VHCF ultrasonic tests on EN AW‐6082 aluminum alloy samples over a wide dimensional range

In the present paper, a very high cycle fatigue test campaign carried out with an ultrasonic testing machine up to 10^10 cycles is presented. The aluminum alloy hourglass and dog-bone samples have dimensions spanning over a very wide range, with the diameter in the middle cross-section comprised between 3 and 30 mm. From the experimental results, the influence of structural size can be clearly detected, and it is possible to observe a transition between small scales, where the size effect is more pronounced, and larger scales, where the size effect is vanishing. This phenomenon can be explained in an effective way by adopting a multifractal formalism, which is equipped with the probabilistic treatment of the statistical dispersion of experimental data

Experimental Evidence of Specimen-Size Effects on EN-AW6082 Aluminum Alloy in VHCF Regime

The present paper investigates the influence of the specimen size of EN-AW6082 wrought aluminium alloy subjected to very high cycle fatigue (VHCF) tests. The hourglass specimens were tested under fully reversed loading condition, up to 109 cycles, by means of the ultrasonic fatigue testing machine developed by Italsigma® (Italy). Three specimens groups were considered, with a diameter in the middle cross-section ranging from 3 mm up to 12 mm. The stress field in the specimens was determined numerically and by strain gauge measurements in correspondence of the cross-section surface. The dispersion of experimental results has been accounted for, and data are reported in P-S-N diagrams. The decrease in fatigue resistance with increasing specimen size is evident. Theoretical explanation for the observed specimen-size effect is provided, based on Fractal Geometry concepts, allowing to obtain scale independent P-S*-N curves. The fatigue life expectation in the VHCF regime of the EN-AW6082 aluminium alloy full-scale components is rather overestimated if it is assessed only from standard small specimens of 3 mm in diameter. Experimental tests carried out on larger specimens, and a proper extrapolation, are required to assure safe structural design

Fatigue assessment of the collapsed XXth Century cable-stayed Polcevera Bridge in Genoa

Abstract The present paper investigates the combined effect of corrosion and fatigue at very-high number of cycles on the recently collapsed Polcevera Bridge. Since the construction, in the mid-sixties, the viaduct has experienced a dramatic increase in the heavy lorries traffic. Although the amplitude of stress oscillation in the strands was limited, it is assessed that the number of larger load amplitude cycles reached eighty million, out of almost half a billion of total vehicles that crossed the bridge. Due to the aggressive environment, the degradation of the bridge has developed much faster than expected. It is likely that, already at the beginning of the Eighties, the effectiveness of the prestressed concrete covering of the strands was vanishing in some sections close to the antenna, both in terms of protection and local stiffness. As a result, the levels of corrosion detected in the strands could have been sufficient to trigger the brittle failure of one of the stay cables, and the subsequent collapse of one of the self-standing structural systems. Besides to figure out the possible collapse mechanism of the Polcevera Bridge, the authors wish to rise the attention of the scientific community on the rather underestimated phenomenon of very-high cycle corrosion fatigue in existing civil infrastructures

Effect of noise and enhancement of nonlocality in on/off photodetection

Nonlocality of two-mode states of light is addressed by means of CHSH inequality based on displaced on/off photodetection. Effects due to non-unit quantum efficiency and nonzero dark counts are taken into account. Nonlocality of both balanced and unbalanced superpositions of few photon-number states, as well as that of multiphoton twin beams, is investigated. We find that unbalanced superpositions show larger nonlocality than balanced one when noise affects the photodetection process. De-Gaussification by means of (inconclusive) photon subtraction is shown to enhance nonlocality of twin beams in the low energy regime. We also show that when the measurement is described by a POVM, rather than a set of projectors, the maximum achievable value of the Bell parameter in the CHSH inequality is decreased, and is no longer given by the Cirel'son bound.Comment: 21 Figure

Innovative technique for the base isolation of existing buildings

An innovative base isolation system has been recently proposed for the retrofitting of existing buildings, in which the isolation layer is inserted under the building foundations so that the building, along with its foundations, is isolated from the surrounding soil. The isolation layer resides in closely-spaced micro-tunnels, constructed under the entire width of the building. These micro-tunnels, along with the trenches around the building, isolate the structure from the surrounding soil. The execution of these micro-tunnels is the most critical construction stage, because it may result in settlements which can damage the structure. In this paper, the behaviour of an existing structure, consisting of a masonry wall subjected to tunnelling-induced ground subsidence, is analysed. A parametric study is conducted using 2-D nonlinear finite element analyses to understand the role of key factors such as strength and stiffness of soil and masonry, roughness of soil-structure interface, excavation sequence of tunnels, wall dimensions and openings configuration. The study identifies the design variables which influence the most the risk of structural damage and suggests the most effective damage symptoms to be monitored during constructio

Stability assessment of masonry arches by evolutionary fracturing process analysis

Masonry arch structures, and, more in general, vaulted structures, are traditionally assessed using a well-established approach, such as linear elasticity or limit analysis, whereby system behaviour at the intermediate stage −that occurs when the material's tensile strength has been exceeded but the collapse mechanism has not yet formed− is disregarded. With an evolutionary fracturing process analysis for the stability assessment of a masonry arch it is possible to capture the damaging process that takes place when the conditions evaluated by means of linear elastic analysis no longer apply, and before the conditions assessed through limit analysis set in. Furthermore, the way the thrust line is affected by the opening of cracks and the redistribution of internal stresses can be checked numerically. The evolutionary calculation method presented in this paper takes into account the intermediate cracking stage and uses a constitutive law providing a closer approximation to the actual behaviour of the structural material. By applying this numerical model the monumental arches of the Vittorio Emanuele I Bridge over the Po River, and the Mosca Arch Bridge over the Dora River both in Turin (Italy) are described. The different behaviors under increasing load of the two structural schemes -the Mosca Bridge is a very thin shallow masonry arch, while the Vittorio Emanuele I Bridge presents three-centered rounded arches- are deeply investigated by means of the evolutionary analysi

Design of a modular exhibition structure with additive manufacturing of eco-sustainable materials

In this paper the mechanical characteristics of an innovative bioplastic material, the HBP - HempBioPlastic filament, is investigated. HBP was recently patented by an Italian company Kanésis that focused its activity on nature-derived materials. The filaments are the upshot of an original process allowing to reuse the surplus of the agricultural supply chains and transform it into new sustainable materials. At first, the 3D printed HBP samples were tested in tensile tests according to the ASTM- D638 standard and monitored in term of deformations by the Digital Image Correlation techniques (DIC) in order to evaluate the stress-strain behavior of different HBP textures under loading. In addition, using the HBP and the results coming from the experimental campaign, the design of an exhibition pavilion was proposed. The pavilion was modelled starting from the geometric construction of the fullerene. The supporting modular structure is combined by HBP modular elements, that can be produced by 3D printing or moulding. Finally, in order to demonstrate the feasibility of the proposed pavilion, a linear finite element analysis is presented on the base of the experimentally determined mechanical properties of HBP elements, under the effects of wind and seismic environmental actions

Innovative technique for the base isolation of existing buildings

An innovative base isolation system has been recently proposed for the retrofitting of existing buildings, in which the isolation layer is inserted under the building foundations so that the building, along with its foundations, is isolated from the surrounding soil. The isolation layer resides in closely-spaced micro-tunnels, constructed under the entire width of the building. These micro-tunnels, along with the trenches around the building, isolate the structure from the surrounding soil. The execution of these micro-tunnels is the most critical construction stage, because it may result in settlements which can damage the structure. In this paper, the behaviour of an existing structure, consisting of a masonry wall subjected to tunnelling-induced ground subsidence, is analysed. A parametric study is conducted using 2-D nonlinear finite element analyses to understand the role of key factors such as strength and stiffness of soil and masonry, roughness of soil-structure interface, excavation sequence of tunnels, wall dimensions and openings configuration. The study identifies the design variables which influence the most the risk of structural damage and suggests the most effective damage symptoms to be monitored during constructio

AE monitoring and structural modelization of the Asinelli Tower in Bologna

The Acoustic Emission (AE) technique was used to assess the structural stability of the Asinelli Tower, the tallest building in the city of Bologna, which, together with the nearby tower, named Garisenda, is the renowned symbol of the city. AE is a passive, non-destructive structural evaluation technique based on the spontaneous emission of pressure waves by evolving fracture processes. The monitoring program was carried out with the aid of a USAM tool, which is part of the equipment used at the Fracture Mechanics Laboratory of the Department of Structural Engineering at the Politecnico di Torino. This tool makes it possible to conduct a complete analysis of AE signals, acquire a huge quantity of data from on site monitoring, and identify the microcracks triggering the damage processes in a structure. In the second part of the paper, the results from a preliminary linear analysis are presented, in order to assess the structural behavior of the tower. The cracking and crushing strengths of the masonry have both been compared with the calculated stresses. The numerical analysis gives a valuable picture of the modal response of the tower, providing useful hints for the prosecution of structural monitorin