On the Crashworthiness of Shear-Rigid Sandwich Structures

[+] Author and Article Information
Dirk Mohr, Tomasz Wierzbicki

Impact and Crashworthiness Laboratory,  Massachusetts Institute of Technology, Cambridge, MA 02139

J. Appl. Mech 73(4), 633-641 (Nov 07, 2005) (9 pages) doi:10.1115/1.2165232 History: Received December 20, 2004; Revised November 07, 2005

This paper deals with the evaluation of the crashworthiness of thin-walled sandwich box structures for automotive applications. Quasi-static crushing simulations are carried out to estimate the energy absorption of prismatic box columns made from sandwich sheets. The sandwich sheets have perforated cores of different densities with staggered holes perpendicular to the panel faces. It is found that the specific energy absorption of columns made of sandwich sheets is approximately the same as that of conventional columns composed of homogeneous sheets of the same total wall thickness. Furthermore, theoretical analysis indicates that by increasing the core thickness, sandwich structures could be up to 50% lighter while providing the same mean crushing force. However, these gains may not be achieved in practical applications since increasing the core thickness also increases the likelihood of premature face sheet fracture during crushing.

Copyright © 2006 by American Society of Mechanical Engineers
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Figure 3

Microstructure of the perforated sandwich core material. The in-plane coordinate axes have been labeled “x” and “y,” while “T” indicates the out-of-plane direction. The dashed wire frame in (a) and the rectangle in (b) highlight the mechanical unit cells which are chosen for numerical analysis of the out-of-plane and in-plane properties, respectively.

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Figure 4

In-plane loading in the x-direction: (a) compression and (b) tension for ρ*=25%, (c) compression and (d) tension for ρ*=60%

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Figure 7

Engineering stress-strain curves for out-of-plane shear loading along the T‐x-plane

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Figure 8

FE-mesh: (a) side view of the quarter model, (b) top view of the eighth model. The red elements represent the t=0.2‐mm-thick face sheets, the blue elements discretized the C=1.2‐mm-thick core material. The total sandwich sheet thickness is h=C+2t=1.6mm.

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Figure 9

Force-displacement curves for the crushing of square sandwich box columns

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Figure 1

Example of a 120‐mm-wide and 100‐mm-high square box column made from an aluminum honeycomb sandwich sheet (a) before and (b) after quasi-static crushing (Mohr and Wierzbicki (6))

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Figure 2

(a) Schematic of the crushing of a square sandwich box column. In the column corners the energy is mostly dissipated through stretching (shaded area) whereas cell wall bending dominates along the hinge lines (thick lines) (b) and (c) Longitudinal cut through a cell wall; in the case of shear-soft sandwich sheets (b), the core material undergoes large shear deformations as the sandwich is bent, whereas in the case of shear-rigid sandwich sheets (c), initially perpendicular cross sections remain perpendicular throughout bending while the two face sheets are respectively compressed or stretched (Mohr and Wierzbicki (7)).

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Figure 5

Engineering stress-strain curves for uniaxial in-plane loading along the x-direction. The results are shown for four different cores densities: ρ*=25%, 37%, 46%, and 60%.

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Figure 6

Out-of-plane shear loading along the x-direction: (a) ρ*=25%, (b) ρ*=60%

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Figure 10

Folded sandwich cross sections for different core densities. The encircled region in (a) highlights the area of partial through-the-thickness crushing of the core material. The insert in (c) shows the 3D view of the bending and stretching of the profile walls (compare with Fig. 1) as obtained from FEA; the color indicates the equivalent plastic strain in the outer face sheet.

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Figure 11

Design for a constant mean crushing force. Relative weight and relative wall thickness of the equivalent sandwich structure as a function of the relative core material density (see Eqs. 39,43).



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