Experimental investigation on stress state and deformation in bolts through tightening of perfect flange connections

The fatigue loads of bolts in ring flange connections are significantly influenced by the pressure body between the compressed flanges, which in turn depends on two main scattering parameters ‐ geometric flange imperfections and the preload level. Depending on the tightening method and geometric boundary conditions, shear and bending stresses occur in addition to the axial stress in the bolt during prestressing of the connection. This multiaxial stress condition leads to different plastic deformations in the threads and thereby influence the performance respective the maximum achievable preload of tightening methods. In accordance with the objective, the authors identify the stress state in HV‐bolts during installation for different tightening procedures through experimental testing. Based on a comparison of the strain measurements with the 3D scan of the bolt geometry, this study evaluate to what extent the initial imperfections corresponds to bolt bending. Derived from the scope of a joint national research project, this contribution point out that the yield controlled tightening ensure prestresses close to the individual yield strength of the bolt within a narrow scatter.