Three‐point impact bending tests, using the split Hopkinson pressure bar method, were performed to evaluate the fracture resistance of monolithic silicon nitride (SN) and carbon‐fiber‐reinforced silicon nitride (CFRSN) ceramics. By applying ramped incident‐stress waves in the split Hopkinson pressure bar apparatus, relatively smooth stress‐time curves could be recorded without using any artificial filtering process. The maximum load in the load‐deflection curve of the CFRSN material increased, in comparison to its static value, when impact testing was applied. Such behavior was substantially different from that of the monolithic SN material, for which the maximum load values from impact and static testing were almost the same. The time dependence of strength in the CFRSN ceramic was then investigated by using relaxation tests, and the impact strength behavior could be explained by these results. Also, the shear strength was significantly dependent on the deformation rate, whereas the tensile strength was almost independent of it. The experimental results were compared with the numerical predictions of the stress distribution that were obtained by using finite‐element analysis.
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OGAWA et al. (1998) studied this question.