Cyclic Crack Growth Behavior and Dynamic Thermal Stresses of SiIicon Nitride under Repeated Thermal Shock Tests

摘要

Dynamic thermal stresses and cyclic crack growth behavior produced by a single and repeated thermal shocks were studied on silicon nitride. Thermal shock was applied to a square shaped bar specimen using the improved water--quenching method. It was clarified that the cyclic crack growth rates, da/dN, under the repeated thermal shock tests are represented by the following expression, da/dN=9.35 × 10~(-6)(K_max—1.36)~3.14. In addition, the experimentally observed maximum thermal stresses, σ_max, for silicon nitride in the present study as well as those for cemented carbides and cermets in the previous report can be approximated by the expression, the, σ _max=0.704αEΔT -57.74, where α, E, ΔT denote a linear coefficient of expansion, Young's modulus of the materials and applied temperature differences at thermal shocks, respectively. By using this expression we can directly evaluate the maximum thermal stresses induced by the thermal shocks without temperature measurements.