Development of Laser Induced Particle Impact Test (LIPIT) as High-Speed Micro Impact Testing

Abstract

Abstract 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 the nanostructure is demanded. This study aims to develop ultrahigh velocity impact testing using microparticle projectile, resulting in generation of impact indentation crater. Due to extreme severe plastic deformation with high strain rate, grain refinement is expected. Regarding the impact test, this study developed Laser Induced Particle Impact Test (LIPIT), in which laser ablation induces supersonic ejection of microparticle, resulting in generation of impact crater. We first proposed a measurement method of particle projectile velocity using mechanoluminescence (ML). A particle collision against the ML emits light due to mechanical stimulus. The light is detected to determine the timing of particle arrival, so that the particle projectile velocity is obtained. This measurement method was verified using a high-speed video camera. Next, LIPIT was applied to a pure copper (Cu), and it is found that nano structure including twinning was developed around the impact indentation crater. The developed microstructure was compared with the crater obtained by quasi-static indentation to investigate strain rate effect on the microstructure. This indicated that plastic deformation due to LIPIT improves the mechanical property owing to extreme plastic strain and strain rate. Therefore, our developed LIPIT may realize a new surface modification technique in order to induce severe plastic deformation with ultrahigh strain rates, resulting in grain refinement.