抄録
A new experimental system was developed to record the optical microscopic image of slow crack growth in ceramics together with the applied stress value. The bending stress was applied to pressurelesssintered alumina with Vickers indentation cracks, and the slow crack growth behavior was observed with this new system. The relation between the applied stress intensity factor Kapp and P/c3/2 (P=the indentation load, c=the half crack length) becomes linear with the crack extension. From the linear relation, the fracture toughness K∞ for long cracks and a χ parameter in equation Kres=χ·P/c3/2 (Kres=the stress intensity factor due to indentation residual stress) were obtained. The increasing R-curve for small cracks was determined by using the above determined χ parameter. The resistance became constant as the crack extension was longer than 0.15mm, and this constant value was identical to the fracture toughness determined by using a single-edge-precracked beam.
