Fracto-mechanoluminescence and mechanics of fracture of solids

Abstract

The present paper explores the correlation between fracto-mechanoluminescence and fracture of solids and thereby provides a clear understanding of the physics of fracto-mechanoluminescence. When a fluorescent or non-photoluminescent crystal is fractured impulsively by dropping a load on it, then initially the mechanoluminescence (ML) intensity increases linearly with time, attains a maximum value Im at a particular time tm and later on it decreases exponentially with time. However, when a phosphorescent crystal is fractured impulsively by dropping a load on it, then initially the ML intensity increases linearly with time, attains a maximum value Im at a particular time tm and later on it decreases initially at a fast rate and then at a slow rate. For low impact velocity the value of tm is constant, however, for higher impact velocity tm decreases logarithmally with the increasing impact velocity. Whereas the peak ML intensity Im increases linearly with the impact velocity, the total ML intensity IT, initially increases linearly with the impact velocity and then it tends to attain a saturation value for higher values of the impact velocity. The value of tm increases logarithmally with the thickness of crystals, Im increases linearly with the area of cross-section of crystals and IT increases linearly with the volume of crystals. Generally, the ML of non-irradiated crystals decreases with increasing temperature of crystals. Depending on the prevailing conditions the ML spectra consist of either gas discharge spectra or solid state luminescence spectra or combination of the both. On the basis of the rate of generation of cracks and the rate of creation of new surface area of crystals, expressions are derived for the ML intensity and they are found to explain satisfactorily the temporal, spectral, thermal, crystal-size, impact velocity, surface area, and other characteristics of ML. The present investigation may be useful in designing of damage sensors, fracture sensors, ML-based safety management monitoring system, fuse-system for army warheads, milling machine, etc. The present study may be helpful in understanding the processes involved in earthquakes, earthquake lights and mine-failure as they basically involve fracture of solids.