectrometer and an electron microscope provides some chemical information at the nanometer scale. The physics of the interaction processes between the incident electron beam and the thin sample foil is reviewed in terms of energy and momentum transfer. This analysis of the content of an electron energy loss spectrum allows us to establish rules for a satisfactory use of the information and to discuss the detection limits of this newly developed microanalytical technique.     

An approach to the reduction of hydrocarbon contamination in the scanning electron microscope

The deposition of electron beam-induced specimen contamination in both the transmission (TEM) and scanning electron microscopes (SEM) has remained a problem since the beginning of these forms of microscopy. Generally, sources of SEM contamination can be attributed to one or a combination of three major contributors: (1) the pumping system; (2) outgassing of other internal SEM component parts (i.e., specimen stage, stage lubricants, O-rings, etc.), or (3) the sample (including its preparation and handling). Generally, because of the nature of SEM, specimen contamination can be minimized but is difficult to avoid fully. This work outlines three approaches taken with instruments at NIST to reduce the deposition of contamination in high-resolution cold-field emission SEMs. With some modification these techniques could be applied to any SEM. These approaches have been in successful operation for several years, resulting in a reduction in electron beam-induced hydrocarbon contamination.     

Parameters affecting specimen flatness of two-dimensional crystals for electron crystallography

The flatness of two-dimensional (2D) crystals on the support film is a critical factor in protein electron crystallography. The influence of the carbon support film and of different grid makes and materials on flatness was investigated, using as a criterion the sharpness of diffraction spots perpendicular to the tilt axis of electron diffraction patterns of purple membrane tilted in the microscope at 45 degrees. In a quantitative test, carbon film that had been evaporated without sparks forming gave a much larger proportion of flat crystals than "sparked" carbon. Titanium grids were superior to copper, probably because they introduce less cryo-crinkling of the carbon film when the sample is cooled to liquid nitrogen temperature, as their thermal expansion coefficient is closer to that of carbon. While the molybdenum grids from Plano were unsuitable for data collection because of their tendency of break the carbon, molybdenum grids from Pacific GridTech gave a much larger yield of flat crystals than the titanium grids. Scanning electron microscope images of the grids as supplied by the manufacturer showed that the Plano grids had very narrow and irregular grid bars, while the Pacific GridTech grids were very smooth with a large surface-to-hole ratio.     

Recent developments in analytical electron microscopy

Recent years have seen the way in which the analytical electron microscope has been applied to problems involving thin specimens in metallurgy, mineralogy and many branches of biology. The limits of sensitivity have been explored and its potential usefulness in these fields investigated. Problems concerning the interaction of electrons with the specimen are discussed in relation to the correct choice of operating conditions and specimen preparation. In biological work, frozen sections provide new information about subcellular elemental localization of mobile electrolytes, while analysis of tissue prepared by conventional means is used to detect physiological levels of some naturally occurring elements. Examination of mineral dispersions provides analysis of particles just 10 nm thick, visible only in transmission electron microscopy, and further work with thin metal foils confirms the value of high resolution transmission imaging as a complementary facility to micro-analysis. Work has been done to investigate the possibilities of improving sensitivities both by changing operational parameters and instrumental design, and the value of quantitation in thin specimen analysis explored.     

A cryostat approach to ultrathin "dry" frozen sections for electron microscopy: a morphological and x-ray analytical study

Conventional preparative procedures for the examination of tissues in the electron microscope involve the use of fixatives, dehydration in alcohol or acetone, embedding in plastics and staining. Such procedures remove soluble components and are therefore often unsuitable for chemical analysis of naturally occurring electrolytes. Ultrathin frozen sections of unfixed, unembedded biological tissue can be cut onto dry glass knives, freeze-dried and viewed in the electron microscope without staining. Morphological detail is sufficient to identify cell types and ultrastructure. X-ray microanalysis in the analytical electron microscope (EMMA-4) has shown that highly soluble electrolytes can be detected and that intracellular compartments are retained.     

Multivariate statistical approach to electron backscattered diffraction

This paper assesses the potential of multivariate statistical analysis (MSA) applied to electron backscattered diffraction (EBSD) data. Instead of directly indexing EBSD patterns on an individual basis, this multivariate approach reduces a large (thousands) set of individual EBSD patterns into a core set of statistically derived component EBSD patterns which can be subsequently indexed. The following hypotheses are considered in this paper: (1) experimental EBSD patterns from a microstructure can be analytically treated as linear combinations of spatially simple components, (2) MSA has an angular resolution on par with standard EBSD, (3) MSA can discriminate between similar and dissimilar phases, and (4) the MSA approach can improve the effective spatial resolution of automated EBSD.     

A new phase consistency criterion and its application in electron crystallography

In this work, we present the principles and potential advantages of a methodology to assess Fourier components in terms of phase consistency. We define a new phase consistency criterion among sets of spatially translated images based upon a novel conception of the spatial shift property of the Fourier transform. The article shows how this criterion can be used in the alignment stage of the 3D reconstruction process with a two-fold objective: Assessment of the frequency components and robustness in the alignment. In that sense, the article shows and analyzes the results obtained from the application of the new index of quality in the context of projection image alignment. We have focussed our attention on the electron crystallography field, by applying such a phase consistency definition over image reflections. The results that have been obtained show that the new phase-consistency definition may complement the traditional SNR-based index of quality (commonly known as IQ) of reflections. As a consequence, the reliability of the alignment may be improved by discarding those reflections judged as non-reliable according to the phase-consistency criterion.     

An accurate temperature-controlled polarimeter

A photoelectric polarimeter has been constructed for the purposes of calibrating polarimetric standards and for redetermining the value for the specific rotation of sucrose in solution. The polarimeter has full circle rotation capability with sensitivity of 0.6 arc-sec (3 μrad) and in specific measurements an estimated accuracy of ±2 arc-sec at the 99% confidence level. The polarimeter uses both arc lamp and laser sources. Sample temperatures can be controlled to within ±0.5 mK per day at, or around, 20°C, and six liquid, solid or gaseous samples may be simultaneously housed. Measurements of all six samples may be completed in a few minutes. In this paper we present the design details of this polarimetric system. The design required the careful application of high precision manufacturing techniques coupled closely with metrology throughout the manufacturing process