Research on Fatigue Crack Arrest Assessment Criteria under Cyclic Thermal Stresses

点击翻译按钮获取中文摘要

This year, we made both analytical and experimental approach to the subject. First, we made a study of the crack arrest depth under cyclic thermal shock for an inner-surface circumferential crack in a finite-length thick-walled (R_m/W =1) cylinder with rotation-restrained edges. The inside of the cylinder is cooled from a uniform temperature distribution. The effects of heat transfer conditions on the maximum transient SIF for the problem were investigated with formerly developed systematical evaluation methods. Then, a tentative value of the threshold stress intensity range ΔK_<th> was assumed together with the Paris law and the evaluation of the crack arrest length under cyclic thermal stress was carried out. The results suggest the existence of an upper limit for the normalized crack growth depth, independent of the cylinder material. And the dominating parameters for this were concluded as the structural ones.Finally, crack propagation tests under equivalent thermal shock loads were conducted to confirm the validity of the criterion ΔK_<max> 【less than or equal】 ΔK_<th> for fatigue crack arrest. The result obtained was that the threshold stress intensity range corresponding to a thermal shock equivalent load was approximately equal to the intrinsic ΔK_<th>. The validity of applying ΔK_<max> 【less than or equal】 ΔK_<th> for crack arrest analysis under cyclic thermal shock was confirmed.