高温繰り返し応力下における窒化ケイ素セラミックスのR曲線挙動

概要

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Static fatigue, cyclic fatigue and constant stress rate tests were carried out at 1200℃ in nitrogen at mosphere for toughened silicon nitride exhibiting a sig nificant rising R-curve. The R-curves both in static and cyclic loading conditions were determined with meas uring crack advance and fracture strength, in order to evaluate cyclic loading effects. The KR value under a static loading condition increases as a crack advances and it reaches 12.5MPa-m^<1/2> at the crack advance greater than 1.5 mm. On the contrary, the K_R value un der cyclic loads increases with advancing a crack and it reaches 9.5 MPa m^<1/2> when the crack advances greater than 1.2 mm. This different R curve behavior suggests that bridging grains responsible for the toughening are damaged with the cyclic loads, resulting in a decrease in the maximum K_R value. Applying a Dug dale model to the bridging stress analysis, the bridging stresses under static and cyclic loading conditions were determined 100 MPa and 65 MPa, respectively.
社団法人日本セラミックス協会の論文
1994-04-01