Citation

Olabi AG, Morris E, Hashmi MSJ, Gilchrist MD. Int. J. Impact Eng. 2008; 35(1): 10-26.

Copyright

(Copyright © 2008, Elsevier Publishing)

DOI

10.1016/j.ijimpeng.2006.11.007

PMID

unavailable

Abstract

The function of an energy absorber is to absorb kinetic energy upon impact and dissipate it in some other form of energy, ideally in an irreversible manner. Non-recoverable (inelastic) energy can exist in various forms such as plastic deformation, viscous energy and friction or fracture energy. Circular or square sectioned tubes are one of the most commonly used structural elements due to their prevalent occurrence and easy manufacturability. Circular tubes, for example, can dissipate elastic and inelastic energy through different modes of deformation, resulting in different energy absorption responses. Such methods of deformation include lateral compression, lateral indentation, axial crushing, tube splitting and tube inversion. It is important to study their energy absorption characteristics and mean crushing loads so as to determine their applicability to practical energy absorption situations. Such practical cases may consist of energy absorbers in the aircraft, automobile and spacecraft industries, nuclear reactors, steel silos and tanks for the safe transportation of solids and liquids. Dynamic lateral crushing of mild steel (DIN 2393) nested tube systems was conducted using a ZWICK ROELL impact tester. The tests were performed with impact velocities ranging between 3 and 5 m/s, achieved using a fixed mass impinging onto the specimens under the influence of gravity. The various nested tube systems consisted of one standard and one optimised design. Their crushing behaviour and energy absorption capabilities were obtained and analysed.
In addition to the experimental work, numerical simulations using the explicit code LS-DYNA were conducted; boundary conditions matching those observed in experiments were applied to the models. Results from the numerical method were compared against those obtained from experiments. An over-prediction in force-deflection responses was obtained from the numerical code. An attempt was made to explain this inconsistency on the basis of the formation of plastic hinges and the validity of strain rate parameters used in the Cowper Symonds relation. It was found that the optimised energy absorbers exhibited a more desirable force-deflection response than their standard counterparts due to a simple design modification which was incorporated in the optimised design.