Study of the experimental modal analysis techniques applied to structural dynamics

The main goal of the present work is to analyze the experimental techniques used in modal analysis, and then apply those techniques to a structural car component in order to evaluate the parameters of the modal test. For this propose the experimental procedure and the equipment are analyzed, specifically the experimental equipment used in the vibration tests, shakers, accelerometers, impact hammers, force transducers, and the support of the structural component. This study will allow a better test performance which will lead to a better interpretation of the analysis results and of the most influent parameters. The experimental modal analysis resorts to the LMS spectral equipment and SCADA-PC associated software: Test Xpress e Test Lab; in manner to obtain the dynamic response of the structure and identify its dynamic characteristics. At the same time is determined the dynamic behavior of the structure using the finite element method through the commercial program ANSYS. The experimental results are extracted by line-fit modal analysis and are used as reference for comparison with the numerical models developed.(undefined

Análise dinâmica de estruturas por modelos de elementos finitos identificados experimentalmente

Tese de Doutoramento em Engenharia Mecânica - Área de Mecânica dos MateriaisO presente trabalho teve como objectivo principal o desenvolvimento de uma nova metodologia de melhoramento de modelos numéricos de elementos finitos aplicados à dinâmica estrutural. Nesta perspectiva foi desenvolvido um programa que, automaticamente, controla um código de elementos finitos e modifica as variáveis iniciais até ser conseguido o melhoramento pretendido. Para o efeito foram analisadas as causas dos erros subjacentes ao método dos elementos finitos, estudada aprofundadamente de sua forma de funcionamento e executados programas de obtenção automática de resultados. Estes programas foram aplicados a exemplos reais formados por conjuntos de peças ligadas de formas diferentes e obtidas as características dinâmicas desses exemplos. Foram realizados ensaios experimentais de análise modal em protótipos semelhantes aos modelos numéricos desenvolvidos. Foram extraídos resultados destes ensaios por identificação modal que foram utilizados como referência para possibilitar a comparação com os modelos numéricos desenvolvidos. Foi desenvolvido um programa de melhoramento de modelos numéricos recorrendo a ferramentas de optimização. Foram analisados os métodos de optimização disponíveis e escolhidos os mais adequados para a aplicação neste problema. Foi criada uma função objectivo específica e introduzida uma nova forma de correlação, que foi designada ASMAC. O programa foi testado com um número elevado de exemplos e por análise de sensibilidade foi comprovado que as funções envolvidas são altamente não lineares. Finalmente, o programa foi aplicado aos protótipos desenvolvidos. Como principal conclusão dos resultados obtidos neste trabalho de investigação pode dizer-se que o melhoramento dos modelos foi conseguido razoavelmente e que o melhoramento dos modelos dos conjuntos formados por modelos de peças que já tinham sido melhorados é melhor conseguido que o melhoramento dos mesmos conjuntos a partir dos valores iniciais.The primary objective of this research work was the development of a new methodology to improve the numerical finite element models applied to structural dynamics. In this perspective, a program was developed that automatically controls a code of finite elements and modifies the initial variables until the intended improvement has been achieved. For this purpose, the causes for the underlying errors to the finite element method were analysed, its operational mode was studied in depth and programs for automatically obtaining the results were executed. These programs were applied to real examples consisting of assemblies of pieces linked in different ways and the dynamic characteristics of those samples were obtained. Experimental modal analysis tests were executed in prototypes similar to the numerical models developed. From these tests, results by modal identification were extracted that served as reference to enable their comparison with the numerical models developed. A program for updating the numerical model was developed with recourse to optimization tools. The available methods were analysed and the most appropriate was chosen to be applied to this problem. A specific objective function was created and a new form of correlation was introduced, designated as ASMAC. The program was tested on a large number of examples and the functions involved were proven by sensibility analysis to be highly non- linear. Finally, the program was applied to the prototypes developed. The main conclusion of the results obtained in this research was that the updating of the models was reasonably successful. Further, the updating of the models of the assemblies consisting of models of pieces that had already been improved achieved better results than those obtained from the updating of the same assemblies derived from initial values

Heat treatment as a route to tailor the yield-damping properties in A356 alloys

A356 is a common industrial alloy due to its relatively good mechanical properties, reduced weight and capability be casted into complex structures. However, in order to display good static mechanical properties (e.g.elevated yield strength) it must be heat treated (usually T6), therefore, compromising its dynamic properties (e.g. damping ratio). This study analyses the role of such heat treatments in the overall microstructure of A356 poured in ceramic block, associating the morphology transformations with the internal mechanisms that enhance yield strength and reduce damping. It is suggested that these variables display an inverse proportionality and a linear model is determined for the design of alloys with tailored yield/damping by the use of different artificial ageing times.Supported by the project iRAIL Innovation in Railway Systems and Technologies Doctoral Programme funds and by national funds through FCT - Portuguese Foundation for Science and Technology and was developed on the aim of the Doctoral grant PD/ BD/114096/2015

A bending cell for small batches

This article presents the study that is done for the conception of an automated bending cell devoted to the processing of parts in small batches, gathering the real necessities of potential customers. Joining the maximum of possible information, on the present cells, is has been able to conceive an automated bending cell devoted to the bending of parts, with dif-ferent form, weight, thickness, etc., in small batches. To be able to reach the proposed objec-tives, the cell is equipped with auxiliary systems, such as ATC (Automatic Tool Change) allied to a tool warehouse, AGC (Automatic Gripper Change) with three different grippers, a repo-sition station, and a dedicated 7th axis in the press brake designed to dock a standard 6 axes robot, that provide to cell a sufficient grade of autonomy. Allied with the idea of creating a cell for small batches, is introduced the target of getting this cell at lower price as possible. Thus the cell acquires an extended application range very important for potential customers. To get real perception of the money saving when working with this automated bending cell comparisons between Man work times vs. machine work times in production of small batches have been made

Improving the dynamical behaviour of a laser cutting equipment by using a carbon fibre composite main structural runway frame

In order to improve the dynamic behaviour of an industrial laser cutting equipment a sandwich solution, using a carbon fibre reinforced polymer (CFRP) and polyester foam core, was implemented to construct its main runway structural frame, which supports the cutting head and major laser beam mirrors and lens. Nowadays, the commercial competiveness of laser cutting equipments is considerable enhanced by their higher cutting speed and precision, as well as, cost. With the recent available higher power laser beam generators and swifter motors quicker and powerful cuts may be already done. However, at accelerations of 3 and 4 g’s already enabled by linear motors, the lack of stiffness and high mass and consequent inertia of the traditional runway structural frames, made from steel and/or aluminium, do not allow achieving high required cutting precisions. Thus, the present study considered replacing those conventional materials by much lighter advanced CRFP composites to improve the dynamic performance of an existing laser cutting equipment. Advanced numeric Finite Element Method (FEM) calculations by using the ANSYS package software were made to verify the static and dynamic behaviours of the new composite structural frame and compare them to simulations made with the currently used steel solution. The composite structural frame processing method has been also studied and defined in this work. Furthermore, the composite laminate has been optimised by defining the better number of stacking layers and fibre orientations to be used, as well as, the foam core thickness. The failure of the new sandwich structural composite runway frame has been verified through the Tsai-Wu criterion. Finally, an economic analysis of the viability of the new composite solution adopted will be also presented.Adira, S

Improving the dynamical behaviour of a laser cutting equipment by using a carbon fibre composite main structural runway frame

In order to improve the dynamic behaviour of an industrial laser cutting equipment a sandwich solution, using a carbon fibre reinforced polymer (CFRP) and polyester foam core, was implemented to construct its main runway structural frame, which supports the cutting head and major laser beam mirrors and lens. Nowadays, the commercial competiveness of laser cutting equipments is considerable enhanced by their higher cutting speed and precision, as well as, cost. With the recent available higher power laser beam generators and swifter motors quicker and powerful cuts may be already done. However, at accelerations of 3 and 4 g’s already enabled by linear motors, the lack of stiffness and high mass and consequent inertia of the traditional runway structural frames, made from steel and/or aluminium, do not allow achieving high required cutting precisions. Thus, the present study considered replacing those conventional materials by much lighter advanced CRFP composites to improve the dynamic performance of an existing laser cutting equipment. Advanced numeric Finite Element Method (FEM) calculations by using the ANSYS package software were made to verify the static and dynamic behaviours of the new composite structural frame and compare them to simulations made with the currently used steel solution.The composite structural frame processing method has been also studied and defined in this work. Furthermore, the composite laminate has been optimised by defining the better number of stacking layers and fibre orientations to be used, as well as, the foam core thickness. The failure of the new sandwich structural composite runway frame has been verified through the Tsai-Wu criterion. Finally, an economic analysis of the viability of the new composite solution adopted will be also presented

Vibration damping and acoustic behavior of PU-filled non-stochastic aluminum cellular solids

Aluminum-based cellular solids are promising lightweight structural materials considering their high specific strength and vibration damping, being potential candidates for future railway vehicles with enhanced riding comfort and low fuel consumption. The filling of these lattices with polymer-based (i.e., polyurethane) foams may further improve the overall vibration/noise-damping without significantly increasing their density. This study explores the dynamic (i.e., frequency response) and acoustic properties of unfilled and polyurethane-filled aluminum cellular solids to characterize their behavior and explore their benefits in terms of vibration and noise-damping. It is shown that polyurethane filling can increase the vibration damping and transmission loss, especially if the infiltration process uses flexible foams. Considering sound reflection, however, it is shown that polyurethane filled samples (0.27–0.30 at 300 Hz) tend to display lower values of sound absorption coefficient relatively to unfilled samples (0.75 at 600 Hz), is this attributed to a reduction in overall porosity, tortuosity and flow resistivity. Foam-filled samples (43–44 dB at 700–1200 Hz) were shown to be more suitable to reduce sound transmission rather than reflection than unfilled samples (21 dB at 700 Hz). It was shown that the morphology of these cellular solids might be optimized depending on the desired application: (i) unfilled aluminum cellular solids are appropriate to mitigate internal noises due to their high sound absorption coefficient; and (ii) PU filled cellular solids are appropriate to prevent exterior noises and vibration damping due to their high transmission loss in a wide range of frequencies and vibration damping.This work was supported by Fundação para a Ciência e a Tecnologia FCT under the research Doctoral Grant PD/BD/114096/2015, project UIDP/04077/2020 and UIDB/04436/2020, and Stimulus of Scientific Employment Application CEECIND/03991/2017

Significance of cell number on the bulk elastic properties of auxetic reentrant lattices

Auxetics are characterized by a negative Poisson’s ratio, expanding/contracting in tension/compression. Given this behavior, they are expected topossess high shear, fracture and indentation resistance, and superior damping. The lack of natural isotropic auxetics promoted an effort to designstructures that mimic this behavior, e.g. reentrant model. This last is based on honeycombs with inverted protruding ribs. Commonly, this modelis employed in lattices and has been thoroughly studied in terms of mechanical properties and deformation behavior. Given that the amount ofcells has an influence in the overall internal structural behavior, there seems to be an absence of data that determines the minimum number of cellsfor such structure to present internal static bulk properties. Recurring to FEA, this study determines the minimum number of cells to obtain anoverall face constrained auxetic lattice with internal bulk elastic behavior, namely in terms of normalized Young’s modulus and Poisson’s ratio. Itis shown that adding reentrant cells increases the Poisson’s ratio on an exponential rise to maximum function, reducing the normalized Young’smodulus on an exponential decay function. Fundamentally, a minimum number of 13 cells per row to obtain an internal bulk behavior in latticeswith constrained faces.Supported by the project iRAIL Innovation in Railway Systems and Technologies Doctoral Programme funds and by national funds through FCT – Portuguese Foundation for Science and Technology and was developed on the aim of the Doctoral grant PD/BD/114096/2015

Structural dynamic updating using a global optimization methodology

In this article, we present the application of a global optimization technique, in particular the GlobalSearch command from MatLab®, in the updating of structural dynamic models. For comparative purposes, we evaluate the efficiency of the global method relatively to the local search method previously used in the Finite Element Model Updating program. The Finite Element Model Updating programs are designed with the primary purpose of validating and optimizing structural numerical models. The first step for structural optimization process is to idealize the desired behavior of the dynamic model to develop, or collect experimental data of a physical model considered as the reference model. The process begins with the construction, on a finite element program, of a numerical model with initial physical parameters, preferably close to the reference model parameters. The numerical model is then submitted, through a Finite Element Model Updating program, to a successive parametric updating until improving its dynamic behavior described by their natural frequencies, mode shapes and damping properties, be similar to the dynamic behavior of the reference model. The Sequential Quadratic Programming algorithm was already used in the optimization of the Finite Element Model Updating program, and the obtained solutions showed that it can’t achieve the global optimal value of the objective function. This kind of methods, used for nonlinear constrained optimization problems, have, generally, difficulties to achieve the global optimum, since they are local optimization methods.Centre for Mechanical and Materials Technologies (CT2M) and Algoritmi R&D Centreinfo:eu-repo/semantics/publishedVersio

Motivation in mechanics of materials classes: An experimental approach

Motivation in mechanics of materials classes: An experimental approachThis work presents a novel didactic methodology for the approximation of the students to the subject of Mechanics of Materials, with the aim of improving the understanding of the inertia moment, and its relevance on the mechanical behaviour of structures. The students have grouped on groups of two to three persons. The work consisted in designing the most efficient beam having in mind several design constraints. Tensile tests were performed to determine the relevant material properties. Those were used for the analytic dimensioning of the beams. The aim of the work is to obtain the highest efficiency possible, since it results in the best mark, as possible. The efficiency was measured by the maximum load on experimental bending testing, divided by the mass of the beam. The results, as well as the interest of the methodology are discussed. It is proved that this methodology can be useful for the students to apply theoretical concepts and, at the same time, to give a deeper understanding of real experimental tests.(undefined)info:eu-repo/semantics/publishedVersio