Mechanical anisotropy of coal under coupled biaxial static and dynamic loads

Studies have been carried out of the influence of strain rate and bedding angle on dynamic coal failure. Coupled biaxial static and dynamic tests were conducted on coal specimens with bedding orientations of 0, 30, 45, 60, and 90 degrees with respect to the direction of loading. Mechanical behaviour, including stress-strain curves and peak stresses, were analysed under a series of impact velocities. Real-time coal fracturing was recorded by two high-speed cameras, and full-field deformation and ejection velocities were identified by 3-D digital image correlation. Results showed that at similar strain rates, the peak stress against bedding orientation shows a “U” shape with the lowest value at an orientation of 60 degrees. The peak stress increased with increasing impact velocity. Coal ejection velocities were positively rate-dependent, with the highest ejection velocity between bedding orientations 45 to 90 degrees increasing with increasing impact velocity. The average fragment size of coal specimens was negatively related to impact velocities and energy absorption, with the smallest fragments at bedding orientation around 45 degrees. It is concluded that dynamic behaviour of coal under biaxial pre-stresses are dependent on bedding structures and strain rates, with the bedding effect becoming weaker as strain rate increases.
Studies have been carried out of the influence of strain rate and bedding angle on dynamic coal failure. Coupled biaxial static and dynamic tests were conducted on coal specimens with bedding orientations of 0, 30, 45, 60, and 90 degrees with respect to the direction of loading. Mechanical behaviour, including stress-strain curves and peak stresses, were analysed under a series of impact velocities. Real-time coal fracturing was recorded by two high-speed cameras, and full-field deformation and ejection velocities were identified by 3-D digital image correlation. Results showed that at similar strain rates, the peak stress against bedding orientation shows a “U” shape with the lowest value at an orientation of 60 degrees. The peak stress increased with increasing impact velocity. Coal ejection velocities were positively rate-dependent, with the highest ejection velocity between bedding orientations 45 to 90 degrees increasing with increasing impact velocity. The average fragment size of coal specimens was negatively related to impact velocities and energy absorption, with the smallest fragments at bedding orientation around 45 degrees. It is concluded that dynamic behaviour of coal under biaxial pre-stresses are dependent on bedding structures and strain rates, with the bedding effect becoming weaker as strain rate increases.