Abstract
Using original cold-formed rivets in repairs of airframes of helicopters is difficult due to no access to inside parts of the airframe. Thus, the main aim of the study was to investigate the possibility to use the blind rivets or hybrid joints by verification the fatigue performance of such joints that must be better than with original rivets. Riveted and hybrid joints have been experimentally tested under static and fatigue loads. Furthermore, numerical calculations of stress distribution for strapped joint have been conducted. The test results covered fatigue life of lap joints and models of repaired airframe sheets using ordinary mushroom head rivets ref. 3558A-4-10, titanium driven blind bolts with pin, ref. MBF2110AB-05-150 and modified hybrid joints. Using titanium driven blind bolts with pin instead of ordinary hammer-bucked rivets, can improve the fatigue life of element made of aluminum alloy AW 2024T3. There are advantages of replacing riveted joints with modified hybrid (rivet & adhesive) joints in threefold increase in fatigue life of repaired airframe structures.
Highlights
There are many aircraft in operation around the world with a service life of more than 30 years
That in the publications on hybrid joint solutions known to authors, nobody take into account the problem of the destruction of the adhesive joint by the pressures generated by mechanical joints during their assembly, authors proposed original modification of the adhesive joints with layers of glass fabric
Cracks can initiate on sites different from those in the case of riveted joints without adhesive, and such cracks can propagate slower
Summary
There are many aircraft in operation around the world with a service life of more than 30 years. Moving the crack initiators beyond the critical zones of the rivet holes can be achieved by generating high pressure forces in the vicinity of the mounting holes For this purpose, instead of riveted joints, bolted joints should be used, which, still does not solve the problem of limited two-sided access to mechanical fasteners in the assembly procedure. Authors proposed that, the target can be achieved by replacing conventional rivets with a blind bolt fastener which have much higher clamping force or by using hybrid joints i.e. mechanical-adhesive joints It is worth mentioning, that in the publications on hybrid joint solutions known to authors, nobody take into account the problem of the destruction of the adhesive joint by the pressures generated by mechanical joints during their assembly, authors proposed original modification of the adhesive joints with layers of glass fabric. Budhe et al analysed main aspects over conventional joining method including mechanical fasteners and adhesive His conclusions pointed out stress concentration as major cause of joint damage. Presented work is a response to the urgent need to develop a modern repair procedure for the aging fleet of the aircraft including Mi-24 helicopter fleet
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