Bearing Strength Characteristics of Standard and Steel Reinforced GLARE

Abstract

Fibre Metal Laminates (FMLs) are hybrid materials, which consist of thin metal sheets bonded together with alternating unidirectional fibre layers. This material concept has resulted in superior fatigue characteristics with respect to the metallic counterpart. Several static characteristics are however negatively influenced due to the fibre addition. This thesis focuses on the description of one of these characteristics: the bearing strength of FMLs. And based on the acquired knowledge, a solution is presented to improve the bearing strength. First, the bolt bearing strength with lateral restraint, of several FMLs of the Glare family was evaluated both experimentally and numerically. Subsequently, a finite element model was developed to describe the behaviour of FMLs under pin loading without lateral restraint. In the model, special attention is given to the interface between the different layers. The model was validated against experimental data of several FMLs. To improve the bearing strength of Glare, thin stainless steel sheets with high strength were selected as local reinforcement. Several steel reinforced Glare laminates were experimentally and numerically investigated on their bearing characteristics. While the improvement in bearing strength can also be reached using an aluminium reinforcement layer, the thin steel strip offers several benefits for actual joints in real aircraft structures. It results in a lower thickness increase and hence a lower eccentricity, which was shown to result in improved fatigue characteristics for actual joints, furthermore a material with higher stiffness is obtained.