Size Effect On The Dynamic Mechanical Properties Under Impact Loads Of Rock

In the experimental study of rocks dynamic properties, a fundamental problem is that the results of laboratory tests varies with the size of the rock samples, which diameters not exactly represent the true mechanical properties of rock material. However, few studies have done on the size effect of dynamic mechanical properties of rock. Therefore, on the basis of the previous work, the five specimens with the ratio of length to diameter of 0.4,0.5,0.6,0.8 and 1 respectively were designed for dynamic experiments by the SHPB system. Stress-Strain curves of the rock specimen in different ratios of length to diameter were analyzed and the relationship among the ratio of length to diameter and dynamic strength of rock specimens, deformation modulus, failure mode, energy law and the fractal dimension were studied. Main contents and conclusions are as follows:(1) On the basis of the data and curve in the tests, the mechanical properties of rock samples with different ratio of length to diameter have been analyzed and the deformation characteristics of in the rock samples have been discussed.(2) The dynamic strength of rock specimen increases with the increasing ratio of the length to diameter, which has a opposite results of the size effect of rock static strength. Moreover, there is a critical value in the sample ratio of length to diameter which affect the rock strength.(3) The variation law among incident energy, rock energy absorption and the energy density of the broken rock with different ratio of length to diameter were studied. By examining the relationship between the ratio, energy consumption density and incident energy, the reasonable length to diameter ratio range of sandstone sample for the SHPB specimen was obtained.(4) Classification and fractal characteristics of the experiment rock fragmentation were analyzed. To analyze the statistics of fragmentation of rock samples under load, the size distribution of broken rock under the load condition can be obtained. On this basis, by using the theoretical formula, the corresponding fractal dimension was obtained. Influence of that the different ratio of length to diameter on the fractal dimension were discussed.