Mario Daniele Piccioni

Monitoring applied and residual stress in materials and structures by non-destructive acoustoelastic techniques

We present an innovative non-destructive approach based on the analysis of acoustoelastic effect for monitoring applied and residual stress in materials and structures. The proposed approach can be considered as base for a structures monitoring system. The analysis of the acoustoelastic effect for solid bodies, i.e., the correlation between the acoustic properties and the stress state, may be suitably exploited for experimental purposes. To this aim, relevant modeling and experimental issues should be overcome. Indeed, the usual theoretical framework of the acoustoelastic measurements is the so-called third-order elasticity, based on the use of the acoustoelastic coefficients, and requiring relatively simple experimental measurements. Here, by adopting an innovative ultrasonic setup, we investigate the capability of a theoretical model developed within the linearized elasticity, and used for describing the propagation of small amplitude waves in prestressed elastic materials. The results of the ultrasonic tests show that this approach in capable of accurate in situ stress measurements. The proposed experimental setup could be further investigated for monitoring applications of stress states in structures during their service life.

Incompressible Elastic Bodies with Non-Convex Energy under Dead-Load Surface Tractions

In this paper we study the equilibrium deformations of an incompressible elastic body with a non-convex strain energy function which is subjected to a homogeneous distribution of dead-load tractions. To determine the stable solutions we consider the mixtures of the phases which minimize the total energy density. In the special case of a trilinear material we discuss the stability of the equilibrium phases in detail. Finally, we show that multiphase solutions are possible when the surface loads correspond to a critical simple shear and we sketch their possible forms.

Mechanical Characterization of Apricena Marble by Ultrasonic Immersion Tests

We characterize the elastic response of Apricena marble by using advanced ultrasonic nondestructive techniques. An innovative experimental device for ultrasonic immersion tests is employed for the determination of ultrasonic velocities of waves travelling into the sample for any angle of propagation. The interpretation of the experimental results within the theoretical framework of wave propagation in elastic materials allows for both the classification of the anisotropy and the determination of the elastic moduli.

Pairwise Deformations of an Incompressible Elastic Body under Dead-Load Tractions

In this paper we obtain necessary conditions for the existence of pairwise deformations of an incompressible, isotropic elastic body subjected to a homogeneous distribution of dead-load tractions. Explicit restrictions on the boundary loads and on the surface of discontinuity between the phases are determined. For hyperelastic bodies with stored energy depending only on the first invariant of strain, we show that pairwise deformations under examination are necessarily (within a rigid rotation) plane deformations.

Ultrasonic immersion tests for mechanical characterization of multilayered anisotropic materials

We apply an innovative experimental approach based on ultrasonic immersion tests for the characterization of the elastic response of a multi-layered anisotropic GFRP composite. The good agreement between the results of the nondestructive measurements and the results of standard destructive mechanical tests shows the effectiveness of the proposed experimental setup. Moreover, the accuracy of the ultrasonic test allows for the identification of the layer of the composite specimen: this can be very useful in view of the characterization of micro-cracks, damage and delamination.

Taylor-like bifurcations for a compressible isotropic elastic tube:

We study the possibility of toroidal twist-like bifurcations for an isotropic Levinson–Burgess compressible elastic tube subject to a pure circular shear. We intend to model forms of instability for solids that are analogous to the classical Taylor–Couette patterns observed in the flow of viscous fluids. We first establish that the axisymmetric circular shear deformation is a fundamental solution of the equilibrium problem, and then investigate the possibility that this primary deformation may bifurcate into an axially periodic toroidal twist-like mode by analyzing the related incremental boundary-value problem. The analysis of the bifurcation problem and the evaluation of the critical load are carried out by following a novel effective procedure, based on the Magnus expansion.

Seismic Response of a Historic Masonry Construction Isolated by Stable Unbonded Fiber-Reinforced Elastomeric Isolators (SU-FREI)

We study the implementation of Stable Unbonded Fiber-Reinforced Elastomeric Isolators (SU-FREI) for the seismic protection of a typical historical masonry construction from Puglia. The effectiveness of this innovative isolation technique is analyzed by means of a non-linear dynamic analysis, which shows substantial improvements of the seismic response with respect to the corresponding fixed base construction.

A lower bound estimate of the critical load in bifurcation analysis for incompressible elastic solids

A procedure for obtaining a lower bound estimate of the critical load for arbitrary incompressible hyperelastic solids is presented. By considering a lower bound estimate for the Hadamard functional based on the Korn inequality, we establish sufficient conditions for the infinitesimal stability of a distorted configuration. We then determine an optimal lower bound estimate of the critical load in a monotonic loading process and specialize our procedure to the case of homogeneous deformations of incompressible, hyperelastic bodies. We apply our procedure to some representative dead-load boundary value problems for Mooney–Rivlin elastic solids and discuss its effectiveness and handiness for applications by comparing our results to other estimates.

Some issues in the structural health monitoring of a railway viaduct by ground based radar interferometry

Operational Modal Analysis (OMA) is extensively used as a tool for the modal identification and the Structural Health Monitoring (SHM) of civil constructions. However, the classical experimental techniques based on the use of accelerometers involve high costs and long times for performing the measurements, and often interrupting the service of the construction is also needed. In this paper, with reference to the specific case study of the identification of modal parameters of a typical span of a railway viaduct, we analyze the capability and the possible improvements of the ground based radar interferometric experimental set-up. This analysis is aimed at developing a fast, inexpensive and practical procedure for the periodic monitoring of the viaduct.

Geometric numerical integrators based on the Magnus expansion in bifurcation problems for non-linear elastic solids

We illustrate a procedure based on the Magnus expansion for studying mechanical problems which lead to non-autonomous systems of linear ODE’s. The effectiveness of the Magnus method is enlighten by the analysis of a bifurcation problem in the framework of three-dimensional non-linear elasticity. In particular, for an isotropic compressible elastic tube subject to an azimuthal shear primary deformation we study the possibility of axially periodic twist-like bifurcations. The approximate matricant of the resulting differential problem and the first singular value of the bifurcating load corresponding to a non-trivial bifurcation are determined by employing a simplified version of the Magnus method, characterized by a truncation of the Magnus series after the second term.