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本文在大型熔铸涡轮疲劳蠕变第一类断裂特征图基础上,进一步研究最大应力保载对疲劳蠕变断裂行为影响及在保载条件下的第一类断裂特征图,实验结果表明断裂周次随交变应力与平均应力变化呈现与无保载相同的,“反C”型规律。与无保载相比,保载显著地降低断裂周次,使断裂曲线向低寿命区移动。保载增大蠕变作用,使疲劳机构转变成蠕变机构,扩大蠕变为主的C区,缩小疲劳为主的F区,以至于保载足够长的时间,疲劳机构消失。在断裂机构理论分析与断口观察以及宏观寿命规律基础上建立在保载条件下的第一类断裂特征图,该图提供了保载下的宏观与微观资料。本文还讨论了保载时间对断裂时间影响的规律,以至竞争模与积累模型在保载条件下的适用性。
Based on the first type of fatigue creep rupture characteristics of large-scale cast-in-place turbine, the effect of the maximum stress on the fatigue creep rupture behavior and the characteristics of the first kind of rupture under the ballast condition are further studied. The experimental results show that the fracture week With the alternating stress and the average stress changes with no load the same, “anti-C” type law. Compared with no ballast, the ballast significantly reduces the number of fractures and moves the fracture curve to the low lifetime. Prototype to increase the creep effect, the fatigue mechanism into a creep mechanism, expand the creep-based C area, reduce the fatigue-based F area, so long enough to hold the load, fatigue agencies disappear. Based on the theoretical analysis of fracture mechanism and fracture observation and the macroscopic life rule, a first type of fault characteristic diagram under the condition of slab loading is established, which provides macroscopic and microcosmic data under loading. The paper also discusses the law of the influence of the holding time on the fracture time, and the applicability of the competition model and the accumulation model under the condition of keeping the load.