Irradiation of granite surface by nanosecond pulsed laser: Optimal softening parameters and properties

Abstract

Irradiating hard rocks by a high-power laser can reduce localized hardness in the rocks; however, continuous lasers produce a large amount of melt that inhibits further heat absorption. Pulsed lasers allow rocks to absorb and dissipate energy and avoid melt formation. In this study, 200 W nanosecond pulsed laser was used to irradiate granite. The effects of laser parameters on the thermal cracking morphology, temperature field, warming pattern, and Leeb hardness of the granite surface were analyzed. The optimal laser parameters for softening granite were determined by performing objective optimization in MATLAB using granite’s melting point as the reference. Nanoindentation techniques were employed to assess the softening characteristics of the granite surface along the longitudinal direction. The results showed that three main forms of thermal damage occurred on the granite surface: oxidative decomposition, spalling, and melting. The damage state was affected by the average laser power, with the pulse width and repetition frequency affecting surface damage differently. Appropriate laser parameters effectively controlled the melt damage on the granite surface, and irradiation with nanosecond pulsed lasers effectively reduced surface hardness. However, excessive power can generate large amounts of hard melts and weaken the softening effect.

Keywords

nanosecond pulsed laser / assisted rock breaking / warming characteristics / Leeb hardness / nanoindentation test / softening characteristics

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Central South University