Investigation on the rock temperature in fiber laser perforating

The characteristics of rock temperature in laser perforating influence the rock breaking efficiency and energy consumption. We report a series of fiber laser perforating experiments on granite, sandstone and basalt to systematically examine temperature variation and correlate these with laser irradiation parameters and rock property. It is found that the rise of rock temperature in laser perforating area could be divided into steep rise, gentle rise and balanced stages. Rock temperature increases linearly in steep rise stage. The rate of temperature rise increases with the laser power, and the temperature rises faster when the rock has higher thermal conductivity in steep rise stage. The temperature limit of the steep rise stage (T₀) is the critical point of rock melting. The rock temperature turns into the gentle rise stage when the rock starts melting. The duration of gentle rise stage would be prolonged if the rock has more refractory phases (quartz), and the temperature rate of gentle rise stage falls more sharply under higher laser power. The rock temperature in the perforating area will remain stable when the rock melts completely. The balanced temperature (T_b) increases with the laser power, and it will be higher when the rock has more refractory phases (quartz). T_b is the sign of complete melting of the perforating rock. Importantly, the phase transition of the rock is the main reason for the inhomogeneous-step rise of temperature in laser perforating, the irradiation power and rock composition are the key influencing factors of the rock temperature profiles.