Micro crack propagation in shale

Three representative test areas, which are dominated by a stiff mineral, a blob of organic matter and clay layers, respectively, are selected in a terrestrial shale sample from Yanchang Formation. Micro cantilever beams are manufactured using micro fabrication method in each test area, and in situ fracture experiments are performed to investigate the crack propagation under a scanning electron microscope. The crack propagation process is characterized at micrometer scale. The crack paths and the load-displacement curves are presented side by side. Through the analysis of the test results, various fracture mechanisms are summarized. Crack defection and crack branching owing to mechanical contrast, toughening in organic matter, and crack bridging of clay layers together influence crack propagation in shale