Experimental Study Of Rock Mechanical Properties And Damage Model Under Cyclical Dynamic Loads

To provide theoretical and technological support for the understanding of rock mechanical properties under dynamic loads and the long-term stability evaluation of engineering rock mass, in this paper the dynamic experiments were carried out with single-pass and cyclical impact loads by using an innovative testing system. The dynamic mechanical properties of rock under different loads were studied. A statistical damage constitutive model for the rock under dynamic loads was developed. The evolution law of the damage degree of specimens were analyzed with the stress-strain curves. The main contents and conclusion are as follows:(1) The innovative SHPB testing system and the experiment principle were introduced. The main experimental technique was analyzed. The length of specimens was calculated by using a look-up table to avoid the randomness and blindness in the choice of the specimen size.(2) The experiments under uniaxial compression static loads and impact compression loads were carried out by using the material testing machines (Instron1346and RMT-150C) and a modified SHPB system. The rock mechanical characters were analyzed, such as the characters of compressive strength and deformation, the transfer law of the energy and the failure mode of specimens. The results show that the dynamic compressive strength are strain rate dependent. The relationship between dynamic compressive strength and average strain rate is approximately exponential function. The modulus of deformation is independent of the strain rate. For the specific energy absorption, the strain rate effect can be expressed by linear approximation. And there is a critical strain rate when the rock specimens absorb energy from the incident shock wave. The specimens mainly show compression-shear failure form in the uniaxial compression experiment under static loads but tensile failure form in the dynamic compression experiment.(3) The dynamic experiments under different cyclical impact loads were carried out. And the experimental results show that the original Young’s modulus of the stress-strain curves are equal. Along with the increase of circular action times of impacts, the modulus of deformation decreases, the accumulation strain increase and the yield stress shows decreasing trend. The impact strength of rock specimens increases because of the axial static loads.(4) The statistical damage constitutive model for rock was established which was based on Weibull random distribution. The way of calculating the model parameters was determined. The model curves are in accord with the actual curves, which shows the rationality of the model. It is found that the damage degree increases along with the increasing strain. At the peak of the stress-strain curve, the damage degree has an obvious inflection point. The maximum of the damage degree actually shows the deformation capacity of the specific material under the different loads, which is concerned with the maximum of the strain.The cumulative damage degree increases with the increasing of the impact times and the cumulative specific energy absorption. And the curves show roughly the same trend.