Experimental study of friction in aluminium bolted joints

Threaded fasteners are used in many mechanical and structural applications because of the easiness of the assembly and disassembly operations for maintenance and repair purposes. Both the level and the stability of the clamp loads, which are created by the tightening process, will govern the safety and reliability of bolted joints. In most of production applications, the fastener tension (preloading force) is achieved by using a torque wrench applied to the head or to the nut. The tribological aspects of the fastener tightening are critical to define the actual torque-tension relationship [1]. The tightening torque is mostly consumed in overcoming two friction components: the underhead friction due to the sliding of the fastener head on the flange and the thread friction consumed between the male and female thread. The residual torque component produces the fastener tension by generating the joint clamping force. Inaccuracies in determining the friction components may lead to an overestimation or underestimation of the bolted joint performances.