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Shortall, Christopher Douglas. "Mechanical characterisation of an isotropic stainless steel fibre network material." Thesis, University of Cambridge, 2009. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.611295.
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Weinberg, Eli 1979. "Dynamic simulation of heart mitral valve with transversely isotropic material model." Thesis, Massachusetts Institute of Technology, 2005. http://hdl.handle.net/1721.1/32376.
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Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2005.<br>Includes bibliographical references (p. 63-69).<br>This thesis develops two methods for simulating, in the finite element setting, the material behavior of heart mitral valve leaflet tissue. First, a mixed pressure-displacement formulation is used to implement the constitutive material behavior with general 3D elements. Second, a shell is formulated that incorporates the 3D material behavior by use of a local plane stress iteration method. Both of these works are based on an existing invariant-based strain energy function that has been experimentally determined for the mitral valve leaflet tissue. Since this material is considered to be nearly incompressible, a mixed pressure-displacement (u/p) formulation is needed to apply the material model in 3D elements. The standard (u/p) formulation is; employed with a modification to ensure positive definiteness of the constitutive tensor at low strains. The shell formulation is introduced as a computationally less expensive alternative to the use of 3D elements. A 4-node shell with mixed interpolation of transverse shears is implemented. To incorporate the 3D material model into this shell, a local plane stress iteration is used to enforce that the shell stress assumption at each integration point. Comparisons of numerical results to analytical predictions verify the accuracy of both the (u/p) formulation and shell element. These methods provide useful bases for finite element simulations of mitral heart valve behavior.<br>by Eli Weinberg.<br>S.M.
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Son, Seyul. "Nonlinear Electromechanical Deformation of Isotropic and Anisotropic Electro-Elastic Materials." Diss., Virginia Tech, 2011. http://hdl.handle.net/10919/28587.
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Electro-active polymers (EAPs) have emerged as a new class of active materials, which produce large deformations in response to an electric stimulus. EAPs have attractive characteristics of being lightweight, inexpensive, stretchable, and flexible. Additionally, EAPs are conformable, and their properties can be tailored to satisfy a broad range of requirements. These advantages have enabled many target applications in actuation and sensing. A general constitutive formulation for isotropic and anisotropic electro-active materials is developed using continuum mechanics framework and invariant theory. Based on the constitutive law, electromechanical stability of the electro-elastic materials is investigated using convexity and polyconvexity conditions. Implementation of the electro-active material model into a commercial finite element software (ABAQUS 6.9.1, PAWTUCKET, RI, USA) is presented. Several boundary and initial value problems are solved to investigate the actuation and sensing response of isotropic and anisotropic dielectric elastomers (DEs) subject to combined mechanical and electrical loads. The numerical response is compared with experimental results to validate the theoretical model.
For the constitutive formulation of the electro-elastic materials, invariants for the coupling between two families of electro-active fibers (or particles) and the applied electric field are introduced. The effect of the orientation of the electro-active fibers and the electric field on the
electromechanical coupling is investigated under equibiaxial extension. Advantage of the constitutive formulation derived in this research is that the electromechanical coupling can be illustrated easily by choosing invariants for the deformation gradient tensor, the electro-active fibers, and the electric field. For the electromechanical stability, it is shown that the stability can be controlled by tuning the material properties and the orientation of the electro-active fibers. The electromechanical stability condition is useful to build a stable free energy function and prevent the instabilities (wrinkling and electric breakdown) for the electro-elastic materials. The invariant-based constitutive formulation for the electro-elastic materials including the isotropic and anisotropic DEs is implemented into a user subroutine (UMAT in ABAQUS: user defined material) by using multiplicative decomposition of the deformation gradient and the applicability of the UMAT is shown by simulating a complicated electromechanical coupling problem in ABAQUS/CAE. Additionally, the static and dynamic sensing and actuation response of tubular DE transducers (silicone and polyacrylate materials) with respect to combined electrical and mechanical stimuli is obtained experimentally. It is shown that the silicone samples have better dynamic and static sensing characteristics than the polyacrylate. The theoretical modeling accords well with the experimental results.<br>Ph. D.
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Messenger, C. R. "Investigation of delamination and matrix cracking in quasi-isotropic GFRP laminates." Thesis, University of Surrey, 1996. http://epubs.surrey.ac.uk/842699/.
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Intra-laminar and inter-laminar cracking in GFRP laminates has been studied. The epoxy matrix used gave a transparent composite and was compatible with polyurethane, enabling a modified system (containing 20% urethane) to be investigated in addition to the standard epoxy. Three stacking sequences of quasi-isotropic laminates, (+45/-45/0/90)s, (0/90/-45/+45)s and (+45/90/-45/0)s were tested. Data were obtained for the growth of damage and its effect on laminate stiffness under increasing quasi-static load and as a function of number of fatigue cycles at two different stress levels. Using the transparent systems enabled a more complete set of damage data to be obtained than by previous workers. The damage comprised 90-ply cracking followed by +45 and -45 cracking and then for (+45/-45/0/90)s [and to a limited extent in (+45/90/-45/0)s], delamination. The initiation and growth of damage was examined with regard to matrix type and stacking sequence. The onset of matrix cracking and delamination are both delayed in the urethane-containing laminates; fracture mechanics tests showed that the urethane system was significantly tourer. Moreover, at a given quasi-static stress or number of fatigue cycles the urethane-modified laminates retain a greater proportion of their initial modulus. The stacking sequence influences interlaminar stresses (thereby controlling delamination) and determines parameters such as ply thickness and neighbouring ply orientation which in turn influence intralaminar cracking. Fracture mechanics has been applied to model the initiation and growth of delamination under quasi-static and cyclic loading using a modified compliance technique. Shear-lag models have been used to determine the stiffness loss due to intralaminar cracking, enabling the stiffness reduction associated with delamination to be deduced empirically. This enables the energy release rates associated with delamination to be derived leading to more sensible results than those obtained using an unmodified technique.
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Roche, Gerald J. "Investigation of the transmission of sound through isotropic, damped material layer(s) bounded by seawater." Thesis, Monterey, Calif. : Naval Postgraduate School, 2008. http://bosun.nps.edu/uhtbin/hyperion-image.exe/08Mar%5FRoche.pdf.
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Thesis (M.S. in Engineering Acoustics)--Naval Postgraduate School, March 2008.<br>Thesis Advisor(s): Scandrett, Clyde. "March 2008." Description based on title screen as viewed on May 5, 2008. Includes bibliographical references (p. 51). Also available in print.
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Bollero, Real Alberto. "Isotropic nanocrystalline (Nd,Pr)(Fe,Co)B permanent magnets." Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2003. http://nbn-resolving.de/urn:nbn:de:swb:14-1069758225796-19366.
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Nanokristalline Permanentmagnete zeigen ungewöhnliche magnetische Eigenschaften aufgrund von Oberflächen- und Grenzflächeneffekten, die verschieden von denen massiver oder mikrokristalliner Materialien sind. Diese Arbeit zeigt Ergebnisse einer systematischen Untersuchung der Beziehung zwischen Mikrostruktur und magnetischen Eigenschaften von isotropen nanokristallinen (Nd,Pr)(Fe,Co)B-Permanentmagneten. Hochkoerzitive Magnete vom Typ (Nd,Pr)FeB wurden durch hochenergetisches Mahlen in der Kugelmühle oder Rascherstarrung hergestellt. Der Einfluss geringer Mengen von Zusätzen wie Dy und Zr und die Substitution von Nd durch Pr auf die magnetischen Eigenschaften wird dargestellt. Weiterhin wurde eine Einschätzung des Warmumformverhaltens dieser Materialien durchgeführt. Hochenergetisches Kugelmahlen einer Legierung mit der Anfangszusammensetzung Pr9Nd3Dy1Fe72Co8B6.9Zr0.1 führte, nach Glühbehandlung, zu fast einphasigem Magnetpulver mit einem maximalen Energieprodukt von (BH)max~140 kJm-3. Das hochenergetische Kugelmahlen wurde zu einer sehr vielseitigen Technik zur Herstellung hochleistungsfähiger Nanokompositmagnete weiterentwickelt. Das Zulegieren unterschiedlicher Anteile von weichmagnetischem alpha-Fe ist damit sehr effektiv möglich. Der Zusatz von 25 Gew.-% alpha-Fe führt zu einem hohen (BH)max=178kJm-3. Dies wird auf eine sehr effektive Austauschkopplung zwischen den hart- und weichmagnetischen Phasen zurückgeführt. Die Natur der intergranularen Wechselwirkungen kann durch die Wohlfarth´sche Remanenzanalyse (?deltaJ-plot¡§) beschrieben werden. Im speziellen wurden deltaJ-Diagramme für verschiedene (i) alpha-Fe Gehalte, (ii) Korngrößen und (iii) Austauschlängen erstellt. Es konnte gezeigt werden, dass in den Nanokompositmagneten auf Pr-Basis keine Spinumorientierung auftritt. Abschließend zeigt die Arbeit die Möglichkeit der Nutzung einer mechanisch aktivierten Gas-Festkörper-Reaktion auf, mit der eine sehr feinkörnige Mikrostruktur erhalten wird. Die Untersuchungen wurden mit stöchiometrischen Nd2(Fe1-xCox)14B-Legierungen begonnen (x=0-1). Die Verbindungen wurden unter höheren Wasserstoffdrücken und Temperaturen gemahlen, wodurch sie zu NdH2+delta und krz-(Fe,Co) (x=0-0.75) oder kfz-Co (x=1) entmischt wurden. Die Korngrößen des rekombinierten Nd2(Co,Fe)14B-Materials liegen im Bereich von 40-50 nm<br>Nanocrystalline permanent magnets present unusual magnetic properties because of surface/interface effects different from those of bulk or microcrystalline materials. This work presents results of a systematic investigation of the relationship between microstructure and magnetic properties in isotropic nanocrystalline (Nd,Pr)(Fe,Co)B permanent magnets. Highly coercive (Nd,Pr)FeB-type magnets have been produced using high energy ball milling and melt-spinning. The influence of small amounts of additives, Dy and Zr, and the substitution of Nd by Pr on the microstructural and magnetic properties are shown. An assessment of the hot deformation behaviour has been carried out. Intensive milling of an alloy with starting composition Pr9Nd3Dy1Fe72Co8B6.9Zr0.1 yields, after annealing treatment, nearly single-phase magnet powders with a maximum energy product (BH)max?î140kJm-3. Co has a beneficial effect on the intrinsic magnetic properties but also on the microstructure, with a mean grain size of 20nm. Intensive milling is used to produce high-performance nanocomposite magnets by blending this latter alloy with different fractions of soft magnetic alfa-Fe. Addition of 25wt.% alfa-Fe leads to a high (BH)max=178 kJm-3 due to an effective exchange-coupling between the hard and the soft magnetic phases. The intergrain interactions between the crystallites of the nanocomposite structure are analysed. Demagnetisation recoil loops of the nanocomposite magnets show relatively open minor loops due to the exchange-spring mechanism. Information about the intergrain interactions during demagnetisation are obtained by plotting the deviation of the demagnetising remanence from the Wohlfarth-model (¡§deltaJ-plot¡¨). Exchange-coupling phenomena are studied by analysing the evolution of the corresponding deltaJ values when varying (i) the alfa-Fe content, (ii) the annealing temperature, i.e. the grain size and (iii) the measurement temperature. Low temperature measurements do not reveal any sign of spin reorientation for these Pr-based nanocomposite magnets. The work concludes showing the possibility of using a mechanically activated gas-solid reaction to obtain an effective grain refined microstructure starting from stoichiometric Nd2(Fe1-xCox)14B alloys (x=0-1). These compounds were milled under enhanced hydrogen pressure and temperature leading to their disproportionation into NdH2+delta and bcc-(Fe,Co) (x=0-0.75) or fcc-Co (x=1). Grain sizes of recombined Nd2(Fe,Co)14B materials were found to be 40-50nm
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Shatalov, MY, AC Every, and AS Yenwong-Fai. "Analysis of non-axisymmetric wave propagation in a homogeneous piezoelectric solid circular cylinder of transversely isotropic material." Elsevier, 2008. http://encore.tut.ac.za/iii/cpro/DigitalItemViewPage.external?sp=1001768.
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a b s t r a c t
A study concerning the propagation of free non-axisymmetric waves in a homogeneous
piezoelectric cylinder of transversely isotropic material with axial polarization is carried
out on the basis of the linear theory of elasticity and linear electro-mechanical coupling.
The solution of the three dimensional equations of motion and quasi-electrostatic equation
is given in terms of seven mechanical and three electric potentials. The characteristic equations
are obtained by the application of the mechanical and two types of electric boundary
conditions at the surface of the piezoelectric cylinder. A novel method of displaying dispersion
curves is described in the paper and the resulting dispersion curves are presented for
propagating and evanescent waves for PZT-4 and PZT-7A piezoelectric ceramics for circumferential
wave numbers m = 1, 2, and 3. It is observed that the dispersion curves are sensitive
to the type of the imposed boundary conditions as well as to the measure of the
electro-mechanical coupling of the material.
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Sang, Yucong. "A REPRESENTATION THEOREM FOR MATERIAL TENSORS OF TEXTURED THIN SHEETS WITH WEAK PLANAR ANISOTROPY." UKnowledge, 2018. https://uknowledge.uky.edu/math_etds/57.
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Herein we consider material tensors that pertain to thin sheets or thin films, which we model as two-dimensional objects. We assume that the thin sheet in question carries a crystallographic texture characterized by an orientation distribution function defined on the rotation group SO(3), which is almost transversely-isotropic about the sheet normal so that mechanical and physical properties of the thin sheet have weak planar-anisotropy. We present a procedure by which a special orthonormal basis can be determined in each tensor subspace invariant under the action of the orthogonal group O(2). We call members of such special bases irreducible basis tensors under O(2). For the class of thin sheets in question, we derive a representation formula in which each tensor in any given tensor subspace Z is written as the sum of a transversely-isotropic term and a linear combination of orthonormal irreducible basis tensors in Z, where the coefficients are given explicitly in terms of texture coefficients and undetermined material parameters. In addition to the general representation formula, we present also the specialized form for subspaces of tensor products of second-order symmetric tensors, a type commonly found in mechanics of materials.
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Algadey, Tarig. "Investigation of Negative Refractive Index in Isotropic Chiral Metamaterials Under First and Second-Order Material Dispersion With and Without Conductive Loss." University of Dayton / OhioLINK, 2016. http://rave.ohiolink.edu/etdc/view?acc_num=dayton1460819619.
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Koseoglu, Devrim. "Material Characterization With Terahertz Time-domain Spectroscopy." Phd thesis, METU, 2010. http://etd.lib.metu.edu.tr/upload/2/12611648/index.pdf.
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Terahertz time-domain spectroscopy systems were developed and used for the anaylsis and characterization of various materials. By using ultra-fast Ti:Sapphire and Er-doped fiber lasers, terahertz time-domain spectrometers of different configurations were constructed and tested. To increase the accuracy and sensitivity of the measurements, the systems were optimized for spectroscopic analysis.
MBE grown nominally undoped epitaxial GaAs samples were used for the spectroscopic measurements. These samples were first charactrized by electrical measurements in order to check the accuracy of the terahertz time-domain experiments. We have shown that the terahertz time-domin spectroscopic techniques provides a quick way of the determining the real ( ) and complex () components of the refractive index of material. In addition, we have investigated the photoexcitation dynamics of these GaAs samples. We have demonstrated that direct and photoexcited terahertz time-domain measurements give an estimate of the carrier densities and both the hole and electron mobility values with good precision. rnin
An algorithm is developed to prevent the unwanted Fabry-Perot reflections which is commonly encountered in Terahertz Spectroscopy systems. We have performed terahertz time-domain transmission measurements on ZnTe <<br>110><br>crystals of various thicknesses to test the applicability of this algorithm. We have shown that the algorithm developed provides a quick way of eliminating the &ldquo<br>etalon&rdquo<br>reflections from the data. In addition, it is also shown that these &ldquo<br>etalon&rdquo<br>effects can be used for the frequency calibration of terahertz time-domain spectrometers.
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Li, Qian. "Finite Deformations of Fiber-Reinforced Rubberlike Solids, and of Adhesively Bonded T-peel Joints." Diss., Virginia Tech, 2018. http://hdl.handle.net/10919/82923.
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Fiber-reinforced rubberlike materials (FRRM) commonly used in tires undergo large deformations, and exhibit different response in tension and compression along the fiber direction. Assuming that the response of a fiber-reinforced rubberlike material can be modeled as transversely isotropic with the fiber direction as the axis of transverse isotropy, we express the stored energy function, W, in terms of the five invariants of the right Cauchy-Green strain tensor and the fiber direction, and account for different response in tension and compression along the fiber direction. It has been shown in the literature that in shear-dominated deformations, the 5th invariant, I5, significantly contribution to the stress-strain curve. We have implemented the constitutive relation in the commercial software, LS-DYNA. The numerical solutions of several boundary value problems studied here agree with their analytical solutions derived by using Ericksen's inverse approach, in which a part of the solution is assumed and unknowns in the presumed solution are then found by analyzing the pertinent boundary value problem. However, computed results have not been compared with experimental findings.
For W of the FRRMs an expression that is a complete quadratic function of the five invariants is also examined. Homogeneous deformations such as simple extension, simple shear, and biaxial loading problems are studied to delineate the mechanical behaviors of FRRMs. Consistency with the infinitesimal deformation theory requires that linear terms in the 4th and 5th invariants, I4 and I5, be included in the expression for W. Stability analysis of deformations reveals the qualitative changes triggered by the second order terms of the quadratic function. Analytical solutions for inflation, extension and twist deformations caused by internal pressure, end torque, and axial force for a pressurized cylindrical laminate are derived using Ericksen's inverse method. Effects of fiber orientations on the mechanical behaviors of a +/-α angle-ply cylindrical tube are investigated using the derived analytical solutions.
The T-peel test, widely used for characterizing adhesion across a plethora of adhesives, adherends, and geometries, results in a range of responses that may complicate meaningful interpretation of the test data. This research effort, involving several specific specimen types, was undertaken to investigate concerns that commonly used configurations may not always result in plateaus in the force-displacement response. We experimentally and numerically study debonding of T-peel specimens having 75 mm bond length and 0.81 mm thick adherends made of either 6061 aluminum (Al) or one of the three steels (G70 70U hot dip galvanized, E60 elctrogalvanized (EGZ), 1010 cold-rolled steel (CRS) bonded with either LORD® 406 or Maxlok™ acrylic adhesive. For the EGZ and the Al adherends, specimens with a bond length of 250 mm and adherend thickness of 1.60 mm are also examined. Effects of adherend materials and thicknesses, bond lengths, and adhesives on test results are examined using three metrics to interpret the T-peel bond performance. We find a limited correlation between the commonly used "T-peel strength" and the energy dissipated per unit debond area. For those two metrics, the relative performances of the CRS and the Al specimens are quite different. Quasi-static plane strain deformations of the test specimens are analyzed by the finite element method (FEM) and a cohesive zone model using the commercial software, ABAQUS, to help interpret the test data. Numerical results provided energies required to elastically and plastically deform the adherends, and help determine the transition from non-self-similar to self-similar debonding. The FE simulations also facilitate determination of the fraction of the crosshead displacement at which self-similar debonding occurs. Results reported herein should help practitioners select appropriate specimen dimensions for extracting meaningful data for adhesive performance.<br>Ph. D.
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Sridaran, Venkat Ramanan [Verfasser], and Christian [Akademischer Betreuer] Boller. "A Structural Health Monitoring Concept on Ultrasonic Based Assessment of Aged Structures with Isotropic and Anisotropic Material Properties / Ramanan Sridaran Venkat ; Betreuer: Christian Boller." Saarbrücken : Saarländische Universitäts- und Landesbibliothek, 2018. http://d-nb.info/1180387228/34.
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Rocha, Gabriel Lopes da. "Aplicação da teoria de representação de funções isotrópicas em sólidos hiperelásticos com duas direções de simetria material." Universidade de São Paulo, 2017. http://www.teses.usp.br/teses/disponiveis/82/82131/tde-20082018-152023/.
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Aplicamos a teoria de representação de funções isotrópicas para determinar o número mínimo de invariantes independentes necessários para caracterizar completamente a densidade de energia de deformação de sólido hiperelástico com duas direções de simetria material. Expressamos a densidade de energia em termos de dezoito invariantes e extraímos um conjunto de dez invariantes para analisar dois casos de simetria material. No caso de direções ortogonais, recuperamos o resultado clássico de sete invariantes e oferecemos uma justificativa para a escolha dos invariantes encontrados na literatura. Se as direções não são ortogonais, descobrimos que o número mínimo também é sete e corrigimos um erro em fórmula encontrada na literatura. Uma densidade de energia deste tipo é usada para modelar, na escala macroscópica, materiais de engenharia, tais como compósitos reforçados com fibras, e tecidos biológicos, tais como ossos.<br>We determine the minimum number of independent invariants that are needed to characterize completely the strain energy density of a hyperelastic solid having two distinct material symmetry directions. We use a theory of representation of isotropic functions to express this energy density in terms of eighteen invariants and extract a set of ten invariants to analyze two cases of material symmetry. In the case of orthogonal directions, we recover the classical result of seven invariants and offer a justification for the choice of invariants found in the literature. If the directions are not orthogonal, we find that the minimum number is also seven and correct a mistake in a formula found in the literature. An energy density of this type is used to model, on the macroscopic scale, engineering materials, such as fiber-reinforced composites, and biological tissues, such as bones.
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Balarezo, Salgado José Illarick, and Arroyo Edgard Cristian Corilla. "Vibración libre de vigas de material isotrópico utilizando el método de elementos finitos." Bachelor's thesis, Universidad Peruana de Ciencias Aplicadas (UPC), 2021. http://hdl.handle.net/10757/654828.
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Esta investigación se enfoca en el análisis de vibración libre de vigas Timoshenko utilizando el método de elementos finitos. Se desarrolla el modelo utilizando el principio de Hamilton y la teoría de vigas Timoshenko que incluye deformaciones por corte. Se asume interpolaciones de alto orden para la aproximación de las variables fundamentales. Los materiales para emplear son isotrópicos. Se implementa un programa para estos materiales en MATLAB. Se comparan resultados con otros obtenidos en la literatura para validar el modelo. Se realiza un estudio paramétrico con una misma longitud y diferentes esbelteces. Se verifica que la formulación sea bastante precisa con resultados muy satisfactorios.<br>This research focuses on the free vibration analysis of Timoshkenko beams using the finite element method. The model is developed using the Hamilton principle and the Timoshenko beam theory that includes shear deformations. high order interpolations are assumed for the approximation of the fundamental variables. The materials to be used are isotropic. A program for these materials is implemented in MATLAB. Results are compared with others obtained in the literature to validate the model. A parametric study is carried out with the same length and different slenderness. It is verified that the formulation is quite precise with satisfactory results to the investigation.<br>Trabajo de investigación
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Gojuri, Arun. "Stability of End Notched Flexure Specimen." Thesis, Högskolan i Skövde, Institutionen för teknik och samhälle, 2010. http://urn.kb.se/resolve?urn=urn:nbn:se:his:diva-4487.
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This paper deals with two-dimensional Finite Element Analysis of the End Notched Flexure (ENF) specimen. The specimen is known to be unstable if the crack length is shorter than some critical crack length acr. A geometric linear two-dimensional Finite Element (FE) analysis of the ENF specimen is performed to evaluate acr for isotropic and orthotropic elastic materials, respectively. Moreover, the Mode II Energy Release Rate (ERR) JII and the compliance of the specimen are calculated. The influence of anisotropy is studied. Comparisons are made with the results from beam theory. This work is an extension of previous work.
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Lokander, Mattias. "Performance of Isotropic Magnetorheological Rubber Materials." Licentiate thesis, KTH, Fibre and Polymer Technology, 2002. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-1497.
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<p>Magnetorheological (MR) rubber materials are controllablecomposites that consist of magnetically polarisable particlesin a rubber matrix. They belong to a group of so-called "smartmaterials" that have seen an increased interest recently. Thesematerials have rheological properties that can be changedcontinuously, rapidly and reversibly by an applied magneticfield. With suitable control algorithms and solid stateelectronics, they can respond to changes in their environment.Although few applications of these materials have yet beenreported in the literature, the possibilities for materialswith controllable stiffness are numerous. Examples of potentialapplications are tuned vibration absorbers, andstiffness-tuneable mounts and suspensions.</p><p>The purpose of this work is to increase our knowledgerelating to magnetorheological materials for dampingapplications, using construction rubber as the matrix. Thematerials should exhibit large responses to an applied magneticfield and have good mechanical properties. In order to simplifytheir manufacture, the use of a magnetic field duringproduction should, if possible, be avoided.</p><p>MR rubber materials were made from nitrile and naturalrubber, and irregularly shaped iron particles severalmicrometers in size. The particles were not aligned by amagnetic field prior to the vulcanisation; hence, the materialscan be considered to be isotropic. These materials show a largeMR effect, e.g. an increase in the shear modulus when amagnetic field is applied, although the particles are notaligned within the material. This is explained by the lowcritical particle volume concentration (CPVC) of suchparticles. Similar behaviour can be obtained with materialscontaining carbonyl iron, if the particles are aggregated andthereby behave like large irregular particles. The ironparticle concentration has to be very close to the CPVC inorder to obtain a large MR effect.</p><p>The absolute MR effect in isotropic MR rubber materials withlarge irregular iron particles is independent of the matrixmaterial, and the relative MR effect can thus be increased bythe addition of plasticisers. Other ways of increasing the MReffect are to increase the strength of the magnetic field,although the materials saturate magnetically at high fieldstrengths, or to use small strain amplitudes. The strong strainamplitude dependence of the MR effect suggests that isotropicMR rubber materials are most suitable for low amplitudeapplications, such as sound and vibration insulation.Measurements at frequencies within the audible frequency rangeshow that this is a promising application for isotropic MRrubber materials.</p>
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Noritomi, Pedro Yoshito. "Desenvolvimento de uma metodologia para analise de bioengenharia em ossos compactos com remodelagem superficial pelo metodo dos elementos de contorno 3D em meios transversalmente isotropicos." [s.n.], 2005. http://repositorio.unicamp.br/jspui/handle/REPOSIP/263134.
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Orientador: Paulo Sollero<br>Tese (doutorado) - Universidade Estadual de Campinas. Faculdade de Engenharia Mecanica<br>Made available in DSpace on 2018-08-06T09:16:06Z (GMT). No. of bitstreams: 1
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Previous issue date: 2005<br>Resumo: Este trabalho mostra o desenvolvimento de uma metodologia para análise de problemas de bioengenharia, aplicando modelagem numérica elastostática de tensões e deformações, baseada no método dos elementos de contorno com formulação 3D para meios transversalmente isotrópicos lineares, incluindo a capacidade de simulação do comportamento de remodelagem óssea superficial. A implementação do núcleo transversalmente isotrópico sobre a estrutura básica de análise por elementos de contorno 3D utilizou a solução fundamental proposta por Pan & Chou e revisada por Loloi, tendo exigido o cálculo adicional das soluções fundamentais de força de superfície a partir da derivação das soluções fundamentais de deslocamento. O modelo de remodelagem óssea superficial baseou-se na hipótese de estímulo biológico por campo de deformação, partindo de um modelo 2D, adaptado para o espaço 3D com o uso de deformações principais como grandezas de referência. As implementações foram testadas através de análises numéricas de problemas com solução analítica e validações com resultados de aplicações comerciais baseadas em elementos finitos, para problemas padrão de engenharia, bem como comparações com resultados da literatura para problemas de bioengenharia. A análise dos resultados mostrará que, tanto a metodologia quanto as implementações são funcionais, oferecendo uma base sólida para desenvolvimento e teste de novas soluções de bioengenharia<br>Abstract: This work shows the development of a methodology to analyse bioengineering problems using elastostatic stress-strain numerical modeling based on a 3D transversely isotropic linear boundary element formulation including surface bone remodeling simulation capabilities. The transversely isotropic kernel implementation on the basic 3D boundary element analysis program used the fundamental solution purposed by Pan & Chou and revised by Loloi, with additional fundamental solutions for traction calculation made with the displacement fundamental solution derivatives. The surface bone remodeling model was based on a 2D strain field biological stimulus, extended to the 3D space by using the principal strain as reference values. The implementations were tested through numerical analysis of problems with analytical solution and validation with commercial finite elements applications for standard engineering problems, as well as comparison with literature data for bioengineering problems. The analysis of results will show that both, the methodology and the implementations are fully functional, offering a solid start for development and test of new bioengineering solutions<br>Doutorado<br>Mecanica dos Sólidos e Projeto Mecanico<br>Doutor em Engenharia Mecânica
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Guth, Danilo Colletta. "Otimização de materiais constituídos de células treliçadas com restrições de isotropia para aplicações termomecânicas." Universidade do Estado de Santa Catarina, 2012. http://tede.udesc.br/handle/handle/1632.
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Previous issue date: 2012-08-24<br>Coordenação de Aperfeiçoamento de Pessoal de Nível Superior<br>Inspirados por materiais encontrados na natureza, pesquisadores têm estudado a utilização de materiais celulares em diversas aplicações como biomedicina, engenharia aeroespacial e militar. O ganho em relação ao material base é a excelente relação entre peso e propriedades diversas como: rigidez ao cisalhamento; condutividade térmica/elétrica; absorção de impacto, ruído e vibrações. Uma classe específica são os materiais constituídos por células treliçadas. Estes possuem estrutura periódica, formada por células-base constituídas de barras distribuídas espacialmente no domínio da célula. Modernos processos de fabricação vêm viabilizando a confecção das células em escalas micro e nanométricas. Técnicas para obtenção de novas configurações são objeto de diversos estudos que buscam obter estruturas ótimas para uma dada função multiobjetivo. O presente trabalho implementa o uso de programação quadrática sequencial para a obtenção de células-base otimizadas para funções termomecânicas incluindo a maximização do módulo de cisalhamento, módulo volumétrico, coeficiente de Poisson e condutividade térmica, permitindo a inclusão de restrições de isotropia. A determinação das propriedades macroscópicas é obtida através do método da homogeneização. Diversos resultados são obtidos para os casos bidimensional e tridimensional.
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Cieaux, Jean-Marie. "Flexion dynamique des poutres composites a phases isotropes : validite du domaine quasi statique." Toulouse 3, 1988. http://www.theses.fr/1988TOU30086.
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Pour poutres de materiaux parfaitement colles, determination de deux coefficients de cisaillement par la notion de variables homogeneisees, calcules en fonction de la frequence pour poutre en vibrations libre-libre. Etude comparatives sur poutres sandwich; determination de la fonction de gauchissement des sections par la resolution d'un probleme de neumann poisson. Calcul par elements finis: adaptation de codes industriels pour poutres homogenes (frequences et modes propres), elaboration d'un code specifique
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Ramteke, Ashok Lahanuji. "Multiaxial creep of isotropic and anisotropic materials." Thesis, Imperial College London, 1987. http://hdl.handle.net/10044/1/47770.
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Balarezo, Salgado José Illarick, and Arroyo Edgard Cristian Corilla. "Análisis de vibración libre de vigas laminadas de materiales compuestos utilizando el método de elementos finitos." Bachelor's thesis, Universidad Peruana de Ciencias Aplicadas (UPC), 2001. http://hdl.handle.net/10757/654828.
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Esta investigación se enfoca en el análisis de vibración libre de vigas Timoshenko utilizando el método de elementos finitos. Se desarrolla el modelo utilizando el principio de Hamilton y la teoría de vigas Timoshenko que incluye deformaciones por corte. Se asume interpolaciones de alto orden para la aproximación de las variables fundamentales. Los materiales para emplear son isotrópicos. Se implementa un programa para estos materiales en MATLAB. Se comparan resultados con otros obtenidos en la literatura para validar el modelo. Se realiza un estudio paramétrico con una misma longitud y diferentes esbelteces. Se verifica que la formulación sea bastante precisa con resultados muy satisfactorios.<br>This research focuses on the free vibration analysis of Timoshkenko beams using the finite element method. The model is developed using the Hamilton principle and the Timoshenko beam theory that includes shear deformations. high order interpolations are assumed for the approximation of the fundamental variables. The materials to be used are isotropic. A program for these materials is implemented in MATLAB. Results are compared with others obtained in the literature to validate the model. A parametric study is carried out with the same length and different slenderness. It is verified that the formulation is quite precise with satisfactory results to the investigation.<br>Trabajo de investigación
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Dalenbring, Mats. "Methods for experimental estimation of anelastic material properties." Doctoral thesis, KTH, Vehicle Engineering, 2001. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-3259.
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Binte, Mokhtar Hanan. "Contribution to the study of impact damage on composite laminates : the effect of hygrothermal ageing and preloading." Thesis, Dijon, 2012. http://www.theses.fr/2012DIJOS045.
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Ce travail a pour but d'étudier la tolérance à l'impact de 3 stratifiés carbone/époxy soumis simultanément à différents types de chargements hygrothermiques et mécaniques. Ces stratifications présentant des caractéristiques mécaniques globales particulières d'isotropie, il s'agit ici de déterminer l'influence de la séquence d'empilement sur le développement de l'endommagement lors d'un impact. Dans un premier temps, la cinétique de vieillissement hygrothermique des trois stratifications est étudiée et analysée. Ensuite, leur tolérance à un unique impact ainsi qu'à des impacts répétés est évaluée. L'endommagement résultant de ces impacts est analysé par contrôle ultrasonore. La morphologie générale et l'amplitude de l'endommagement dans la profondeur des matériaux sont mises en relation avec les propriétés mécaniques et la séquence d'empilement spécifique à chaque stratifié. Dans un deuxième temps, l'influence combinée de plusieurs sollicitations est étudiée. Différents scénarii associant un vieillissement hygrothermique ainsi qu'un ou deux impacts sont mis en oeuvre. L'endommagement résultant est mis en rapport avec les temps relatifs de vieillissement et la position des impact durant le cycle de vieillissement. Ensuite, l'influence d'une précharge de traction sur la tolérance à l'impact est mise en évidence. Un montage spécifique a été conçu et fabriqué pour réaliser ces tests. Enfin, l'association d'un vieilllissement hygrothermique et d'une précharge de traction est abordée afin d'identifier la sollicitation la plus pénalisant en terme de tolérance et d'impact<br>This study examines impact damage processes in three types of CFRP composite materials simultaneously subjected to different hygrothermal and mechanical loading conditions. The composite structures tested are chosen for having particular global isotropic responses when loaded, the aim being to ascertain the exact influence of lay-up sequence on impact damage propagation. The work is presented in four main sections. Firstly by establishing hygrothermal ageing dynamics for the three composite structure types and their behaviour when impacted once or several times ; impact damage is measured and analysed using ultrasonic method. The extent and general morphology of the damage through the material thickness is correlated with mechanical properties and lay-up sequence specific to each material. Secondly the influence of simultaneous load combinations is examined. These include different durations of hygrothermal ageing associated with single or double impacts.The resulting damage incurred is analysed with respect to overall ageing time and time during the ageing cycle when the impact was applied. Thirdly the effect of tensile loading during impact on damage within the material was studied. This was achieved using a specially designed test apparatus that allows loading and impacting conditions to be independently modified. By associating a high-speed digital camera to film specimen impacts it is possible to evaluate a relationship between overall composite specimen stiffness and the impact damage. Finally, in order to identify the most unfavourable situation with regard to impact damage resistance an association between hygrothermal ageing and an applied tensile load is examined
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Yildirim, Alper. "Development Of A Micro-fabrication Process Simulator For Micro-electro-mechanical-systems(mems)." Master's thesis, METU, 2005. http://etd.lib.metu.edu.tr/upload/12606850/index.pdf.
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ABSTRACT
DEVELOPMENT OF A MICRO-FABRICATION PROCESS SIMULATOR FOR MICRO-ELECTRO-MECHANICAL SYSTEMS (MEMS)
Yildirim, Alper
M.S, Department of Mechanical Engineering
Supervisor: Asst. Prof. Dr. Melik Dö<br>len
December 2005, 140 pages
The aim of this study is to devise a computer simulation tool, which will speed-up the design of Micro-Electro-Mechanical Systems by providing the results of the micro-fabrication processes in advance. Anisotropic etching along with isotropic etching of silicon wafers are to be simulated in this environment. Similarly, additive processes like doping and material deposition could be simulated by means of a Cellular Automata based algorithm along with the use of OpenGL library functions. Equipped with an integrated mask design editor, complex mask patterns can be created by the software and the results are displayed by the Cellular Automata cells based on their spatial location and plane. The resultant etched shapes are in agreement with the experimental results both qualitatively and quantitatively.
Keywords: Wet Etching, Anisotropic Etching, Doping, Cellular Automata, Micro-fabrication simulation, Material Deposition, Isotropic Etching, Dry Etching, Deep Reactive Ion Etching
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Hagnell, Christian, and Mosanen Kiavosh Saidi. "Topology optimization : A comparison between the SIMP and BESO methods using open-source software." Thesis, Uppsala universitet, Tillämpad mekanik, 2021. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-447869.
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Structural optimization is a useful tool for engineers and designers in construction technology as well asvehicle and mechanical engineering. With structure optimization, a computer can, with the help of finiteelement analysis, calculate the smallest possible amount of material needed to meet the requirements onthe part to be produced.The purpose of this report is to use two different implementations for finite element calculations fortopology optimization of a beam. Results from the optimizations will then be 3D printed with differentsettings. The beam will be tested for displacement, stress and strain in a universal testing machine. Theresults from the experiment will be compared with computed simulations of the same beam.For the structural optimization, two methods are used and compared: Solid Isotropic Material withPenalization and Bidirectional Evolutionary Structural Optimization. A total of eight beams, four fromeach method, were printed with a 3D printer with two different positions on the printer bed and withdifferent degrees of infill ratios. These were tested with a machine that could register both pressure anddeformation and were filmed to be able to see the strain. The deformation of the beams was alsosimulated in a software computer program to see what deformation difference there was betweenexperiment and reality.It turned out that the beams that were printed behaved anisotropic even though solid plastic should beincluded among isotropic materials. The deformation of the model looked like the finite elementcalculation, but the actual deformation was significantly larger than what was calculated by the computersoftware.
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Li, Yuan. "Synthesis and mechanical characterization of transversely isotropic nanoporous platinum." Thesis, Georgia Institute of Technology, 2011. http://hdl.handle.net/1853/42927.
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Nanoporous (NP) metal foams combine desirable characteristics of metals with unique nanoarchitectural features to yield weight normalized properties far superior than either dense metals or bulk metal foams. Due to their high surface to volume ratios these structures show great promise as components of fuel cells, as sensors and have been suggested for use in biological applications, for example as antimicrobial scaffolds or as platforms on which to explore biological material behavior. While most NP metal foams are isotropic, structures with anisotropic features spanning different length scales can further extend applications. This work examines the parameters controlling the synthesis of transversely isotropic NP Platinum foam by dealloying an amorphous Pt-Si alloy. The structure that is examined in this work is hierarchical with Voronoi polyhedra that form on the free surface and under each polyhedral hyper-structure, nanocrystalline NP Pt foam forms with radial struts of length ~60 nm and grain size of 5 nm. The size of the polyhedra can be tailored by changing the dealloying potential. In turn, the mechanical properties of these structures as assessed by nanoindentation can range from 1 to 3GPa depending on the geometric arrangement of the struts. Finally, the initiation location of these structures and the relationship between electrochemical parameters and dealloying front evolution is examined.
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Maheu, Bruno. "Généralisation de la théorie de Lorenz-Mie et applications." Rouen, 1987. http://www.theses.fr/1987ROUES025.
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Théorie de la diffusion d'un faisceau gaussien par un diffuseur sphérique homogène et isotrope. Les résultats ouvrent sur des applications à la granulométrie optique. On expose par la suite un modèle à quatre flux pour décrire la diffusion multiple d'une onde électromagnétique par un nuage dense de diffuseurs
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Zhao, Huyue. "Stress Analysis of Tapered Sandwich Panels with Isotropic or Laminated Composite Facings." Fogler Library, University of Maine, 2002. http://www.library.umaine.edu/theses/pdf/ZhaoH2002.pdf.
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Woudberg, Sonia. "Laminar flow through isotropic granular porous media." Thesis, Link to the online version, 2006. http://hdl.handle.net/10019/1320.
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Lyengar, Nirmal. "Failure analysis of a quasi-isotropic laminated composite plate with a hole in compression /." This resource online, 1992. http://scholar.lib.vt.edu/theses/available/etd-07102009-040536/.
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Verstappen, André Paul. "Passive damping treatments for controlling vibration in isotropic and orthotropic structural materials." Thesis, University of Canterbury. Mechanical Engineering, 2015. http://hdl.handle.net/10092/10197.
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The structural vibration damping behaviour of plates and beams can be improved by the application of viscoelastic passive damping materials. Unconstrained layer damping treatments applied to metal plate systems were studied experimentally. Design and modelling of novel fibre reinforced constrained layer damping materials was performed, and implementation of these composite damping materials into laminated composite sandwich constructions commonly used as structural elements within large composite marine vessels was explored. These studies established effective methods for examining, designing and applying damping materials to metal and composite marine structures.
Two test fixtures were designed and constructed to facilitate testing of viscoelastic material damping properties to ISO 6721-3 and ASTM E756. Values of material damping made in accordance with ASTM E756 over a range of temperatures were compared to values produced by a Dynamic Mechanical Analyser (DMA). Glass transition temperatures and peak damping values were found to agree well, although results deviated significantly at temperatures above the glass transition temperature.
The relative influence of damping layer thickness, ambient temperature, edge conditions, plate dimensions and substrate material on the system damping performance of metal plates treated with an unconstrained viscoelastic layer was investigated experimentally. This investigation found that substrate material had the greatest influence on system damping performance, followed by damping layer thickness and plate size. Plate edge conditions were found to have little influence on the measured system damping performance. These results were dependent on the values of each variable used in the study.
Modal damping behaviour of a novel fibre reinforced composite constrained layer damping material was investigated using finite element analysis and experimental methods. The material consisted of two carbon fibre reinforced polymer (CFRP) layers surrounding a viscoelastic core. Opposing complex sinusoidal fibre patterns in the CFRP face sheets were used to achieve stress-coupling by way of orthotropic anisotopy about the core. A finite element model was developed in MATLAB to determine the modal damping, displacement, stress, and strain behaviour of these complex patterned fibre constrained layer damping (CPF-CLD) materials. This model was validated using experimental results produced by modal damping measurements on CPF-CLD beam test specimens. Studies of multiple fibre pattern arrangements found that fibre pattern properties and the resulting localised material property distributions influenced modal damping performance.
Inclusion of CPF-CLD materials in laminated composite sandwich geometries commonly used in marine hull and bulkhead constructions was studied experimentally. Composite sandwich beam test specimens were fabricated using materials and techniques frequently used in industry. It was found that the greatest increases in modal damping performance were achieved when the CPF-CLD materials were applied to bulkhead geometries, and were inserted within the sandwich structure, rather than being attached to the surface.
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Masad, Sanaa Ahmad. "Sensitivity analysis of flexible pavement response and AASHTO 2002 design guide for properties of unbound layers." Thesis, Texas A&M University, 2004. http://hdl.handle.net/1969.1/528.
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Unbound granular materials are generally used in road pavements as base and subbase layers. The granular materials provide load distribution through aggregate contacts to a level that can help the subgrade to withstand the applied loads. Several research studies have shown that unbound pavement layers exhibit anisotropic properties. Anisotropy is caused by the preferred orientation of aggregates and compaction forces. The result is unbound pavement layers that have higher stiffness in the vertical direction than in the horizontal direction. This behavior is not accounted for in the design and analysis procedures included in the proposed AASHTO 2002 design guide. One of the objectives of this study is to conduct a comparative analysis of flexible pavement response using different models for unbound pavement layers: linear isotropic, nonlinear isotropic, linear anisotropic and nonlinear anisotropic. Pavement response is computed using a finite element program. The computations from nonlinear isotropic and anisotropic models of unbound layers are compared to the AASHO field experimental measurements. The second objective is to analyze the influence of using isotropic and anisotropic properties for the pavement layers on the performance of flexible pavements calculated using the AASHTO 2002 models. Finally, a comprehensive sensitivity analysis of the proposed AASHTO 2002 performance models to the properties of the unbound pavement layers is conducted. The sensitivity analysis includes different types of base materials, base layer thicknesses, hot mix asphalt type and thickness, environmental conditions, and subgrade materials.
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Cooper, James Roger. "Novel wireless sensor configurations incorporating isotropic radiators on conformal artificial magnetic conductors." Diss., Georgia Institute of Technology, 2014. http://hdl.handle.net/1853/52246.
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The objective of the presented research is to develop a novel, ink-jet printed, chipless, passive, wireless sensor topology, which can radiate in a near isotropic pattern without interference from embedded devices, for use in dispersed sensor networks. This objective includes the development of a hardware based, uniquely identifiable, collision avoidance communication method, and an integrated sensor system that is easily integrated into the topology.
Wireless sensor networks can be and are used in military, medical and industrial applications; and the demand for them is ever growing. However, current sensor networks have various trade-offs and limitations, including cost, number of distinguishable nodes, and ease of manufacturing. These trade-offs lead to unique sensors needing to be designed for each situation. To develop a widely used module, a topology must be developed that can meet as many demands as possible with fair tradeoffs.
Many of the above proposed criteria for the topology are already integrated into RFID technology. Therefore, much of the research is the application and advancement of current RFID technology for the purpose of designing the topology. The research begins with the theory and design of conformal artificial magnetic conductors, which is used in the design of a near isotropic radiator and isolated core for device embedding. Then, novel fabrication techniques will be investigated and deployed in the fabrication of the topology. Next, a novel "smart skin" sensor is developed which is easily integrated into the desired fabrication technique. Finally, an anti-collision RFID circuit for on-tag placement, which is based on frequency-doubling transceivers, is designed, which can also be easily integrated into the final topology.
This module is designed for use with a variety of different sensors. This versatility gives it ruggedness for use in many different environments. For proof of concept, this topology is fabricated and tested against current commercially sold tags.
Through the design and testing of the radiator, circuitry, and embedded sensors, it is shown that this design is a suitable topology for use in many different environments and applications.
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Khan, Kamran-Ahmed. "A time integration scheme for stress - temperature dependent viscoelastic behaviors of isotropic materials." [College Station, Tex. : Texas A&M University, 2006. http://hdl.handle.net/1969.1/ETD-TAMU-1146.
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Ljungberg, Adam, and Nathalie Schmidt. "Deformationsstrukturer i ett duplext rostfritt stål (SAF 2507)." Thesis, Högskolan Dalarna, Materialteknik, 2014. http://urn.kb.se/resolve?urn=urn:nbn:se:du-15770.
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För att kunna förbättra processer och användning av det duplexa rostfria stålet SAF 2507 måste dess deformationsegenskaper undersökas och förklaras. Genom EBSD-analyser har deformationsstrukturer och polfgurer tagits fram för att kunna beskriva materialets beteende vid deformation. Även Taylorfaktorer, E-moduler och Poissons tal har tagits fram för att kunna undersöka materialets anisotropi. Experimenten har utförts på prov av SAF 2507 som har deformerats plastiskt till olika töjningar. Det som undersökts är odeformerat prov, prov som dragits enaxligt till 7,7 % och 24,3 % töjning, samt ett prov som är cykliskt belastat till 3 % töjning. Det undersökta stålet tillverkas genom två olika metoder, men i denna rapport har enbart det extruderade stålet undersökts. Genom att jämföra hur stålets olika mekaniska egenskaper beter sig under plastisk deformation har resultatet blivit att stålets ferritfas beter sig anisotropt med en antydan till ökande isotropi vid ökande deformation. Austenitfasen beter sig däremot isotropt och blir varken mer eller mindre isotropt vid ökande deformation. Substrukturerna i ferritfasen ökar tydligt vid ökande deformation, och ses framför allt i austenitfasen efter 24 % deformation.<br>In order to improve the processes and the use of the duplex stainless steel SAF 2507, its deformation properties has to be investigated and explained. Through EBSD-analysis deformation structures and pole figures have been developed to describe the behavior of the material during deformation. Also Taylor factors, Young’s modules and Poisson's ratio have been developed in order to investigate the material's anisotropy. The experiments have been performed on samples of SAF 2507 which has been plastically deformed at different strains. The strains studied are undeformed sample, samples drawn uniaxial drawn to 7.7 % and 24.3 % elongation, and one sample which is cyclically loaded to 3% elongation. The steel we have investigated is produced by two different methods, but in this report, only the extruded steel is investigated. By comparing how different mechanical properties of the steel behave during plastic deformation, the result shows that the steel’s ferrite phase behaves anisotropically with a hint of increasing isotropy when the deformation is increasing. The austenite phase behaves isotropic and does not become more or less isotropic with increasing deformation. The substructures in the ferrite phase are clearly increasing with increasing deformation, and are seen mainly in the austenite phase after 24 % deformation.
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Hadian, Mohammad Jafar. "Modal interactions in the dynamic response of isotropic and composite plates." Diss., Virginia Tech, 1991. http://hdl.handle.net/10919/39785.
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Hamilton's principle and a third-order shear-deformation theory are used to derive a set of five coupled partial-differential equations governing the nonlinear response of composite plates. The reduction of these equations by using classical plate theory is discussed and the corresponding partial-differential equations governing both rectangular and circular plates are derived.
Generalized Levy-type solutions are obtained for the problem of linear free vibrations and linear stability of shear-deformable cross-ply laminated plates. The governing equations are transformed into a set of first-order linear ordinary-differential equations with constant coefficients. The general solution of these equations is obtained by using the state-space concept. Then, the application of the boundary conditions yields equations for the natural frequencies and critical loads. However, a straightforward application of the state-space concept yields numerically ill-conditioned problems as the plate thickness is reduced. Various methods for overcoming this problem are discussed. An initial-value method with orthonormalization is selected. It is shown that this method not only yields results that are in excellent agreement with the results in the literature, but it also converges fast and gives all the frequencies and buckling loads regardless of the plate thickness. Further It is shown that the application of classical plate theory to thick plates yields inaccurate results. The influence of modal interactions on the response of harmonically excited plates is investigated in detail. The case of a two-to-one autoparametric resonance in shear-deformable composite laminated plates is considered. Four first-order ordinary-differential equations describing the modulation of the amplitudes and phases of the internally resonant modes are derived using the averaged Lagrangian when the higher mode is excited by a primary resonance. The fixed-point solutions are determined using a homotopy algorithm and their stability is analyzed. It is shown that besides the single-mode solution, two-mode solutions exist for a certain range of parameters. It is further shown that in the multi-mode case the lower mode, which is indirectly excited through the internal resonance may dominate the response. For a certain range of parameters, the fixed points lose stability via a Hopf bifurcation, thereby giving rise to limit cycle solutions. It is shown that these limit-cycles undergo a series of period-doubling bifurcations, culminating in chaos.
Finally, the case of a combination resonance involving the first three modes of axisymmetric circular plates is studied. The method of multiple scales is used to determine a set of ordinary-differential equations governing the modulation of phases of the modes involved and that the excited mode is not necessarily the dominant one.
Furthermore, it is shown that for a choice of parameters the multi-mode response loses stability through a Hopf bifurcation, resulting in periodically or chaotically modulated motions of the plate.<br>Ph. D.
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PUCCIA, Marianna. "Strain localization and fracture in isotropic damaging materials: a novel augmented-finite element strategy." Doctoral thesis, Università degli Studi di Palermo, 2022. https://hdl.handle.net/10447/575588.
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Iyengar, Nirmal. "Failure analysis of a quasi-isotropic laminated composite plate with a hole in compression." Thesis, Virginia Tech, 1992. http://hdl.handle.net/10919/43638.
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The ability to predict failure of laminated composites in compression has been doggedly pursued by researchers for many years. Most have, to a limited extent, been able to predict failure for a narrow range of laminates. No means, as yet, exist for predicting the strength of generic laminates under various load conditions. Of primary concern has been the need to establish the mode at failure in compression. Even this has been known to vary for fiber and matrix dominated laminates.
This study has been carried out to analyze the failure of specimens with a hole made of laminates with various quasi-isotropic stacking sequences. Different stacking sequences are achieved by rotating a [±45/90/0]s stacking sequence laminate as a whole with respect to the loading axis of the specimens. Two- and three-dimensional finite element models, using commercial packages, were generated to evaluate the stresses in the region of the hole. Two different compressive failure prediction techniques based on distinctly different failure modes have been used. The validity of these techniques was measured against experimental data of quasi-isotropic specimens tested. To investigate the applicability of the failure criteria for different laminated composite plates, analyses were repeated for specimens with different stacking sequences resulting from the rotation of the laminate.
The study shows the need for the use of three-dimensional analysis of the stress state in the vicinity of the hole in order to be able to accurately predict failure. It also shows that no one mode of failure is responsible for limiting the strength for all laminate orientations but rather the mode changes with change in stacking sequence. The failure of the laminate with a hole was seen to be very sensitive to the stacking sequence. Experimental data presented also shows that the peak strength obtainable from the laminate analyzed, [±45/90/0]s, is going to be in the off-axis configuration rather than on-axis placement of the stacking sequence with respect to the loading direction.<br>Master of Science
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Al-Kinani, Raad [Verfasser]. "Thermo-mechanical coupling of transverseley isotropic materials using high-order finite elements / Raad Al-Kinani." Clausthal-Zellerfeld : Universitätsbibliothek Clausthal, 2014. http://d-nb.info/1060926369/34.
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Kinani, Raad al [Verfasser]. "Thermo-mechanical coupling of transverseley isotropic materials using high-order finite elements / Raad Al-Kinani." Clausthal-Zellerfeld : Universitätsbibliothek Clausthal, 2014. http://nbn-resolving.de/urn:nbn:de:gbv:104-1119966.
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Vure, Narayana Rao S. "Effect of cooling rate and stacking sequence on the fatigue behavior of notched quasi-isotropic APC-2 laminates." Thesis, This resource online, 1993. http://scholar.lib.vt.edu/theses/available/etd-03042009-040905/.
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Smith, Anthonie Gronum. "An experimental study of artificial isotropic chiral media at microwave frequencies." Thesis, Stellenbosch : Stellenbosch University, 1994. http://hdl.handle.net/10019.1/58253.
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Thesis (PhD)--Stellenbosch University, 1994.<br>ENGLISH ABSTRACT: An artificial chiral medium can be made by embedding metal helices (chiral or handed structures)
with random orientation inside au achiral hnst medium. The electromagnetic behaviour
of such artificial chiral media can be explained by an additional (to p. and t') constitutive parameter,
the chirality parameter e. Chiral media have certain special properties of which
optical activity is the most prominent. Optical activity is the term used to describe the
rotation of the polarization plane of a linearly polarized wave as it travels through a chiral
medium. The chirality parameter is directly linked with this rotation.
The reflection and the transmission coefficients from a chiral slab are well known in terms of
the constitutive parameters and the thickness of the sample. In the thesis a set of .inversion
equations are derived that can be used to determine the constitutive parameters (p., £, e) of
a chiral medium from the measured S-parameters 811, S21x and S2l'jJ (Le. the reflection and
co- and cross-polarized transmission coefficients respectively).
An accuracy analysis of the measurement method is made. This is done by using the first
order partial derivatives of the inversion equations. A sensitivity analysis is done on the
inversion equations and the results are in an analytical form. This makes it possible to
determine the contribution of each of the measurement errors to the total expected error. A
statistical root mean square method is used to predict the expected error in the measured
constitutive parameters.
Several artificial chiral samples are measured and an accuracy analysis done on the measurements.
The inaccuracy of the method of inversion for low loss samples that are multiples of
half a wavelength thick is illustrated by example and explained by the sensitivity analysis.
The free-space system (11-17 GHz) used to measure the S-parameters is described in detail.
The radiation patterns of the focused lens antennas are measured and compared to those
obtained from two theoretical models. A free-space calibration procedure is developed and the
dispersion in the focal region of the antennas incorporated into it. The results from different
combinations of calibration standards are compared and related to the idea of minimum
sensitivity calibration.
The possible use of an artificial chiral medium as a microwave absorber is also discussed.<br>AFRIKAANSE OPSOMMING: Kunsmatige kirale media kan gemaak word deur metaalhelikse lukraak te orienteer in 'n mekirale
(bv. diEHektriese) medium. Die mikrogolfeienskappe van kirale media kan toegeskryf
word aan die anti-simmetrie van die mikroskopiese insluitings. 'n Voorwerp word as kiraal
beskryf indien dit nie deur translasie of rotasie op die spieelbeeld daarvan gepas kan word
nie. Die menslike hand is 'n goeie voorbeeld van so 'n kirale struktuur.
Die elektromagnetise eienskappe van 'n kunsmatige kirale medium kan beskryf word deuT 'n
addisionele (tot j.t en E) samestellingsparameter, die kiraliteitsparameter ~. Kirale media het
verskeie ongewone eienskappe waarvan opti~se aktiwiteit waarskynlik die prominentste is. Optiese
aktiwiteit beskryf die verskynsel waar die polarisasierigting van 'n lineer-gepolariseerde
golf geroteer word terwyl dit deur 'n kirale medium beweeg. 'n Direkte verband bestaan
tussen die rotasie en die kiraliteitsparameter.
Die weerkaats- en transmissiekotHfisiente van 'n kirale plaat is bekend in terme van die
samestellingsparameters (j.t, f. en {) en die dikte van die plaat. In die tesis word 'n ste1 inversievergelykings
afgelei wat gebruik kan word om die samestellingsparameters van 'n kirale
medium te bepaal vanuit die gemete weerkaats- en transmissiekoeffisiente, Sl1, S'lIz en SUg.
(S213/ is die kruis-gepolariseerde komponent van die transmissiekoeffisient wat 'n aanduiding
van die rotasie gee.)
,n Analise word gedoen op die akkuraatheid waarmee metings uitgevoer kan word. Dit word
gedoen deur gebruik te maak van die eerste orde parsHHe afgeleide van die inversievergelykings.
'n Sensitiwiteitsanalise van die inversievergelykings word gedoen en in 'n analitiese vurm
aangebied. Die vorm maak dit moontlik om die bydrae van elke meetfout in S11, S2l:c en
S21'!J tot die totale meetfout in p., € en ete bepaal. 'n Statistiese metode (wortel gemiddelde
kwadraat) word gebruik om die verwagte foutwaardes in die gemete samestellingsparameters
te bepaal.
Verskeie kunsmatige kirale media word gemeet en 'n analise word gedoen op die akkuraatheid
waarmee elk gemeet is. Die onakkuraatheid van die inversiemetode vir plate met lae verliese
en wat veelvoude van 'nhalwe golflengte dik is, word getoon deur middel van 'n sensitiwiteitsanalise.
Die vryeruimte meetstelsel (11-17 GHz) wat gebruik word om die weerkaats- en transmissiekoeffisH~
nte te meet, word breedvoerig bespreek. Die gemete stralingspatrone van die
gefokusseerde lens antennes word vergelyk met teoreties bepaalde waardes. 'n Vryeruimte
kalibrasietegniek word ontwikkel en die gemete dispersie in die fokusgebied word daarby ingesluit.
Die resultate, soos verkry van verskillende kalibrasiestandaarde, word vergelyk en in
verband gebring met die tegniek van kalibrasie-met-minimum-sensitiwiteit.
Ten slotte word die moontlike gebruik van kunsmatige kirale media as mikrogolfabsorbeerders
ondersoek.
43
Thompson, Luke Francis. "Through-thickness compression testing and theory of carbon fibre composite materials." Thesis, University of Manchester, 2011. https://www.research.manchester.ac.uk/portal/en/theses/throughthickness-compression-testing-and-theory-of-carbon-fibre-composite-materials(02ad7cfa-b779-4e69-9361-3c5bb44c6114).html.
Full textAbstract:
This study investigates the through-thickness behaviour of carbon/epoxy laminates. A through-thickness compression test regime was conducted utilising three specimen designs, which are waisted, hollow cylindrical and cubic specimens. An assessment and comparison of each specimen is given regarding their advantages and disadvantages in characterising the through-thickness response of [+45/-45/90/0]s quasi-isotropic AS4/8552 carbon/epoxy laminates. A finite element (FE) study of the three specimens is presented which results in specimen geometries that provided a macroscopically uniform stress response throughout the gauge length whilst also minimising other features such as stress concentrations. Further to the final geometries being presented, the method of manufacture for the laminate and machining processes for each of the specimens is given. A mesoscopic FE study is presented relating to the free-edge effects induced by through-thickness loading in quasi-isotropic laminates. The results presented show that free-edge effects will be present in the test specimens and will have a larger overall impact on the hollow cylindrical specimen. The free-edge effects also increase the stress concentrations present in the corners of the waisted and cubic specimens. Characteristic stress strain curves are presented for each specimen with strain data taken from post yield strain gauges attached to the specimens. The extracted initial Young's modulus Ez and Poisson's ratios vzx and vzy show a small variation between specimens. The strength values for the three specimens vary greatly with the waisted specimen being the strongest and cylindrical specimen the weakest, indicating that the chosen specimen geometry dominates failure. The experimental data will be used for test case 12 in the Second World Wide Failure Exercise (WWFE-II). A study is presented to predict the effective elastic properties of Z-pinned laminates. The materials under consideration are UD and [0/90]s cross-ply AS4/3501-6 carbon/epoxy laminates. Estimates on the effective properties are provided by two FE approaches and two analytical bounding approaches; namely Voigt and Reuss bounds and Walpole's bounding theory. The two FE approaches are based on extreme assumptions about the in-plane fibre volume fraction in the presence of Z-pins and provide a tight range of values in which the real result should lie. Furthermore, whilst the bounding methods are simple and in the case of Young's moduli produce very wide bounds the selection of the suitable bound result can lead to a good estimate in comparison with the FE data. Typically the best bounding method result for each elastic property is within 10% of the FE predictions.
44
Stewart, Calvin. "TERTIARY CREEP DAMAGE MODELING OF A TRANSVERSELY ISOTROPIC NI-BASED SUPERALLOY." Master's thesis, University of Central Florida, 2009. http://digital.library.ucf.edu/cdm/ref/collection/ETD/id/3606.
Full textAbstract:
Anisotropic tertiary creep damage formulations have become an increasingly important prediction technique for high temperature components due to drives in the gas turbine industry for increased combustion chamber exit pressures, temperature, and the use of anisotropic materials such as metal matrix composites and directionally-solidified (DS) Ni-base superalloys. Typically, isotropic creep damage formulations are implemented for simple cases involving a uniaxial state of stress; however, these formulations can be further developed for multiaxial states of stress where materials are found to exhibit induced anisotropy. In addition, anisotropic materials necessitate a fully-developed creep strain tensor. This thesis describes the development of a new anisotropic tertiary creep damage formulation implemented in a general-purpose finite element analysis (FEA) software. Creep deformation and rupture tests are conducted on L, T, and 45°-oriented specimen of subject alloy DS GTD-111. Using the Kachanov-Rabotnov isotropic creep damage formulation and the optimization software uSHARP, the damage constants associated with the creep tests are determined. The damage constants, secondary creep, and derived Hill Constants are applied directly into the improved formulation. Comparison between the isotropic and improved anisotropic creep damage formulations demonstrates modeling accuracy. An examination of the off-axis creep strain terms using the improved formulation is conducted. Integration of the isotropic creep damage formulation provides time to failure predictions which are compared with rupture tests. Integration of the improved anisotropic creep damage produces time to failure predictions at intermediate orientations and any state of stress. A parametric study examining various states of stress, and materials orientations is performed to verify the flexibility of the improved formulation.
A parametric exercise of the time to failure predictions for various levels of uniaxial stress is conducted.<br>M.S.M.E.<br>Department of Mechanical, Materials and Aerospace Engineering;<br>Engineering and Computer Science<br>Mechanical Engineering MSME
45
Le, Menestrel Maxime. "Finite element modeling of the elastic properties of isotropic and anisotropic synthetic foams." Thesis, Georgia Institute of Technology, 2002. http://hdl.handle.net/1853/16038.
Full text
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Yu, Quanwei. "Ionene and ionene alkyl sulfate stoichiometric complexes." Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2004. http://nbn-resolving.de/urn:nbn:de:swb:14-1099409249500-35629.
Full textAbstract:
Stoichiometric polyelectrolyte-surfactant complexes represent a type of comb-shaped polymers, in which every polymer chain unit has an electrostatically bound &quot;side chain&quot;. These complexes are water-insoluble. In the solid state they assemble spontaneously into mesogenic structures. The [X,Y]-ionenes ([(CH2)XN+(CH3)2(CH2)YN+(CH3)2]nBr-2n) investigated formed stoichiometric complexes with alkyl sulfates. The ionene alkyl sulfate complexes display mesogenicity, i.e. optically isotropic dry complexes underwent lyotropic and thermotropic phase transitions to the optically anisotropic phase (and vice versa) under controlled relative humidity. The optically anisotropic phases exhibited hexagonal textures as revealed by polarizing microscopy. A new feature is the lyotropic transition brought about by the uptake of water through the gas phase. The complexes were all sensitive to both humidity and temperature. In principle, the effects can be applied to measure humidity.
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Sehnal, Dominik. "Nízkocyklová životnost v podmínkách jaderné energetiky." Master's thesis, Vysoké učení technické v Brně. Fakulta strojního inženýrství, 2019. http://www.nusl.cz/ntk/nusl-399581.
Full textAbstract:
Fatique life extension of nuclear powerplants lies in the search for project reserves. This work deals with the evaluation of low-cycle fatigue of nuclear installations of the VVER type and the assessment of the influence of the computational model level. Fatigue tests of austenitic steel using optical method of digital image correlation for which the evaluation procedure is designed and used is performed. Selected model of plasticity with kimenatic (Chaboche) and combinated hardening (Chaboche, Voce) are calibrated from the obtained data. Subsequently, the durability of the test specimen is determined by computational modeling for different material models. From the comparison of the results of fatigue tests with the calculation, the material models suitable for the description of fatigue life and their validity are determined.
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Casini, Federico. "Vibrazioni di Piastre in Materiale Composito con Elementi Finiti in Forma Forte." Master's thesis, Alma Mater Studiorum - Università di Bologna, 2016.
Find full textAbstract:
In questa tesi si affronta lo studio di piastre isotrope e laminate mediante metodo GDQ e si confrontano i risultati con quelli ottenuti, per le stesse tipologie di piastre, mediante metodo FEM. Lo scopo del lavoro e quello di certificare la maggior efficienza del software di calcolo DiQuMASPAB, basato su teorie in forma forte, rispetto ai tradizionali software di calcolo agli elementi finiti attualmente in commercio. Il confronto ha come obiettivo quello di evidenziare i punti deboli dal punto di vista dell'approssimazione delle soluzioni e del costo computazonale.
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Salehi, Leili [Verfasser], Georg Gutachter] Schmitz, and Michael [Gutachter] [Hübner. "Nonlinear tomographic reconstruction of elastic properties of isotropic solid materials from ultrasound measurements / Leili Salehi ; Gutachter: Georg Schmitz, Michael Hübner." Bochum : Ruhr-Universität Bochum, 2017. http://nbn-resolving.de/urn:nbn:de:hbz:294-52083.
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Rinker, Brett A. "A single-sided access simultaneous solution of acoustic wave speed and sample thickness for isotropic materials of plate-type geometry." Diss., Columbia, Mo. : University of Missouri-Columbia, 2006. http://hdl.handle.net/10355/4585.
Full textAbstract:
Thesis (M.S.)--University of Missouri-Columbia, 2006.<br>The entire dissertation/thesis text is included in the research.pdf file; the official abstract appears in the short.pdf file (which also appears in the research.pdf); a non-technical general description, or public abstract, appears in the public.pdf file. Title from title screen of research.pdf file (viewed on April 17, 2009) Vita. Includes bibliographical references.