Experimental Study on Crashworthiness of Functionally Graded Thickness Thin-Walled Tubular Structures

This paper is an experimental investigation of the crashworthiness behavior of functionally graded thickness (FGT) thin-walled tubular structures. Aluminum alloy AA6061-T5 was chosen because of its high strength to weight ratio and high stiffness. A series of FGT tubes with thicknesses varying linearly from one end to the other were evaluated in quasi-static crushing and three-and four-point bending tests for the purpose of evaluating their energy absorption characteristics. AA6061-T5 FGT tubes with four thickness distributions were considered, namely: t(top)= 0.6, 0.8, 1.0, 1.2 mm, t(bottom)= 1.5 mm. Specific energy absorption (SEA) and crush force efficiency (CFE) under maximum deformed displacement (delta(max)) were measured from the tests to infer crashworthiness of the FGT tubes. It was found that the FGT tubes exhibit superior performance relative to a uniform thickness (UT) counterpart especially at the highest displacements and deformed more stably in overall crashing behaviors or collapsed modes. For example, the CFE of the AA6061-T5 FGT tube with t(top)= 0.6 mm at delta= 80 mm was similar to 105 %; however, that for an AA6061-T5 UT counterpart with a 1.5 mm thickness tube is only 62 %. This suggests the possibility that crash energy absorption management in ground transportation vehicles may be enhanced through the use of the FGT tube designs.