Fatigue crack growth behavior of silicon nitride under repeated two-step loadings
Koyama Atsuhiro; Sugeta Atsushi; Uematsu Yoshihiko; Jono Masahiro
Abstract:In order to investigate the cyclic fatigue crack growth behavior of a gas-pressure-sintered silicon nitride under repeated two-step loadings, fatigue crack growth tests were carried out using compact type (CT) specimens. Crack length and macroscopic crack closure were measured using the unloading elastic compliance method. Regardless of repeated two-step loading patterns, the acceleration of fatigue crack growth rate was observed. High-level load execution was found to crash grain interlocking more severely and result in decrease of crack opening stress intensity factor, Kop, under low-level loadings. The fatigue crack growth acceleration behavior under repeated two-step loadings, where maximm load was kept constant, could be explained by crack closure behavior measured by the macroscopic method. However, under repeated two-step loadings where minimm load was kept constant, macroscopic crack closure behavior could account for the acceleration behavior qualitatively but not quantitatively. Key Words:fatigue crack growth, clack closure behavior, unloading elastic compliance method, gas-pressured-sintered silicon nitride, repeated two-step loading, linear accumulation law