High cycle thermal fatigue crack growth and high temperature crack growth law

为了模拟快堆钠冷组件的热条带情况，研制了一种以直流加热和循环淋浴相结合的方式对试样施加1Hz高频率热应力循环的装置。对厚度为10mm、直径为0.4mm的小半圆形预裂纹奥氏体不锈钢陡板试样在低、中、高三个热应力循环水平下进行裂纹扩展试验。在热应力循环过程中，样品表面温度为540*80ºC，处于中间水平。裂纹在第一阶段的扩展是加速的，但是在任何水平的热应力循环之后，它在进一步的扩展中是减速的。在低水平的热应力循环下，裂纹在厚度方向上的长度为0.6mm时最终停止扩展。研制了一种小散斑位移计，用于监测热应力循环作用下扩展裂纹的开闭情况。根据实验得到的温度分布，采用有限元法对热应力进行了估算。并在此热应力的基础上估算了应力强度因子。讨论了热应力循环下裂纹扩展与常温下常规应力循环下裂纹扩展的关系。发现这两个数据都经过应力强度因子有效范围的调整。

In order to simulrate the thermal striping situation in the sodium-cooled components of fast breader reactors, an apparatus was developed in which a high frequency of 1Hz in thermal stress cycling was applied to the test sample by a combination of direct current heating and cyclic shower. Crack growth tests were conducted for austenitic stainless steep plate samples of 10mm in thickness with a small semi-circular precrack of 0.4mm in diameter under the three levels (low, intermediate and high) of thermal stress cycling. The surface temperature of the sample was 540*80ﾟC in the intermediate level in the thermal stress cycling. The crack was accelerated in the first stage of growth, but it was decelerated for further growth after for any level of thermal stress cycling. The crack finally stopped growing under the low level of thermal stress cycling at a crack length of 0.6mm in a thickness direction. A leser speckle displacement gage was developed and used to monitor the crack opening and closure of the growing crack under thermal stress cycling. The thermal stress was estimated by the finite element analysis by using the temperature distribution obtained experimentally. The stress intensity factor was also estimated on the basis of this thermal stress. The correlation between the crack growth under thermal stress cycling and that under conventional stress cycling at constant temperatures was discussed. Both the data were found to be adjusted by the effective range of the stress intensity factor.