Three-point Bending Fatigue Tests Research Articles

Size Effect on Fatigue Behavior in Structural Ceramics

Three-point bending, 4-point bending and tensile fatigue tests were carried out on sintered silicon nitride at room temperature and 1000°C, and size effect on the fatigue behavior was discussed. The difference in room temperature fatigue behavior estimated by different testing methods was explained by effective volume of the surface layer with a depth of 100μm. At high temperature, the difference was explained substantially by the effective volume of the whole specimen, but, the tensile fatigue data did not agree with the bending one in a low stress region in spite of the data correction by effective volume. The different cavitation effects on crack growth properties under bending and tensile loading conditions were considered to be responsible for the disagreement.

Three-point bending strength and cyclic bending fatigue strength of hot-pressed silicon nitride containing a small crack.

Three-point bending and cyclic bending fatigue tests were conducted on two kinds of hot-pressed silicon nitride. To examine the relationship between the defect size 2c and the static and fatigue strength σF, σw respectively a semicircular crack with a radius of 70μm to 310μm long was introduced on each specimen surface with the aid of a Knoop indentation. The result shows that up to a critical value of 2cc, both σF and σw were insensitive to 2c. For 2c > 2cc, both σF and σw decreased with increasing 2c. Both materials had almost the same value of 2cc. The fatigue strength of the materials with a small crack was found to be about 40% of the static bending strength.