常圧焼結窒化ケイ素の常温における繰返し疲労

概要

論文の詳細を見る
The cyclic fatigue behavior of sintered silicon nitride was inverstigated at room temperature. Flexure specimens, with an indentation induced flaw at the center of the reduced gage section, were tested, where the cyclic load was applied by four-point bending up to frequencies of 10 Hz using an electrohydraulic testing machine. Sintered silicon nitride showed a susceptibility to cyclic fatigue limit was about 70% of the flexural strength. A couple of crack arrest position marks aroud the indentation were detected in the fracture surface of both flexure and fatigue test specimens, and the size of each mark well corresponded with the analytical result based on a contact residual stress. Frquency did not affect the lowest limit of the fatigue lifetime, although a scatter of the data and the highest limit of the lifetime incresed as the frequency was lowed from 10 Hz to 0.01Hz. High magnification fractography revealed an intergranular dominant fatigue failure with partial transgranular fatigue at perpendicularly elonrated ctystals. It suggests that the intergranular fatigue crack can be arrested at grain boundary triplets, and also can be reactivated by subsequent cyclic loadings. Thes crack growth rate calculated from the fatigue lifetime showed a three region characteristics having a plateau at 70 to 90% of the fracture toughness, which suggests the possible intergranular stress corrosion cracking mechanism resembling that in glass or alumina.
1985-12-15