高温部件蠕变-疲劳裂纹扩展行为表征

Characterization of creep-fatigue crack growth bahehavior for high temperature components

能源发展新形势下深度调峰将成为在役和新建火电机组的运行新常态,深度调峰引起的交变热应力和机械应力使得火电机组高温部件承受蠕变和疲劳交互环境作用。蠕变-疲劳裂纹扩展性能主要受保载时间/频率、载荷水平、温度、微观组织、环境(氧化、蒸汽)的影响,其并非单纯的有利或有害于裂纹扩展性能,而是受到其他因素的影响;裂纹扩展机制有穿晶扩展、沿晶扩展和混合扩展,裂纹扩展的变化是蠕变损伤和疲劳损伤相互竞争的结果。蠕变-疲劳下由疲劳导致的裂纹扩展主要由△K来表征;而蠕变裂纹扩展行为主要用△K、C*和(Ct)avg来表征,其中△K更适用于蠕变脆性材料,而C*和(Ct)avg能实现不同保载时间、不同温度和不同合金的蠕变裂纹扩展行为表征.蠕变-疲劳裂纹扩展还会受到蠕变与疲劳之间交互作用的影响,通常是引入裂纹扩展速率加速第三项或者考虑蠕变-疲劳非线性交互损伤来实现蠕变-疲劳交互下寿命的精准预测。

Under the situation of energy development,deeply peak shaving adjusting will become a new normal for the operation of in-service and new construction thermal power units.The alternating thermal stress and mechanical stress caused by deeply peak shaving adjusting make the high temperature components of thermal power units under the interaction of creep and fatigue.The crack growth behavior in the case of creep-fatigue interaction is greatly affected by the hold time/load frequency,load levels,temperature,microstructure and enviorment,however,these factors would be benefical or adverse to the crack growth properties and are influenced by the mutal effects among these factors.The crack growth manner can be divied into transgranular,intergranular and mixed mode.These crack growth modes are dominatd by the competion between creep damage and fatigue damage.In the creep-fatigue,the fatigue crack is determined by△K,and the creep crack is determined by△K,C*and(Ct)avg,where the△K is only suitable for creep brittle material and in contrast the C*and(Ct)avg could well demonstrate the crack growth behaviors of the majority materials.Furthermore,the crack propataion behavior is also influenced by the interaction effect between creep and fatigue.The accerlered crack growth rate led by the creep-fatigue interacion could be represented by third variable or incorpored into the non-linear creep-fatigue damage accumulation models.