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Mechanical response of notched marble beams under bending versus acoustic emissions and electric activity

Kourkoulis S. K., Pasiou E. D., Dakanali I., Stavrakas I., Triantis D.

Journal of Theoretical and Applied Mechanics

2018

Vol. 56 nr 2

523--547

An experimental protocol, including the combined application of both innovative and traditional sensing techniques, is described aiming to explore the mechanical response of marble and also to check the possibilities of detecting precursor phenomena designating upcoming catastrophic fracture. The protocol consisted of three-point bending tests with notched prismatic beams made of Dionysos marble, the material extensively used for restoration of the Acropolis of Athens monuments. The sensing system improvised included techniques relying on completely different physical foundations, which permit simultaneous detection and recording of the Pressure Stimulated Currents, Acoustic Emissions, three dimensional displacement fields and Notch Mouth Opening Displacements. Analysis of the results revealed interesting features of the mechanical response of Dionysos marble and indicated, also, that classical Continuum Fracture Mechanics fails to describe accurately the response of marble, at least in the presence of notches. In addition, strong correlations between the Pressure Stimulated Currents, the rate of acoustic hits and the rate of change of the opening of the pre-existing notch have been enlightened. Moreover, the onset of catastrophic crack propagation appears following distinguishable changes of the Pressure Stimulated Currents recorded. Therefore (and taking into account the very small size of the respective sensors as well as the simple complementary equipment needed), it is concluded that the specific technique could be considered as a simple and reliable tool for an alternative approach to the in-situ Structural Health Monitoring of classical stone monuments.

A multi-layered ring under parabolic pressure

Markides Ch. F., Pasiou E. D., Kourkoulis S. K.

Engineering Transactions

2016

Vol. 64, iss. 4

433--440

The stress- and displacement-fields developed in a circular ring consisting of a finite number of linearly elastic homogeneous and isotropic concentric layers are determined. The composite ring is subjected to a distribution of radial stresses (acting along two finite arcs of its periphery) varying according to a parabolic law. The problem is solved analytically adopting Savin’s approach for an infinite plate with a hole strengthened by rings. Taking advantage of the analytic solution, a numerical model is properly calibrated and validated by considering the case of a three-layered ring. It is concluded that the constructed model simulates reality in an excellent manner and therefore it can be safely used for a thorough parametric analysis of the numerous factors influencing the stress- and displacement-fields.