FIBERGLASS BOX BEAM: J. Beam Wellington IIIShawn Baker and Tim Carlson

Dept. of Materials Science & Engineering, University of Washington

Bridge #: S6-3946

 

PROBLEM STATEMENTDesign a box beam using a combination of fiberglass plies and resin that will hold a distributive load of 7,000 lbf applied at the center.

MANUFACTURINGHigh thread count fiberglass was used in the final iteration to avoid soaking up unnecessarily large amounts of resin. Most plies were cut using an automated fabric cutter or by hand (Figure 1). Each ply is then wetted with resin and assembled in specific directions to withstand the most applied force (Figure 2 and 3). The top, bottom, core, and webs are pressed and bound tightly together (Figure 4 and 5). The beam is wrapped in breather and sealed in an air-tight bag to be cured in the autoclave at 270 F for 2 hours (Figure 6). ᵒ

TESTINGThe first iteration was made with wide tow fibers that held over 15000 lbf, but weighed 1432g. The second iteration was made with more consideration of optimizing weight while maintaining strength. However, the second beam failed early at 3429 lbf at 698g because of dry spots at the supports of the beam that acted as stress concentrators. The final build maintains this optimized design while ensuring adequate resin distribution.

DESIGNThere are four components to this beam, entirely made of fiberglass weave fabric:• Two C-channels on either side of a center

square section are constructed with plies mostly oriented at ±45° angles to account for shear stress.

• Top flange plies oriented in 0° or 0°/90° directions and consists of more plies than the bottom flange because of a greater compressive stress.

• Bottom flange has more plies of fiberglass at the ends, to withstand more tensile stress.

FUTURE IMPROVEMENTS• Minimize resin content and pooling between plies to

reduce the weight of the beam.• All beams tested failed at the ends of the beam. I suggest

to replace more plies on the top and bottom with tabs to strengthen the ends of the beam while maintaining low weight.

ACKNOWLEDGEMENTS• Brian Flinn, Ph. D- UW MSE• UW SAMPE Officers & Members• Jeffrey Wollschlager- Altair EngineeringFigure 6: Vacuum bagged beam

Figure 8: Side by side comparison of the first two iterations.

Figure 1: Cutting unidirectional plies Figure 2: Wet layup process Figure 3: Bottom being assembled

Figure 4: Pressing the core together with the bottom and top

Figure 5: All pieces of the beam are assembled together

Figure 7: Using liquid nitrogen to help release the beam from the core tool

Figure 9: Load vs. extension graph of second iteration beam that failed early

Figure 10: Assembly drawing of the beam