Development of mechanoluminescence technique for impact studies

A new technique called, mechanoluminescence technique, is developed for measuring the parameters of impact. This technique is based on the phenomenon of mechanoluminescence (ML), in which light emission takes place during any mechanical action on solids. When a small solid ball makes an impact on the mechanoluminescent thin film coated on a solid, then initially the elastico ML (EML) intensity increases with time, attains a maximum value I-m at a particular time t(m), and later on it decreases with time. The contact time T-c of ball, can be determined from the relation T-c=2t(c), where t(c) is the time at which the EML emission due to compression of the sample becomes negligible. The area from where the EML emission occurs can be taken as the contact area A(c). The maximum compression h is given by h=A(c)/(pi r), where r is the radius of the impacting ball, and thus, h can be determined from the known values of A(c) and r. The maximum force at contact is given by F-m=(2mU(0))/T-c, where m is the mass of the impacting ball and U-0 is the velocity of the ball at impact. The maximum impact stress sigma(m) can be obtained from the relation, sigma(m)=F-m/A(c)=(2mU(0))/(T(c)A(c)). Thus, ML provides a real-time technique for determining the impact parameters such as T-c, A(c), h, F-m and sigma m. Using the ML technique, the impact parameters of the SrAl2O4:Eu film and ZnS:Mn coating are determined. The ML technique can be used to determine the impact parameters in the elastic region and plastic region as well as fracture. ML can also be used to determine the impact parameters for the collision between solid and liquid, if the mechanoluminescent material is coated on the surface of the solid. The measurement of fracto ML in microsecond and nanosecond range may provide a tool for studying the fragmentations in solids by the impact. Using the fast camera the contact area and the depth of compression can be determined for different intervals of time. (C) 2011 Elsevier B.V. All rights reserved.