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It has become a norm that the general strategic mechanical development goal forautomotive engineering of highsafety, convenience, and ride comfort is contrary to the

environmental concerns, leading its focus towards an increase in the automobil

weight.Recent strategic mechanical development goals have turned their directionto the application of high-quality aluminum for the vehicle structure design and

manufacturing technology in aluminum space frame vehicles.

Structural foam is used for the purpose of improving both structural stiffness and strength

of each part consisting the aluminum space frame. It is a kind of chemical material,

which is composed of epoxy resin, hardener, filler, etc. Because it has a low density, it is

very effective for mass reduction. In order to evaluate the realistic crashworthiness ofthis, there are two tests that are being done axial collapse test and 3-point bending

collapse test (Kim et al., 2002)

Thin-walled structural shell elements such as cylindrical shells, conical shells, and domes

are commonly used as energy absorbing elements in crashworthiness applications.

Axial

Axial compression tests were performed on round tubes of different sizes made ofaluminium and mild steel in an Instron machine. The diameter to thickness ratios were

varied from 11.1 to 37.46 in the case of aluminium tubes,

Geometrical parameters, such as bottom diameter, height, and semi-apical angle were

considered to obtain the design space. The numerical analysis and impact experimentswere designed using design of experiments (DOE). A three-level, second-order BoxBhenken technique was used to select the design points from the design space. Various

set of numerical simulations were carried out using LS-DYNA. To investigate the

influence of flow stress of the material on the energy absorption, numerical simulationswere carried out using frusta made of aluminium, zinc, and mild steel.

Metallic tubes which dissipate the kinetic energy by undergoing plastic deformation are

found to be efficient energy absorbers. Many experimental and theoretical studies havebeen carried out on plastic collapse of thin-walled shells of various shapes, sizes and

materials under different loading conditions [15]. Important characteristics of the impact

energy absorbers, their selection criteria and various modes of plastic deformation ofthin-walled shells such as splitting, tube inversion and folding are discussed in detail in

[6,7].

A Finite Element computational model of development of the axisymmetric mode of

collapse is presented and analyzed, using a nonlinear Finite Element code FORGE2. The

material of the frustas was idealized as rigid visco-plastic. Experimental and computed

results of the deformed shapes and their corresponding load- and energy-compression

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curves were presented and compared to validate the computational model. Typical

contours of equivalent strain, equivalent strain rate, nodal velocity distribution, hoop

stress and principal stress are presented to help in predicting the mode of collapse. Onthe basis of the obtained results development of the axisymmetric mode of collapse has

been presented, analyzed and discussed.

Lateral

Collapse behaviour of thin-walled tubular structures made of metals and composites has

received considerable attention [1,2] for their application to the design for crash-worthiness of road and air-vehicles and energy absorbing devices. Metallic tubes are

frequently used as energy absorbing devices. They deform plastically in several different

modes such as inversion and folding. Each mode has an associated energy dissipation

capacity [1]. The tubular elements in energy absorbers can be confined in various waysso that when an impact does occur, they deform axially, laterally or in some combination.

In the last few decades, several investigations have been carried out to study the response

of metallic tubes for their use as energy absorbing elements [24]. Earlier studies

conducted on lateral collapse of round tubes differ in the mechanisms assumed for theanalysis

Simulation

A three dimensional numerical simulation was carried out for all samples tested under

quasi-static loading using ANSYSs. Various stages of collapse of the shell, including

non-symmetrical lobe formation were simulated for the first time, and mageometric and contact non-linearities were incorporated. The plastic region of the

material curve was assumed to be piecewise linear. Tensile tests were performed on

standard samples to obtain stressstrain curves. Results thus obtained compared well withthe experiments. Based on the formation of rolling and stationary plastic hinges an

analysis was also carried out to study the behaviour of shells under axial compression and

results were compared with experimental and numerical results.

All model parameters viz. size of fold, optimal value of folding parameter, maximum

hinge angle and the final radius of curvature of fold have been evaluated analytically. Anexpression has been derived for determining the variation of crushing load during the

formation of a fold. The total outside and total inside fold models can be easily derived

from the present model. The results have been compared with experiments

reasonably good agreement has been observed. The incorporation of change in thicknessof tube during folding has been found to reduce the folding parameter thus bringing it

closer to the experiments. Some parametric studies by varying the length of straight

portion of the fold have also been conducted. The results are of help in understanding thephenomenon of actual fold formation.