1,721,083 research outputs found
Mechanical properties updating of a non-uniform natural fibre composite panel by means of a parallel genetic algorithm
No full textThis article presents an investigation on the mechanical properties of a composite panel made of unidirectional flax fibres embedded in a polyethylene matrix (flax-PE). An initial set of mechanical properties was identified by classical static tests. Then, an experimental modal analysis was performed in order to get information on natural frequencies and mode shapes, which are related to the mechanical properties. The experimental modal results were compared with numerical ones, obtained through finite element model using the initial set of mechanical properties. Finally, in order to get a good numerical-experimental correlation, the mechanical properties throughout the panel were updated using an inverse modelling method based on parallel genetic algorithms
Innovative Honeycomb Design for Low Frequency Applications
No full textThis work is centered on the development of a novel honeycomb structure configuration that is industrially viable, aiming to create absorbers with classical mechanical properties inherent to sandwich structures. The objective is to achieve improved sound absorption performance at lower operating frequencies than currently attainable. The reference case for this study is the sandwich panels utilized in the construction of liners, featuring a rigid plate at the bottom, a honeycomb core, and a microperforated panel as the upper skin to facilitate interaction with disturbances.In order to ensure the comparability of the proposed configuration with commercially available counterparts, the external macro geometry of the panel remains consistent. Notable variations, as illustrated in the presented models, are confined to the internal structure of the honeycomb. To validate the numerical results obtained thus far and to explore the implications arising from the reduction in the number of inlet holes characteristic of this new structure, experimental tests are planned. These tests will serve to corroborate the numerical findings and contribute to a comprehensive understanding of the performance of this innovative honeycomb configuratio
Possibilità di impiego del legname di cerro nell'industria per imballaggio di ortofrutti
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Damage detection through structural intensity and vibration based techniques
No full textThe development systems for the Structural Health Monitoring has attracted considerable interest from several engineering fields during the last decades and more specifically in the aerospace one. In fact, the introduction of those systems could allow the transition of the maintenance strategy from
a scheduled basis to a condition-based approach providing cost benefits for the companies. The research presented in this paper consists of a definition and next comparison of four methods applied to numerical measurements for the extraction of damage features. The first method is based on the determination
of the Structural Intensity field at the on-resonance condition in order to acquire information about the dissipation of vibrational energy throughout the structure. The Damage Quantification Indicator and the Average Integrated Global Amplitude Criterion methods need the evaluation of the Frequency Response Function for a healthy plate and a damaged one. The main difference between these two parameters is their mathematical definition and therefore the accuracy of the scalar values provided as output. The fourth and last method is based on the Mode-shape Curvature, a FRF-based technique which requires the application of particular finite-difference schemes for the derivation of the curvature of the plate. All the methods have been assessed for several damage conditions (the shape, the extension and the intensity of the damage) on two test plates: an isotropic (steel) plate and a 4-plies composite plat
Damping evaluation on eco-friendly sandwich panels through reverberation time (RT60) measurements
No full textProblems involving vibrations occur in many fields of engineering. Thus, it is necessary to increase the knowledge of the damping, offered by new structural configurations and materials in order to reduce the vibration levels. The present paper focuses its attention on the measurements of the structural loss factor of different types of sandwich panels made of eco-friendly materials. The interest in natural materials, for structural applications, has considerably increased in the last years thanks to the growing environmental concerns. The influence on the loss factor of face sheet materials, core types and configurations is experimentally evaluated by means of measurements of the reverberation time (RT 60). The reported data represent a good initial database for more detailed analyses of these new materials
Similitudes for Acoustic Volumes: Analytical Models for the Response
No full textThe paper presents some updates about the search for exact and/or distorted similitudes to be applied to vibroacoustic models. These similitudes are aimed at obtaining prototypes which would be able to reproduce at convenient sizes the dynamic response of a fluid-filled elastic containers.Some experiences have been gained for the structural response involving panels and shells and some experimental evidences are already available. The attention is herein focused on the isolated volumes in view of reproducing the full coupled models. By adopting the modal approach, the main points are in the distribution of the natural frequencies, the damping conditions and the mode shapes. The incomplete (or distorted) similitudes and the related scaling laws will define the avatars which will not be replicas but will be able to replicate the original contents to some extent; they can be used for analysing the response at local scales by invoicing also some specific metrics, as the Hausdorff distance. The test-cases refer to a parallelepiped and cylindrical rooms which are represented by analytical solutions, but it is clear that the approach can be reformulated easily in generalised discrete coordinates scheme as for the finite element method
MECHANICAL CHARACTERISATION OF A BIO-BASED COMPOSITE PANEL
No full textThe increasing demand for environmentally friendly materials and the desire to reduce the cost of traditional fibre, has led to the development of new bio-based composite panels using natural fibres. These fibres offer specific benefits such as low density, low pollutant emissions, biodegradability, high specific properties and low cost. Nevertheless, the mechanical properties of these panels have a large variability, which depends on the manufacturing process, the quality of the
fibres and the humidity level, among others. Thus, their properties must be evaluated experimentally by tensile tests or by inverse modelling methods. This article presents an investigation on the mechanical properties of a composite panel made of unidirectional flax fibres embedded in a polyethylene matrix (flax-PE). An initial set of mechanical properties has been carried out by classical static tests. Then, an experimental modal analysis was performed in order to get information
on natural frequencies and mode shapes, which are related to the mechanical properties. The experimental results were compared with numerical ones, obtained by means of a finite element model in which the mechanical properties carried out by static test were used. Finally, in order to get a good numerical-experimental correlation, the mechanical properties used in the FE model were updated using an inverse modelling method based on parallel genetic algorithms. Special consideration is taken on the variation of the mechanical properties throughout the panel due to manufacturing or the variability of flax fibres
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