The experimental and finite element study of friction in aircraft riveted joints

Abstract

This article presents the results of a study on the factors determining the effect of film-forming anticorrosive compounds on the fatigue of riveted joints. Anti-corrosion compounds recommended for protecting the structure of transport category aircraft, based on the experience of their use by well-known developers of aviation equipment, were studied. Two treatment variants with film-forming anticorrosive compounds were considered, defined as: a) "excessive amount of compound" and b) "limited amount of compound". An excessive amount of compound in the joint gap caused a negative effect on fatigue life. The relationship between the viscosity of the studied compounds and the number of loading cycles to failure under the "excessive" processing mode was experimentally revealed, which can be explained by the penetration of compounds into joint gaps. Using an original device for studying the friction forces between joint elements in the presence of anticorrosive compounds, the static friction coefficient was determined using several anticorrosive materials. The results of determining the coefficients of static friction indicate that anticorrosive materials have a significant effect on the forces of static friction (friction at rest) and the necessity to select them based on a set of characteristics. It has been established that the thickness of the compound layer does not affect the value of static friction. The primary factor in determining the effect of compounds on friction and the corresponding decrease in cyclic durability is the fraction of the surface covered with a lubricating layer, which determines one of the possible friction modes: boundary, dry, or mixed. It has been experimentally established that the resting friction force increases with the duration of the interval between the application of anticorrosive compounds and testing. The effect of compressive forces on friction in the joints was also investigated. Finite-element modeling of the formation of a riveted joint was carried out, considering the plastic deformation of the rivet material. Based on the obtained results, a conclusion was drawn about the local nature of the contact interaction between the plates, which was concentrated exclusively in the hole zone. The finite element analysis and numerical experiments led to an important conclusion: the local stresses in the hole zone that determine the durability significantly depend on the coefficient of static friction between the skin sheets.