The electrical behaviour of geomaterials under a regime of mechanical stressing by uniaxial compression

The electrical behaviour of geomaterials under a regime of mechanical stressing by uniaxial compression
Framework:
Archimedes II – Support to the Research Teams at the Technological Educational Institutes, Education and Primary Vocational Training (EPEAEK II)

Starting Date: 01-01-2005

End Date: 30-06-2007

Budget: 60,000.00€

 

Description:
The aims of the project were the use of the techniques of dielectric spectroscopy seeking of differentiations caused by the application of pressure in the dielectric response of geomaterials and the realization of laboratory experiments to show up electric signal emissions from geomaterials under temporally varying uniaxial compression up to failure.

1. Dielectric spectroscopy:
The electric properties of basic geomaterials were studied with the use of dielectric spectroscopy (D.S.) techniques. The laboratory experiments were initially performed under atmospheric pressure and consequently after mechanical stressing by uniaxial compression or by bending. The differentiations caused to the dielectric constant and to conductivity by the influence of compression as well as to the characteristic parameters of isothermal depolarization currents (IDC) have been discussed in published papers. The development and even the origination of microcracks in geomaterials at early stages is detectable through the dielectric spectroscopy technique. Consequently, the dielectric spectroscopy can be established as one of Non-Destructive Testing (NDT) techniques for the localization of catastrophic processes that show up in geomaterials after mechanical stressing.

2. Pressure stimulated electric currents:
After systematic laboratory experiments performed, the emission of weak electric currents (Pressure stimulated currents – PSC) was experimentally proved when geomaterial specimens are under temporally varying uniaxial compression up to fracture. The PSC characteristics support the conjecture that the microcrack formation and development processes are escorted by electric polarization. PSC was also detected for the first time within cement based products in the present research project. This fact enables development of a new research area for the mentioned material. Wavelet analysis was also performed for the first time on electric PSC signals within the present research project. This analysis showed that conclusions related with the magnitude of sample deformation as well as with the determination of the stage of deformation of the material sample before failure.

 

Research group:

  • Dimos Triantis, Professor, Department of Electronics, TEI of Athens, Team coordinator
  • Cimon Anastasiadis, Associate Professor, Department of Electronics TEI of Athens
  • Zacharias Agioutantis, Professor, Technical University of Crete
  • Fillipos Vallianatos, Professor, T.E.I. of Crete
  • Vassilios Saltas, Assistant Professor, T.E.I. of Crete
  • Antonios Kyriazopoulos, Lecturer T.E.I. of Athens
  • Ilias Stavrakas, scientific fellow, T.E.I. of Athens
  • George Hloupis, PhD Candidate
  • Panagiotis Kyriazis, PhD candidate
  • Constantinos Ninos, PhD candidate

 

Publications:

Dielectric spectroscopy 

  1. C. Anastasiadis, I. Stavrakas, D. Triantis, A. Kyriazopoulos, K. Ninos: «Rock damage estimation with dielectric loss (tanδ) measurements», International Journal of Microstructure and Materials Properties, vol. 1, pp. 421-429 (2006).
  2. N. Mitritsakis, I. Stavrakas, S. Maurigiannakis, C. Anastasiadis, D. Triantis, Z. Agioutantis. «Investigation and quantification of damage in geomaterials with the technique of Dielectric Spectroscopy», Proc. of the 9th ECNDT Berlin 2006, Sept. 25-29, 2006. P.222.
  3. V. Saltas F. Vallianatos C. Anastasiadis, D. Triantis and P. Kyriazis: «Dielectric spectroscopy of bentonite samples originated from Milos Island», Proc. of the 2nd Int. Conf. Adv. in Mineral Resources Management and Environmental Geotechnology, 25-27 Sept., 2006, Hania Crete Greece, pp. 425-430.
  4. Ι. Stavrakas, D. Triantis, C. Anastasiadis: «The Influence of externally applied uniaxial stress on Isothermal Depolarization Current mechanisms on rock samples», Journal of Materials Science, Vol. 40, pp. 4593-4596 (2005).
  5. C. Anastasiadis, D. Triantis, I. Stavrakas, A. Kyriazopoulos and F. Vallianatos: Ac conductivity measurements of rock samples after the application of stress up to fracture. Correlation with the damage variable», WSEAS Transactions on Systems, Vol. 4, Issue 3 pp. 185-190 (2005).

 

Pressure stimulated electric currents

  1. C. Anastasiadis, D. Triantis and C. A. Hogarth: «Comments on the phenomena underlying pressure stimulated currents (PSC) in dielectric rock materials», Journal of Materials Science, vol. 42, pp. 2538-2542 (2007)
  2. C. Anastasiadis, I. Stavrakas, D. Triantis, F. Vallianatos: «The correlation of Pressure Stimulated Currents in rocks with the damage variable», Annals of Geophysics, vol. 50, pp.1-6 (2006).
  3. P. Kyriazis, C. Anastasiadis, D. Triantis, F. Vallianatos: «Wavelet analysis on Pressure Stimulated Currents emitted by marble samples», Natural Hazards and Earth System Sciences, vol. 6, pp. 889-894 (2006)
  4. Α. Kyriazopoulos, C. Anastasiadis, D. Triantis and I. Stavrakas: «Experimental Pressure Stimulated Currents (PSC) recordings on cement mortar under mechanical stress», Proc. of the 2nd Int. Fib Congress, Naples, Italy, 5-8 June 2006, ID 13-19.
  5. D. Triantis, C. Anastasiadis, A. Kyriazopoulos, P. Kyriazis and N. Alexis: «Electric current emissions during bending of FRP samples up to fracture», Proc. of the 2nd Int. Conf. Advances in Mineral Resources Management and Environmental Geotechnology, 25-27 Sept., 2006, Hania Crete Greece, pp. 425-430.
  6. D. Triantis, I. Stavrakas, C. Anastasiadis, A. Kyriazopoulos and F. Vallianatos: «An analysis of Pressure Stimulated Currents (PSC), in marble samples under mechanical stress», Physics and Chemistry of the Earth, vol. 31, pp. 234-239 (2006).