Development of Mechanoluminescent (ML) Sensor for Velocity Measurement of Microparticle Collision and Particle Collision Testing

<p>Since grain refinement such as nano twin and nano crystalline in a metallic material is possible to improve the mechanical property, surface modification to generate such nanostructure is demanded. This study aims to develop ultrahigh velocity impact testing using microparticle to vary metallic microstructure due to severe plastic deformation with high strain rate. Regarding an impact test, this study developed Laser Induced Particle Impact Test (LIPIT), in which laser ablation induces supersonic ejection of microparticle. We first proposed a measurement method of particle velocity using mechanoluminescence (ML). It is found that a particle collision with the ML emits light due to mechanical stimulus. The light is detected using the photomultiplier tube (PMT), so that timing of particle arrival is determined, and then the particle impact velocity is estimated. This measurement method was verified using a high-speed video camera. In addition, to investigate the light emission response of ML, mechanical stimulus using pulsed laser irradiation was applied to the ML. It is found that the peak intensity and decay time in the emission response were dependent on the irradiated laser energy. By converting the irradiated laser energy to impact force using elastic plate theory of transverse impact, the relationship between emission response and impact force was discussed. Finally, our developed LIPIT was applied to a pure copper, producing nano crystalline structure on the surface around the impact indentation crater. In contrast, no deformation twinning was observed in the quasi-static indentation crater. Therefore, the developed LIPIT may realize a new surface modification technique, because this induces severe plastic deformation with ultrahigh strain rates, resulting in microstructural changes.</p>