Improvement of fatigue life of riveted joints in helicopter airframes

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.