Abstract
Recently, as methods to control the tightening force in bolted joints, the torque gradient control method and the turn of nut method in which bolts are tighten in plastic region attract notice. However, the behavior of bolted joints subjected to external load after preload is not sufficiently clear. Therefore, some experimental studies on the behavior of the bolted joints in elastic region and in plastic region are carried out. A new extensometer and a bolted joint model are trially designed and produced. Then direct-tension test of bolt, torqued-tension test and direct-tension-after-torqued-tension test of bolted joints are carried out. The main conclusions are summarized as follows : (1) The axial tension-elongation curve of the bolt in the bolted joint under the external axial loading comes near that in the simple bolt. (2) New tightening diagrams of bolted joints in elastic region and in plastic region are presented. (3) The new torque control method in which the maximum axial tension of about 0.8·Fy (Fy; yielding load or proof load) can be introduced by tightening, is presented. (4) The new design system of the bolted joint on the basis of (2) and (3) should be constructed.
