Design and fabrication of composite beam

Abstract

Carbon fibre reinforced polymers are commonly used in widespread applications in many industries due to its enhanced mechanical properties and low density. With the increasing number of applications, carbon fibre reinforced composites are now used for load bearing applications such as the floor beams in aircraft bodies and wing structures.

This report examines the fabrication of such an I-section beam using unidirectional carbon fibre laminas through the fabrication of different components consisting of C-channels and flat facesheets and bonding them together using the vacuum bag process and a wooden mould reinforced with aluminium channels. The orientation of the C-channels used in the beam have the orientation of [-45o, 90o, 45o, 0o, 0o, 45o, 90o, -45o] and the facesheets are all in the direction of 0o. Each of the C-channels and facesheets consists of eight plies each and the entire structural beam has sixteen plies throughout the structure after being bonded. The problems faced during the fabrication process using this method are also discussed in this report.

The structure is subsequently placed under a three point bending test using both a hydraulic jack and a free weights setup to determine the structural integrity of the beam without failure. The results obtained from each setup were then compared against each other by plotting the stress strain graphs and the load displacement graphs. Results obtained by the finite element analysis method were also used to compare against the results obtained. The results collected shows that the deflection due to the loads applied fall within the elastic range and no plastic deformation was observed. The failure stress of the beam was also approximated using the Tsai-Wu failure criterion in the finite element analysis.

C-channels of different ply orientation were also tested using the loading test to determine the amount of deflection experienced by the different ply orientations. The orientations used in the comparison are the angle ply used in the structural beam and the cross-ply ([0, 90, 0, 90]s orientations. The displacement and strains experienced were recorded and compared against the ply orientations. Strain values recorded were also compared against the calculated values obtained by the mechanics of materials approach. The shear centre location of the C-channels was also tested and compared against the theoretical values calculated and the deviation of the results discussed in detail.