Study on initial self-loosening of bolts in curvic coupling

Under the guidance of ratcheting constitutive theory, the self-loosening of bolts in curvic coupling was analyzed in the cases of cyclic torque loads on discs after pre-load of bolts. The models about curvic coupling and thread were established by three-dimensional finite element method in commercial finite element software ANSYS. The uniaxial ratcheting experimental data of materials was used to calculate the initial input parameters for the simulations. The course of the stress loss at thread root due to the plastic accumulation of materials and further leading to the reduction of the bolt pre-load were studied. According to the analysis results, the plastic deformation could be found firstly at the first thread boot. The yield could take place with more chance if the thread was closer to the disc. The pre-load of bolt decreased with the torque cyclic loading. The magnitude of the bolt pre-load decreasing was most significant in the first cyclic loading. The rapid of the bolt pre-load decreasing degraded with the continuance of the cyclic loading. The effects on the contact stress of curvic and bolt head, the structure equivalent stress of thread boot, due to the self-loosening of bolts were studied simultaneously, providing a basic research for rotor with curvic coupling in the simulation analysis of the self-loosening of bolt.