Critical Speed Of The Rotor-shaft System Of 680 Gas Turbine And The Shielding Effects Of The Crack-tip Plastic Zone

Critical speed is a key technical indicator of the rotor-shaft system of steam turbine and gas turbine generators, therefore its accurate calculation is essential. The SIEMENS gas turbine of Shanghai Turbine Co., Ltd. (STC) has multi-level wheels connected with each other by transverse teeth subjected to axial pre-tightening forces. The first part of the thesis models the rotor-shaft system, analyzes the vibration characteristics of 680 gas turbine by studying the relationships of the critical speed and the transverse parameters, pre-tightening force and rotational speed by means of Finite Element Method (FEM), and thus provides basis for the vibration analysis, failure diagnosis and safe operation of 680 gas turbine.In the second part of the thesis, a plastically deformed zone around a stressed crack tip is demonstrated to be mechanically identified with a transformation inclusion by Eshelby inclusion theory. Thus, the shielding effects of the plastic zone can be quantitatively evaluated by the present transformation toughening theory. A closed-form solution to determine the change in the stress intensity factor induced by the plastic zone is given both for plane stress and plane strain mode I cracks under small-scale yielding conditions. By using the present solution, the effects of the strain-hardening behavior of the material, the stress state and the T-stress on the near tip stress intensity factor are identified.In the third part, it is proved that the established method in the previous part can be used to calculate the effect of the voids and gas bubbles in materials on the crack-tip stress intensity factor.