UCSD Jacobs School of Engineering University of California San Diego
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Engineering Students Get Hands-On Experience in Composite Design

STUDENTS JOSHUA HU AND A.J. HUBNER successfully fabricated a composite trick water ski for Professor Vistasp Karbhari's composite structural design class. Their goals were to construct a ski that was cheaper and lighter than those currently on the market, maintain or enhance performance, and support an adult weighing over 180 pounds. Trick skis are used for a variety of surface and aerial maneuvers. Store-bought models typically cost about $550 each and are made of graphite and a honeycomb core.

After testing several composites, Hu and Hubner decided to use carbon/graphite fiber for stiffness and a PVC core. The PVC core provides good compression strength and costs less than honeycomb, which also requires a rather expensive autoclave manufacturing technique. They used a pressure mold process to produce the 43-inch long by 11-inch wide, ½-inch thick ski.

"The disadvantages of store-bought skis are uniformity and density. They have a lot of excess material that's not needed and which adds extra weight. The foot bed carries most of the weight and takes the greatest impact, and therefore must withstand a variety of forces. Other areas of the ski do not need to be as dense," explains Hubner, who is also a member of the UCSD water ski team.

In the end, the team's ski with bindings weighed only 6.63 lbs., compared to the store-bought ski with bindings that weighed 7.96 lbs. They also increased the surface area by making their model one inch longer and a ½-inch wider. These savings were extremely noticeable when Hubner tested it in 38-degree weather. "It really had better control and was much more maneuverable. Tricks that are usually very difficult actually seemed easier. The added stiffness in the board also really helped," says Hubner.

"This project allows students to apply theory learned in the classroom to real-world applications," says Karbhari. "The students spend many hours of their own time working on the projects." Other notable composite design projects this quarter included a leaf spring for automotive suspensions, a therapeutic bathtub, and a twist-resisting girder for wide pedestrian bridges.