Creep crack growth in shale

This paper describes an attempt to use fracture mechanics concepts to the problems associated with creep crack growth in shale. Chevron-notched Brazilian disk (CDISK) specimens were used in this investigation. Before the creep tests, the samples were loaded until failure in order to determine the fracture toughness. This critical value was then used as an index for creep-induced rupture. The crack mouth opening displacement (CMOD) was used to calculate the crack length and the stress intensity factor. Unlike load-point displacement (LPD), CMOD varied significantly when the creep test reached the rupture stage. At the same time, the stress intensity factor reached its critical value, indicating that the fracture toughness can be used as a failure criterion in short-term creep fracture tests.