Flaw tolerance evaluation of helicopter rotor parts

The current airworthiness regulations FAR and JAR 29.571 prescribe that a fatigue tolerant design, including the effects of environment, flaws or accidental damage, is accomplished in order to avoid catastrophic failure during the operational life of the rotorcraft. So far, different methodologies have been recognized to demonstrate the fatigue tolerance capabilities of the helicopter critical parts, supporting the establishment of replacement times or inspection intervals. The methodology adopted by Agusta for the substantiation of metallic rotor parts is the “no crack growth” approach, whose general procedures are presented in this paper by means of a practical application to a helicopter Main Rotor critical component. The approach, developed and implemented in cooperation with Politecnico di Milano, Dipartimento di Meccanica, is based upon both experimental activities, aimed at the material characterization in the threshold region, and detailed analytical assessments