Advances in scanning electron microscope moiré

The scanning electron microscope (SEM) moiré method for microscopic measurements based on electron beam lithography and an SEM has been well developed. Although it has been a reliable method, some drawbacks exist: reinforcement effects, complicated processing and low sensitivity. To improve the SEM moiré method, new grating-casting techniques and a fringe-viewing technique must be developed. In this study, a carbonaceous grating technique and a total imaging technique are introduced. Accordingly, there are two techniques available for grating-casting (i.e., the carbonaceous grating technique and the existing lithography grating technique) and three techniques available for fringe viewing (i.e., the total imaging technique, the existing, monitor viewing technique and the existing photographic viewing technique). A total of six new imaging techniques of SEM moiré methods are available for microscopic measurements by combining one technique from each of the two groups. This study demonstrates the feasibility of the individual techniques and discusses the characteristics and limitations of each. Based on the presented total imaging technique, the sensitivity of the moiré method is only dependent on the frequency of specimen grating. Because it can be made as high as 10,000 lines/mm, the SEM moiré method can achieve sensitivity as high as 0.01 percent.     

Grid Method for Microscale Discontinuous Deformation Measurement

The objective of this paper is to explore both grid method and Digital Image Correlation (DIC) technique for microscale and discontinuous displacement measurements, such as those associated with crack tips. First, the principle of the grid method is revisited. The grid method and DIC technique are then applied to computer generated images to calculate the displacement field around crack tips. Finally, the grid method is applied to actual experimental images of fracture tests which are conducted inside a Scanning Electron Microscope (SEM) chamber. A new technique is developed to generate microscale pattern that is suitable for both grid method and DIC technique. The displacement fields calculated from grid method are compared with those from DIC technique to identify the strengths and weaknesses of each technique for the microscale and discontinuous displacement measurements. It has been determined that grid method can obtain data closer to the discontinuity than DIC; however, DIC produces smoother displacement fields at the far field. Using this new pattern generation technique, both grid method and DIC technique can be applied to the fracture test at the microscale to complement with each other to achieve the best experiment results.     

基于多边界切割插值的改进子模型分析方法

应用传统子模型技术进行结构的有限元分析,可以提高计算精度,得到局部的精确解,但仅适用于切割边界为体单元和壳单元的模型,当有其他类型单元通过切割边界时将产生很大的误差。本文对传统子模型技术及存在的问题进行了系统分析,提出了多边界插值方法和改进多边界插值方法,并应用于深水张力腿平台的整体模型和子模型分析,探讨了传统边界插值方法、多边界插值方法和改进多边界插值方法的计算精度。计算结果表明,相比传统边界插值方法,多边界插值方法具有更高的计算精度,随着内外切割边界距离的增大,误差逐渐减小并趋于稳定;改进多边界插值方法能进一步提高内外切割边界距离较小时的计算精度,可以满足梁单元通过切割边界的情况,拓宽了子模型技术的应用范围。     

Periodic solutions for certain non-smooth oscillators by iterated homotopy perturbation method combined with modified Lindstedt-Poincaré technique

In this paper, a new technique is introduced by combining Homotopy perturbation method and modified Lindstedt-Poincaré technique to obtain the periodic solutions of certain non-smooth oscillators. In this technique, homotopy perturbation method is re-written in iterative form to linearize perturbation process by homotopy, and then, the modified Lindstedt-Poincaré method is utilized to obtain next approximation for each iteration step. We realize that this new technique works very well for the whole range of initial amplitudes, and the excellent agreement of the approximate frequencies and periodic solutions with the exact ones has been confirmed and discussed. Only one or two iterations lead to high accuracy of the solutions. The result obtained and comparison with analytical solution and different methods provide confirmation for the validity of the technique.     

New developments in the localized hybrid method of stress analysis

Developments of the localized hybrid method which combines an experimental technique, moiré interferometry, and a numerical method, finite-element analysis, are presented. In this localized hybrid method, the displacement fields which the moiré experiments provide in some local regions of interest are used as input data for finite-element stress analyses. Based on finite-element theory, several variations on this localized hybrid method, associated with different displacement boundary conditions, are developed. Applications and limitations of the localized hybrid method are discussed in detail. In particular, applications of the localized hybrid method of stress analysis are presented for three-dimensional problems in the mechanics of solids. It is shown that this localized hybrid analysis not only provides a powerful and efficient technique for the reduction of moiré experimental data, but also gives a good insight into the mechanics of the experimental observations.     

Simultaneous recording of fringe patterns with one camera

A novel method to separate and simultaneously record the Moiré interferometry fringe patterns of three deformation fields with only one CCD camera is developed; details of its operation principle, key points and error analysis are presented. With this technique, the deformation inU, V andW fields can be measured simultaneously, so dynamic test with comprehensive information can be performed. The advantage of this technique over other similar techniques lies in its simplicity, easy implementation and low cost. An application of this technique is given to show its feasibility. Technical problems that may be caused with this technique are also analyzed.     

A hybrid method for computing the flow of viscoelastic fluids

A hybrid method for computing the flow of viscoelastic and second-order fluids is presented. It combines the features of the finite difference technique and the shooting method. The method is accurate because it uses central differences. Its convergence is at least superlinear. The method is applied to obtain the solutions to three problems of flow of Walters' B' fluid: (a) flow near a stagnation point, (b) flow over a stretching sheet and (c) flow near a rotating disk. Numerical results reveal some new characteristics of flows which are not easy to demonstrate using the perturbation technique.     

Application of second‐order adjoint technique for conduit flow problem

This paper presents the way to obtain the Newton gradient by using a traction given by the perturbation for the Lagrange multiplier. Conventionally, the second‐order adjoint model using the Hessian/vector products expressed by the product of the Hessian matrix and the perturbation of the design variables has been researched (Comput. Optim. Appl. 1995; 4 :241–262). However, in case that the boundary value would like to be obtained, this model cannot be applied directly. Therefore, the conventional second‐order adjoint technique is extended to the boundary value determination problem and the second‐order adjoint technique is applied to the conduit flow problem in this paper. As the minimization technique, the Newton‐based method is employed. The Broyden–Fletcher–Goldfarb–Shanno (BFGS) method is applied to calculate the Hessian matrix which is used in the Newton‐based method and a traction given by the perturbation for the Lagrange multiplier is used in the BFGS method. Copyright © 2007 John Wiley & Sons, Ltd.     

A meshless finite point method for three‐dimensional analysis of compressible flow problems involving moving boundaries and adaptivity

A finite point method for solving compressible flow problems involving moving boundaries and adaptivity is presented. The numerical methodology is based on an upwind‐biased discretization of the Euler equations, written in arbitrary Lagrangian–Eulerian form and integrated in time by means of a dual‐time steeping technique. In order to exploit the meshless potential of the method, a domain deformation approach based on the spring network analogy is implemented, and h‐adaptivity is also employed in the computations. Typical movable boundary problems in transonic flow regime are solved to assess the performance of the proposed technique. In addition, an application to a fluid–structure interaction problem involving static aeroelasticity illustrates the capability of the method to deal with practical engineering analyses. The computational cost and multi‐core performance of the proposed technique is also discussed through the examples provided. Copyright © 2013 John Wiley & Sons, Ltd.     

Finite element analysis of filling stage in die‐casting process using marker surface method and adaptive grid refinement technique

The marker surface method and the adaptive grid refinement technique have been applied to the three‐dimensional (3‐D) finite element analysis of the filling stage in the die‐casting process. Especially, the marker surface plugging technique and the marker surface regeneration technique incorporated in the marker surface method have been proposed for the efficient analysis of 3‐D practical problems. Through the marker surface plugging technique, new parts of marker surface are effective lycreated in order to eliminate the gaps between the parts of marker surface or between the edge of marker surface and cavity wall. By using the marker surface regeneration technique, the marker surface including a great number of marker elements is recreated on the basis of its original shape in order to decrease the number of marker elements and computational time. A3‐D example used as the benchmark test and a typical industrial problem of the die‐casting process have been analysed. The numerical results have been in good agreement with the experimental results and the efficiency of the adaptive grid refinement technique has been verified. It has been shown that the proposed techniques incorporated in the marker surface method and the adaptive grid refinement technique can be effectively applied to general industrial problems. Copyright © 2004 John Wiley & Sons, Ltd.     

Rheological study of concentrated suspensions in pressure-driven shear flow using a novel in-line ultrasound Doppler method

 In this work a novel in-line non-invasive rheological measuring technique is developed and tested in pilot plant and industrial-scale applications. The method is based on a combination of the ultrasonic pulsed echo Doppler technique (UVP) and pressure difference method (PD). The rheological flow properties are derived from simultaneous recording and on-line analysis of the velocity profiles across the tube channel and related radial shear stress profiles calculated from the pressure loss along the flow channel. It is shown that the in-line UVP-PD technique allows for the non-invasive rheological flow behaviour characterization of non-transparent and highly concentrated suspensions. Received: 8 May 2000 / Accepted: 22 June 2001 Published online: 29 November 2001     

Modern Methods of Drying Nanomaterials

This paper presents the types of nanomaterials whose technology requires drying during processing. The methods of drying of three groups of nanomaterials are discussed: nanoparticles, nanolayers (nanofilms), and nanoporous materials. Principally the method of spray drying using ultrasonic nebulizers and electrospraying is presented for the first group. The Langmuir–Blogget technique is presented for the second group. The method of supercritical drying and the solvent replacement technique is described for the third group. Technological aspects of the presented methods are also briefly described.     

Variational asymptotic micromechanics modeling of heterogeneous porous materials

This paper presents a numerical technique to predict the effective elastic properties of heterogeneous fluid-filled porous media where the heterogeneity may result from dissimilar solid and fluid phase properties or due to mismatch in porous microstructure. The technique is based on the variational asymptotic method of homogenization where finite element method is employed for discretization. Biot’s theory of poroelasticity is used to describe porous media where both solid and fluid phase motions (u ? U formulation) are considered with associated strain measures. The method estimates the poroelastic constitutive law in single analysis which makes it very efficient compared to other finite element based homogenization techniques. The method is also general enough to compute all 28 elements of an anisotropic constitutive matrix. Other than estimating the effective properties the micro-stress/strain distribution is also obtained at no additional cost.The method is successfully applied for homogenization of porous media, fluid-filled cavity and finally for effective property estimation of bone lamella. In absence of any other direct method of porous media homogenization, the present technique is compared with classical homogenization methods with fluid approximated as solid of very high Poisson’s ratio. The suitability of this approximation and various other alternatives are also discussed. It is shown that the present homogenization method can be an efficient tool for bone property estimation where fluid-filled porous hierarchical micro-/nanostructure must be respected at all steps.     

固体的弹性模量和内耗测量方法研究进展

弹性模量和内耗是固体材料的基本力学性质, 其测量的准确性和便捷性对工业生产和科学研究都很重要. 本文回顾了近一百年来固体材料弹性模量和内耗的测量方法, 主要分为四类: 准静态方法、低频法、共振法和波传播法. 首先对每类方法的测量原理进行了简单介绍及总体评价. 接着对几种共振方法, 包括自由梁共振法、脉冲激励法、超声共振谱方法和压电超声复合振动技术(PUCOT)进行了详细介绍和评价. 然后, 重点介绍了本课题组最新提出的基于机电阻抗的模量内耗测量方法(称之为M-PUCOT或Q-EMI), 它可以同时、准确、快速地测量杨氏/剪切模量及相应内耗. 最后, 对这种新型弹性模量/内耗测量方法的意义和应用前景进行了讨论和展望.      

Analysis of phase-jitter evolution in a reattaching shear layer

A modification to the phase-jitter calculation procedure of Ho et al. (J Fluid Mech 230:319–337, 1991), called the HZFB method (Ho, Zohar, Foss, and Buell), and an extension of the pattern recognition technique for phase-jitter calculation are presented in this work. Results for the phase jitter calculated using the three methods are compared for a separated shear layer past a surface-mounted rib. The original HZFB method is shown to yield inaccurate results in the presence of small-scale turbulence, while the modified HZFB method and the pattern recognition technique provide the correct estimates of phase jitter.     

The adjoining cell mapping and its recursive unraveling,part II: Application to selected problems

Several applications of the adjoining cell mapping technique are provided here by employing the adaptive mapping unraveling algorithm to analyze smooth and pathological autonomous dynamical systems. The performance of an implementation of recursive unraveling algorithm is also illustrated regarding its low memory requirements for computational purposes when compared with the simple cell mapping method. The applications considered here illustrate the effectiveness of the adjoining cell mapping technique in its ability to determine limit cycles and to unravel nonstandard dynamics. The advantages of this new technique of global analysis over the simple cell mapping method are discussed.     

An analytical approximate technique for a class of strongly non-linear oscillators

An analytical approximate technique for large amplitude oscillations of a class of conservative single degree-of-freedom systems with odd non-linearity is proposed. The method incorporates salient features of both Newton's method and the harmonic balance method. Unlike the classical harmonic balance method, accurate analytical approximate solutions are possible because linearization of the governing differential equation by Newton's method is conducted prior to harmonic balancing. The approach yields simple linear algebraic equations instead of non-linear algebraic equations without analytical solution. With carefully constructed iterations, only a few iterations can provide very accurate analytical approximate solutions for the whole range of oscillation amplitude beyond the domain of possible solution by the conventional perturbation methods or harmonic balance method. Three examples including cubic-quintic Duffing oscillators are presented to illustrate the usefulness and effectiveness of the proposed technique.     

Application of the laser beam deflection to the study of temperature fields in Rayleigh–Benard convection

An optical integral and unobtrusive method is developed to determine the temperature gradient field by measurement of laser beam deflection induced by optical index changes. The technique is inexpensive and easy to perform. It allows the study of the temperature gradient at a large number of points simultaneously (over 400/cm²). This technique is particularly adapted to two-dimensional convection flow in both unsteady and steady conditions. For illustration purposes, such a technique is applied to the roll pattern of Rayleigh-Bénard convection. The agreement between theory and experiments is fair.     

Digital image correlation using Newton-Raphson method of partial differential correction

Digital image correlation is finding wider use in the field of mechanics. One area of weakness in the current technique is the lack of available displacement gradient terms. This technique, based on a coarse-fine search method, is capable of calculating the gradients. However the speed at which it does so has prevented widespread use. Presented in this paper is the development and limited experimental verification of a method which can determine displacements and gradients using the Newton-Raphson method of partial corrections. It will be shown that this method is accurate in determining displacements and certain gradients, while using significantly less CPU time than the current coarse-fine search method. Paper was presented at the 1988 SEM Spring Conference on Experimental Mechanics held in Portland, OR on June 5–10.