1,721,104 research outputs found
Effect of an axial pre-load on the flexural vibrations of viscoelastic beams
Full text linkPolymers are ultra-versatile materials that adapt to a myriad of applications, as they can be designed appropriately for specific needs. The realization of new compounds, however, requires the appropriate experimental characterizations, also from the mechanical point of view, which is typically carried out by analyzing the vibrations of beams, but which still have some unclear aspects, with respect to the well-known dynamics of elastic beams. To address this shortcoming, the paper deals with the theoretical modeling of a viscoelastic beam dynamics and pursues the elucidation of underlying how the flexural vibrations may be affected when an axial pre-load, compressive or tensile, is applied. The analytical model presented is able to shed light on a peculiar behavior, which is strongly related to the frequency-dependent damping induced by viscoelasticity. By considering as an example a real polymer, that is, a synthetic rubber, it is disclosed that an axial pre-load, in certain conditions, may enhance or suppress the oscillatory counterpart of a resonance peak of the beam, depending on both the frequency distribution of the complex modulus and the length of the beam. The analytical model is assessed by a finite element model, and it turns out to be an essential tool for understanding the dynamics of viscoelastic beams, typically exploited to experimentally characterize polymeric materials, and which could vary enormously simply through the application of constraints and ensued pre-loads
Damping control in viscoelastic beam dynamics
No full textViscoelasticity plays a key role in many practical applications and in different research fields, such as in seals, sliding-rolling contacts, and crack propagation. In all these contexts, a proper knowledge of the viscoelastic modulus is very important. However, experimental characterization of the frequency-dependent modulus, carried out through different standard procedures, still presents some complexities; then possible alternative approaches are desirable. For example, experimental investigation of viscoelastic beam dynamics would be challenging, especially for the intrinsic simplicity of this kind of test. This is why a deep understanding of damping mechanisms in viscoelastic beams is found to be a quite important task to better predict their dynamics. With the aim to enlighten damping properties in such structures, an analytical study of the transversal vibrations of a viscoelastic beam is presented in this article. Some dimensionless parameters are defined, depending on the material properties and the beam geometry, which enable to accurately design the beam dynamics. In this way, by properly tuning such disclosed parameters, for example the dimensionless beam length or a chosen material, it is possible to enhance or suppress some resonant peaks, one at a time or more simultaneously. This is a remarkable possibility to efficiently control damping in these structures, and the results presented in this article may help in elucidating experimental procedures for the characterization of viscoelastic materials
Presentazione al volume AA.VV., Innovazioni tecnologiche e scelte alimentari. Responsabilità e tutele nel mercato globale, a cura di Francesco Aversano, Prospero Di Pierro e Antonio Musio, Cacucci, Bari, 2025.
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Vibration-based identification of mechanical properties of viscoelastic materials
No full textRecent scientific advancements in field of automotive, electronics, micromechanical systems, pipe technologies, have led to new technologies where the use of lightweight, tough, soft and high deformable materials has become ubiquitous. In this scenario, viscoelastic materials have spread in many different contexts, from seals to bio-inspired adhesives, because of their superior damping and frictional properties. For an appropriate use of such materials, however, the proper knowledge of their mechanical properties is a basic requirement. In this paper we present an innovative easy-to-use approach for determining the viscoelastic modulus, based on the experimental vibrational identification of viscoelastic beams of different lengths. A very simple setup and instrumentation are utilized for acquisitions, and an accurate analytical model of the beam is considered to determine the viscoelastic modulus, which takes into account multiple relaxation times of the material
A new technique for the characterization of viscoelastic materials: Theory, experiments and comparison with DMA
No full textIn this paper we present a theoretical and experimental study aimed at characterizing the hysteretic properties of viscoelastic materials. In the last decades viscoelastic materials have become a reference for new technological applications, which require lightweight, deformable but ultra-tough structures. The need to have a complete and precise knowledge of their mechanical properties, hence, is of utmost importance. The presented study is focused on the dynamics of a viscoelastic beam, which is both experimentally investigated and theoretically characterized by means of an accurate analytical model. In this way it is possible to fit the experimental curves to determine the complex modulus. Our proposed approach enables the optimal fitting of the viscoelastic modulus of the material by using the appropriate number of relaxation times, on the basis of the frequency range considered. Moreover, by varying the length of the beams, the frequency range of interest can be changed/enlarged. Our results are tested against those obtained with a well established and reliable technique as compared with experimental results from the Dynamic Mechanical Analysis (DMA), thus definitively establishing the feasibility, accuracy and reliability of the presented technique
On the peeling of elastic tapes from viscoelastic substrates: Designing materials for ultratough peeling
No full textThe present paper deals with the peeling of an elastic thin tape from a viscoelastic substrate. A previous investigation of the authors has disclosed several physical aspects of such phenomenon by focusing the attention on an ideal viscoelastic substrate with one-single relaxation time. However, for real viscoelastic solids, the spectrum of relaxation times may cover more than 10 decades. For this reason, it is of interest investigating the influence of the number of relaxation times on the peeling mechanism. More specifically, it is possible to enlarge the frequency range where the material shows significant damping and energy dissipation by increasing such number. This may help in properly designing viscoelastic materials with ultra-tough adhesion properties. As a practical example, a widespread viscoelastic material is considered, the PMMA (polymethyl methacrylate), which presents high damping at low-frequencies, thus making tough the peeling behavior at small velocities
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