350 Mechanoluminescent Materials: A New Way to Measure Stress by Light

The monitoring of stress changes in structural components under various kinds of
dynamical loading is crucial for the assessment of their integrity and lifetime. In addition to many
methodologies available, such as strain gauges, optical fiber sensors, X-Ray diffraction and digital
image correlation, we introduce a novel non-contact method to visualize stress distributions based
on mechanoluminescence (ML). ML is a phenomenon occurring in some materials that emit light
upon an applied stress level. In this paper, we develop the ML material (Ca_0.4Sr_0.6)Al₂Si2O8:Eu²⁺,Ho³⁺,
a glow-in-the-dark material, to visualize stress distribution in a disc, as well as the stress field of an
ultrasonic transducer. The properties of defects in the ML phosphors, which are responsible for ML
in this material, are vital for stress visualization.