The mechanical properties of WC-Co cemented carbides were investigated in order to find the way to lengthen the lives of the bits including WC-Co cemented carbides, installed in tunnel boring machines. The compression and bending tests were first carried out using the test pieces made of the WC-Co cemented carbides including Co of 10%, of which grain size was 3, 6, 20 or 30 [μm], and the ones of which grain size was 20 [μm], including Co of 5, 10, 15 or 20%. The finite-element analysis was performed to find the tensile strength using the results of the compression and bending tests. We were able to draw an interesting results as follows : WC-Co cemented carbides of which grain size is 20 or 30 [μm] has the property of ductility, while the ones of which grain size is 3 or 6 [μm] has the property of brittleness.
