FEM STRESS ANALYSES OF THE CONTACT STRESS DISTRIBUTIONS AT THE BEARING SURFACES IN BOLTED JOINTS USING HEXAGON BOLTS WITH FLANGES

In designing bolted joints, it is important to understand the contact stress distribution and permanent set at the bearing surface in the case of high initial axial tension. They are investigated using elasto-plastic FEM for hexagon bolts with flange. It is found that the difference in the contact stress distribution is large between elastic FEM and elasto-plastic FEM. Effects of the flange thickness and the flange slope angle on the contact stress distribution and permanent set are examined, and it is shown that they are substantially influential. In the experiments, hollow cylindrical specimens are compressed by the bolts with flange and permanent sets are measured at the bearing surface. The permanent sets are compared with permanent sets obtained from the elasto-plastic FEM and they are in a fairly good agreement. In addition, the equivalent length for the hexagon bolt with flange is proposed.