Abstract
The impact loading of a notched semi-circular bend (NSCB) specimen of outcrop shale in Changning Sichuan was carried out using a split Hopkinson pressure bar (SHPB) to study the effect of shale bedding on the dynamic crack initiation toughness. Three loading configurations were tested: Crack-divider, Crack-splitter and Crack-arrester loading. Bedding plane has a significant effect on the crack initiation of shale. Under the Crack-divider and Crack-splitter modes, shale had lower dynamic crack initiation toughness. The dynamic crack initiation toughness of the shale was affected by the loading rate for all three loading configurations. The correlation between loading rate and dynamic crack initiation toughness was most significant for the Crack-arrester mode, while the Crack-splitter mode was the weakest. When loading was carried out on Crack-arrester, the bedding plane could change the direction of crack growth. In the Crack-splitter mode, only a small impact energy was needed to achieve effective expansion of a crack. The research results provide a theoretical basis for shale cracking.
Highlights
China’s shale gas resource reserves are huge
The loading rate depends on the impact velocity of the split Hopkinson pressure bar (SHPB) bullet
We studied the influence of bedding plane on dynamic crack initiation toughness of shale
Summary
China has begun commercial development of shale gas, it is still in its infancy and there are many technical difficulties. Shale exhibits bedding characteristics in its structure, which leads to anisotropy in the vertical bedding direction and isotropy in the parallel bedding direction, so shale can be regarded as a transversely isotropic material [1]. Many scholars have studied the physico-mechanical properties of shale and rock with bedding structures. Zhao [2] reported anisotropy of the strength of argillaceous siltstone along the angle between the bedding plane and the principal stress axis. The strength was lowest when the principal stress axis and the weak surface were at an angle of 30◦. Mao et al [3] analyzed the influence of the orientation of slate bedding on development of its compressive strength and failure mechanism. Gao et al [4]
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