超超临界锅炉过热器管裂纹尖端塑性区数值研究

Numerical Research on Plastic Zong at Crack Tip of Superheater Tube for Supercritical Critical Boier

针对超超临界锅炉含裂纹的过热器管,采用数值模拟对长时间高温高压下裂纹尖端的应力应变场进行分析,并结合塑性区理论,对裂纹尖端塑性区的大小进行估算,提出一种有限元求解塑性区大小的方法。结果表明,裂纹尖端的应力、应变及塑性区的大小不仅与内压大小有关,而且与温度高低有关,在温度一定时,内压越大,塑性应变越大;在内压相同而温度越高时,塑性应变也越大。在长时间高温高压下,有限元求解塑性区结果与塑性区理论结果存在一定差别,并分析了这种差别出现的原因。最后,利用小范围屈服条件对裂纹尖端塑性区在长时间高温高压下进行了评估,表明采用应力强度因子K作为T92过热器管疲劳裂纹扩展的断裂参量是合适的。

For ultra-supercritical boiler of a super-heater tube with cracks,the stress-strain field at the crack tip is analyzed by numerical simulation under high temperature and high pressure for a long time.According to the theory of plastic zones,the size of the plastic zone at the crack tip is estimated,and a finite element method for calculating,the size of plastic zone is proposed.The research results indicate that the stress and strain,as well as the size of the plastic zone at the crack tip are related not only to the internal pressure but also to the temperature.At a certain temperature,the plastic strain increases with the increase of internal pressure and when the internal pressure is constant,the plastic strain increases with the increase of temperature.Under high temperature and high pressure for a long time,there is some difference between the result of finite element method and that of plastic zone theory,and the reason of the difference is analyzed.The plastic zone at the crack tip is evaluated by using a small range of yield conditions under high temperature and high pressure for a long time,it is shown that the stress intensity factor K is an appropriate fracture parameter for the fatigue crack growth of the T92 superheater tube.