FATIGUE BEHAVIOR OF MECHANICALLY FASTENED JOINTS IN COMPOSITE-MATERIALS

This paper describes the results of a research activity, carried out a t the Department of Aerospace Engineering at the University of Pisa in conjunction with AGUSTA, aimed at the characterisation of the fatigue behaviour of composite joints. The activity was performed as a suppor t to the certification of the tail of the new helicopter EH 101. Two t ypes of specimens were defined taking the move from the design of the structure; they mainly differed in the thickness of the laminates, 2 a nd 4 mm, and were representative of critical areas. The specimens were impact damaged with an energy level capable of inducing a barely visi ble indentation, as required by the Certification Authority. Fatigue t ests, under sinusoidal loading, R=0.2, were carried out both in dry an d wet conditions; the stiffness of the specimens was monitored during the fatigue tests. The comparison between the results obtained shows t he considerable effect of impact damage and of humidity absorption on the fatigue resistance of composite joints.