Comments and Remarks on the recordings of Pressure Stimulated Currents (PSC), in marble samples in the range of microcracking. D. TRIANTIS, I. STAVRAKAS, C. ANASTASIADIS Department of Electronics Technological Educational Institution of Athens Athens, 122 10, Tel/Fax: 0030-210-5316525 GREECE Abstract: - The results of Pressure Stimulated Currents systematic recordings, in dielectric solids like marbles are presented. The stimulus of such currents was a fast, step-like, increase of uniaxial stress on the samples. Results are extracted and discussion is made on the mode of PSC emissions, the duration of the emission and the correlation of PSC to the damage variable that quantifies the deviation from linearity on stress-strain characteristic curve. Key-Words: - Pressure Stimulated Currents, PSC, marble, damage. 1 Introduction The material fracture phenomena, particularly those concerning inhomogeneous materials, such as geomaterials, in association with transient electric phenomena, attract the interest of the scientific community. An additional reason is that such phenomena are promising candidates of earthquake precursors. During the development of the geomaterial deformation, there appear mechanisms of generation of electric signal emission and a number of researchers acknowledge such mechanisms as related to crack generation and propagation in the Earth’s crust [1-4]. Although important similarities exist between the fracture of a pristine rock and an earthquake rupture, there are also important differences [5]. In order to understand the mechanisms that produce these electric signals, a number of laboratory experiments of mechanical stress up to sample fracture have been conducted on minerals and rocks (dry and saturated) [6-11]. Furthermore, there are numerous studies and recordings of acoustic emissions due to microcrack opening in rocks and other materials during mechanical stress application [12]. Kaiser effect is also under investigation in order to study materials’ behavior when it is subjected to cyclic loading / unloading [13-15]. Recent laboratory experiments conducted on Penteli marble samples have confirmed that the application of a uniaxial stress on geomaterial samples is accompanied by the production of weak electric currents (Pressure Stimulated Currents- PSC) [16-19]. The above experimental procedure is described by the term PSC technique and after the most recent experiments, consists of recording of the currents emitted by geomaterial samples when subjected to either an abrupt stress increase or a monotonically increasing stress up to fracture. In this paper we will consider in detail PSC recordings that occur during the application of abrupt uniaxial stress increase on marble samples and particularly in the range where the material shows a deviation from linear elasticity in terms of mechanical behaviour, and microcracking is occurring. In this range, the material appears damaged and there is irreversible deformation. Such microcracks weaken the material and result in PSC emissions. 2 Theoretical concepts The stress on the material is given as a function of the strain ε . For the linear elasticity range it can be stated that: S ε ⋅ Υ = 0 S (1) where 0 Υ is the Young’s modulus of the undamaged material which is constant in the elastic range. When the stress takes values that lead further than the (linear) elastic region then microcracks occur. For a prescribed stress S , the strain ε is greater than the value given by Eq. 1. Accordingly, we write [5]: ε ⋅ Υ = eff S (2)