Crack propagation measurement in brittle materials like rocks are vital important in geophysics and geoengineering application. Here, the optical full-field measurement of digital image correlation (DIC) combined with ultra-high speed photography was adopted to investigate the dynamic fracture behavior of rocks plate loaded by a split Hopkinson pressure bar apparatus. The fracture behavior under different loading speed without and with different confinement stress before dynamic loading were first studied. The crack initiation, crack propagation and crack arrest were clearly recorded using ultra-high speed photography, and the deformation fields of the plate specimen during dynamic loading process were obtained using DIC method. The crack propagation velocity and fracture toughness were obtained combined the deformation field with fracture mechanics analysis. Results show that the crack propagation velocity and fracture toughness increase with incident velocity. Crack propagation velocity of plate specimen is higher than that in small specimen such as notched semi circular bending specimen. Crack propagation velocity and crack arrest length decrease with increase the confinement pressure that before dynamic loading. There are many micro cracks near the crack path and the crack tip. Therefore DIC method combined with ultra-high speed photography could be used to study the dynamic rock fracture under confinement stress, which provides a new method for high speed failure investigation that concerned in earthquake.
Dynamic fracture of rock materials play a very important role in engineering application. Lots of work are focused on fracture initiation toughness (Shiryaev and Kotkis 1983, Guo et al. 1993, Kuruppu 1997, Zhou et al. 2012), especially in static cases where some standard tests have been proposed (Ouchterlony 1989, Fowell et al. 1995, ISRM 2007). However, researches on the crack propagation of rock under dynamic loading have rarely been reported.