Issue 40

A. Kyriazopoulos, Frattura ed Integrità Strutturale, 40 (2017) 52-60; DOI: 10.3221/IGF-ESIS.40.05 52 Focussed on Recent advances in “Experimental Mechanics of Materials” in Greece Acoustic emissions and electric signal recordings, when cement mortar beams are subjected to three-point bending under various loading protocols A. Kyriazopoulos Laboratory of Electronic Devices and Materials, Technological Educational Institute of Athens, 12210, Athens, Greece. akyriazo@teiath.gr A BSTRACT . Two experimental techniques are used study the response of cement mortar beams subjected to three-point bending under various loading protocols. The techniques used are the detection of weak electric current emissions known as Pressure Stimulated Currents and the Acoustic Emissions (in particular, the cumulative AE energy and the b-value analysis). Patterns are detected that can be used to predict upcoming fracture, regardless of the adopted loading protocol in each experiment. The experimental results of the AE and PSC techniques lead to the conclusion that when the calculated I b values decrease, the PSC starts increasing strongly. K EYWORDS . Pressure Stimulated Currents; Acoustic Emissions; Cement mortar; Three point bending; b-value. Citation: Kyriazopoulos, A., Acoustic emissions and electric signal recordings, when cement mortar beams are subjected to three point bending under various loading protocols, Frattura ed Integrità Strutturale, 40 (2017) 52-60. Received: 05.01.2017 Accepted: 26.02.2017 Published: 01.04.2017 Copyright: © 2017 This is an open access article under the terms of the CC-BY 4.0, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. I NTRODUCTION he mechanical behavior and the evolution of damage in heterogeneous materials under compressive loading are of great interest in a wide range of application fields. Particularly, the Service Life of cement-based structures deteriorates due to heavy loads, fatigue, aging and natural disasters. Accordingly, diagnostic methods for damage assessment have been developed and implemented, aiming to assess the impending failure. To this end, the Acoustic Emissions (AE) technique was developed and is being improved continuously in order to provide a useful tool for monitoring and understanding the mechanisms of dynamic processes, but also for warning of upcoming failure [1]. Acoustic Emission events occur due to sudden release of mechanical energy in the form of short mechanical vibrations due to the fact that a material is under mechanical loading. This mechanical vibration travels in the form of spherical waveforms through the material’s bulk. The AE event analysis is used to estimate the damage degree when brittle materials such as concrete and rocks are subjected to mechanical loading [2-5]. Acoustic Emission (AE) due to crack growth in brittle materials is usually observed in the high frequency range, typically between 50 kHz and 800 kHz. AE are recorded even from the early stages of the damage process. During the fracture process in quasi-brittle materials, the micro cracks formation and growth are manifested by a number of AE events released at different amplitudes. It has been shown that as a specimen under mechanical loading approaches failure, there is T