Physics Letters A 356 (2006) 160–163 www.elsevier.com/locate/pla Crack velocity measurement by induced electromagnetic radiation V. Frid a,∗ , A. Rabinovitch b , D. Bahat a a The Deichmann Rock Mechanics Laboratory of the Negev, Geological and Environmental Sciences Department, Ben Gurion University of the Negev, Beer Sheva, Israel b The Deichmann Rock Mechanics Laboratory of the Negev, Physics Department, Ben Gurion University of the Negev, Beer Sheva, Israel Received 11 December 2005; received in revised form 10 March 2006; accepted 10 March 2006 Available online 22 March 2006 Communicated by R. Wu Abstract Our model of electromagnetic radiation (EMR) emanated from fracture implies that EMR amplitude is proportional to crack velocity. Soda lime glass samples were tested under uniaxial tension. Comparison of crack velocity observed by Wallner line analysis and the peak amplitude of EMR signals registered during the test, showed very good correlation, validating this proportionality.  2006 Elsevier B.V. All rights reserved. PACS: 81.70.-q; 61.80.-x; 62.20.Mk Keywords: Crack velocity; Fracture; Electromagnetic radiation 1. Introduction Electromagnetic radiation (EMR) emanating from frac- ture is an extensively investigated phenomena, e.g., [1–3]. The correlation between crack sizes and pulse parameters were carefully verified [4–6]. Our EMR model [6,7] pre- dicts (see below) that crack velocity should be proportional to the EMR amplitude. However no actual proof of EMR use for crack velocity evaluation has hitherto been provided. Here we compare crack velocity evaluations by both Wallner line analysis and EMR, and demonstrate that EMR amplitude can indeed be used for quantitative analysis of crack velocity changes. Note that other methods to measure crack velocity are known, e.g., changes of electrical conductivity. These meth- ods require either special preparation of the sample surfaces or be used only for transparent materials. These limitations could be avoided by using EMR as the measuring mecha- nism. * Corresponding author. E-mail address: vfrid@bgu.ac.il (V. Frid). 2. Brief theoretical considerations We describe briefly the aspects of both EMR and Wallner lines which are relevant for our analysis. 2.1. EMR A model to explain EMR emitted by fracture was devel- oped by our group [6,7] and is briefly presented here. In this model it is assumed that, following the breaking of bonds by the moving fracture, the atoms on both created sides are moved to “nonequilibrium” positions relative to their steady state ones and oscillate around them. Lines of oscillating atoms move to- gether and, being connected to atoms around them (both in the forward direction and on their side), the latter also par- ticipate in the movement. The ensuing vibrations are surface vibrational waves: positive charges move together in a dia- metrically opposite phase to the negative ones while decay- ing exponentially into the material, like Rayleigh waves. The resulting oscillating electric dipoles act as the source of the EMR. The wave’s amplitude decays by an interaction with bulk phonons. In this model [6,7], the shape of an individual EMR pulse has the form [4] given by 0375-9601/$ – see front matter  2006 Elsevier B.V. All rights reserved. doi:10.1016/j.physleta.2006.03.024