DETERMINATION OF FRACTURE-TOUGHNESS AT HIGH-TEMPERATURES AFTER SUBCRITICAL CRACK EXTENSION

As a consequence of R-curve behavior, ceramic materials may exhibit increased fracture toughness (K(Ic)) following slow crack extension. In this investigation, the effect of crack propagation on fracture toughness is studied in static bending tests. For the calculation of stress intensity factors (K(I)) the stress distribution must be known at the moment of fracture. As a consequence of creep, this stress distribution must deviate from the linear distribution. The corresponding stress intensity factors are computed using the fracture mechanical weight function. Experimental results for fracture toughness are communicated for a 2.5%-MgO-doped hot-pressed Si3N4 at 1300-degrees-C.