Crashworthiness study on functionally graded thin-walled structures

Thin-walled structures have been used in a range of energy absorption devices attributable to their lightweight and stable responses to impact loading. As a relatively new component with a higher efficiency of material utilisation, functionally graded thickness (FGT) structures with desired varying wall thickness become attractive. This paper aims to provide a comparative study on the advantages of FGT structures over more conventional thin-walled structures such as tapered square and circular tubes that have uniform thickness (UT) with the same weight. It relates the equivalent thickness t(U) of straight uniform thickness (SUT) tubes and inclined angle theta of tapered uniform thickness (TUT) tubes to gradient exponent n of FGT tubes. A new indicator for spatial efficiency of energy absorption (SEEA), defined as the energy absorption per unit occupation of area, E-TA, is introduced to evaluate their relative spatial performance for the cases where structure space is restricted. The comparison reveals that the FGT tube is superior to its SUT and TUT counterparts under the conditions of the same weight and the same spatial occupation in overall crashing behaviours as per energy absorption and peak crushing force. The FGT structures are thus recommended as a potential element for crashworthiness applications.