基于有限元计算的汽缸紧固螺栓应力分布研究
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摘要
某电厂新建机组中压外缸螺栓在168试运行过程中发生断裂,并有多条螺栓的螺纹处产生裂纹。失效分析认为该螺栓基本属于轴向大应力脆性断裂,为分析螺栓受力情况,采用有限元的方法对螺栓螺纹及螺柱的受力状况进行计算。为得到较高的精度,采用全螺纹、精细分网模型进行计算,结果表明螺纹的受力与螺柱内平均应力及螺栓材料的应力应变曲线有紧密联系;接触的前3阶螺纹承受的应力较大,最大应力约为螺杆平均应力的2. 5倍,工况下达到了屈服强度的82. 8%,往后各阶螺纹应力逐步递减;对螺栓加载过程进行了模拟,发现应力水平受加载历史影响。结合螺栓服役条件,认为本次螺栓裂纹与安全裕度不足有关,在附加应力的影响下造成螺栓开裂失效。
The intermediate pressure outer cylinder of steam-turbine of new units fractured during the 168 h running. The cracks were also found on the other bolts used on the intermediate pressure outer cylinder. It showed by the failure analysis that the brittle fracture occurred because of the high axial stress. The stress distribution was studied based on finite element analysis.The full screw thread and fine grid blocks were used to gain the higher calculation accuracy. It said that the stress of the screw thread was closely influenced by the stress of the mean stress of screw and the stress-strain curve. The force on the three screw threads which near the screw was higher than other screw threads.The maximum stress on the screw threads was 2.5 times of the screw and reached 82.8% of yield strength at the operating condition. The loading process was simulated and it showed that the stess was influenced by the loading process. Considering the service condition of the bolts,the fracture of the bolts was mainly caused by the lack of safety tolerance and the additional stress.
The intermediate pressure outer cylinder of steam-turbine of new units fractured during the 168 h running. The cracks were also found on the other bolts used on the intermediate pressure outer cylinder. It showed by the failure analysis that the brittle fracture occurred because of the high axial stress. The stress distribution was studied based on finite element analysis.The full screw thread and fine grid blocks were used to gain the higher calculation accuracy. It said that the stress of the screw thread was closely influenced by the stress of the mean stress of screw and the stress-strain curve. The force on the three screw threads which near the screw was higher than other screw threads.The maximum stress on the screw threads was 2.5 times of the screw and reached 82.8% of yield strength at the operating condition. The loading process was simulated and it showed that the stess was influenced by the loading process. Considering the service condition of the bolts,the fracture of the bolts was mainly caused by the lack of safety tolerance and the additional stress.
引文
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[2]尹益辉,余绍蓉.基于3D有限元模拟的螺栓接头变形---内力关系及在设计中的应用[J].机械强度,2008,30(6):947-952.YIN Yi Hui,YU ShaoRong.Relations between internal forces and deformation of a bolt joint with their application to design based on3D fem simulation[J].Journal of Mechanical Strength,2008,30(6):947-952(In Chinese).
[3]Tohnichi.Technical Data[R].Chapter 2 Bolt Tightening.
[4]史利军,黄文涛,杜奇圣,等.20Cr1MoVNbB钢汽轮机螺栓断裂的SEM分析[J].电子显微学报,2000,19(4):547-548.SHI Li Jun,HUANG Win Tao,DU Qi Sheng,Fracture analysis of20Cr1Mo1VNbB steel steam turbine bolt by SEM[J].Journal of Chinese Electron Microscopy Society,2000,19(4):547-548(In Chinese).
[5]董瑾,安江英.弯曲应力对汽轮机螺栓疲劳寿命影响的研究[J].华北电力大学学报,2010,37(6):95-98.DONG Jin,AN Jiang Ying.The research of effect of bend stress on the fatigue life of steam turbine bolts[J].Journal of North China Electric Power University,2010,37(6):95-98(In Chinese).
[6]姜帆.浅析汽缸螺栓的受力及拧紧方法[J].上海电力,2004(3):259-260.JIANG Fan.Analysis of The cylinder bolt force and tightening method[J].ShangHai Power,2004(3):259-260(In Chinese).
[7]金永明,王争艳.汽轮机高强度螺栓设计方法探讨[J].热力透平,2004(02):96-100.JINYongMing,WANGZhengYan.Discussion on design method of high strength bolt for steam turbine,2004(02):96-100(In Chinese).
[8]张守文,余化文,熊伟,等.1000 MW汽轮机中压主汽门和中压调门螺栓断裂原因分析[J].电力与能源,2016,37(4):483-485.ZHANG ShouWen,YU HuaWen,XIONG Wei.Bolt fracture cause analysis for MV main throttle valve and control valve of 1 000 MWSteam turbine[J].Power&Energy,2016,37(4):483-485(In Chinese).
[9]杨超,冯立中,吴红涛等.超超临界汽轮机IN783螺栓断裂原因分析[J].PTCA(PARTA:PHYS.TEST),2015,51(5)346-349.YANG Chao,FENG Li Zhong,WU HongTao.Analysis on Fracture Reason of IN783 Bolt Applied in Ultra Supercritical Steam Turbine[J].PTCA(PARTA:PHYS.TEST),2015,51(5)346-349(In Chinese).
[10]韩宇,安江英.汽轮机高温螺栓的断裂特性分析[J].中国电力教育2010,2010(S1):402-403.HAN Yu,AN JiangYing.Fracture characteristics analysis of steam turbine high temperature bolt[J].China Electric Power Education.2010,2010(S1):402-403(In Chinese).