Executive Summary : | The prime object of the proposed work is to design and fabricate a mechanoluminescence (ML) based crack indicator/sensor. Recently, there were reports of ML from nano and micro sized particles, which repeatedly emitted light in response to small applied stresses, such as friction, deformation, impact, etc. When such particles are coated onto some structure, each particle acts as a sensitive mechanical sensor, while the two-dimensional emission pattern of the whole assembly reflects the dynamical stress distribution inside the structure. This stress visualization technique, which provides a novel way of diagnosing the structural health of a machine/apparatus/instrument is advantageous over the conventional point-by-point measurement method. The light emissions induced by elastic deformation, plastic deformation and fracture of solids are known as elastico mechanoluminescence (EML), plasticomechanoluminescence (PML) and fractomechanoluminescence (FML), respectively. Although, the phenomenon of ML is known for long time, no remarkable application of ML materials could be realized because of their low ML intensity and lack of reproducibility. It is proposed to develop a material that can continuously emit high intensity visible light upon the application of mechanical stress such as friction, deformation and impact. At present, widely known EML materials are: X or -irradiated alkali halide crystals: ZnS: Mn, SrAl2O4: Eu, SrAl2O4: Ce, SrMgAl6O11: Eu, SrCaMgSi2O7: Eu, SrBaMgSi2O7: Eu, Sr2MgSi2O7: Eu, Ca2MgSi2O7: Eu, Dy, Ca2Al2SiO7: Ce, ZrO2: Ti, CaZnOS:Mn, LiNbO3:Pr and ZnS: Mn, Te. The EML materials can help in developing new generation optical sensors for recording defects and damages inside the sample, and for developing a safety monitoring network system.
The ML materials which emit intense light when fractured can be designed as real-time optical damage sensor. In a defense system, army uses many powerful, sensitive, accurate, defect free weapons like tanks, missiles, canons, etc. During the application of any of these, a crack (defect) in the system can cause deep trouble to the user resulting in even their failure. The ML diagnosis technique can provide information on the location of deformation and dangerous points and the level of threat. Secondly, invisible cracks and defects existing at the backside and inner side of a weapon can be visualized with the responding ML intensity (luminance) reflecting the degree of defect. This feature is useful for the monitoring of canons, where most defects tend to be located at the invisible inner side, or the monitoring of the dangerous prospect of micro-cracks generated on the inside of a structure. |