Crack propagation on helicopter aluminum panel with bolted stringers

Abstract: Aerospace structures need excellent structural efficiency and damage tolerant behaviour to avoid critical failure in presence of small defects and repeated small loads typical of contingent loads. In order to verify the damage tolerant performance of a rear helicopter frame, a series of tests have been performed on panel specimens representative of the structure. In particular, the central part of the specimens is representative of the real frame structure, while the extremity (in particular the constraint and the load application zones) are reinforced to avoid failures due to fatigue. Dedicated test equipment has been designed and built in order to apply the effective service load. An artificial damage has been created in each panel to start a crack, and a variable load with a fixed load ratio has been applied. During the tests the propagation of the crack has been acquired, from the starting of the crack at the two apexes of the artificial damage, until the progressive f...