Static and Cyclic Fatigue Characteristics of Glass, Glass Ceramics and Silicon Nitride under Tensile and Tension-Compression Tests

Abstract

Static and cyclic fatigue tests were made under static tensile loading and tension-compression cyclic loading at the stress ratios of R=0 and -1 on silicon nitride-A, -B, glass ceramics and borosilicate glass. In these tests a specially designed apparatus was used. This apparatus was equipped with the device to minimize the load eccentricity, and it worked satisfactorily in performing cyclic tension-compression tests at any arbitrary stress ratio as well as static tensile tests. Crack growth tests were also made in order to obtain the crack growth rate, da/dt, as a function of stress intensity factor, K, in slow crack growth.
The effects of cyclic stress on fatigue strength were investigated. Almost no effect of cyclic loading was observed on silicon nitride-A and borosilicate glass, while appreciable degradation in strength due to cyclic loading was observed on silicon nitride-B and glass ceramics. In static fatigue tests on smooth round bar tensile specimens, borosilicate glass showed the same fracture stress in air and in water, while, according to the results by crack growth tests, the da/dt in water showed appreciably higher values than that in air. K-V characteristics obtained from static fatigue tests (σ=const.) and constant stress rate tests (σ=const.) on round bar tensile specimens showed much larger values of da/dt than the values obtained from the tests n large cracks mentioned above. These results indicate that the crack growth characteristics of small cracks originated in smooth specimens are different from those obtained from crack growth tests on large cracks.