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This report summarizes the drop tower testing of initially circular straight aluminum tubes that had been hydroformed to a square section with round corners. Drop tower test conditions and test setup were determined for the AlMg3.5Mn aluminum alloy circular (76.2 mm outside diameter) tubes of either 2.0 or 3.5 mm thickness, which had been hydroformed into a square tube with corner radii of 38.1 (unformed), 33, 30, 27 and 24 mm. To initiate test setup, theoretical equations were found to be reasonable indicators of displacement and load cell requirements. Four-lobe symmetric modes were found for the square tubes, and three-lobe asymmetric modes for the circular tubes. The number of folding half-waves of seven for 3.5 mm tubes, and thirteen for 2 mm tubes, was generally overpredicted by theory. Aluminum end plates that were welded onto the tube ends allowed for fast test setup, but may have resulted in some sliding and tipping of the drop tower. The tubes were found to have decreasing average crush force with smaller corner radii, esp. for the 3.5 mm thick tubes.Copyright © 2007 by General Motors |
