高温合金的裂纹扩展与强韧化

用直接流位法研究了高温合金涡轮材料的裂纹扩展速率，结果表明，高温合金涡轮盘材料的裂纹扩展速率快不完全取决于材料强度，更主要地取决于持久塑性，在考察高温合金涡轮盘材料的裂纹扩展时，不能仅以速率ｄａ／ｄｔ的绝对值来衡量，还应看裂纹扩展速率曲线的斜率是否锐减或曲线出现明显的拐点，以及曲线所对应的应力强度因子△Ｋ的范围。     

Fatigue-Crack Propagation in Heat-Resistant Alloys under Thermomechanical Loading. Part 2. A Method of Accounting for the Influence of Thermomechanical Loading on the Material Resistance to Fatigue-Crack Growth

A method is proposed for a comprehensive consideration of the influence of thermomechanical-loading components on the variation of the fatigue-crack propagation rate. The method takes into account the variability of the values of the calculated stress intensity factors over the crack front and with the time of a thermal cycle. Experimental results obtained for alloys KhN70VMTYu (Eacute;I617) and KhN73MBTYu (Eacute;I698) are described. For two regimes of thermal cycling, near-threshold and medium sections of kinetic diagrams of fracture of these alloys are constructed.     

Microscopic and Macroscopic Growth Rates of Fatigue Cracks in Steels and Alloys under the Influence of Crack Closure

On the basis of the experimental data, we show that the difference between the macroscopic and microscopic fatigue crack growth rates in the second section of the kinetic diagram of fatigue fracture is caused by the effect of crack closure within the limits of its existence. We establish the relationships between the macroscopic and microscopic fatigue crack growth rates and the structure of the material in the second section of the diagram for various values of the load ratio with regard for the effect of crack closure and propose a procedure of examination of the fracture processes in structural materials based on the analysis of microscopic and macroscopic fatigue crack growth rates.