Balsa Structures Testing

by Raj Raman
Balsa Structures

Students in the department's new one credit hour freshman course, BsE 103 (Introductory Design and Fabrication) spent several weeks designing, building, and then crushing, small balsa-wood structures. Each structure had to be large enough to contain a ping-pong ball, and had to protect the ball from a vertical load. (Structures were tested without the ball in place, so the ball could not contribute to the strength of the structure.)

Each structure was judged not only on its strength, but on its weight (lower was better), and on its size (smaller was better). Specifically, we calculated a coefficient of performance (COP) for each structure, which took into account the strength-to-weight ratio, as well as the overall volume of the structure. The department's INSTRON testing machine was used to crush the structures, and a datalogger and PC were used to collect and display the results.

The first structures built by the students had COP values ranging from 20 to 180. However, four weeks of testing, evaluation, redesigning, and rebuilding, resulted in significant gains in performance, and gave the students significant insight into the BsE 103 Students challenges, joys, and frustrations of design. Final COP values ranged from 500 to 4900, with individual students all showing 2000 to 4000 percent increases in the strength of their structures. Several of the strongest structures are shown in the top photo. Students in BsE 103 are shown in the photo at left. They are from left to right, Carl Hudson, Chris Helton, Tonya Denton, Ross Kingery, Eric Goodman, and Trent Pearce.

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