Papers by Author: Erasmo Viola

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Authors: Manabu Enoki, Yozo Fujino, Elisa Sorrivi, S. Takayuki, Erasmo Viola
Abstract: In this study, a new wireless smart sensor for fatigue damage detection of a single steel bar is proposed. A modified stress intensity factor is used to introduce a master curve of fatigue crack growth. Acoustic Emission signals are also measured and incorporated in the procedure for the structural health monitoring.
Authors: Erasmo Viola, Nicholas Fantuzzi, Alessandro Marzani
Abstract: This study is an extension of the paper by E. Viola and A. Marzani [1] where the eigenfrequencies and critical loads of a single cracked beam subjected to conservative and nonconservative forceshave been investigated. Here the aim is to analyze the dynamic stability of T cross section beams withmultiple cracks. A doubly cracked Euler-Bernoulli beam subjected to triangularly distributed subtangential forces, which are the combination of axial and tangential forces, is considered. The governingequation of the system is derived via the extended Hamilton’s principle in which the kinetic energy, theelastic potential energy, the conservative work and the nonconservative work are taken into account. Thelocal flexibility matrix for a beam with T cross-section is used to model the cracked section. The resultsshow that for given boundary conditions cracked beams become unstable in the form of either flutter ordivergence depending on the crack parameters, the nonconservativeness of the applied load as well as theinteraction of the two cracks.
Authors: Aldino Piva, Erasmo Viola, Cristina Gentilini
Authors: Alessandro Marzani, Marco Miniaci, Erasmo Viola
Abstract: Stress guided waves in the sonic and ultrasonic regime are acknowledged as a powerful too lto inspect pipes in a non-invasive manner.A key point of the inspection procedure is related to the dispersive behavior of guided waves, that for agiven pipe is defined by the so-called dispersion curves. Such behavior, is generally predicted bymeans ofanalytical formulations. However, when the geometry of the pipe cross-section is not axially symmetric,such as in the presence of an open internal crack running along the pipe length, analytical formulations fail. Here, the computation of the guided waves properties for such a scenario is addressed via a SemiAnalytical Finite Element (SAFE) formulation in which the open crack is modeled at the mesh level.Different crack depths are considered and their effect on the waves dispersion curves are highlighted.The results could be of interest in pipeline inspection and monitoring.
Authors: Gabriella Faiella, Vincenza Antonucci, Michele Giordano, Federica Daghia, Erasmo Viola
Abstract: Due to the complex microstructure and phase transformations taking place in Shape Memory Alloys (SMA), the behaviour and properties of these materials are deeply influenced by their loading history in terms of stress, strain and temperature. Indeed, a thorough understanding of the effects of the loading history on SMA properties is fundamental for a correct modelling and design of SMA applications, in particular in the case of complex loading. An example are shape memory alloys embedded in composite systems, in which stress, strain and temperature vary simultaneously depending upon the properties of the SMA and composite. This work presents the first results of an experimental investigation on the effects of the loading history on SMA transformation temperatures. Nitinol wires of untrained material were considered. Specimens consisting of Martensite and R-phase were subjected to different loading histories, keeping in turn stress, strain or temperature at a constant value. Transformation temperatures at zero stress of these samples were measured via Differential Scanning Calorimetry. Contrarily to most constitutive models assumptions, the DSC results highlight a dependence of the transformation temperatures on the loading history, influencing in particular the Martensite to Austenite phase transformation.
Authors: Franceso Ubertini, Erasmo Viola, Patrizia Ricci
Authors: Erasmo Viola, Paolo Bocchini
Abstract: The topic of this paper lies in the field of non-destructive parametric identification. Its objective is to evaluate the mechanical characteristics of constituent bars in existing truss structures. In particular, it locates bars with reduced mechanical properties and quantifies the loss of stiffness. The suggested algorithm takes into account plane and three-dimensional structures, both statically determinate and indeterminate. In the case where it is possible to measure strains only on some bars, the procedure uses Genetic Algorithms to overcome the lack of information.
Authors: Erasmo Viola, Claudia Belmonte, Giuseppe Viola
Abstract: The aim of this paper is to seek the solution to the electromechanical field equations for a cracked linear piezoelectric body using an analytical approach which is based on the decomposition theorem of linear algebra. The electroelastic fields around the crack tip are given. The energy release rate is written in terms of those fields intensity factors.
Authors: Erasmo Viola, Francesco Tornabene, Nicholas Fantuzzi, Michele Bacciocchi
Abstract: The present study aims to show a novel numerical approach for investigating composite structures wherein inclusions and discontinuities are present. This numerical approach, termed Strong Formulation Finite Element Method (SFEM), implements a domain decomposition technique in which the governing partial differential system of equations is solved in a strong form. The provided numerical solutions are compared with the ones of the classic Finite Element Method (FEM). It is pointed out that the stress and strain components of the investigated model can be computed more accurately and with less degrees of freedom with respect to standard weak form procedures. The SFEM lies within the general framework of the so-called pseudo-spectral or collocation methods. The Differential Quadrature (DQ) method is one specific application of the previously cited ones and it is applied for discretizing all the partial differential equations that govern the physical problem. The main drawback of the DQ method is that it cannot be applied to irregular domains. In converting the differential problem into a system of algebraic equations, the derivative calculation is direct so that the problem can be solved in its strong form. However, such problem can be overcome by introducing a mapping transformation to convert the equations in the physical coordinate system into a computational space. It is important to note that the assemblage among the elements is given by compatibility conditions, which enforce the connection with displacements and stresses along the boundary edges. Several computational aspects and numerical applications will be presented for the aforementioned problems related to composite materials with discontinuities and inclusions.
Authors: Erasmo Viola, Alessandro Marzani
Abstract: This work presents a numerical simulation of the behavior of stress guided waves (GWs) propagating in a multilayer system composed of porous materials. To this end, the damped Semi-analytical Finite Element (SFE) formulation proposed in [1] is extended to take the dry porosity into account. An application of waves propagating in two squared aluminum bars jointed by a weaker layer of porous adhesive is presented. Numerical results show that variations of the adhesive's porosity modify the GWs spectro-temporal patterns. These changes could be exploited to detect the level of adhesive porosity in a total nondestructive manner for the above structures.
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