Étude de l'autodesserrage des assemblages boulonnés

Abstract

Self-loosening of bolted plates has long been a known phenomenon. Indeed, bolts joints are present in several industrial fields such as machinery, automotive, aerospace, oil and gas. A failure or a simple loosening can have serious consequences on maintenance costs, environment and humans. It is therefore essential to understand the physical phenomenon behind self-loosening to anticipate and avoid its occurrence. Self-loosening of bolted joints can be studied experimentally by testing, numerically using FE simulations and theoretically using analytical modeling. In this thesis, theoretical and numerical models are used to understand the phenomenon while experimental tests are used for verification. Experimental investigations use a test machine called a Junker machine for self-loosening testing. Unlike previous studies that uses sensors like load cell that affect the self-loosening process, the testing device used in this study has sensors that affect the phenomenon to a minimum. The rig is equipped with a strain gauge inserted in the bolt to measure the tightening force, a rotational velocity differential transformer located on the nut, a linear velocity differential transformer measuring the relative displacement between the plates, a load cell measuring the transverse force and a magnetic cycle counter. Various numerical FE models have been developed during this project. The first category of models simulates the self-loosening of bolted joints, with different preloads, transverse displacements and plate thicknesses. The second category of models is based on previous models and is used to determine the bending stiffness of the different parts of the assembly required. These stiffnesses are used for the developed theoretical model. As far as the theory is concerned, friction models have been developed at the different contact zone levels. Friction is an important key factor in solving the theoretical model. In addition, an elaborate model of the bolt under bending was also proposed. Based on the developed model, a criterion to avoid self-loosening of the bolted joints was developed. Finally, a relationship between the relative displacement between the bolt head and the plates on the one hand and the relative rotation between the nut and the bolt on the other hand has been proposed. The effects of different parameters have been studied theoretically and are in agreement with the literature. In addition, the proposed criterion provides a good match between the numerical and theoretical results. As far as the bending stiffness of the bolt is concerned, under the non-slip condition the results are in good agreement. On the other hand, during the sliding phase the model does not reproduce the real behavior, shown by the lack of agreement between the results. The friction equations under the bolt head and under the nut and the numerical simulations give very close results, which shows a good modelling of this friction. The overall rigidity of the system was also studied, showing mitigated results. The use of formulas from the literature does not necessarily give good results depending on the case to which the system is subjected to.

Date	19 Sept 2018
Original language	French
Awarding Institution	École de technologie supérieure
Supervisor	Hakim A. Bouzid (Supervisor) & Michel Gratton (Co-supervisor)