Fracture toughness of coal under quasi-static and impact loading

The fracture toughness of specimens of Canadian coal, expressed as k_q, was determined under both quasi-static and dynamic loading conditions. In all tests, a wedge loaded compact tension (WLCT) specimen was used. The quasi-static tests were carried out in a servohydraulic testing machine while in the dynamic testing, a Split Hopkinson Bar was used. Also studied was the effect of orientation of the crack with respect to the coal seam. Loading rates ranging from 0.1 MPa √m/sec. to 6 × 10⁴ MPa √m/sec. were investigated. The results show a large increase of over one order of magnitude between k_q in the quasi-static and that obtained at high loading rates.