Fracture tests can be conducted in a closed-loop servo hydraulic 20-kips load frame from MTS systems with the feedback signal taken as the crack mouth opening displacement (CMOD) across the notch at a gauge length of 15 mm. During the loading, the strain gauge based transducer monitors the CMOD and is programmed to increase at a rate of 0.05 μm/s. The applied load is recorded with a load cell with a capacity of 11 kN. The scaling effects of fracture toughness and fracture process zone of rock are investigated by utilizing AE sensors and the displacement which is captured by the digital image correlation (DIC) method.

• Measurements: Crack-mouth opening displacement, point load displacement, accurate (few microns resolution) 2D displacement fields, 3D monitoring of damage points.