Double torsion testing a 3Y-TZP ceramic

Double torsion tests were performed to study subcritical crack growth of a 3Y-TZP ceramic. A significant variation of stress intensity factor K-I, with crack length was observed. In order to take into account this variation a correction factor is introduced into the well-known analytical expression of stress intensity factor in mode I. This has enabled us to obtain accurate crack growth parameters i.e. an accurate measurement of (i) the three propagation stages of the subcritical crack growth and (ii) a threshold value equal to k(IO) = 3.5 MPa root m. Analytical expression of K-I based on a compliance analysis was shown to be unsatisfactory for slow crack growth analysis because of the influence of the unbroken ligament on the compressive side arising from the curved crack front.