| Bolt is widely used in fastening mechanical parts and appears in a large number of various equipment and structures.Its fatigue performance and life are directly related to the safety of equipment and structures.Traditional fatigue analysis only considers the influence of a single normal stress,while the root of the thread is usually in a complex stress state,so the effects of both normal stress and shear stress should be considered.Based on the Gough criterion,this paper studies the life prediction of bolt fatigue under different average stresses.The main work and results are as follows:(1)Combined with the three-direction stress circle,the Gough ellipse criterion is generalized to the general complex stress situation,and the effective stress parameter method is adopted to introduce the influence of average stress,so as to obtain the complex stress Gough fatigue criterion with a wider application range and different average stress.(2)Used the fatigue test data of notched parts with similar stress concentration coefficient as the thread,combining with the finite element analysis,the equivalent stress of notched parts based on complex stress Gough fatigue criterion was calculated,and the equivalent stress-life curve was obtained through data fitting,laying a foundation for the fatigue life analysis of bolts.(3)Based on the ANSYS Workbench virtual thread method,optimized the pre-contact processing of thread and completed the numerical simulation analysis of the bolt contact problem.Through this method,the stress data of the joint in the thread region were obtained and the equivalent stress of bolts under various working conditions was obtained.The life prediction analysis of the bolt fatigue performance was carried out by combining the equivalent stress-life curve of notched parts.(4)In view of the negative stress ratio conditions,the finite element calculation of arbitrary cross section on principal stress will change,and the plastic stage principal stress direction change problem,put forward using Euler angle complete two principal stress rotation matrix projection to get the calculation method of the main stress amplitude,and plastic state is obtained by calculation of bolt plastic stress amplitude under bolt equivalent stress and the expected life.The comparison results show that the proposed method is small compared with the measured results. |
