Three Dimensional Elastic-Plastic Finite Element Simulation on Bolt Tightening Beyond Yield

This paper presents 3-dimensional elastic-plastic finite element stress analysis simulating the behaviors of bolt and nut during the tightening process beyond the bolt yield so called plastic region tightening. The finite element model has the shape of helical threads as it is shown in the actual M16 stud bolt and heavy hex nut. The stress analysis is solved as contact problem among the engaged threads and the nut bearing surface to the clamped body. Tightening torque, thread torque, bearing surface torque and bolt axial force are calculated. They are compared with the experimental test results and show a fairly good agreement. Stress distribution as well as the development of plastic zone in the bolt and nut during the tightening are also demonstrated by this simulation. In addition, the load distribution in the engaged threads are computed and clarified the difference from those based on elastic analysis.