IASPEI - Picture Gallery

IUGG XXIV General Assembly July 2-13, 2007 Perugia, Italy
(S) - IASPEI - International Association of Seismology and Physics of the Earth's
Interior
JSS009 Poster presentation 2055
Electric current emissions from brittle materials suffering near fracture
mechanical stress
Dr. Ilias Stavrakas
Department of Electronics Technological Educational Institution ofAthens
Panayiotis Kyriazis, Antonis Kyriazopoulos, Cimon Anastasiadis, Dimos Triantis,
Filippos Vallianatos
Pressure stimulated current (PSC) effects have been studied on various materials. In a number of
previous presentations the applied mechanical stress has been correlated with the emitted current. In
the present work current emissions are studied on a set of natural brittle materials like marble and
amphibolite as well as on composite man-made materials like cement paste. Specifically, the stress was
applied on the referred samples close to mechanical failure along with emitted PSC measurements. The
recordings manifest that, dynamic phenomena, like macro-crack propagation and failure plane creation,
result in current emissions. In these experiments despite the fact that the stress level was maintained
practically constant in the vicinity of failure, significant PSC emissions of long duration were observed.
The emitted PSC can be attributed to charge rearrangements due to dynamic change of the sample
structure while new cracks are formed and the existing ones extend. In general, both the existence and
interpretation of the PSC are consistent with the Moving Charged Dislocations (MCD) theory which
relates the emitted current to crack formation and propagation and to the consequent strain variation.
Strain recordings in the range near fracture support these findings since strain variations have been
recorded without any change of stress. A deep and fast PSC reduction has always been recorded before
fracture predicting the inevitable failure. This effect can be attributed to two coexisting causes: The
former is related to the lack of any obvious triggering, i.e. stress or strain in the bulk of the material,
that could lead to charge rearrangement since in this stage all the applied stress is localized at the
edges of the main macro-crack that guides the failure plane. The latter is related with the observation
that the failure plane limits significantly the available paths for the charges to move across the sample
bulk which makes the detection of any emitted PSC even more difficult.
Keywords: pressure stimulated currents, brittle materials fracture