Modelling of fracto-mechanoluminescence damage sensor for structures

Abstract

The present paper reports the modelling of fracto-mechanoluminescence damage sensor which is useful for real-time and remotely monitoring of both the magnitude and location of damage of the structure without the use of electrodes. In this technique, the intense fracto-mechanoluminescent material of several micron size is mixed in liquid resin and then coated on the surface of structure whereby the occurrence and strength of the damage is given by the intensity of the resulting mechanoluminescence (ML) light. Monitoring of the position of damage is achieved by identifying the colour of ML light emitted as the ML particles coated in different locations emit ML light of different colours. The modelling of fracto-mechanoluminescence damage sensor is based on the fact that the total ML intensity depends on the total area of the newly created surfaces (damage). For a projectile having large contact area such as a cylinder, below the characteristic impact velocity vc, at which the sample is compressed to 1/e of its thickness, both the peak ML intensity Im and the total ML intensity IT increase linearly with the impact velocity; however, above vc, both Im and IT tend to attain saturation value. In the case of impact of a projectile having small contact area such as a ball, below vc, both Im and IT increase quadratically with the impact velocity; however, above vc, both Im and IT tend to attain saturation value. In the case of a projectile having large contact area the total volume of the sample is compressed and only the rate of creation of new surfaces increases with the impact velocity; however, in the case of a projectile having small contact area, in addition to the increase of strain rate with impact velocity, the effective volume compressed by the impact also increases linearly with the impact velocity, and therefore, the rate of creation of new surfaces increases quadratically with the impact velocity. A good agreement is found between the experimental and theoretical results.