Strain-rate effect on mechanical properties of rock-like specimens with narrow crack under uniaxial compression

Uniaxial compression tests were carried out on rock-like specimens containing prefabricated narrow crack under various strain rates. Experimental observations and numerical results show that narrow crack will close or partially close or expand under low compressive stress. Due to the unidirectional loading of loading device, the deformation degree of crack tip near the loading end was different with that of crack tip near the bearing end. With the increase of strain rate, the cracking modes can be divided into 3 categories, near vertical splitting failure affected by horizontal crack (alpha = 0(degrees)), anti-N-wing crack (15 degrees <=alpha <= 60(degrees)) and wing crack (60 degrees<alpha <= 90(degrees)). Both of the initiation angle theta 1 of crack tip near the loading end and theta 2 of crack tip near the bearing end decreased with the increase of alpha and strain rate. Specially, when alpha = 90 degrees, both theta 1 and theta 2 rose with the increase of strain rate. Moreover, the value of theta 2 was greater than that of theta 1 under the same alpha value because of the different deformation characteristics at two tips. Besides, the mechanical properties of fissured rock including peak compressive stress, residual compressive stress, strain at peak stress, elastic modulus and post-peak softening modulus were significantly influenced by the strain rate and inclination angles.