Boundary integral equations for the scattering of elastic waves by elastic inclusions with thin interface layers

Elastic waves are scattered by an elastic inclusion. The interface between the inclusion and the surrounding material is imperfect: the displacement and traction vectors on one side of the interface are assumed to be linearly related to both the displacement vector and the traction vector on the other side of the interface. The literature on such inclusion problems is reviewed, with special emphasis on the development of interface conditions modeling different types of interface layer. Inclusion problems are formulated mathematically, and uniqueness theorems are proved. Finally, various systems of boundary integral equations over the interface are derived.     

ERD facility for analysis of hydrogen and deuterium in solids

Hydrogen is the lightest element in nature, and so, its detection and quantitative analysis is difficult by the conventional methods utilized for other elements. In the recent years the technique of elastic recoil detection analysis (ERD) using 1–2 MeV He⁺ beam has been developed to quantitatively and simultaneously analyze hydrogen and its isotopes in solids. Such a facility has been set up using the 2 MeV Van-de-Graaff accelerator at IIT Kanpur. It facilitates H and D analysis in a material up to a depth of ∼ 1μm with a detection sensitivity of 0·1 at.% and depth resolution of about 300 ?. The application potential of this setup is illustrated by presenting the results of measurements performed on Al:H:D systems prepared by plasma source ion implantation and highT _c YBCO pellets exposed to humid atmosphere.     

Compositional analysis of polycrystalline hafnium oxide thin films by heavy-ion elastic recoil detection analysis

The composition of polycrystalline hafnium oxide thin films has been measured by heavy-ion elastic recoil detection analysis (HI-ERDA). The films were deposited by high-pressure reactive sputtering (HPRS) on silicon wafers using an oxygen plasma at pressures between 0.8 and 1.6 mbar and during deposition times between 0.5 and 3.0 h. Hydrogen was found to be the main impurity and its concentration increased with deposition pressure. The composition was always slightly oxygen-rich, which is attributed to the oxygen plasma. Additionally, an interfacial silicon oxide thin layer was detected and taken into account. The thickness of the hafnium oxide film was found to increase linearly with deposition time and to decrease exponentially with deposition pressure, whereas the thickness of the silicon oxide interfacial layer has a minimum as a function of pressure at around 1.2 mbar and increases slightly as a function of time. The measurements confirmed that this interfacial layer is formed mainly during the early stages of the deposition process.     

退火对 a-Si∶H/a-SiN_x∶H 多层膜光致发光和红外吸收谱的影响

本文报道了经300℃到800℃退火后的氢化非晶硅(a-Si∶H)/氢化非晶氮化硅(a-SiN_x∶H)多层膜77K 的光致发光性能。77K 的光致发光峰值能量随 T_a 增加而减少,其减少速度对几种样品是不同的,由厚度为20(?)的 a-Si∶H 子层组成的多层膜(d_(?)=20(?))要来得慢。当退火温度达到800℃时,d_(?)=20(?)的多层膜仍保留有光致发光特性,而对于 d_(?)=300(?)多层膜和单层 a-Si∶H 膜,当退火到600℃后光致发光特性已消失。文中提出了不同 a-Si∶H 子层厚度的多层膜光致发光特性上的差别是与 a-Si∶H/a-SiN_x∶H 界面氢比体内氢热稳定性来得高有关。后者由多层膜的红外吸收谱与退火温度依赖关系得到证实。     

Transient and thermal contact analysis for the elastic behavior of functionally graded brake disks due to mechanical and thermal loads

In this paper, the transient and contact analysis of functionally graded (FG) brake disk is presented. The analysis was carried out using ANSYS parametric design language (APDL). The FG brake disk is made of metal–ceramic material. The material properties vary in radial direction with the values from full-metal at the inner radius to that of full-ceramic at the outer radius. In the analysis, FG brake disk is in contact with one pure pad disk and coulomb contact friction is considered as heat source. The non-dimensional results are obtained for specific value of grading index (n = 1) by considering different material property divisions of 25, 50, 100 and 200. The results presented are for the pressure distribution, total stress, pad penetration, friction stress, heat flux and temperature during contact, for different values of contact stiffness factor, F_kn, which depends on the property gradation of FG brake disk with 200 material property divisions. The results show that the contact pressure and contact total stress increase with increasing values of F_kn, and hence it can be concluded that gradation of the metal–ceramic has significant effect in the thermomechanical response of FG brake disks.     

A comparison of exact first order and spring boundary conditions for scattering by thin layers

In scattering problems for time-harmonic elastic waves, thin elastic layers are often of interest, e.g., in laminates. Various ways of substituting such layers by some effective boundary conditions have been proposed, and these are briefly reviewed. A rational way of obtaining boundary conditions that are exact to first order in the layer thickness is then described. For a thin spherical layer numerical comparisons are performed between these exact first order boundary conditions, the commonly used spring boundary conditions and the exact solution, and it is shown that the exact boundary conditions are far superior to the spring boundary conditions in most situations. A drawback with the exact boundary conditions is that they are quite complicated.     

退火对UHVCVD外延生长锗硅碳三元合金的影响

采用傅立叶红外吸收光谱(FTIR)和X射线衍射(XRD)研究了超高真空化学气相沉积外延生长的Si1-x-yGexCy三元合金的热稳定性.在比较高的退火温度下(950℃或以上),Si1-x-yGexCy中的替代位的C逐渐形成SiC沉淀,减弱了应变的补偿作用,从而增大了合金中的应变,显示出不同于Si1-xGex的弛豫行为.     

Modeling of elastic thermal stresses in two materials joined by a graded layer

The distribution of elastic thermal stresses in two dissimilar materials joined by a graded layer is a critical issue and has been analyzed previously. However, numerical methods have often been used. The difficulty in obtaining an analytical solution in existing analyses is discussed, and an exact closed-form solution is derived in the present study. To illustrate applications of the present solution, results are calculated for elastic thermal stresses in thermal barrier coatings, which consist of substrate, graded bond coat, and top coat. Different profiles of the thermomechanical properties in the bond coat are considered to examine how the graded interlayer modifies the elastic thermal stress distribution in the system.     

TEM analysis of InMnAs layers and dots prepared by low pressure MOVPE

The properties of InMnAs epitaxial layers and quantum dots prepared on (100) GaAs substrates using Metal-Organic Vapor Phase Epitaxy (MOVPE) are reported. Transmission Electron Microscopy (TEM) observation confirmed that the quantum dot structures were plastically relaxed. The degree of relaxation depends on the amount of Mn incorporated in the structure. Moiré fringes at TEM plan view images were used to evaluate strain in the InMnAs quantum dot structures. TEM observation confirmed that the InMnAs dots were uniform and they grew in the zinc-blende structure. The bright field TEM micrographs (cross-sectional) of the epitaxial layers showed the presence of InMnAs precipitates located under the interface between the InMnAs and substrate.     

Reactively sputtered TiO2 layers on SnO2:F substrates: A Raman and surface photovoltage study

DC reactively sputtered TiO₂ layers on SnO₂:F substrates were investigated by Raman and surface photovoltage spectroscopy. The stoichiometry and layer thicknesses were investigated by elastic recoil detection analysis. The deposition temperature, the O₂/(O₂ + Ar) ratio and the deposition time were varied systematically. With increasing temperature, the layers become crystalline with the rutile modification dominating. Rutile phase preferentially forms on vertical facets of SnO₂ crystallites. Anatase phase starts to form during prolonged deposition and at lower O₂/(O₂ + Ar) ratios. The energy of the exponential absorption tails below the band gap, a measure of the defect density of the films, is determined by the deposition temperature and not by other parameters if the deposition temperature is relatively high, irrespective of the content of crystalline phases or the value of the band gap. Charge separation takes place at length scales significantly shorter than the layer thicknesses (diffusion length less than 6 nm). TiO₂ films sputtered at 380 °C show rectifying behaviour with a carbon contact.     

Feasibility of fast neutron analysis for the detection of explosives buried in soil

A commercialized thermal neutron analysis (TNA) sensor has been developed to confirm the presence of buried bulk explosives as part of a multi-sensor anti-tank landmine detection system. Continuing improvements to the TNA system have included the use of an electronic pulsed neutron generator that offers the possibility of applying fast neutron analysis (FNA) methods to improve the system's detection capability. This paper describes an investigation into the use of FNA as a complementary component in such a TNA system. The results of a modeling study using simple geometries and a full model of the TNA sensor head are presented, as well as preliminary results from an experimental associated particle imaging (API) system that supports the modeling study results. The investigation has concluded that the pulsed beam FNA approach would not improve the detection performance of a TNA system for landmine or buried IED detection in a confirmation role, and could not be made into a practical stand-alone detection system for buried anti-tank landmines. Detection of buried landmines and IEDs by FNA remains a possibility, however, through the use of the API technique.     

Developments in nuclear techniques for hydrogen depth profiling

Hydrogen plays a crucial role in the properties of various materials, devices and in growth of hydrogenated amorphous materials. Therefore, its quantification and determination of concentration at various depths is of immense interest. Among various techniques of hydrogen depth profiling, the nuclear techniques being non-destructive in nature are widely used. Elastic recoil detection analysis (ERDA) with helium ions was first used for hydrogen depth profiling. Later on, the heavy ions were utilised due to certain advantages. It has been shown recently by us that H alongwith other elements in thin film up to Ca can be detected simultaneously with heavy ion ERDA, if the elements being detected are well separated in masses. It also has been shown that even the neighbouring elements such as C, N, O alongwith H can be detected provided a ΔE-E detector telescope is used in ERDA. The time of flight (TOF) with ERDA, nuclear reaction analysis (NRA), neutron TOF are other nuclear techniques such as hydrogen loss during the measurement, which must be taken into account for accurate and reliable results. A scenario of developments in nuclear techniques with suitable examples is given in this brief review.     

Behaviour analysis of numerical solutions and simulation of coherent structures in compressible mixing layers

For understanding the correctness of simulations the behaviour of numerical solutions is analysed. In order to improve the accuracy of solutions three methods are presented. The method with GVC (group velocity control) is used to simulate coherent structures in compressible mixing layers. The effect of initial conditions for the mixing layer with convective Mach number 0.8 on coherent structures is discussed. For the given initial conditions two types of coherent structures in the mixing layer are obtained.     

Modifications in thin film structures by swift heavy ions

We review older and more recent work concerning modification of thin films during irradiation with heavy ions in the electronic energy deposition regime: loss of H₂ and N₂ from the bulk of several thin film materials, electronic sputtering of SiO₂ and oxygen diffusion across an interface in SiO₂.     

A sweeping window method for detection of flaws using an explicit dynamic XFEM and absorbing boundary layers

We present a sweeping window method in elastodynamics for detection of multiple flaws embedded in a large structure. The key idea is to measure the elastic wave propagation generated by a dynamic load within a smaller substructural detecting window domain, given a sufficient number of sensors. Hence, rather than solving the full structure, one solves a set of smaller dynamic problems quickly and efficiently. To this end, an explicit dynamic extended FEM with circular/elliptical void enrichments is implemented to model the propagation of elastic waves in the detecting window domain. To avoid wave reflections, we consider the window as an unbounded domain with the option of full‐infinite/semi‐infinite/quarter‐infinite domains and employ a simple multi‐dimensional absorbing boundary layer technique. A spatially varying Rayleigh damping is proposed to eliminate spurious wave reflections at the artificial model boundaries. In the process of flaw detection, two phases are proposed: (i) pre‐analysis—identification of rough damage regions through a data‐driven approach, and (ii) post‐analysis‐–identification of the true flaw parameters by a two‐stage optimization technique. The ‘pre‐analysis’ phase considers the information contained in the ‘pseudo’ healthy structure and the scattered wave signals, providing an admissible initial guess for the optimization process. Then a two‐stage optimization approach (the simplex method and a damped Gauss–Newton algorithm) is carried out in the ‘post‐analysis’ phase for convergence to the true flaw parameters. A weighted sum of the least squares, of the residuals between the measured and simulated waves, is used to construct the objective function for optimization. Several benchmark examples are numerically illustrated to test the performance of the proposed sweeping methodology for detection of multiple flaws in an unbounded elastic domain. Copyright © 2015 John Wiley & Sons, Ltd.     

Hydrogen influence on the structure and properties of amorphous hydrogenated carbon films deposited by direct ion beam

The present work provides results for amorphous hydrogenated carbon (a-C:H) films grown by direct ion beam deposition method. Acetylene and its mixtures with hydrogen were used. The films were characterized by Rutherford backscattering spectrometry, elastic recoil detection, Raman spectroscopy, ellipsometry, infrared spectroscopy, and microhardness measurements. These techniques indicated that an admixture of hydrogen yields a lower deposition rate, a higher content of total and bounded hydrogen in the a-C:H films, and a lower film density. The optical and mechanical properties depend on both, hydrogen concentrations in the gas phase and in the films, and show a strong diamond-like component, which reaches maximum at 34 at.% of hydrogen. Further hydrogen dilution enhanced only sp² clustering and possible reduced a number of both sp³ and C-C sp³ bonds. We suppose that these effects (in the high hydrogen concentration range) are not only related to the ion irradiation difference between the light hydrogen and the much heavier carbon but also to the diffusion in the a-C:H films.     

Damage detection in beams from modal and wavelet analysis using a stationary roving mass and noise estimation

This paper uses the Continuous Wavelet Transform Analysis on mode shapes for damage identification. The wavelet analysis is applied to the difference in the mode shapes between a healthy and a damaged state. The paper also includes a novel methodology for estimating the level of noise of the experimental mode shapes based on a standard Signal to Noise Ratio (SNR). The estimated SNRs are used for identifying and making emphasis on the less noisy data. Moreover, a mass attached to the structure is considered to enhance the sensitivity of the structure to damage. Modal analysis is performed for different positions of the mass along the beam. The results obtained for all the positions of the mass are combined so an averaging process is implicitly applied. The paper presents the results from an experimental test of a cantilever steel beam with different severity levels of damage at the same location. The results show that the use of the attached mass reduces the effect of noise and increases the sensitivity to damage. Little damage can be identified with the proposed methodology even using a small number of sensors and only the first five bending modes.     

Tensor-valued random fields for meso-scale stochastic model of anisotropic elastic microstructure and probabilistic analysis of representative volume element size

The main objective of this paper is to present a generic meso-scale probability model for a large class of random anisotropic elastic microstructures in order to perform a parametric analysis of the Representative Volume Element (RVE) size. This new approach can be useful for a direct experimental identification of random anisotropic elastic microstructures when the standard method cannot easily be applied to anisotropic elastic microstructures. Such a RVE is used to construct the macroscopic properties in the context of stochastic homogenization. The probability analysis is not performed as usual for a given particular random microstructure defined in terms of its constituents. Instead, it is performed for a large class of random anisotropic elastic microstructures. For this class, the probability distribution of the random effective stiffness tensor is explicitly constructed. This allows a full probability analysis of the RVE size to be carried out and its convergence to be studied. The procedure of homogenization is based on a homogeneous Dirichlet condition on the boundary of the RVE. The probability model used for the stiffness tensor-valued random field of the random anisotropic elastic microstructure is an extension of the model recently introduced by the author for elliptic stochastic partial differential operators. The stochastic boundary value problem is numerically solved by using the stochastic finite element method. The probability analysis of the RVE size is performed by studying the probability distribution of the random operator norm of the random effective stiffness tensor with respect to the spatial correlation length of the random microstructure.     

Effects of elastic unloading on multiple necking in tensile bars

The deformation of round tensile bars subject to dynamic loading is studied numerically using two different plasticity theories: J₂-flow theory and J₂-deformation theory. Time development of neck localization is visualized and a comparison of the necking patterns obtained using the two different constitutive models is presented. The possibility of using J₂-deformation theory as an alternative to J₂-flow theory to model the dynamic behaviour of tensile bars subject to high rate deformation is investigated and the effects of elastic unloading are discussed. Influence of specimen geometry and initial thickness imperfections is also considered. The effects of elastic unloading on multiple necking are of particular interest, since elastic unloading may serve as a restricting factor regarding the growth of multiple neck localizations. In the present analysis, multiple necking is found to appear using both J₂-flow theory and J₂-deformation theory. The use of stubby bars leads to similar necking patterns when comparing the results obtained with J₂-flow theory and J₂-deformation theory. For slender bars subject to certain loading conditions a larger number of necks is obtained when J₂-deformation theory is applied rather than J₂-flow theory. In addition, results of simulations near the ideal-plastic limit are discussed as well as results where the yield stress is varied.