WS7a2 - STATIC AND CYCLIC FATIGUE OF SMOOTH TENSILE SPECIMENS AND CRACK GROWTH IN GLASS AND SILICON NITRIDE

Abstract

Static and cyclic fatigue tests were made on glass and silicon nitride under static tensile loading and tension-compression cyclic loading at the stress ratios between R = -1 and 1, by using an apparatus specially designed with a device to minimize the load eccentricity. Crack growth tests were also made under static loading and cyclic loading in order to obtain the crack growth rate da/dt, as a function of stress intensity factor K. Test results on smooth round bar specimens show that almost no effects of stress cycling were seen on silicon nitride A and borosilicate glass, while appreciable degradation in strength due to cyclic loading was observed on silicon nitride B. The relation, da/dt versus K, of small cracks obtained from the tensile test on smooth round bar specimens showed much higher values than those of large cracks obtained from the crack growth tests. The increase in crack growth rate due to cyclic stress was observed in both silicon nitride B and A, in the latter of which no effects of stress cycling were observed in the tests on smooth round bar specimens.