The self-loosening of a bolted assembly is a phenomenon that has been studied several times in the past. Among the stresses present, it has been shown that transverse loading might cause the most severe loosening. Thus, different explanations have been proposed. In spite of their similarity, as they all consider sliding as the root cause, they can be distinguished from one another by the surface that is considered to slide. This paper aims to give another point of view of the overall problem in order to support Zadoks' theory [7], which highlights the transverse sliding of components. For this, firstly, a double-shear assembly will be modeled. Its specificities are the preload application by screwing the nut, and the use of a self-locking nut. Secondly, some tests will be done in order to validate the model built. The experiments will also take account of the effect of the thickness of the assembly in the self-loosening. Thirdly, the analysis of the numerical results and of the experiments, especially the interface surfaces, will give us a clue enabling us to approach the sliding phenomenon, which is, according to Zadoks, the movement leading to self-loosening of the assembly.

The self-loosening of a joint through unscrewing of the bolt is a phenomenon mainly occurring when the assembly is solicited by transverse repeated loads. Previous works highlighted that the transversal sliding of the bearing surfaces, either in the threads or underneath the bearing surfaces of bolts and/or nuts, is its root cause and that this phenomenon begins during the first loading cycles. In order to study the early stage of this self-loosening, a simplified numerical model has been developed. The latter factors the bearing surfaces of the bolt, the preload, the friction coefficient, the amplitude of the shear-load and the fastener's material. Through measurements and interpretation of the results, the shearing of the fastener has been identified as the main deformation leading to the self-loosening of the assembly, while the bending of the fastener shank limits the self-loosening. Moreover, according to the values of preload and shear-load, the behaviors were identified, and an interpretation has been proposed.