Modeling the dynamic behavior of laminate structures with cork compounds

Tese de mestrado. Engenharia Mecânica. Faculdade de Engenharia. Universidade do Porto. 200

Impact of composite plates: Analysis of stresses and forces

The foreign object damage resistance of composite fan blades was studied. Edge impact stresses in an anisotropic plate were first calculated incorporating a constrained layer damping model. It is shown that a very thin damping layer can dramatically decrease the maximum normal impact stresses. A multilayer model of a composite plate is then presented which allows computation of the interlaminar normal and shear stresses. Results are presented for the stresses due to a line impact load normal to the plane of a composite plate. It is shown that significant interlaminar tensile stresses can develop during impact. A computer code was developed for this problem using the fast Fourier transform. A marker and cell computer code were also used to investigate the hydrodynamic impact of a fluid slug against a wall or turbine blade. Application of fluid modeling of bird impact is reviewed

Comparison of extensional and flexural modes for the design of piezoelectric ice protection systems

Many researches focus on piezoelectric ice protection systems with the objectives to develop light and low consumption electromechanical systems for de-icing. These systems use vibrations, generated by the excitation of flexural, extensional or coupled resonance modes, to produce tensile stresses in the ice or shear stresses at the interface ice/support in order to remove ice. The objectives of this work are to analyse flexural and extensional resonance modes according to important design drivers for this type of systems: resonance frequency range, generation of tensile and shear stresses, electromechanical coupling factor, damping and fracture propagation. A final comparison gives pro and cons of each mode type for each design drivers for helping the designer of piezoelectric ice protection systems

Vibro-acoustical analysis and design of a multiple-layer constrained viscoelastic damping structure

The goal of this research is to provide a framework for vibro-acoustical analysis and design of a multiple-layer constrained damping structure. The existing research on damping and viscoelastic damping mechanism is limited to the following four mainstream approaches: modeling techniques of damping treatments/materials; control through the electrical-mechanical effect using the piezoelectric layer; optimization by adjusting the parameters of the structure to meet the design requirements; and identification of the damping material’s properties through the response of the structure. This research proposes a systematic design methodology for the multiple-layer constrained damping beam giving consideration to vibro-acoustics. A modeling technique to study the vibro-acoustics of multiple-layered viscoelastic laminated beams using the Biot damping model is presented using a hybrid numerical model. The boundary element method (BEM) is used to model the acoustical cavity whereas the Finite Element Method (FEM) is the basis for vibration analysis of the multiple-layered beam structure. Through the proposed procedure, the analysis can easily be extended to other complex geometry with arbitrary boundary conditions. The nonlinear behavior of viscoelastic damping materials is represented by the Biot damping model taking into account the effects of frequency, temperature and different damping materials for individual layers. A curve-fitting procedure used to obtain the Biot constants for different damping materials for each temperature is explained. The results from structural vibration analysis for selected beams agree with published closed-form results and results for the radiated noise for a sample beam structure obtained using a commercial BEM software is compared with the acoustical results of the same beam with using the Biot damping model. The extension of the Biot damping model is demonstrated to study MDOF (Multiple Degrees of Freedom) dynamics equations of a discrete system in order to introduce different types of viscoelastic damping materials. The mechanical properties of viscoelastic damping materials such as shear modulus and loss factor change with respect to different ambient temperatures and frequencies. The application of multiple-layer treatment increases the damping characteristic of the structure significantly and thus helps to attenuate the vibration and noise for a broad range of frequency and temperature. The main contributions of this dissertation include the following three major tasks: 1) Study of the viscoelastic damping mechanism and the dynamics equation of a multilayer damped system incorporating the Biot damping model. 2) Building the Finite Element Method (FEM) model of the multiple-layer constrained viscoelastic damping beam and conducting the vibration analysis. 3) Extending the vibration problem to the Boundary Element Method (BEM) based acoustical problem and comparing the results with commercial simulation software

Workshop 2 Expanding Horizons: New strategies for multifield fracture problems across scales in heterogeneous systems for energy, health and transport

NewFrac Workshop-2 is especially focused on Phase Field and Finite Fracture Mechanics. It is open to senior researchers and PhD students in fracture mechanics.Horizonte 2020 (Unión Europea) 86106

Finite element modeling of sandwich structures with viscoelastic core

The present study emerges from the need for reduction of noise and vibrations in almost all industrial fields and the need for an accurate and reliable low-cost numerical model capable of predicting the vibro-acoustic response of structures containing viscoelastic materials. Indeed, the use of steel/viscoelastic/steel sandwich panels has motivated the development of accurate prediction methods for their vibration and acoustic indicators. Moreover, such theories may support the development of new damping materials while prioritizing strategies for low cost and weight and maintaining component rigidity and feasibility. A new sandwich finite element is presented for the specific case of unsymmetrical three-layered damped sandwich beam with internal viscoelastic damping.The model is based on a discrete displacement approach and accounts for the curvature effect.The element uses C[superscript 0] continuous linear and cubic polynomials to interpolate the in-plane and transverse displacement fields, respectively.The rotational influence of the transversal shearing in the core on the skins' behaviours ensures displacement consistency over the interfaces between the viscoelastic core and the elastic skins, resulting in accurate representations of the physics. To take the frequency dependence into account, viscoelastic models such as ADF, GHM and MSE models are implemented.The element is extended to the vibration of unsymmetrical damped sandwich plates. Two efficient finite element sandwich plates are developed; refined rectangular and triangular elements having four and three-corner nodes, respectively. Each node of both elements contains seven degrees of freedom. To allow for analysis with arbitrary orientation in three-dimensional space, two drilling degrees of freedom are added. A formulation with nine degrees of freedom per node is thus employed.The present sandwich element is easy to interface with classical elements.The element is fully validated through both experimental tests and classical 3D FE modeling to prove its accuracy and computational efficiency.The tests consist of various configurations of sandwich panels in a coupled and uncoupled plate-cavity system. A parametric study is finally presented to highlight the effects of skin and core properties on the vibration and radiation of such structures under both airborne and structure-borne excitations. Finally, to illustrate practical use of the element, NVH simulations were conducted on laminated steel panels with added sound packages and compared to steel panels

Vibration, Control and Stability of Dynamical Systems

From Preface: This is the fourteenth time when the conference “Dynamical Systems: Theory and Applications” gathers a numerous group of outstanding scientists and engineers, who deal with widely understood problems of theoretical and applied dynamics. Organization of the conference would not have been possible without a great effort of the staff of the Department of Automation, Biomechanics and Mechatronics. The patronage over the conference has been taken by the Committee of Mechanics of the Polish Academy of Sciences and Ministry of Science and Higher Education of Poland. It is a great pleasure that our invitation has been accepted by recording in the history of our conference number of people, including good colleagues and friends as well as a large group of researchers and scientists, who decided to participate in the conference for the first time. With proud and satisfaction we welcomed over 180 persons from 31 countries all over the world. They decided to share the results of their research and many years experiences in a discipline of dynamical systems by submitting many very interesting papers. This year, the DSTA Conference Proceedings were split into three volumes entitled “Dynamical Systems” with respective subtitles: Vibration, Control and Stability of Dynamical Systems; Mathematical and Numerical Aspects of Dynamical System Analysis and Engineering Dynamics and Life Sciences. Additionally, there will be also published two volumes of Springer Proceedings in Mathematics and Statistics entitled “Dynamical Systems in Theoretical Perspective” and “Dynamical Systems in Applications”