Experimental study on modified specific energy, temperature field and mechanical properties of Xuzhou limestone irradiated by fiber laser

This paper reports the experimental investigation of the modified specific energy, mechanical properties and temperature field of limestone rock that was irradiated by continuous wave fiber laser at different irradiation powers. Results show that the specific energy decreases nonlinearly from 17 kJ/cm3 to 11 kJ/cm3 and rate of perforation increases from 0.2 mm/s to 0.65 mm/s with laser power increasing from 600 W to 1000 W. The modified specific energy which is used to evaluate rock excavation efficiency is observed to decrease monotonously from 0.27 kJ/cm3 to 0.068 kJ/cm3 with increasing laser power. Higher laser power results in larger surface temperature and temperature gradient. The rate of rock surface temperature irradiated by laser with power of 1000 W reaches 14 °C/ms within 140 ms. The temperature gradient, with largest value of 1400 °C/mm near to the sample axis, decreases sharply with radius. The high solution 3D X-ray microanalyser (XRM) images show that the rock perforation is a V-shaped hole and obvious cracks penetrate the whole rock sample. The extremely rough surface and well-developed cracks for irradiated samples are observed through scanning electron microscope (SEM). X-ray diffraction (XRD) results also show that the main minerals of rock after irradiation are quite different from that of original sample. The maximum reduction rate of compressive strength of irradiated rock with laser power of 1000 W is 60%, and the maximum increasing rate of peak strain of irradiated rock with laser power of 800 W is 65%.