Abstract

A tightening system and method and a fastener assembly usable therewith are disclosed in this specification. According to the method a fastener assembly is provided that causes a change in the slope of the torque-rotation curve which could be plotted while the joint is being tightened, which change occurs at a known load. While tightening the joint, the torque applied to the fastener assembly when the slope of the torque-rotation curve changes is noted and is used to calculate the torque necessary to induce a desired load in the joint. Additional torque is applied to the fastener until the actual torque being applied substantially equals the calculated torque. The tightening system includes a wrench for tightening the joint and a control system associated with the wrench including a system responsive to the change in slope of the torque-rotation curve for calculating the torque corresponding to the desired load to be induced in the fastener assembly and for shutting off the tool when the actual torque corresponds to the calculated torque.In accordance with the preferred embodiment disclosed herein, the fastener assembly includes a washer member which is seated between the bearing surface of the rotating fastener member and the outer surface of one of the structural members comprising the joint assembly. The washer member includes a bearing pad projecting above one of the main bearing surfaces of the washer member and located at the mean diameter thereof. As the fastener assembly is tightened, the bearing pad is deformed at a predetermined load temporarily changing the slope of the torque-rotation curve which is sensed by the tool as noted above.