Towards smart tightening in aeronautical assemblies

Abstract

Exogenous disturbances, the tolerances of bolted joints, and the large number of possible combinations and configurations make it difficult to control the preload in bolted joints. Direct measurement of joint preload is not possible without calling upon laboratory testing or instrumented fasteners. The objective of smart tightening would be to compensate for the current dispersions by detecting events occurring during the tightening process that have an impact on the final value of the preload. Since the number of possible parameters, such as coating or diameter, to be considered in the selection of a bolted joint is large, this article focuses on a precise list of the main parameters characteristic of a bolted joint and the major dispersions they induce. It is first shown that dispersions in the joint parameters interfere with the evaluation of the torque and should be limited, in order to reduce the uncertainty of the preload in the joint. It is then shown that the contact torque and the tightening coefficient are key parameters for controlling the preload installed in the coupling. To detect the contact torque and tightening coefficient, a method based on real-time measurable data obtained with an instrumented screwdriver is also presented. Thus, the smart tightening method proposed in this article guarantees better respect of the preload target and limits the risks of over or under torque.