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2 2012

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Wpływ długości nitu na naprężenia własne w połączeniu nitowym

Szymczyk E., Puchała K.

Przegląd Mechaniczny

2012

nr 7-8

59-64

Wytrzymałość połączeń nitowych zależy od czynników konstrukcyjnych, technologicznych i materiałowych. Nity tak jak wszystkie części mechaniczne produkowane są z określoną tolerancją, a ich wymiary zawierają się w ustalonych granicach. W artykule przedstawiono analizę wpływu czynnika technologicznego, jakim jest długość nitu, na naprężenia własne w połączeniu. Obliczenia wykonano dla blach ze stopu aluminium 2024T3, stosowanego na pokrycia lotnicze, łączonych nitami z materiału PA25 o podwyższonej wytrzymałości. Analiz´ stanu naprężenia przeprowadzono dla trzech długości nitu. Zwrócono uwagę na naprężenia styczne, które mogą powodować pękanie zakuwek.

The load carrying capacity of riveted joints depends on many structural, manufacturing and material factors. Rivets, like all mechanical parts, are produced with certain tolerance, therefore their dimensions are enclosed in fixed limits. The paper presents an influence of such a technological factor as a rivet length on a residual stress state in the riveted joint. Numerical calculations were performed for sheets made of 2024T3 alloy commonly used in aircraft fuselages joined together with rivets of high-strength PA25 alloy. The analysis of residual stresses is performed for three different rivet lengths. The shear stress field which tends to cause cracking of the formed rivet head is taken into account.

Some aspects of dynamic riveting simulations

Szymczyk E., Jachimowicz J., Puchała K.

Journal of KONES

2012

Vol. 19, No. 1

423-430

Riveting is a commonly used (especially in aircraft structures) method of joining metal and composite components. The methods of forming solid shank rivets can be classified in two types: static and dynamic. The static method is the most efficient one. Regrettably, its application is limited. A popular upsetting tool used in an aircraft is a pneumatic riveter. The rivet driving requires a few hammer strokes. The total stress in a riveted joint depends on the residual and applied stress. Residual post-riveting stress fields are widely accepted to have a beneficial influence on the fatigue life of aircraft structures. The analysis is carried out for a solid mushroom rivet (made of PA25 alloy) joining two sheets (made of 2024T3 alloy). Nonlinear dynamic simulations of the upsetting process are carried out. Simulation of the riveting process is significantly influenced by a material model. The numerical calculations are performed for three different cases of upsetting described by the formed rivet head diameters 1.4d, 1.5d and 1.6d, respectively. The rivet head diameter and, consequently, the residual stress state depend on hammer stroke energy. It has a significant influence on a plastic region around the rivet hole, whereas the influence of a number of strokes can be neglected. The strain rate in both local and global (average) formulation is analysed in the paper. For one hammer stroke, the global strain rate of the rivet shank is about 1.0 thousand per second. The local strain rate is about two times greater than the global one, so a strain rate factor has an effect on the residual stress state. For a few hammer strokes, the strain rate is lower than for one stroke; however, it increases a little in each stroke. The hole deformation can be treated as a function of the internal energy of the sheet. The lower total energy of the part the greater influence of the strain rate on the internal energy is observed.