Aerospace Engineering Department
BS in Aerospace Engineering
Eltahry I. Elghandour
Composites are a type of material that generally combines two materials yielding mechanical properties that are different than its constituent parts. These constituents are classified as either a fiber or a matrix. The objective of this project is to create a carbon-fiber composite I-beam that meets the specifications of the SAMPE student bridge competition. The I-beam consists of carbon fiber unidirectional and woven laminas, as well as aluminum honeycomb and high density polystyrene foam to stiffen the structure. The bridge contest rules limit the dimensions and weight of the bridge. The cross-section must be within 4 inches x 4 inches with a minimum length of 24 inches, and a maximum weight 600 grams. Theoretical stress and deflection analysis of the bridge was performed using MSC Nastran finite element software. All bridges were manufactured using a wet layup technique and cured under vacuum. Composite bridges were tested using the Instron machine belonging to the Architectural Engineering department at Cal Poly San Luis Obispo. Through analysis and testing, it was determined that web stability was the driving failure mode to design for. Our final bridge failed under 3000 lbf due to buckling of the web directly beneath the applied load. Our first and fourth iterations saw twisting of the flanges because of the lack of stiffness in the flange structure. Our second bridge iteration had the highest strength-to-weight ratio and also took the highest load (3100 lbf) before failing. Based on testing and performance at the SAMPE competition, there are many aspects of this project that can be improved, most importantly through manufacturing techniques. Use of an autoclave as well as using metal molds for curing the beam will dramatically increase load carrying capability.