In Situ Scanning Electron Microscope (SEM) Observations of Damage and Crack Growth of Shale.

摘要: To better understand the formation and evolution of hierarchical crack networks in shales, observations microscopic damage, growth were conducted using an situ tensile apparatus inside a scanning electron microscope. An arched specimen with artificial notch incised into curved edge was shown to afford effective observation damage process that occurs during brittle fracturing shale. Because this design can induce squeezing effect, reducing stress concentration at tip, preventing shale from unstable some extent. Both induced natural pores cracks observed different scales around main path or on fractured surfaces. Observations indicate initiation zone develops tip where stresses are concentrated micro/nanoscale nucleate. Crack advancement generally by continuous generation coalescence zones having intermittent en echelon located ahead tips. Mineral anisotropy pressure build-up tips causes kinking, deflection, branching. is often accompanied cessation closure former branch due elastic recovery compressive stress. The branching interactions form three-dimensional network includes similar paths, as well structures such nanopores, bedding planes, cracks.