Study on the Mechanism of Dynamic Size Effect on the Strength of Sandstone

Experimental studies show that the dynamic size effect is opposite to the static size effect of rock strength, but the intrinsic micro-dynamic mechanism of the dynamic size effect of rocks has not been clarified yet. In this paper, sandstone sample is selected as the research object, and based on the wing-crack model of rock, the crack motion equation and loading equation of sample are jointly calculated, the mechanism of rock specimen size on strength under dynamic loading, namely the dynamic size effect of rock strength is analyzed. The results show that: Under the same dynamic loading rate, with the larger the specimen size, more time is required for crack coalescence, and the applied stress at the moment of the specimen failure (dynamic strength) is greater, the dynamic size effect is more evident, and the rock dynamic strength increases with strain rate approximately in a power law; The critical strain rate range at a definite size range of specimen of rock is obtained by numerical calculation, and the static size effect takes the dominant position when the strain rate is below the critical strain rate, while the dynamic size effect dominates when the strain rate is above the critical strain rate, and the critical strain rate decreases with the increase of specimen size; The critical size of the specimen decreases with the increase of the strain rate.