1,721,036 research outputs found
Un nuovo approccio teorico e sperimentale alla caratterizzazione dell’anisotropia indotta da danno nei materiali compositi fibro-rinforzati
No full textLo studio teorico e sperimentale dell’anisotropia indotta da danno nei materiali compositi fibrorinforzati risulta molto complesso in quanto l’anisotropia indotta si sovrappone all’anisotropia costitutiva del materiale. Sulla base di recenti lavori sperimentali da noi condotti sulla caratterizzazione meccanica dei materiali anisotropi mediante tecniche ultrasoniche ad immersione [1- 2], abbiamo sviluppato un nuovo approccio teorico e sperimentale alla caratterizzazione dell’anisotropia indotta da danno nei materiali [3-4]. In questo studio, mostriamo i risultati sperimentali ottenuti da prove ultrasoniche effettuate su campioni di compositi fibro-rinforzati (GFRP) prima e dopo test di danneggiamento artificiale. L’analisi delle curve di ritardo e l’impiego di un modello di danno anisotropo hanno permesso di riconoscere la variazione della risposta acustica dei materiali compositi e di stimare l’anisotropia indotta da danno.The theoretical and experimental analysis of the damage induced anisotropy in fiber-reinforced composite materials is very difficult because the damage induced anisotropy is superimposed to the constitutive anisotropy of the material. Based on some recent experimental works by us on the mechanical characterization of anisotropic materials by ultrasonic immersion techniques [1-2], we developed a new theoretical and experimental approach for characterizing the damage induced anisotropy of materials [3-4]. In this study, we show the experimental results obtained by ultrasonic tests carried out on samples of a glass fiber-reinforced polymer composite (GFRP) before and after artificial damage tests. The analysis of the slowness curves and the use of an anisotropic damage model allowed us for recognizing the variation of the acoustic response of the composite and for estimating the anisotropy induced damage
Radar Interferometric Experimental Reconstruction of Three-Dimensional Displacement Vectors and Mode Shapes for Masonry Constructions
No full textRadar interferometry is an innovative measurement technique capable of remotely measuring vibrations in terms of displacement history. It apparently allows overcoming some major drawbacks of the plodding and time-consuming conventional accelerometric experimental setup for vibration testing. Indeed, radar interferometry does not require any access to the structure; moreover, its use is simpler and faster. Therefore, this technique appears very appealing for ambient vibration testing on structures, and in particular on architectural heritage masonry constructions. However, radar interferometry is still affected by some relevant limitations, that currently outweigh the advantages. One of the most important limitations is that displacements are measured only along the line-of-sight; therefore, it is not possible to determine the whole three-dimensional displacement vector for moving structural points and, consequently, to reconstruct three-dimensional mode shapes of structures, whose knowledge is crucial for characterizing the dynamic behavior of structures and for detecting eventual damages. In this paper, a theoretical and experimental approach for reconstructing both three-dimensional displacement vectors and mode shapes of masonry constructions is proposed. This approach is based on the simultaneous use of two synchronized radar interferometers, and on the application of a theoretical model assuming a specific kinematical constraint, which is generally plausible in the case of masonry constructions. The proposed approach has been validated through in-situ experimental tests on a masonry bell towe
Shear driven planar Couette and Taylor-like instabilities for a class of compressible isotropic elastic solids
No full textWe study the possibility for an isotropic elastic body to support forms of instability induced by shear stress states which are reminiscent of the planar Couette and the Taylor-Couette patterns observed in the flow of viscous fluids. Here, we investigate the emergence of bifurcating periodic deformations for an infinitely long compressible elastic block confined between and attached to parallel plates which are subject to a relative shear displacement. We specialize our analysis by considering a generalized form of the Blatz-Ko strain energy function and show through numerical representative examples that planar Couette modes are always preferred with respect to the twisting Taylor-Couette modes. Finally, we introduce a suitably restricted form of the strong ellipticity condition for the incremental elasticity tensor and discuss its significance in this bifurcation problem
Bifurcation and stable post-critical response of a Mooney-Rivlin elastic body subject to a multiaxial stress state
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In-situ estimation of axial force in tie rods of masonry structures by radar interferometry
No full textTie rods are often used in historical masonry constructions to improve structural stability. Tensile force in tie rods can be estimated from experimental measurements through dynamic methods. Generally, these methods are based on the measurement of the vibration of the tie rod through contact sensors. Here, we study the in-situ application of an innovative remote sensing technique, the ground-based radar interferometry, to the estimation of tensile force in tie rods through dynamic methods. Our purpose is to highlight the main potentials and limitations related to this application. We found that one of the most critical issues that may arise concerns the presence of static clutters. Indeed, static clutters may generate spurious frequencies that could lead to errors in the estimation of tensile force. Results show that this issue could be overcome by applying robust and effective clutter removal techniques
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