Bending of fibre metal sandwich beams
See, Regina Xiu Ying
Date of Issue2015
School of Mechanical and Aerospace Engineering
The high bending strength to weight ratio of a sandwich structure makes it advantageous to the aerospace industry where weight is a concern. However, these sandwich structures are vulnerable to damage, such as impact damage and debonding. With the use of fibre metal laminates which have higher ductility and impact resistance, it would hopefully allow more successful uses of sandwich structures in the industry. Thus, it is important to understand the failure modes of these fibre metal sandwich beams when exposed to loads experienced during flight, such as bending. The aim of this project is to investigate the structural response of sandwich beams, made of fibre metal face sheets with a Nomex honeycomb core, when it is subjected to bending loads. Sandwich beams with face sheets of varying metal volume fraction (0%, 20% and 50%) were subjected to three-point bending tests to observe the different failure modes. A comparison was also done between sandwich beams of different core thicknesses (10mm and 25mm) to study the effects of core thickness. Based on the observations of the experiments, core shear was the first mode of failure that caused the decrease in load. After which, other modes of failure occurred which further weakened the beams. Fibre metal sandwich beams were observed to have more globalized damage as compared to a carbon fibre sandwich beam which had more localized damage. Data from the bending tests were used to plot load versus central deflection graphs. From these graphs, it could be seen that carbon fibre sandwich beams were able to withstand higher loads as compared to fibre metal sandwich beams. However, fibre metal sandwich beams had higher residual loads and absorbed more energy, making them more impact resistant. The stiffness of the beams could also be seen to be affected by the thickness of the core where the stiffness of the thinner beam was reduced by half, even with the same face sheets. However, a thinner beam would allow more effective load transfer between the top and bottom face sheets. With these benefits, the consideration of using fibre metal laminates in sandwich beams should also take in account the additional weight from the metal.
Final Year Project (FYP)
Nanyang Technological University