Evaluation method of loading condition based on the time response of Mechanoluminescence

Abstract

Mechanoluminescence (ML) intensity is proportional to magnitude of load and loading rate in elastic region. However, ML intensity is affected by initial excitation level, concentration of ML materials and so on, resulting in difficulties to evaluate the stress quantitatively. Controlling the initial conditions for the quantitative measurement requires a long stand-by time. In this study, we evaluated relations between increasing/decreasing stress and the response characteristics of ML. The transient ML intensity was measured by a photomultiplier tube. The rise time of ML, τup, and decay time, τdown, were proportional to maximum load and inversely proportional to loading rate. Furthermore, τup and τdown were not affected by initial excitation level, concentration of ML materials. Investigating responses to the cyclic load, τ was not affected by cycle stress. In order to confirm whether external force affects the value of τ, same loading time and various magnitude of external force were added to the sample and calculated τ. Results show τup was affected only by loading time. On the other hand, τdown was affected by loading time and rate of time variation of strain energy. Appling to two-dimensional measurement, qualitatively correct results were obtained in each area. The above results indicate τ would be a useful parameter to visualize stress field in elastic body arbitrary and sequentially.