Investigation of Coal Failure Characters Based on Jet Energy and Impact Frequency During Particle Jets Coal Breaking

During mining and underground excavation, when particle jets assist in coal rock breaking, the impact frequency and energy of the particle jets can significantly affect the strain and strain rate of the coal rock, which determines the fragmentation of the coal rock. However, studies on the particle jets impact frequency and the evolution development of coal rock strain and strain rate under dynamic impacts are limited. Therefore, the impact frequency of particle jets was measured using a vibration sensor, and then E (the ratio of particle jet energy to impact frequency) was calculated. Based on E, the strain field of coal was measured through the digital image correlation (DIC) experiments. The strain rate was then calculated, and the failure characteristics of coal were analyzed. The main conclusions are as follows. The impact frequency increases as jet pressure, but the rang of frequency is concentrated in 500-1500 Hz. The E increases as jet pressure, but the uptrend slows down. The E increases and then decreases as the particle mass flow rate increases. As impacting time increases, the strain field can be divided into the stages of erosion pit formation, stress wave propagation, and strain accumulation. The transition time for each phase shortens with increasing E. The strain rate can be divided into slowly increasing, stable and rapidly decaying as impacting time increases, and the strain rate values decreases along the direction of the jet axis. As the E increases, the strain ratio increases, but the trend is similar under different E. The failure characteristics of coal are determined by the local strain and strain rate. When the local elastic potential energy exceeds the limit of the potential energy under this strain rate, local failure occurs.

Automated summary

This study measured the impact frequency of particle jets using a vibration sensor and calculated the ratio of particle jet energy to impact frequency (E). Based on E, the strain field of coal was measured using digital image correlation experiments. The strain rate was then calculated, and the failure characteristics of coal were analyzed.