Abstract

Recent seismic events occurred in areas rich of ancient remains and full of cultural and artistic heritage in terms of artworks. Earthquakes may damage buildings, but the vibrations may also induce the uplift and overturning of their content, implying irreparable loss of cultural values. The seismic assessment of objects is usually tackled modelling them as rigid blocks. This paper focuses on statues, which generally present a very complicated geometry, and proposes a general methodology involving different disciplines, for their experimental seismic assessment. The methodology is here applied to the masterpiece of “Paolo Orsi” museum in Syracuse (Italy), that is the “Venere Landolina”. Due to the complexity of statues, traditional techniques cannot be considered reliable for a proper geometry reconstruction; therefore, Terrestrial Laser Scanner (TLS) and Unmanned Aerial System (UAS) technologies are here employed to obtain a highly detailed and complete digital model. Aiming at providing a low-cost scaled physical model of the statue, a wooden specimen has been arranged employing a Computer Numerical Control (CNC) milling machine, cutting off disks from flat panels which are then superimposed and glued, progressively reconstructing the actual geometry of the statue. The specimen, able to approximately reproduce the scaled actual geometry, was then tested on a shaking table with ground motions compatible with those expected for the site where the statue is located. The obtained results are finally correlated with those expected for the real scale statue.

Abstract

From the beginning of the application of composite materials, different theories to predict their behaviour and failure have been developed. The authors have already made a previous study, analyzing at the macroscopic level (both from an experimental and theoretical point of view), the failure of non-conventional laminates changing the thickness of the laminas that form it, in order to evaluate the “scale effect” (also known as “in-situ strength”) present in them. Results of this study proved the strength variation of the laminate with its configuration (scale effect) and it was found that the presence of laminas with fibres oriented in the direction of the load diminishes this effect. This paper is focused on the understanding of the aforementioned effect, conducting a study at  micromechanical level (the level where the damages leading to the failure are generated) of the scale effect with an energetic approach, in order to progress in the understanding of this phenomenom. To this end, the Boundary Element Method (BEM) has been used. It has been applied to a laminate model with [0, 90n]S stacking sequence, where the influence of n at different stages of the generation and progression of damage has been studied: the beginning of the damage (that takes place when the debonding between fibre and matrix happens) and during the change of direction of the debonding crack towards the matrix (kinking). The models developed are multiscale, involving a mesoscale representation of the laminas of the laminates (modelled as homogeneous) and with micromechanics cells that simulate fibre and matrix and therefore with the capacity for collecting information about damage mechanisms observed experimentally.

Abstract

The scale effect in Composite Materials, consisting in the delay in the first damage appearance as ply thickness decreases, is, at present, a phenomenon under study due to the use of ultrathin plies (whose thickness may reach 20 microns) in the most leading industries. Based on this, the appearance of the first damage is experimentally analysed in this work for [04,90n,04] conventional laminates where n=1,2,4,8,16,32. The objectives are to study damage mechanisms occurrence as the thickness of the weakest layer varies when subjecting the laminate to uniaxial tension and to check if the scale effect is present. Acustical techniques have been employed for damage detection and optical and electronical microscopy have been used for its observation. The conclusions lead to well-diferenced mechanisms of damage for the different thicknesses analysed: high thicknesses show unstable damage resulting in an explosive failure of the whole laminate, whereas low thicknesses show a more stable damage, it being less significant for the laminate integrity. In addition, an scale effect is detected, since the load at which the failure is generated decreases as the thickness increases. In future works the same analysis will be presented for ultrathin plies.

Abstract

The scale effect in Composite Materials is known as the delay in the appearance of damage in the weakest laminas of a laminate (typically 90 degrees laminas). The availability of ultra-thin plies, of up to 20 microns of thickness, has attracted the attention on this effect, as the use of these plies can imply the delay of the onset of damage at a laminate in a significant manner. The frame of the present work is a micromechanical study of the different phases of damage assumed to lead to the failure of the weakest lamina. Thus, it is assumed that the damage starts by isolated debondings between fibres and matrix, then continuing by the abandon of the interphase, the debonding crack kinking into the matrix, and finally the damage progressing either through the matrix itself or along the interfaces between fibres and matrix, to generate a transversal crack in the 90 degrees lamina. The study is carried out using a multi-scale model based on the Boundary Element Method, with control cells in which the damage at micromechanical level previously described is allowed. Concepts derived from Fracture Mechanics and Interfacial Fracture Mechanics are applied in the analysis. The conclusions obtained with this study are compared with those that clearly manifest the scale effect based on a global energy balance from the pristine state to the final situation with the 90 degrees lamina having a complete transverse crack.