Analysis of the fatigue behaviour of laminated composite holes subjected to pin-bearing loads

For the civil aircraft industry, the preferred process for joining composite structures is mechanical fastening. This process requires a large number of drilled holes for the positioning of the numerous rivets and bolts. During the life cycle of these aircraft structures, the assembly holes are thus pin-loaded by the fasteners under cyclic loading. Mastering the mechanism of fatigue pin-bearing damage is thus essential to optimize the sizing and the tolerancing of the drilled holes. This paper proposes an experimental protocol to monitor the mechanical response of a pin-loaded CRFP laminate under different cyclic loadings. This study is conducted on both microscopic and macroscopic scales. The drilling process results in flaws on the bearing surface of the hole. The evolution of the initial surface topography at the microscopic scale is correlated with the mechanical response of the laminate through macroscopic measurements. The effects of the fatigue loading conditions on the different damage mechanisms are identified through various configurations. Using the proposed methodology, a generic damage scenario is identified for the tested material.