Abstract
The Punch-Through Shear (PTS) test was introduced as a method to determine the ModeII fracture toughness of rock material (Backers et al., 2002). Its unique feature is the ability to apply a confining pressure independent of the Mode II (shear) loading. This contribution reports new data on Mode II fracture toughness', KIIC, dependency on confining pressure, loading rate, sample size, and cyclic loading for six different rocktypes. Samples are subjected to different confining pressures up to 70 MPa. KIICincreases with increasing confining pressure and tends to reach a constant value at confining pressures higher than 20-35 MPa. Evidence for 'pure' Mode II fracturetoughness at high confining pressures is reported. Variation of loading rate over five orders of magnitude (10-8 - 10-3 m/s) does not change KIIC. The influence of sample size on coarser grained rocks is verified. Cyclic loading illustrates change of stiffness of the system as fracture propagation takes place. It is concluded that the PTS- test is a suitable future method for KIICtermination.
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