Identification of the elastic stiffness matrixes on thin plates of composite materials

Orientadores: Eder Lima de Albuquerque, Milton Dias JuniorTese (doutorado) - Universidade Estadual de Campinas, Faculdade de Engenharia MecanicaResumo: Neste trabalho é apresentado um estudo direcionado à caracterização elástica de materiais compósitos e se encontra dividido em duas partes. Na primeira é proposto o uso da série de Fourier discreta regressiva (RDFS) para a suavização dos modos próprios utilizados como dados de entrada para um método direto e não iterativo de identificação das constantes de rigidez elástica à flexão já existente na literatura e cuja solução se dá pelo método dos campos virtuais. Por envolver o cálculo de derivadas de segunda ordem, é um método muito sensível à presença de ruído. A verifica¸c¿ao foi realizada numericamente adicionando-se níveis de ruído à uma placa anisotrópica e, experimentalmente, utilizando-se uma placa de aço isotrópica e uma de carbono/epóxiortotrópica. Na segunda parte do trabalho é proposto um método, também baseado no método dos campos virtuais, para a identificação das constantes de rigidez elástica à extensão. A solução é obtida a partir das equações diferenciais que governam a vibração livre no plano de placas finas anisotrópicas e simétricas. São propostos dois grupos de campos virtuais, um de primeira e um de segunda ordem, para serem utilizados juntamente com várias combinações entre modos próprios específicos e suas respectivas freqüências naturais. A verificação do método foi realizada somente numericamente em laminados de diferentes níveis de anisotropia. De uma maneira geral, os resultados obtidos nas duas partes do trabalho foram muito satisfatóriosAbstract: In this work is presented a study on the elastic characterization of composite materials, and it is divided in two parts. In the first part is proposed the application of regressive discrete Fourier series (RDFS) to smooth mode shapes used as input data in a direct and no-iteractive identification method of the bending elastic stiffness constants already available in the literature, and whose solution is obtained by virtual fields method. It is a very noise sensitive method because it requires the computation of second-order derivatives. To assess the accuracy of the method, noise levels were numerically created to an an isotropic plate, and experimentally, were used an isotropic steel plate and an orthotropic carbon/epoxy plate. In the second part of the work, a method also based in the virtual fields method to identify the extensional elastic stiffness constants is proposed. The solution is obtained from the differential equations that govern the free-free in-plane vibration of thin symetric anisotropic plates. Two groups of virtual fields are proposed, one with first order and another with second order functions, to be used together with many in-plane mode shape combinations and their respective natural frequencies. The accuracy of this proposed identification method was carried out only numerically by using laminates having differents anisotropy levels. In general, the obtained results from the two parts of this work were very satisfactoryDoutoradoMecanica dos Sólidos e Projeto MecanicoDoutor em Engenharia Mecânic

Identification of elastic parameters on thin plates of composite materials

Orientadores: Eder Lima de Albuquerque, Milton Dias JuniorDissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia MecanicaResumo: Neste trabalho são abordados dois métodos para identificar constantes elásticas em materiais compósitos de aplicações estruturais. São métodos que apresentam características não destrutivas, envolvem testes simples e não requerem grandes esforços computacionais. Podem ser aplicados a materiais anisotrópicos e, conseqüentemente,a materiais isotrópicos e ortotrópicos, o que os tomam ferramentas optativas de grande auxílio ao estudo dos materiais compósitos. No primeiro método, as freqüências naturais e os modos próprios adequados, obtidos da análise moda!, serão os dados de entrada para a solução de um sistema linear de equações oriundas da equação diferencial que representa a vibração transversal de placas finas anisotrópicas sob a condição de todos os bordos livres. As constantes elásticas desta equação são os parâmetros desconhecidos e estão associadas aos devidos modos próprios de vibrar. A verificação da precisão deste método é feita baseada em simulações numéricas realizadas em um software de Elementos Finitos, Ansys 7.0, e testado experimentalmente em uma placa isotrópica de aço. O segundo método trata-se de um problema de projeto ótimo cuja solução é feita através da combinação do método dos Elementos Finitos e um método de otimização, ambos executados em um único software comercial, Ansys 7.0. A análise moda! é requerida para obtenção somente das freqüências naturais, que são variáveis utilizadas na função objetivo. A verificação do método é feita em simulações numéricas e testada experimentalmentecom a mesma placa isotrópica de aço utilizada no método anterior. Para esta placa de aço, os resultados obtidos através dos dois métodos foram muitos satisfatórios. Entretanto, com relação à placa anisotrópica utilizada, os resultados obtidos pelo segundo método não foram satisfatóriosAbstract: In this work two methods are analyzed to identify elastic constants in composite materiais of structural application. They are methods that have nondestructive eharacteristie, comprised of simple tests and don't require high computational efforts. They can be employed to anisotropic materials as well as isotropic or ortotropic materials, making them useful alternative tools to composite materiais studies. In the first method, both natural frequencies and suitable mode shapes are input data for the solution of a linear system that come from differential equation that governs the transverse vibration of a free-free thin plate. Elastic constants of this equation are unknown parameters and are associated with vibration mode shape. Numerical simulations of Finite Element software, Ansys 7.0, and experimental modal analysis indicate the accuracy of this method. The second method refers to an optimum design problem and its solution is obtained by combining both Finite Elements and optimization methods in a single eommercial software, Ansys 7.O. The modal analysis is required to obtain only the natural frequencies that are the variables used in the objective function. The second method is verified using numerical simulations and tested experimentally with the same isotropic steel plate used in the first method. Results obtained for this steel plate from both methods were highly satisfactory. In relation to the anisotropic plate, results obtained ftom the second method weren't satisfactoryMestradoMecanica dos Sólidos e Projeto MecanicoMestre em Engenharia Mecânic

An Empirical Demodulation For Electrical Fault Detection In Induction Motors

Signal demodulation is a fundamental procedure in many situations during a spectral analysis. Through an envelope analysis, it becomes possible to identify fault frequencies that are embedded in a modulated signal and that are not clearly visible only by directly applying some signal processing techniques such as the Fourier transform and filtering. In this paper, a very simple and empirical technique for demodulation is proposed. It is based only on the analysis of local extremes from a modulated time sequence to find a new time sequence that carries the wanted relevant fault data. The method of analysis is a good alternative tool for electrical fault detection in induction motors. The numerical and experimental results demonstrate the effectiveness of the proposed technique.65355956

An empirical demodulation for electrical fault detection in induction motors

Signal demodulation is a fundamental procedure in many situations during a spectral analysis. Through an envelope analysis, it becomes possible to identify fault frequencies that are embedded in a modulated signal and that are not clearly visible only by directly applying some signal processing techniques such as the Fourier transform and filtering. In this paper, a very simple and empirical technique for demodulation is proposed. It is based only on the analysis of local extremes from a modulated time sequence to find a new time sequence that carries the wanted relevant fault data. The method of analysis is a good alternative tool for electrical fault detection in induction motors. The numerical and experimental results demonstrate the effectiveness of the proposed technique6555956

Hybrid composites reinforced with short sisal fibres and micro ceramic particles

<div><p>ABSTRACT Biocomposites reinforced with natural fibres have been extensively investigated as a promising replacing material for synthetic ones, such as the glass fibre reinforced composites. The length of natural fibres depends not only on the plant species, but also on the extraction processing. The heterogeneity of natural fibres, in terms of length, can be considered a problem for some industrial applications. A little amount of work has been conducted towards the use of short natural fibres in composite materials. In order to balance the reduction of strength due to the use of short length fibres, ceramic particles can be incorporated. This paper describes the experimental characterization of hybrid biocomposites consisted of epoxy polymer, short random sisal fibres and Portland cement particles. A full factorial design was performed to investigate the effect of the factors and levels, such as fibre length (4 mm and 8 mm) and Portland cement inclusion (0wt%, 5wt% and 10wt%) on the following properties, flexural modulus and strength (via three-point bending test), damping ratio, apparent porosity and water absorption. The fibre volume fraction was kept constant at 25%. The Design of Experiment (DoE) analysis revealed the “Fibre length” factor does not affect the responses. The interaction “Fibre length and Cement inclusion” affected only the stiffness. Portland cement particles statistically revealed a noticeable contribution to the apparent porosity and water absorption. The presence of cement particles at 5wt% provided not only the increase in the damping ratio response, but also the reduction in the flexural strength and stiffness.</p></div