Effect of Stress Cycling on Fatigue Behavior of Mica Glass Ceramics and Alumina

In order to investigate the effect of cyclic stress on fatigue behavior of mica glass ceramics and alumina, the specimens with an indentation induced flaw were tested under static tensile loading and cycling loading at stress ratio R=0 and -1. The frequencies in the cyclic loading tests were 5 and 20 Hz respectively. The main results were as follows ; (1) A significant decrease in fatigue lifetime by cyclic loading was observed on both materials, though there being large scatters on mica glass ceramics. (2) An appreciable decrease in fatigue lifetime due to the increase of frequency was observed on mica glass ceramics, while a little effect of frequency was observed on alumina. (3) The effect of stress ration under cyclic loading was small on both materials, though a somewhat significant decrease in fatigue lifetime being observed in the case of frequency of 20 Hz on alumina. (4) SEM fractography revealed a dominant interglanular fracture on both materials, but in the case of cyclic fatigue fracture of alumina more comminution was observed than in the case of static fatigue fracture. (5) It was considered that the decrease in fatigue lifetime due to cyclic loading in mica glass ceramics results on the degradation of grain briding effect by the pull-out of mica from glass matrix, while the effect of cyclic stress in alumina results on the degradation of grain bridging effect by comminution and fretting in the grain.