圧こん予き裂からのき裂進展によるアルミナのR曲線挙動(<特集>X線材料強度)

概要

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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 pressureless-sintered 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 K_<app> and P/c^<3/2>(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 K_<res>=χ・P/c^<3/2>(K_<res>=the stress intensity factor due to indentation residual stress)were obtained. The incrreasing 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 0.15 mm, and this constant value was identical to the fracture toughness determined by using a single-edge-precracked beam.
1995-09-15