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Composite Structures (composite + structure)
Selected AbstractsMagnetoelectric Coupling Effects in Multiferroic Complex Oxide Composite StructuresADVANCED MATERIALS, Issue 26-27 2010Carlos A. F. Vaz Abstract The study of magnetoelectric materials has recently received renewed interest, in large part stimulated by breakthroughs in the controlled growth of complex materials and by the search for novel materials with functionalities suitable for next generation electronic devices. In this Progress Report, we present an overview of recent developments in the field, with emphasis on magnetoelectric coupling effects in complex oxide multiferroic composite materials. [source] Ceramic,Polymer Ba0.6Sr0.4TiO3/Poly(Methyl Methacrylate) Composites with Different Type Composite Structures for Electronic TechnologyINTERNATIONAL JOURNAL OF APPLIED CERAMIC TECHNOLOGY, Issue 4 2010Hong Wang Ba0.6Sr0.4TiO3 (BST)/poly(methyl methacrylate) (PMMA) composites with 0,3, 1,3, and 2,2 type structures were prepared and studied. The effect of composite type on the dielectric properties of BST/PMMA composites was comprehensively investigated by both theoretical and experimental methods. The 1,3 type composite shows the highest permittivity and dielectric tunability, while the 2,2 and 0,3 type composites show lower permittivity as well as lower dielectric tunabilities. The experimentally measured dielectric properties are in agreement with the theoretically calculated values. The results help in understanding and tailoring the dielectric properties of ceramic,polymer composites by choosing a suitable composite structure. [source] Damage analysis for structural integrity and durability of composite materialsFATIGUE & FRACTURE OF ENGINEERING MATERIALS AND STRUCTURES, Issue 7 2006R. TALREJA ABSTRACT Composite structures for mechanical and aerospace applications are designed to retain structural integrity and remain durable for the intended service life. Since the early 1970s important advances have been made in characterizing and modelling the underlying mechanical behaviour and developing tools and methodologies for predicting fracture and fatigue of composite materials. This paper presents a review of the concepts and analyses related to this area, and illustrates these by a few examples. The topics discussed are composite material strength in tension, compression and shear, damage and its progression in monotonic and cyclic loading, fatigue life prediction and damage induced changes in visco-elastic response. [source] Fracture analysis of composite co-cured structural joints using decohesion elementsFATIGUE & FRACTURE OF ENGINEERING MATERIALS AND STRUCTURES, Issue 9 2004P. P. CAMANHO ABSTRACT Delamination is one of the predominant forms of failure in laminated composite structures, especially when there is no reinforcement in the thickness direction. To develop composite structures that are more damage tolerant, it is necessary to understand how delamination develops, and how it can affect the residual performance. A number of factors such as residual thermal stresses, matrix-curing shrinkage and manufacturing defects affect how damage will grow in a composite structure. It is important to develop computationally efficient analysis methods that can account for all such factors. The objective of the current work is to apply a newly developed decohesion element to investigate the debond strength of skin-stiffener composite specimens. The process of initiation of delaminations and the propagation of delamination fronts is investigated. The numerical predictions are compared with published experimental results. [source] Enhanced Adsorption of Ammonia on Metal-Organic Framework/Graphite Oxide Composites: Analysis of Surface InteractionsADVANCED FUNCTIONAL MATERIALS, Issue 1 2010Camille Petit Abstract Composites of the metal-organic framework (MOF), MOF-5, and graphite oxide (GO) with different ratios of the two components are prepared and tested in ammonia removal under dry conditions. The parent and composite materials are characterized before and after exposure to ammonia by sorption of N2, X-ray diffraction, thermal analyses, and FT-IR spectroscopy. The results show a synergetic effect resulting in an increase in the ammonia uptake compared to the parent materials. It is linked to enhanced dispersive forces in the pore space of the composites. Additionally, ammonia interacts with zinc oxide tetrahedra via hydrogen bonding and is intercalated between the layers of GO. Retention of a large quantity of ammonia eventually leads to a collapse of the MOF-5 structure in the composites. The effect resembles that observed when MOF-5 is exposed to water. Taking into account the similarity of ammonia and water molecules, it is hypothesized that ammonia causes a destruction of the MOF-5 and composite structure as a result of its hydrogen bonding with the zinc oxide clusters. [source] Ceramic,Polymer Ba0.6Sr0.4TiO3/Poly(Methyl Methacrylate) Composites with Different Type Composite Structures for Electronic TechnologyINTERNATIONAL JOURNAL OF APPLIED CERAMIC TECHNOLOGY, Issue 4 2010Hong Wang Ba0.6Sr0.4TiO3 (BST)/poly(methyl methacrylate) (PMMA) composites with 0,3, 1,3, and 2,2 type structures were prepared and studied. The effect of composite type on the dielectric properties of BST/PMMA composites was comprehensively investigated by both theoretical and experimental methods. The 1,3 type composite shows the highest permittivity and dielectric tunability, while the 2,2 and 0,3 type composites show lower permittivity as well as lower dielectric tunabilities. The experimentally measured dielectric properties are in agreement with the theoretically calculated values. The results help in understanding and tailoring the dielectric properties of ceramic,polymer composites by choosing a suitable composite structure. [source] Composite Zirconium Silicides Through an In Situ ProcessINTERNATIONAL JOURNAL OF APPLIED CERAMIC TECHNOLOGY, Issue 1 2006Jérôme Canel Zirconium silicides are being investigated for use as neutron reflector materials for the next generation of nuclear power devices. Hot isostatically pressed monolithic Zr3Si2 and reactive sintered ZrXSiY composite are currently under development. The composite is obtained in situ and contains a ZrSi matrix embedding shell-like Zr, Zr2Si, and ZrSi2 domains with volume ratios depending on the initial Zr/Si ratio. Despite the lack of information on the mechanical properties of zirconium silicides, the composite structure is assumed to have enhanced fracture toughness; conditions to improve it further are discussed on the basis of microstructural observations of crack deflection. [source] Ordered Supramolecular Assembly of Porphyrin,Fullerene Composites on Nanostructured SnO2 Electrodes,ADVANCED MATERIALS, Issue 19 2006S. Kang Very high photocurrent generation is seen for an ordered supramolecular composite structure of C60 and porphyrin assembled on SnO2 electrodes. The simple substitution of methoxy groups at the meta positions of the meso -phenyl groups on the porphyrin ring leads to the ordered stacking arrangement shown in the figure, with separate electron and hole transport paths along the 1D porphyrin chains and 2D C60 sheets. [source] New Low Bandgap Dithienylbenzothiadiazole Vinylene Based Copolymers: Synthesis and Photovoltaic PropertiesMACROMOLECULAR RAPID COMMUNICATIONS, Issue 4 2010Bo Liu Abstract Two new low-bandgap block copolymers derived from dithienylbenzothiadiazole (DTBT) and different electron-rich functional groups (dioctoxyl benzene and N -octyl-diphenylamine), poly(1,4-dioctoxyl-2,5-divinylbenzene- co -4,7-dithiophene-2,-yl-2,1,3-benzothiadiazole) (PPV-DTBT), poly(3,8-divinyl- N -octyl-diphenylamine- co -4,7-dithiophene-2,-yl-2,1,3-benzothiadiazole) (PDPAV-DTBT), were synthesized by Heck cross-coupling polymerization. PPV-DTBT and PDPAV-DTBT are easily soluble in common organic solvents such as o -dichlorobenzene and chloroform. DSC and TGA results indicate that these copolymers possess good thermal stabilities. PPV-DTBT and PDPAV-DTBT films exhibit broad absorption bands at 300,765,nm (with an optical bandgap of 1.62,eV) and 300,733,nm (with an optical bandgap of 1.69,eV), respectively. The highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) of PPV-DTBT were estimated by cyclic voltammetry to be ,5.43 and ,3.74,eV, respectively, and the HOMO and LUMO of PDPAV-DTBT were ,5.37 and ,3.7,eV, respectively. Preliminary photovoltaic cells based on the composite structure of ITO/PEDOT: PSS/PPV-DTBT:PCBM (1: 2, w/w)/Al showed an open-circuit voltage of 0.75,V, a power conversion efficiency of 0.6%, and a short circuit current of 1.7,mA,·,cm,2. [source] Whey protein isolate coating on LDPE film as a novel oxygen barrier in the composite structurePACKAGING TECHNOLOGY AND SCIENCE, Issue 1 2004Seok-In Hong Abstract To examine the feasibility of whey protein isolate (WPI) coating as an alternative oxygen barrier for food packaging, heat-denatured aqueous solutions of WPI with various levels of glycerol as a plasticizer were applied on corona-discharge-treated low-density polyethylene (LDPE) films. The resulting WPI-coated LDPE films showed good appearance, flexibility and adhesion between the coating and the base film, when an appropriate amount of plasticizer was added to the coating formulations. WPI-coated LDPE films showed significant decrease in oxygen permeability (OP) at low to intermediate relative humidity, with an Arrhenius behaviour and an activation energy of 50.26,kJ/mol. The OP of the coated films increased significantly with increasing relative humidity, showing an exponential function. Although the coated films showed a tendency to have less oxygen barrier and more glossy surfaces with increasing plasticizer content, differences in the OP and gloss values were not significant. Haze index and colour of the coated films were also little influenced by WPI coating and plasticizer content. The results suggest that whey protein isolate coating could work successfully as an oxygen barrier and have potential for replacing synthetic plastic oxygen-barrier layers in many laminated food packaging structures. Copyright © 2004 John Wiley & Sons, Ltd. [source] Structures of incommensurate and commensurate composite crystals RbxMnO2 (x = 1.3711, 1.3636)ACTA CRYSTALLOGRAPHICA SECTION B, Issue 1 2010Jürgen Nuss Rb1.3711MnO2 (Rb11Mn8O16) has been synthesized via the azide/nitrate route from a stoichiometric mixture of the precursors Mn2O3, RbNO3 and RbN3. The structure of this extremely air- and moisture-sensitive compound can best be described in terms of an incommensurate composite structure, built up by a honeycomb-like framework of Rb ions, as one subsystem and by a second subsystem of chains, consisting of edge-sharing MnO4/2 tetrahedra. These two composite substructures interpenetrate in such a way that the manganate chain polyanions centre the channels of the Rb-honeycomb framework. Crystals transform by an aging process into Rb1.3636MnO2 (Rb15Mn11O22), which has a similar structure but a different commensurate modulation. Two reasons can be established for the origin of the modulations: the charge ordering of Mn2+/Mn3+ on one hand, and the incompatibility of the Mn,Mn and Rb,Rb separations on the other. [source] Multilayer Substrate-Mediated Tuning Resonance of Plasmon and SERS EF of Nanostructured Silver,CHEMPHYSCHEM, Issue 12 2010Lian C. T. Shoute Dr. Abstract A thin-film of dielectric on a reflecting surface constituting a multilayer substrate modulates light intensity due to the interference effect. A nanostructure consisting of randomly oriented silver particles of different shapes, sizes, and interparticle spacings supports multiple plasmon resonances and is observed to have a broad extinction spectrum that spans the entire visible region. Combining the two systems by fabricating the nanostructure on the thin-dielectric film of the multilayer substrate yields a new composite structure which is observed to modulate both the extinction spectrum and the SERS EF (surface enhanced Raman scattering enhancement factor) of the nanostructure as the thickness of the thin-film dielectric is varied. The frequency and intensity of the visible extinction spectrum vary dramatically with the dielectric thickness and in the intermediate thickness range the spectrum has no visible band. The SERS EF determined for the composite structure as a function of the thin-film dielectric thickness varies by several orders of magnitude. Strong correlation between the magnitude of the SERS EF and the extinction intensity is observed over the entire dielectric thickness range indicating that the extinction spectrum corresponds to the excitation of the plasmon resonances of the nanostructure. A significant finding which has potential applications is that the composite structure has synergic effect to boost SERS EF of the nanostructure by an order of magnitude or more compared to the same nanostructure on an unlayered substrate. [source] Investigations into the Sealing of Heat Damaged Areas by Applying Polymer Powders During Laser Cutting of Carbon Fiber Reinforced Composites,ADVANCED ENGINEERING MATERIALS, Issue 7 2010Peter Jaeschke Endless carbon fiber reinforced plastics are recognized as having the greatest lightweight construction potential of all materials. Fully automated process chains for the manufacturing of composite structures are needed in order to achieve production rates and cycle times required in many industrial sectors. In this paper, a new technique, based on the in situ sealing of the kerf during high power laser cutting by application of polymer powder is presented. The degree of sealing is analyzed as a function of powder mass flow as well as carrying gas flow and it is shown that moisture uptake can be reduced compared to unsealed laser cut specimens. [source] Bio-mimetic scaling of mechanical behavior of thin films, coatings, and surfaces by Laser Interference MetallurgyADVANCED ENGINEERING MATERIALS, Issue 9 2005C. Daniel Biological solutions to enhance strength and stability often use hierarchical composite structures. The effect is not based on large chemical variations, but instead is realized by structural composites with long-range order. Laser Interference Metallurgy is a newly developed technique that utilizes this biological approach to optimize the mechanical properties of surfaces and thin films. The possibility of scaling mechanical properties is quantitatively analyzed and compared with the biological approach. [source] Fracture analysis of composite co-cured structural joints using decohesion elementsFATIGUE & FRACTURE OF ENGINEERING MATERIALS AND STRUCTURES, Issue 9 2004P. P. CAMANHO ABSTRACT Delamination is one of the predominant forms of failure in laminated composite structures, especially when there is no reinforcement in the thickness direction. To develop composite structures that are more damage tolerant, it is necessary to understand how delamination develops, and how it can affect the residual performance. A number of factors such as residual thermal stresses, matrix-curing shrinkage and manufacturing defects affect how damage will grow in a composite structure. It is important to develop computationally efficient analysis methods that can account for all such factors. The objective of the current work is to apply a newly developed decohesion element to investigate the debond strength of skin-stiffener composite specimens. The process of initiation of delaminations and the propagation of delamination fronts is investigated. The numerical predictions are compared with published experimental results. [source] Numerical studies of shear banding in interface shear tests using a new strain calculation method,INTERNATIONAL JOURNAL FOR NUMERICAL AND ANALYTICAL METHODS IN GEOMECHANICS, Issue 12 2007Jianfeng Wang Abstract Strain localization is closely associated with the stress,strain behaviour of an interphase system subject to quasi-static direct interface shear, especially after peak stress state is reached. This behaviour is important because it is closely related to deformations experienced by geotechnical composite structures. This paper presents a study using two-dimensional discrete element method (DEM) simulations on the strain localization of an idealized interphase system composed of densely packed spherical particles in contact with rough manufactured surfaces. The manufactured surface is made up of regular or irregular triangular asperities with varying slopes. A new simple method of strain calculation is used in this study to generate strain field inside a simulated direct interface shear box. This method accounts for particle rotation and captures strain localization features at high resolution. Results show that strain localization begins with the onset of non-linear stress,strain behaviour. A distinct but discontinuous shear band emerges above the rough surface just before the peak stress state, which becomes more expansive and coherent with post-peak strain softening. It is found that the shear bands developed by surfaces with smaller roughness are much thinner than those developed by surfaces with greater roughness. The maximum thickness of the intense shear zone is observed to be about 8,10 median particle diameters. The shear band orientations, which are mainly dominated by the rough boundary surface, are parallel with the zero extension direction, which are horizontally oriented. Published in 2007 by John Wiley & Sons, Ltd. [source] An enriched element-failure method (REFM) for delamination analysis of composite structuresINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN ENGINEERING, Issue 6 2009X. S. Sun Abstract This paper develops an enriched element-failure method for delamination analysis of composite structures. This method combines discontinuous enrichments in the extended finite element method and element-failure concepts in the element-failure method within the finite element framework. An improved discontinuous enrichment function is presented to effectively model the kinked discontinuities; and, based on fracture mechanics, a general near-tip enrichment function is also derived from the asymptotic displacement fields to represent the discontinuity and local stress intensification around the crack-tip. The delamination is treated as a crack problem that is represented by the discontinuous enrichment functions and then the enrichments are transformed to external nodal forces applied to nodes around the crack. The crack and its propagation are modeled by the ,failed elements' that are applied to the external nodal forces. Delamination and crack kinking problems can be solved simultaneously without remeshing the model or re-assembling the stiffness matrix with this method. Examples are used to demonstrate the application of the proposed method to delamination analysis. The validity of the proposed method is verified and the simulation results show that both interlaminar delamination and crack kinking (intralaminar crack) occur in the cross-ply laminated plate, which is observed in the experiment. Copyright © 2009 John Wiley & Sons, Ltd. [source] Optimal solid shell element for large deformable composite structures with piezoelectric layers and active vibration controlINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN ENGINEERING, Issue 15 2005X. G. Tan Abstract In this paper, we present an optimal low-order accurate piezoelectric solid-shell element formulation to model active composite shell structures that can undergo large deformation and large overall motion. This element has only displacement and electric degrees of freedom (dofs), with no rotational dofs, and an optimal number of enhancing assumed strain (EAS) parameters to pass the patch tests (both membrane and out-of-plane bending). The combination of the present optimal piezoelectric solid-shell element and the optimal solid-shell element previously developed allows for efficient and accurate analyses of large deformable composite multilayer shell structures with piezoelectric layers. To make the 3-D analysis of active composite shells containing discrete piezoelectric sensors and actuators even more efficient, the composite solid-shell element is further developed here. Based on the mixed Fraeijs de Veubeke,Hu,Washizu (FHW) variational principle, the in-plane and out-of-plane bending behaviours are improved via a new and efficient enhancement of the strain tensor. Shear-locking and curvature thickness locking are resolved effectively by using the assumed natural strain (ANS) method. We also present an optimal-control design for vibration suppression of a large deformable structure based on the general finite element approach. The linear-quadratic regulator control scheme with output feedback is used as a control law on the basis of the state space model of the system. Numerical examples involving static analyses and dynamic analyses of active shell structures having a large range of element aspect ratios are presented. Active vibration control of a composite multilayer shell with distributed piezoelectric sensors and actuators is performed to test the present element and the control design procedure. Copyright © 2005 John Wiley & Sons, Ltd. [source] Behaviour control of modern composite structuresINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN ENGINEERING, Issue 14 2004Alexander Tesar Abstract Numerical and experimental assessment of modern composite structures provided with knowledge-based joints for their behaviour control is treated in the present paper. Special connection strip, joining composite materials, is adopted. The wave approach of the back propagation neural network in micro- and macromechanical modelling is used for the numerical analysis of the problem. Some numerical and experimental results are given in order to demonstrate the efficiency of the control joint suggested. Copyright © 2004 John Wiley & Sons, Ltd. [source] Tailored composite polymer,metal nanoparticles by miniemulsion polymerization and thiol-ene functionalizationJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 7 2010Kim Y. van Berkel Abstract A simple and modular synthetic approach, based on miniemulsion polymerization, has been developed for the fabrication of composite polymer,metal nanoparticle materials. The procedure produces well-defined composite structures consisting of gold, silver, or MnFe2O4 nanoparticles (,10 nm in diameter) encapsulated within larger spherical nanoparticles of poly(divinylbenzene) (,100 nm in diameter). This methodology readily permits the incorporation of multiple metal domains into a single polymeric particle, while still preserving the useful optical and magnetic properties of the metal nanoparticles. The morphology of the composite particles is retained upon increasing the inorganic content and also upon redispersion in organic solvents. Finally, the ability to tailor the surface chemistry of the composite nanoparticles and incorporate steric stabilizing groups using simple thiol-ene chemistry is demonstrated. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 1594,1606, 2010 [source] Electrical properties and optical absorption in InN:In structuresPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 6 2008T. A. Komissarova Abstract Electrophysical and optical absorption measurements have been performed for conventional InN epilayers and InN:In composite structures grown by plasma-assisted molecular beam epitaxy. It is shown that intentional periodical introduction of In metallic inclusions into InN layers results in formation of inhomogeneous arrays of clusters. Their presence modifies the shape of absorption spectra. At the same time, significant amount of indium (up to 1/3 of a thickness) in these structures does not influence noticeably the carrier concentration and mobility. These parameters fall in the range of published data for the conventional InN layers. These finding can indicate that formation of In clusters in InN is a more frequent event than it is currently accepted. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Resin infusion of triaxially braided preforms with through-the-thickness reinforcementPOLYMER COMPOSITES, Issue 2 2003Jay R. Sayre Vacuum assisted resin transfer molding (VARTM) has shown potential to significantly reduce the manufacturing cost of high-performance aerospace composite structures. In this investigation, high fiber volume fraction, triaxially braided preforms with through-the-thickness stitching were successfully resin infiltrated by the VARTM process. The preforms, resin infiltrated with three different resin systems, produced cured composites that were fully wet-out and void free. A three-dimensional finite element model was used to simulate resin infusion into the preforms. The predicted flow patterns agreed well with the flow patterns observed during the infiltration process. The total infiltration times calculated using the model compared well with the measured times. [source] On predicting elastic moduli and natural frequencies of multi-phase composites with randomly distributed short fibersPOLYMER COMPOSITES, Issue 1 2000Lu-Ping Chao This study presents a formulation to determine the overall stiffness of an n -phase short fiber composite to include the inclusions' aspect ratio ranging from less than one to greater than one. The Mori-Tanaka theory is initially employed to investigate the overall stress-strain relation of a multi-phase short-fiber-reinforced composite material, particularly whether or not the fibers and the matrix are isotropic, cubic, or transversely isotropic material. The effective stiffness tensor of a multi-phase composite is then denoted as a function of the matrix's elastic moduli, the n -phases' inclusions' elastic moduli, the n -phases' inclusions' Eshelby tensor, and the n -phases' inclusions' volume fractions. Utilizing the equivalent inclusion method allows us to model inclusions of n -phases that consist of fictitious eigenstrains. In addition, the corresponding Eshelby tensors' values for ellipsoidal inclusion embedded in the isotropic matrix with the variation of aspect ratio are presented. Numerical results of the proposed formulation in solving a two-phase composite closely correspond to the Halpin-Tsai Equation. Results presented herein provide valuable information on the appropriate manufacturing requirements of multi-phase composite materials or the design and optimization of multi-phase composite structures. [source] Crack propagation in anisotropic, plane composite structuresPROCEEDINGS IN APPLIED MATHEMATICS & MECHANICS, Issue 1 2008Martin Steigemann No abstract is available for this article. [source] Atmospheric pressure chemical ionisation reversed-phase liquid chromatography/ion trap mass spectrometry of intact bacteriohopanepolyolsRAPID COMMUNICATIONS IN MASS SPECTROMETRY, Issue 7 2003Helen M. Talbot Atmospheric pressure chemical ionisation liquid chromatography/multi-stage ion trap mass spectrometry (APCI-LC/MSn) has been applied to the study of intact bacteriohopanepolyols. Spectral characterisation of bacteriohopanepolyols of known structure present in bacterial extracts (Zymomonas mobilis and a fermenter containing methanotrophs including Methylococcus capsulatus) has revealed greater structural detail than previous liquid chromatography/mass spectrometry (LC/MS) methods and identified characteristic fragmentations indicative of numerous biohopanoid structures. Analysis of a Recent sedimentary extract from Lake Druzhby (Antarctica) has demonstrated the power of this technique to detect biohopanoids in complex samples including at least partial characterisation of previously unknown composite structures. Copyright © 2003 John Wiley & Sons, Ltd. [source] Numerische Modellierung von Holz und Verbindungselementen in Holz-Beton-VerbundkonstruktionenBAUTECHNIK, Issue 6 2005Marco Grosse Dipl.-Ing. Durch die Anwendung der FEM können auch komplexe Strukturen berechnet werden, die sich nicht mehr als Stab- oder Flächentragwerke abbilden lassen. Es ist daher naheliegend, auch das Tragverhalten von Bauteilen oder Bauteilkomponenten in Abhängigkeit von verschiedenen Einflußparametern mit Hilfe von FE-Modellen zu simulieren. Um dabei aber Versagensmechanismen abbilden zu können, ist es notwendig, das Materialverhalten der Baustoffe im Nachbruchbereich zu berücksichtigen. Es wird ein konstitutives Materialmodell für den Werkstoff Holz vorgestellt, welches das räumlich anisotrope und vom Beanspruchungsmodus abhängige, nichtlineare Tragverhalten einbezieht. Durch die Kombination mit einem leistungsfähigen Betonmodell ist es möglich, Holz-Beton-Verbundkonstruktionen zu untersuchen. Anhand der Simulationen von Scherversuchen mit verschiedenen Schubverbindungselementen soll die Leistungsfähigkeit solcher numerischer Modelle verdeutlicht werden. Numerical modelling of timber and connection elements used in timber-concrete composite structures. Complex load carrying structures that can not be reproduced as framework ore simple surface models can be calculated using the Finite Element Method. Therefore it seems desirable to simulate the structural behaviour of members or components considering several influence parameters with the help of FE-models too. However, to model the failure mechanism it is necessary to take into account the material behaviour in the critical and post critical range. An adequate numerical model for timber that considers the specific anisotropic and load dependent strength and degradation behaviour is introduced. In combination with an capable model for concrete it is possible to examine timber concrete composite structures. The effectiveness of such models is verified by simulations of shear tests with several fastener elements. [source] Vereinfachtes Verfahren zur Vorhersage des Langzeitverhaltens von Holz-Beton-VerbundkonstruktionenBAUTECHNIK, Issue 4 2005Ralf Avak Prof. Dr.-Ing. Für die Bemessung von nachgiebig verbundenen Biegeträgern aus Holz und Beton wird vom praktisch tätigen Ingenieur in der Regel das ,-Verfahren bevorzugt. Das Verfahren ist Bestandteil nationaler, sowie europäischer Holzbauvorschriften [4], [5]. Für die Berechnung des Langzeitverhaltens ist das ,-Verfahren in seiner derzeitigen Form jedoch nur bedingt geeignet, da es z. B. das Schwinden des Betons nicht berücksichtigt. Im folgenden wird aus diesem Grund ein einfaches analytisches Verfahren vorgestellt, bei dem neben dem Kriechverhalten der Materialien Holz und Beton auch deren Schwind- bzw. Quellverformungen sowie das Langzeitverhalten der Schubverbindungsmittel berücksichtigt werden können. Die Anwendung des Verfahrens ist momentan noch auf Innenbauteile beschränkt. Simplified procedure for the description from the long-term behaviour of timber-concrete composite structures. The ,-procedure is favoured to design timber-concrete composite structures. This procedure is component of current national as well as European timber standards [4], [5]. The ,-procedure isn't suitable to describe the long-term behaviour, because it does not consider the shrinkage of concrete for example. A simplified procedure is introduced in the following. This procedure considers creeping of timber and concrete and , for the first time , swelling and shrinkage of these materials, as well as the long-term behaviour of the shear connectors. Currently it is applicable only to inner structures. [source] Dynamische Zustandsbewertung einer Verbundbrücke: Beobachtung äußerer und nichtlinearer Einflüsse auf die modalen EigenschaftenBETON- UND STAHLBETONBAU, Issue 8 2010Volker Bungard Dipl.-Ing. Bauwerksüberwachung; Dynamische Einwirkungen/Erdbeben; Brückenbau; Versuche Abstract Bei der Anwendung dynamischer Untersuchungsmethoden zur Zustandsbewertung von Ingenieurbauwerken aus Stahl- und Spannbeton sowie Verbundbau spielen Veränderungen von Rand- und Umweltbedingungen auf die modalen Parameter eine wesentliche Rolle. Während man diese im Laborexperiment weitest gehend überwachen bzw. ausschließen kann, sind sie bei in-situ Versuchen nur schwer zu kontrollieren. Am Beispiel einer Verbundbrücke soll demonstriert werden, welche Größenordnung die Veränderung von Randbedingungen (z. B. Veränderung von anregenden Kräften) und Umwelteinflüsse (z. B. Temperatur) auf die dynamischen Parameter einer in-situ Struktur haben können. Die Größenordnung dieser Veränderungen wird mit Veränderungen, die aus wirklichen Strukturschäden resultieren können, verglichen und bewertet. Dynamic Condition Assessment of a Composite Bridge: Investigation of External and Nonlinear Influences on the Modal Properties Using dynamic investigation methods to assess the state of civil constructions like reinforced and prestressed concrete structures as well as composite structures, changes in boundary conditions and environmental influences play a decisive role. Under laboratory conditions it is possible to control respectively to exclude these influences but it is not always possible to control and to exclude them when testing in-situ. By means of dynamic measurements which are conducted on a composite bridge, possible changes in dynamic properties resulting from changes in the amplitude of the excitation force and resulting from changes in the temperature conditions are demonstrated. The dimension of these changes is compared with changes in modal properties resulting from real structural defects and structural damages. [source] | ||||||||||||||||||||||||||||