Research on high temperature creep fracture of cylinder fastening
Bolts of super(super)critical steam turbines Xu Hong Zheng Shanhe MAILEKarl2(1.Key points of equipment monitoring and control of power station equipment of North China Electric Power University),the damage accumulated to a certain extent,resulting in macroscopic voids or cracks.The damage is defined as the uniaxial test bar and the hollow bolt made by the experimental Nimonic 80A.The experimental temperature is 550 C.The HTDMS high temperature strain gauge is used to measure the strain of the test piece.The uniaxial test bars were tested in groups of 702,760,801,830,and 862 MPa(U1-U5).The experimental results are shown in Table 1.
For the structure of the bolt test piece,the diameter of the screw is 41 mm,the diameter of the middle hole is 18 mm,and the total length of the bolt is 284mm,both ends are threaded,the diameter of the thread is 52mm,the nut material is 30CrMoNiV511.The creep of the bolt is introduced into the strain threshold sD.At that time,the calculation and experimental results are analyzed.3.1 The determination of the parameters of the creep damage formula is based on the experimental data.Creep damage formula parameters,see Table 2.Calculated valuesof the Kachanov model,improved model calculations and experimental comparisons.It can be seen that the calculated value of the improved creep model is consistent with the experiment under each stress,and is more suitable for describing the whole process of creep than the Kachanov model.
The variation of creep strain and damage variable with time under 702MPa stress for uniaxial test bars.The time tD corresponds to the strain threshold eD,and the damage after tD is calculated.
