フランジ付き六角ボルト締結体の座面応力分布の弾塑性有限要素法応力解析と永久変形量推定 : 初期締付け時の場合

抄録

The contact stress distributions and permanent sets at the bearing surfaces in bolted joints under initial clamping load are analyzed using an elasto-plastic FEM calculation when hexagon bolts with flanges are used. It is found that the difference of the contact stress distributions between elastic analyses and elasto-plastic analyses is large when the bolt preload is high. The effects of the flange slope angle θ and the flange thickness t in the bolts with flanges on the contact stress distributions at the bearing surfaces are examined. It is seen that the flange slope angle θ and the flange thickness t substantially effect on the contact stress distribution and permanent sets at the bearing surface. In the case where θ is 0.25°, the thicker flange of the bolt head and the slope angle of θ=0.25° cause smaller permanent set. In addition, the equivalent length for the bolt with flange is proposed. Furthermore, in the experiments, hollow cylindrical specimens fabricated with mild steel and aluminum alloy were compressed by the bolts with flanges and the permanent sets at the bearing surfaces were measured. The permanent sets at the bearing surfaces obtained from the FEM calculations are in a fairly good agreement with the measured results. It is shown that the permanent set can be estimated by elasto-plastic FEM calculations. Discussion is made on the critical stress at the bearing surfaces. Taking into account the deformation of bolt head with flange, its equivalent length in the spring constant of the bolt is proposed.