Recent Progress of Experimental and Measuring Technology. Inelastic Stress-Strain Response in Silicon Nitride Ceramics at Elevated Temperatures.

Abstract

The closed loop type push-pull fatigue test system available at ultra-high temperatures was developed, where special attention was given to the extensometer. Then the tensile stress-strain response, tensile creep behavior and cyclic stress-strain response were investigated for sintered silicon nitride ceramics at elevated temperatures. The great amount of inelastic strain, which is greatly dependent on stress rate, was produced under tensile and cyclic push-pull loadings in this material at 1 300°C. Moreover, the gradual increase in resistance to cyclic deformation was revealed during cyclic loading at 1 300°C. It was found that inelastic strain is easier to generate under tensile loading than under compressive one in cyclic loading test ; the stress-inelastic strain hysteresis loop was characterized by the fatter shape on the tensile stress side than on the compressive stress side. Furthermore, existence of transient creep stage was clearly exhibited in the creep curves obtained from tensile creep test in Si3N4 ceramics at 1 300°C.