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Refined sandwich model for the vibration of beams with embedded shear piezoelectric actuators and sensors

TRINDADE, Marcelo A.; BENJEDDOU, Ayech
Fonte: PERGAMON-ELSEVIER SCIENCE LTD Publicador: PERGAMON-ELSEVIER SCIENCE LTD
Tipo: Artigo de Revista Científica
ENG
Relevância na Pesquisa
37.06%
This work extends a previously presented refined sandwich beam finite element (FE) model to vibration analysis, including dynamic piezoelectric actuation and sensing. The mechanical model is a refinement of the classical sandwich theory (CST), for which the core is modelled with a third-order shear deformation theory (TSDT). The FE model is developed considering, through the beam length, electrically: constant voltage for piezoelectric layers and quadratic third-order variable of the electric potential in the core, while meclianically: linear axial displacement, quadratic bending rotation of the core and cubic transverse displacement of the sandwich beam. Despite the refinement of mechanical and electric behaviours of the piezoelectric core, the model leads to the same number of degrees of freedom as the previous CST one due to a two-step static condensation of the internal dof (bending rotation and core electric potential third-order variable). The results obtained with the proposed FE model are compared to available numerical, analytical and experimental ones. Results confirm that the TSDT and the induced cubic electric potential yield an extra stiffness to the sandwich beam. (C) 2007 Elsevier Ltd. All rights reserved.

Analise de estruturas sanduiche : parametros de projeto; Sandwich structures analysis : design parameters

Debora Pierini Gagliardo
Fonte: Biblioteca Digital da Unicamp Publicador: Biblioteca Digital da Unicamp
Tipo: Dissertação de Mestrado Formato: application/pdf
Publicado em 21/08/2008 PT
Relevância na Pesquisa
37.06%
As estruturas sanduíche têm despertado grande interesse e já estão bastante difundidas em diversos segmentos industriais, sendo suas principais utilizações nas indústrias aeroespacial, militar, naval e civil. Este fato se deve à sua propriedade de combinar alta rigidez à flexão e baixo peso, resultando em uma estrutura muito eficiente. Neste sentido, a análise e cálculo das estruturas sanduíche são de extrema importância no desenvolvimento de projetos de aplicação do mesmo. Neste trabalho, foram analisados os critérios de falha dos painéis, bem como os materiais e suas propriedades mecânicas, considerando as alterações e considerações que devem ser feitas nos projetos de acordo com as características do material. Na parte final dessa pesquisa, são apresentadas a teoria de cálculo e a rotina para elaboração de projetos relacionados com a construção civil utilizando as estruturas sanduíche, com ênfase em estruturas planas, tais como vigas e placas. Por fim emprega-se uma ferramenta, planilha eletrônica, para analisar e avaliar a aplicação de diversos materiais de construção em estruturas sanduíche; The sandwich structures have aroused great interest and have already been very widespread in several branches in industries...

Development of reinforced composite sandwich panels based on 3D fabrics

Fangueiro, Raúl; Velosa, J. C.; Hattum, F. W. J. van; Soutinho, F.
Fonte: Universidade do Minho Publicador: Universidade do Minho
Tipo: Conferência ou Objeto de Conferência
Publicado em //2010 ENG
Relevância na Pesquisa
37.21%
relative new type of sandwich material was investigated, based on 3D knitted sandwich fabric preforms. Due to the integrally interlacement of both sandwich-fabric the skins by the connection yarns – core debonding resistance of panels and structures based on the perform is very high. [1]. In this work the mechanical performance of sandwich composite panels based on sandwich knitted fabrics is presented and discussed. Different 3D sandwich knitted fabric performs have been produced varying the thickness and the interlacement pattern. Composite panels using these performs have been produced using vacuum infusion technique. Panel thicknesses of 8, 15 and 25 mm, using two resin types – polyester and epoxy – have been produced. Materials thus obtained have been tested in tensile, bending and impact. The results obtained are presented, discussed and compared to models. Various samples of 3D sandwich spacer fabrics using vacuum infusion process have been produced in order to study the impregnation process. The dimensional properties investigated for non-impregnated core structures include cross-threads density, areal mass, yarns linear density, etc. Results obtained show that the mechanical performances vary according to the type of 3D knitted sandwich perform and the type of resin used.

Conception of sandwich structural panels comprising thin walled steel fibre reinforced self-compacting concrete (SFRSCC) and fibre reinforced polymer (FRP) connectors

Lameiras, Rodrigo; Barros, Joaquim A. O.; Azenha, Miguel; Valente, Isabel
Fonte: Universidade do Minho Publicador: Universidade do Minho
Tipo: Conferência ou Objeto de Conferência
Publicado em //2012 ENG
Relevância na Pesquisa
37.06%
In this paper, an innovative thermally efficient sandwich structural panel is proposed for the structural walls of a pre-fabricated modular housing system. Traditionally, sandwich concrete panels consist of conventional reinforced concrete wythes as external layers, polystyrene foam as core material and steel connectors. However, steel connectors are known to cause thermal bridges on the building envelope and possibly condensation and mould problems. Furthermore, the possibilities for thickness reduction/optimization of conventionally reinforced concrete layers are frequently limited by minimum cover requirements. To overcome these issues, the proposed sandwich panel comprises Fibre Reinforced Polymer (FRP) connectors and two thin layers of Steel Fibre Reinforced SelfCompacting Concrete (SFRSCC). This paper presents the basic conception of the proposed building system together with preliminary parametric numerical analyses to define the arrangement and geometry of the elements that constitute the sandwich panels. Finally, the feasibility of using the proposed connector and SFRSCC on the external wythes is experimentally investigated through a series of pull-out tests where failure modes and load capacity of the connections are analysed.

Flexural and shear behaviour of precast sandwich slabs comprising thin walled steel fibre reinforced self-compacting concrete

Sousa, Christoph Fernandes; Barros, Joaquim A. O.; Azenha, Miguel; Lameiras, Rodrigo
Fonte: RILEM Publicador: RILEM
Tipo: Conferência ou Objeto de Conferência
Publicado em //2013 ENG
Relevância na Pesquisa
37.11%
Publicado em "Rheology and processing of construction materials", ISBN 978-2-35158-137-7; Insulated sandwich panels are often composed of external concrete layers, mechanically connected through metallic elements, such as trusses. Due to their high thermal conductivity, metallic connectors tend to cause thermal bridges on the building envelope. In view of this problem, an innovative solution for sandwich slabs is proposed within the framework of a pre-fabricated modular housing system. The referred slabs are based on a sandwich solution composed by two thin layers of Steel Fibre Reinforced Self-Compacting Concrete (SFRSCC) that are connected by thin perforated plates of Glass Fibre Reinforced Polymer (GFRP), used together with a thermal insulation core-layer. The bottom concrete layer is reinforced with conventional steel rebars and steel fibres, whereas the upper one does not have conventional reinforcement. This paper presents a preliminary experimental program aiming to assess the flexural and shear behaviour of this type of sandwich panel solution. The obtained results confirm the feasibility of the proposed sandwich slab system, revealing its capacity in terms of load carrying capacity and ductility performance. In addition...

Aplicação de técnicas BIM à construção modular com Painéis Sandwich

Silva, Pedro Daniel Moreira da
Fonte: Universidade do Minho Publicador: Universidade do Minho
Tipo: Trabalho de Conclusão de Curso
Publicado em //2012 POR
Relevância na Pesquisa
37.15%
Dissertação de mestrado integrado em Engenharia Civil; A construção modular é um processo construtivo que permite a conceção em ambiente controlado de módulos habitacionais que podem ser transportado para qualquer local e instalado em menor tempo, comparativamente aos processos tradicionais, introduzindo novas vantagens económicas e construtivas. A utilização de painéis sandwich em betão estrutural permite a conceção de módulos que combinam os benefícios integrados da utilização do isolamento para o conforto térmico com o suporte estrutural desempenhado pelas camadas de betão do painel. BIM – Building Information Modeling é uma nova metodologia de projeto apoiado no desenvolvimento de modelos virtuais, que são integrados com as diversas informações e dados funcionais do edifício, que são transacionados entre aplicações BIM através de ficheiros IFC, estimulando a interoperabilidade entre os intervenientes da elaboração de projeto e construção. Neste trabalho pretende-se aferir o nível de interoperabilidade entre aplicações preparadas para o conceito BIM, através da conceção de um caso de estudo que simula as interações entre as equipas de arquitetura e as equipas de especialidades hidráulica e térmica. O modelo de arquitetura foi concebido com o apoio da aplicação ArchiCAD através da modelação paramétrica em GDL dos painéis sandwich. A comunicação entre as aplicações BIM é realizada através da utilização do ficheiro IFC...

Helly property, clique graphs, complementary graph classes, and sandwich problems

Dourado,Mitre C.; Petito,Priscila; Teixeira,Rafael B.; Figueiredo,Celina M. H. de
Fonte: Sociedade Brasileira de Computação Publicador: Sociedade Brasileira de Computação
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/01/2008 EN
Relevância na Pesquisa
37.21%
A sandwich problem for property Π asks whether there exists a sandwich graph of a given pair of graphs which has the desired property Π. Graph sandwich problems were first defined in the context of Computational Biology as natural generalizations of recognition problems. We contribute to the study of the complexity of graph sandwich problems by considering the Helly property and complementary graph classes. We obtain a graph class defined by a finite family of minimal forbidden subgraphs for which the sandwich problem is NP-complete. A graph is clique-Helly when its family of cliques satisfies the Helly property. A graph is hereditary clique-Helly when all of its induced subgraphs are clique-Helly. The clique graph of a graph is the intersection graph of the family of its cliques. The recognition problem for the class of clique graphs was a long-standing open problem that was recently solved. We show that the sandwich problems for the graph classes: clique, clique-Helly, hereditary clique-Helly, and clique-Helly nonhereditary are all NP-complete. We propose the study of the complexity of sandwich problems for complementary graph classes as a mean to further understand the sandwich problem as a generalization of the recognition problem.

The mechanical response of metallic sandwich beams under foam projectile impact loading

Jing,Lin; Wang,Zhihua; Ning,Jianguo; Zhao,Longmao
Fonte: Associação Brasileira de Ciências Mecânicas Publicador: Associação Brasileira de Ciências Mecânicas
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/01/2011 EN
Relevância na Pesquisa
37.19%
The dynamic response of the clamped sandwich beams was investigated by impacting the beams at mid-span with metal foam projectiles. Efects of applied impulse, face-sheet thickness and core thickness on the impact resistance of sandwich beams are discussed. Using strain gauge measurement technique, the deformation mechanism of sandwich beams was analyzed in the paper. The results indicate that the structural response is sensitive to the configuration of sandwich structures. Based on the experiments, corresponding finite element simulations have been undertaken using the LS-DYNA software. A good agreement has been obtained between the numerical and experimental results. The deformation and failure modes of sandwich beams under impact loading are presented, i.e. large inelastic deformation, core compression and core shear with interfacial failure. Numerical results also show that the velocity-time histories of the mid-span of the front and back sheet of sandwich beams are related to not only core strength but also core thickness. The research results are of worth to the theoretical prediction of the dynamic response of metallic sandwich beam.

An analytical model of a clamped sandwich beam under low-impulse mass impact

Jiang,Wen-zheng; Liu,Ying; Gu,Yu; Lu,G X
Fonte: Associação Brasileira de Ciências Mecânicas Publicador: Associação Brasileira de Ciências Mecânicas
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/01/2014 EN
Relevância na Pesquisa
37.19%
An analytical model is developed to examine a low impulsive projectile impact on a fully clamped sandwich beams by considering the coupled responses of the core and the face sheets. Firstly, based on the dynamic properties of foam cores, the sandwich beam is modeled as two rigid perfectly-plastic beams connected by rigid perfectly-plastic springs. Different from the previous sandwich beam model, the transverse compression and bending effects of the foam core are considered in the whole deformation process. Based on this model, different coupling mechanism of sandwich beams are constructed so that an analytical solution considering small deformation is derived. The coupled dynamic responses of sandwich beams with different core strengths are investigated. The results indicate that this model improves the prediction accuracy of the responses of the sandwich beams, and is available for the situation when the sandwich beam undergoes moderate global deformation.

Behavior of sandwich structures and spaced plates subjected to high-velocity impacts

García-Castillo, Shirley K.; Buitrago, Brenda L.; Barbero, Enrique
Fonte: Wiley Online Library Publicador: Wiley Online Library
Tipo: info:eu-repo/semantics/acceptedVersion; info:eu-repo/semantics/article Formato: text/plain; application/pdf
Publicado em /02/2011 ENG
Relevância na Pesquisa
37.11%
This work evaluates the behavior of sandwich and spaced plates subjected to high-velocity impacts. The sandwich structures were made of glass/polyester face-sheet and a PVC foam core. The spaced plates were made of two plates of the same material of the sandwich face-sheet at a distance equal to the core thickness. The residual velocity, the ballistic limit, and the damage area were selected to compare the response of both structures. The residual velocity and ballistic limit was very similar in both cases. Nevertheless, the damage area of sandwich structures and spaced plates differed due to the dissimilar properties between the sandwich core and the air inside of the spaced plates. An analytical model, based on energy criteria, was applied to estimate the residual velocity of the projectile, the absorbed energy by each facesheet, and the ballistic limit in the spaced plates; Spanish Comision Interministerial de Ciencia y Tecnologia; contract grant number: TRA2007-66555.

Thermo-mechanical load interactions in foam cored axi-symmetric sandwich circular plates – High-order and FE models

Santuiste, Carlos; Thomsen, Ole T.; Frostig, Yeoshua
Fonte: Elsevier Publicador: Elsevier
Tipo: info:eu-repo/semantics/acceptedVersion Formato: application/pdf
Publicado em /01/2011 ENG
Relevância na Pesquisa
37.25%
This work presents analytical and finite element analysis (FEA) results of the thermo mechanical non linear response of an axi symmetric circular sandwich plates with a compliant foam core. The study investigates the load thermal interaction response of a sandwich panel where the properties of the core are temperature dependent and degrade as the temperatures are raised. It presents briefly the governing equations for a sandwich plate based on the principles of the high order sandwich panel theory (HSAPT) which incorporates the effects of the vertical flexibility of the core material as well as the effects of tem perature independent/dependent mechanical properties of the foam core. The effects of the thermal deg radation of core material on the thermo mechanical non linear response of a simply supported circular sandwich plate are studied through the analytical and FE models. The difficulties involved in non linear geometrical FE modeling of sandwich panels with a compliant ‘‘soft” core with temperature dependent mechanical properties are discussed. The HSAPT model predictions are compared very well with FE result. An important conclusion of the study is that the interaction between mechanical loads, tempera ture induced deformations...

Modelización analítica de paneles sandwich sometidos a impactos de baja velocidad

Rueda Lastres, Daniel
Fonte: Universidade Carlos III de Madrid Publicador: Universidade Carlos III de Madrid
Tipo: info:eu-repo/semantics/bachelorThesis; info:eu-repo/semantics/masterThesis Formato: application/pdf
SPA
Relevância na Pesquisa
37.19%
En este Proyecto Fin de Carrera se ha estudiado el comportamiento de un panel sándwich frente a impacto de baja velocidad en el que se obtiene la fuerza de contacto entre el proyectil y el panel sándwich en función del tiempo de impacto. Los paneles que se han estudiado están constituidos por las pieles, formadas por laminas de carbono-epoxy, y el núcleo de nido de abeja, de Nomex. Estos paneles tienen un laminado ortótropo, son simétricos y están empotrados en dos de sus caras. Para ello, se ha analizado un modelo dinámico que consiste en representar un sistema de dos grados de libertad mediante masas, resortes y un amortiguador, simulando el impacto de un proyectil sobre una estructura sándwich. Las masas representan las masas efectivas del sándwich y del proyectil, el amortiguador representa la resistencia al aplastamiento del núcleo y los resortes representan la rigidez del laminado y del panel sándwich. Las fuerzas de los resortes y del amortiguador se hallarán en primer lugar en un estudio estático y se ajustarán posteriormente con propiedades dinámicas del material. Las soluciones analíticas de este modelo se han comparado con datos experimentales para validar el modelo dinámico. Se ha desarrollado y mejorado dicho modelo analítico para obtener unos resultados que se ajustaran mejor a los datos experimentales y una vez conseguido se ha realizado un estudio paramétrico donde se determina cómo varía la fuerza de contacto máxima entre el proyectil y el panel sándwich en función de parámetros que intervienen en el problema de impacto...

Análisis y modelización de vigas sándwich sometidas a impactos de baja velocidad

Iváñez del Pozo, Inés
Fonte: Universidade Carlos III de Madrid Publicador: Universidade Carlos III de Madrid
Tipo: Tese de Doutorado
SPA
Relevância na Pesquisa
37.27%
En esta Tesis Doctoral se ha estudiado el comportamiento frente a impactos de baja velocidad de vigas sándwich constituidas por pieles de material compuesto de tipo laminado y núcleo de nido de abeja de aluminio. Existen tres clases de metodologías para hacer frente a este estudio: el análisis experimental, los modelos analíticos y las simulaciones numéricas. La realización de un estudio experimental exhaustivo supone una gran inversión, tanto en términos económicos como temporales, por lo que la utilización de modelos analíticos y herramientas de simulación representa una alternativa eficiente. Los modelos analíticos permiten evaluar variables globales como la fuerza o el desplazamiento pero sin llegar a profundizar en el proceso de fallo de pieles y núcleo. Las simulaciones numéricas suelen lograr descripciones más precisas y detalladas de la respuesta a impacto y su flexibilidad en relación a las variaciones de condiciones de contorno, geometría y material, es muy apreciada en el campo de la investigación. Disponer de modelos numéricos permite profundizar en el conocimiento del comportamiento a impacto de las estructuras sándwich, proporcionando información que es difícilmente extraíble de forma experimental. No obstante...

Análisis de la respuesta dinámica de estructuras sandwich

González Gijón, Álvaro Javier
Fonte: Universidade Carlos III de Madrid Publicador: Universidade Carlos III de Madrid
Tipo: Trabalho de Conclusão de Curso
SPA
Relevância na Pesquisa
37.19%
En este Trabajo de Fin de Grado se ha estudiado el comportamiento dinámico a flexión de una viga biapoyada tipo sándwich ante esfuerzos variables con el tiempo, este tipo de material se utiliza en las industrias de la construcción, aeronáutica, y de refrigeración. Para la realización del estudio se han tenido en cuenta resultados experimentales obtenidos en el laboratorio del departamento de Mecánica de Medios Continuos y Teoría de Estructuras de la Universidad Carlos III de Madrid, mediante la utilización una probeta tipo sándwich compuesta por dos láminas compuestas por láminas de fibra de vidrio clase E y resina de polyester AROPOL FS6902, con un espesor de 3mm. Y un núcleo de foam PVC de espesor 30mm. Y una máquina para ensayos de flexión a tres puntos. Estos ensayos de flexión en tres puntos se han realizado en condiciones ambientales de temperatura y humedad. El trabajo consiste en el análisis de la respuesta dinámica de estructuras sándwich mediante la creación de un programa escrito en Matlab que sea capaz de calcular la respuesta de cualquier viga de tipo sándwich mediante el uso de las teorías de vibración, las teorías de laminado y simplificaciones para estructuras tipo sándwich, así como el concepto de integral de Duhamel. Ha sido necesario filtrar tanto la respuesta como los datos de esfuerzo del indentador para eliminar el ruido presente y poder de ese modo comparar con mayor exactitud ambas respuestas en busca de posibles diferencias. Para ello ha sido necesario estimar frecuencias propias y modos propios de vibración. Posteriormente se ha utilizado el programa mencionado para calcular la respuesta dinámica de distintas configuraciones de vigas tipo sándwich y su respuesta ante esfuerzos de distintas magnitudes...

Behavior of Sandwich Panels Subjected to Bending Fatigue, Axial Compression Loading and In-Plane Bending

Mathieson, Haley
Fonte: Quens University Publicador: Quens University
Tipo: Tese de Doutorado
EN; EN
Relevância na Pesquisa
37.19%
This thesis investigates experimentally and analytically the structural performance of sandwich panels composed of glass fibre reinforced polymer (GFRP) skins and a soft polyurethane foam core, with or without thin GFRP ribs connecting skins. The study includes three main components: (a) out-of-plane bending fatigue, (b) axial compression loading, and (c) in-plane bending of sandwich beams. Fatigue studies included 28 specimens and looked into establishing service life (S-N) curves of sandwich panels without ribs, governed by soft core shear failure and also ribbed panels governed by failure at the rib-skin junction. Additionally, the study compared fatigue life curves of sandwich panels loaded under fully reversed bending conditions (R=-1) with panels cyclically loaded in one direction only (R=0) and established the stiffness degradation characteristics throughout their fatigue life. Mathematical models expressing fatigue life and stiffness degradation curves were calibrated and expanded forms for various loading ratios were developed. Approximate fatigue thresholds of 37% and 23% were determined for non-ribbed panels loaded at R=0 and -1, respectively. Digital imaging techniques showed significant shear contribution significantly (90%) to deflections if no ribs used. Axial loading work included 51 specimens and examined the behavior of panels of various lengths (slenderness ratios)...

Effect of block copolymer nano-reinforcements on the low velocity impact response of sandwich structures

RAMAKRISHNAN, Karthik Ram; GUERARD, Sandra; VIOT, Philippe; SHANKAR, Krishna
Fonte: Elsevier Publicador: Elsevier
EN
Relevância na Pesquisa
37.21%
Sandwich composites with fibre reinforced plastic (FRP) facesheets have emerged as a major class of lightweight structural materials in a wide range of engineering fields including aerospace, automotive and marine structures. This is due to attractive mechanical properties such as high specific stiffness and high strength. However, sandwich structures are susceptible to damage caused by impact. The objective of this paper is to evaluate the dynamic response of sandwich composites based on Kevlar fibre reinforced epoxy and Rohacell foam. The improvement in impact performance of these sandwich structures that can be achieved by the addition of nanoparticles in the resin matrix is investigated. Nanostrength, an acrylate triblock copolymer that self-assembles in the nanometer scale is added to the epoxy matrix. The effect of the nano-reinforcements on flat sandwich plates under low velocity impact is investigated at different scales. An instrumented drop tower setup is used for the low velocity impact tests of the sandwich plates with neat or nano-reinforced epoxy matrix, at different energies. The macroscopic response of the sandwich structure and the microscopic phenomena involved in dissipating the impact energy are identified and compared for sandwich plates with and without nanoparticles.

Análise estrutural de vigas sandwich de alumínio-aglomerado de cortiça

Pereira, Rui Jorge Barros
Fonte: Universidade de Aveiro Publicador: Universidade de Aveiro
Tipo: Dissertação de Mestrado
POR
Relevância na Pesquisa
37.25%
O estudo de vigas sandwich em que as peles (lâminas externas) são metá-licas (correntemente em alumínio laminado) e o núcleo interno de material polimérico expandido (espuma de alta resistência) constitui um elemento de valor no projecto estrutural aplicado à construção de veículos de transporte, casos em que a relação rigidez/massa tem importância crítica. Daí a dedicada investigação no comportamento estrutural de componentes tipo placa na ou casca fabricados por técnica sandwich. Este estudo baseia-se no desenvolvimento de modelos numéricos e experimentais, sendo o objectivo deste último a validação dos primeiros. No caso de utilização de modelos numéricos existe um considerável número de técnicas de aproximação ao comportamento estrutural de vigas sandwich como elemento caracterizador de comportamentos mais complexos construí-dos sob a mesma técnica. Nesta dissertação, são recuperados os coe cientes e recalculados pelo procedimento conhecido como Direct Sti ness Method em que os coe cientes da matriz de rigidez são obtidos impondo deslocamentos ou rotações, tendo constrições devidamente incluídas nos elementos estruturais. Os esforços assim obtidos permitem o preenchimento da matriz de rigidez. Baseando o procedimento usado na determinação de tais coe- cientes para vigas homogéneas...

The quasi-static and dynamic responses of metallic sandwich structures

St-Pierre, Luc
Fonte: University of Cambridge; Department of Engineering Publicador: University of Cambridge; Department of Engineering
Tipo: Thesis; doctoral; PhD
EN
Relevância na Pesquisa
37.23%
Lattice materials are used as the core of sandwich panels to construct light and strong structures. This thesis focuses on metallic sandwich structures and has two main objectives: (i) explore how a surface treatment can improve the strength of a lattice material and (ii) investigate the collapse response of two competing prismatic sandwich cores employed in ship hulls. First, the finite element method is used to examine the effect of carburisation and strain hardening upon the compressive response of a pyramidal lattice made from hollow tubes or solid struts. The carburisation surface treatment increases the yield strength of the material, but its effects on pyramidal lattices are not known. Here, it is demonstrated that carburisation increases the plastic buckling strength of the lattice and reduces the slenderness ratio at which the transition from plastic to elastic buckling occurs. The predictions also showed that strain hardening increases the compressive strength of stocky lattices with a slenderness ratio inferior to ten, but without affecting the collapse mode of the lattice. Second, the quasi-static three-point bending responses of simply supported and clamped sandwich beams with a corrugated core or a Y-frame core are compared via experiments and finite element simulations. The role of the face-sheets is assessed by considering beams with (i) front-and-back faces present and (ii) front face present...

Design of Sandwich Structures

Petras, Achilles
Fonte: University of Cambridge; Department of Engineering Publicador: University of Cambridge; Department of Engineering
Tipo: Thesis; doctoral; PhD
EN
Relevância na Pesquisa
37.27%
Failure modes for sandwich beams of GFRP laminate skins and Nomex honeycomb core are investigated. Theoretical models using honeycomb mechanics and classical beam theory are described. A failure mode map for loading under 3-point bending, is constructed, showing the dependence of failure mode and load on the ratio of skin thickness to span length and honeycomb relative density. Beam specimens are tested in 3-point bending. The effect of honeycomb direction is also examined. The experimental data agree satisfactorily with the theoretical predictions. The results reveal the important role of core shear in a sandwich beam's bending behaviour and the need for a better understanding of indentation failure mechanism. High order sandwich beam theory (HOSBT) is implemented to extract useful information about the way that sandwich beams respond to localised loads under 3-point bending. 'High-order' or localised effects relate to the non-linear patterns of the in-plane and vertical displacements fields of the core through its height resulting from the unequal deformations in the loaded and unloaded skins. The localised effects are examined experimentally by Surface Displacement Analysis of video images recorded during 3-point bending tests. A new parameter based on the intrinsic material and geometric properties of a sandwich beam is introduced to characterise its susceptibility to localised effects. Skin flexural rigidity is shown to play a key role in determining the way that the top skin allows the external load to pass over the core. Furthermore...

Investigation of sound and vibrational performance of sandwich composite structures through wave number analysis

Sargianis, James
Fonte: University of Delaware Publicador: University of Delaware
Tipo: Tese de Doutorado
Relevância na Pesquisa
37.19%
Suhr, Jonghwan; Sandwich structures are utilized in many applications for their superior mechanical performance including strength and stiffness-to-weight ratios compared to metallic structures. Unfortunately as a result of these mechanical properties, sandwich composites are also excellent radiators of noise beginning at low vibrational frequencies. However, in applications which require the materials with the highest mechanical performance at a low-weight, such as aircraft, rotorcraft, wind turbine blades, or automobiles, acoustic performance remains a secondary design requirement. Current state-of-art methods involve additional vibration and sound absorbing layers, which are costly and increase manufacturing time. Therefore, solutions are sought to achieve improved acoustic and vibrational performance without the sacrifice of mechanical performance or weight. This study employs a wave number approach to characterize the acoustic performance from the vibrational response of sandwich composite beams, along with their structural loss factor (??). It was first determined that the effect of changing the beam???s core thickness on the acoustic performance is non-linear, having a hyperbolic profile. Secondly, the core material???s specific shear modulus is inversely proportional to acoustic performance. Moreover...