Damage in composite-metal adhesive joints under low velocity impact conditions

Abstract

Since the advancement of science and technology, the field of composites has moved from basic composite material such as wood to strongest composite materials such as graphene. Unfortunately, the cost of the most advanced composite materials is very high mainly due to their production processes. Considering the cost factor, we need to work on reducing the cost of composite materials without altering their other properties mainly their strength. Composite materials are known for their excellent stiffness to weight ratio and strength to weight ratio. The most known composite materials are fiberglass, Kevlar, carbon fiber and basalt fiber. Carbon fiber is the most widely used composite material since it has a high strength. The drop test impact is a very short duration phenomenon with impact time being less than 20milliseconds. The material for the target point and its geometry plays a very important role in the phenomenon followed by certain boundary conditions. The impactor possesses gravitational potential energy and on striking that energy is absorbed by the targeted patch. The impactor with Gravitational Potential Energy less than the energy absorbing capability of the composite material only damages the composite patch in terms of cracks, some indentation or delamination of the composite patch layers. But if the Gravitational Potential Energy is greater than the energy absorbing capability of the composite material, the impactor will penetrate through the composite material leaving a hole. Hence the amount or intensity of the damage in composite patch is directly related to the energy absorbing ability of the composite patch. In current study, the behavior of three different combinations composed of basalt fiber and flax fiber were studied. The 3 combinations include BF4B11, BFB5FB5FB, B5F3B5 (Asymmetric, symmetric and sandwich) respectively. The test specimen was composed of Aluminum 2024 of thickness 3mm bonded with one of the circular shaped composite patch of thickness 3mm. Single impact strikes were carried out on the targeted composite patch at certain energies with aluminium plate acting as back plate. The numerical results along with graphs were taken from the software followed by the results gathered through studying damage caused due to indentation and by investigating the propagation of cracks formed. All of these results of the 3 combinations were thoroughly checked and a comparison between the 3 combinations was carried out involving theamount of indentation, force displacement, bending stiffness, damage area and cracks propagation. It was found that among the 3 configuration layups Asymmetric performed better than symmetric and sandwich layup