Damage of integrated circuits by high-velocity microparticles penetrating thick-wall obstacles

A flux of high-velocity microparticles, transmitted through a thick steel obstacle in the regime of superdeep penetration, also passes through the case of an integrated circuit (IC) situated behind this wall and produces damage of the IC chip.     

A shape optimization approach for simulating contact of elastic membranes with rigid obstacles

The obstacle problem consists in computing equilibrium shapes of elastic membranes in contact with rigid obstacles. In addition to the displacement u of the membrane, the interface Γ on the membrane demarcating the region in contact with the obstacle is also an unknown and plays the role of a free boundary. Numerical methods that simulate obstacle problems as variational inequalities share the unifying feature of first computing membrane displacements and then deducing the location of the free boundary a posteriori. We present a shape optimization-based approach here that inverts this paradigm by considering the free boundary to be the primary unknown and compute it as the minimizer of a certain shape functional using a gradient descent algorithm. In a nutshell, we compute Γ then u, and not u then Γ. Our approach proffers clear algorithmic advantages. Unilateral contact constraints on displacements, which render traditional approaches into expensive quadratic programs, appear only as Dirichlet boundary conditions along the free boundary. Displacements of the membrane need to be approximated only over the noncoincidence set, thereby rendering smaller discrete problems to be resolved. The issue of suboptimal convergence of finite element solutions stemming from the reduced regularity of displacements across the free boundary is naturally circumvented. Most importantly perhaps, our numerical experiments reveal that the free boundary can be approximated to within distances that are two orders of magnitude smaller than the mesh size used for spatial discretization. The success of the proposed algorithm relies on a confluence of factors- choosing a suitable shape functional, representing free boundary iterates with smooth implicit functions, an ansatz for the velocity of the free boundary that helps realize a gradient descent scheme and triangulating evolving domains with universal meshes. We discuss these aspects in detail and present numerous examples examining the performance of the algorithm.     

Improved shape memory composites combined with TiNi wire and shape memory epoxy

In order to develop high functionality of shape memory materials, the shape memory composites combined with TiNi wire and shape memory epoxy were fabricated, and the mechanical and thermomechanical properties were studied. The results showed that TiNi wire can compensate for the stiffness decrease of SMPs at elevated temperature, and the strength of interface and strength of interface matrix were important to further increase elevated temperature mechanical properties. The recovery stress of composites could be adjusted by changing the pre-strain, and the maximum recovery stress was obtained at 8% which was TiNi wire maximum recoverable strain. The addition of 1 vol% TiNi wire could increase the maximum recovery stress from 1.36 MPa to 4.04 MPa, which was almost 3 times of the matrix and at the same time maintained the rates of shape fixity and shape recovery close to 100%.     

形状记忆材料的新进展

除高分子形状记忆材料外,按目前发展态势,将形状记忆材料分为四类(1)具热弹性马氏体相变、呈温控形状记忆效应(SME)的材料,(2)具半热弹性马氏体相变,由应力诱发马氏体,呈SME的材料,(3)具热弹性马氏体相变、由温控及磁控呈SME的铁磁材料,(4)具热弹性马氏体相变,在马氏体态由磁控呈现SME的材料.简述前一、二类材料的发展现状.阐述三、四类材料的研究现状和应用前景.     

Detection and characterization of penetrating pores in porous materials

Sintered porous materials fabricated from powdered super-alloy are considered to be prime candidates for applications requiring transpiration cooling. The characteristics of these materials, especially the distribution and size of the penetrating pores at the surface exposed in high heat flux, are important because they directly affect the cooling and burned-out location. Thus, it is necessary to detect and characterize quantitatively the penetrating pores at the surface. This paper describes a digital image processing technique that was successfully used to detect the penetrating pores at the surfaces of porous plates. It is suggested that the homogeneous dimension minimum concept can be used to describe quantitatively the exterior property of the porous materials.     

Flammability of raw insulation materials made of hemp

Due to the fact that natural materials are more sensitive to flammability, it is necessary to determine flammability properties of nonwovens from natural fibers. This paper reports the fire reaction test results comparison of non-woven hemp fibers insulation materials made by three technologies. Hydro-entangling, thermal-bonding and needle-punching technologies were used for samples production from carded web. This review particularly compares the effects of flammability to find out influences of fibers properties and applied non-woven technologies.     

Nonstationary vibrations of structures made of composite materials

An efficient method for the analysis of nonstationary vibrations of structures by finite element modeling in the space of Fourier transforms is presented.     

Differential theory of gratings made of anisotropic materials

Arbitrary profiled gratings made with anisotropic materials are discussed; the anisotropic character concerns electric and/or magnetic properties. Our aim is to avoid the use of the staircase approximation of the profile, whose convergence is questionable. A coupled first-order differential-equation set is derived by taking into account Li's remarks about Fourier factorization [J. Opt. Soc. Am. A 13, 1870 (1996)], but the present formulation shows that, in return for a convenient form of the differential system, it is possible to use only the intuitive Laurent rule. Our method, when applied to the simpler case of isotropic gratings, is shown to be consistent with that of previous studies. Moreover, from the numerical point of view, the convergence of our formulation for an anisotropic grating is faster than that of the conventional differential method.     

Generalized shape optimization of three-dimensional structures using materials with optimum microstructures

This paper deals with generalized shape optimization of linearly elastic, three-dimensional continuum structures, i.e. we consider the problem of determining the structural topology (or layout) such that the shape of external as well as internal boundaries and the number of inner holes are optimized simultaneously. For prescribed static loading and given boundary conditions, the optimum solution is sought from the condition of maximum integral stiffness (minimum elastic compliance) subject to a specified amount of structural material within a given three-dimensional design domain. This generalized shape optimization problem requires relaxation which leads to the introduction of microstructures. A class of optimum three-dimensional microstructures and explicit analytical expressions for their optimum effective stiffness properties have been developed by Gibiansky and Cherkaev (1987) [Gibiansky, L.V., Cherkaev, A.V., 1987. Microstructures of composites of extremal rigidity and exact estimates of provided energy density (in Russian). Report (1987) No. 1155. A.F. Ioffe Physical-Technical Institute, Academy of Sciences of the USSR, Leningrad. English translation in: Kohn, R.V., Cherkaev, A.V. (Eds.), Topics in the Mathematical Modelling of Composite Materials. Birkhaüser, New York. 1997]. The present paper gives a brief account of the results in Gibiansky and Cherkaev (1987) which will be utilized for our microlevel problem analysis. It is a characteristic feature that the use of optimum microstructures renders the global problem convex if an appropriate parametrization is applied. Hereby local optima can be avoided and we can construct a simple gradient based numerical method of mathematical programming for solution of the complete optimization problem. Illustrative examples of optimum layout and topology designs of three-dimensional structures are presented at the end of the paper.     

三维障碍物形状近场反演的一种快速算法

文章研究了从点声源散射场的有限孔径近场测量信息来再现多个三维障碍物形状的反问题。指出了数值求解这类反问题的一种简单快速逄。数值结果表明了该算法是有效和实用的。     

Temperature measurements made with a combined Rayleigh -Mie and Raman lidar

The NASA Goddard Space Flight Center stratospheric ozone lidar system has the capability of collecting both Rayleigh -Mie and Raman backscatter data simultaneously at a number of wavelengths. Here we report on an improved method by which temperature can be derived from a combination of the Rayleigh -Mie return at 351-nm lidar channels and the Raman nitrogen return at 382-nm lidar channels. We also examine some common techniques by which temperatures are retrieved from lidar data. Finally, we show results obtained in 1995 during two Network for the Detection of Stratospheric Change intercomparison campaigns at Lauder, New Zealand and Mauna Loa, Hawaii.     

Reformulation of the fourier modal method for surface-relief gratings made with anisotropic materials

Abstract

By the use of the correct Fourier factorization rules presented in an earlier paper by Li the Fourier modal method (FMM) for anisotropic surface-relief gratings is reformulated. The newly formulated FMM converges much faster than the old formulation when the permittivity contrast in the grating groove region is large. Highly conducting lamellar gratings coated with anisotropic materials can now be analysed easily. In addition, a simple set of criteria are given for determining the energy propagation directions of the plane waves associated with the real solutions of the Booker quartic.     

Transient response analysis of structures made from viscoelastic materials

The response of structures made from viscoelastic materials to transient excitations is studied using the finite element method. The viscoelastic material behaviour is represented by the complex modulus model. An efficient method using fast Fourier transform has been developed. This method is based on the trigonometrical representation of the input signals and matrix of the transfer functions. The present implementation gives the possibility to preserve exactly the frequency dependence of the storage and loss moduli of materials. On this reason this time‐domain representation is a mathematically correct way to avoid the non‐causal effect. Test problems and numerical examples are given to demonstrate the validity and effectiveness of the approach suggested in this paper. Copyright © 1999 John Wiley & Sons, Ltd.