Acoustic emission monitoring of the Syracuse Athena temple: scale invariance in the timing of ruptures

We perform a comparative statistical analysis between the acoustic-emission time series from the ancient Greek Athena temple in Syracuse and the sequence of nearby earthquakes. We find an apparent association between acoustic-emission bursts and the earthquake occurrence. The waiting-time distributions for acoustic-emission and earthquake time series are described by a unique scaling law indicating self-similarity over a wide range of magnitude scales. This evidence suggests a correlation between the aging process of the temple and the local seismic activity.     

A finite-element-based coarse-grained model for global protein vibration

Meccanica - Protein mechanical vibrations play a pivotal role in biological activity. In particular, low-frequency (terahertz) modes are related to protein conformational changes, which represent...     

Particle-based numerical modeling of AE statistics in disordered materials

We present some numerical simulations of AE due to damage propagation in disordered materials under compression and bending. To this purpose, the AE cumulative number, the time frequency analysis and the statistical properties of AE time series will be numerically simulated adopting the so-called “particle method strategy” (Cundall in Proceedings ISRM Symp., Nancy, France, vol. 2, pp. 129–136, 1971). The method provides the velocity of particles in a set simulating the behavior of a granular system and, therefore, is suitable to model the compressive wave propagation and acoustic emission (corresponding to cracking) in a solid body. The numerical simulations (Abe et al. in Pure Appl. Geophys. 161:2265–2277, 2004) correctly describe the compression test in terms of mean stress-strain response and crack pattern (Invernizzi et al. in Proceedings of the SEM annual conference, Society for Experimental Mechanics Inc., USA, SEM Annual Conference, Indianapolis, Indiana, USA, June 7–10, 2010). The size effects on the peak compressive strength and on the AE count are correctly reproduced. In addition, the amplitude distribution (b-value) and temporal evolution of AE events due to cracking, crucial for the evaluation of damage and remaining lifetime, were simulated and result in agreement with the experimental evidences.     

Neutron emissions in brittle rocks during compression tests: Monotonic vs. cyclic loading

Neutron emission measurements, by means of ³He devices and bubble detectors, were performed during two different kinds of compression tests on brittle rocks: under monotonic and cyclic loading. The material used for the tests was Green Luserna Granite, with different specimen sizes and shapes, and consequently with different brittleness numbers. Since the analyzed material contains iron, our conjecture is that piezonuclear reactions involving fission of iron into aluminum, or into magnesium and silicon, should have occurred during compression damage and failure. Some studies have been already conducted on the different forms of energy emitted during the failure of brittle materials. They are based on the signals captured by acoustic emission measurement systems, or on the detection of electromagnetic charge. On the other hand, piezonuclear neutron emissions from very brittle rock specimens in compression have been discovered only very recently. In this paper, the authors analyse this phenomenon from an experimental point of view.     

Critical defect size distributions in concrete structures detected by the acoustic emission technique

Extensive research and studies on concrete fracture and failure have shown that concrete should be viewed as a quasi-brittle material having a size-dependent behavior. Numerous experimental techniques have been employed to evaluate fracture processes, and a number of modeling approaches have been developed to predict fracture behavior. A non-destructive method based on the Acoustic Emission (AE) technique has proved to be highly effective, especially to assess and measure the damage phenomena taking place inside a structure subjected to mechanical loading. In this paper, comparing AE frequency-magnitude statistics in solids subjected to damage processes with defect size distributions for disordered materials, critical parameters defining instability conditions for monitored structures are found. In addition, an experimental investigation conducted on concrete and RC structures by means of the AE technique is described. Experimental results confirm the described theories.