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A new method is proposed to measure initiation and propagation toughness of
Laurentian granite (LG). This method is based on three point bending tests at high
loading rates, performed using a modified Split Hopkinson Pressure Bar (SHPB).
The semi-circular bend (SCB) sample is used in our experiment. In addition, a
laser displacement meter is used to measure the crack surface opening
displacement (CSOD) of the specimen directly. A two-dimensional numerical
simulation is carried out with ANSYS to determine the initiation fracture
toughness with the experimental recorded loading history of the sample. From
CSOD, the residual kinetic energy of the sample can be estimated, together with
the estimation of the total consumed energy with stress waves recorded, the
average propagation fracture energy and the propagation toughness can be
calculated. Three loading rates are achieved in our tests and both the initiation
toughness and propagation toughness are rate depend.