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Research Papers

Finite Element Modeling and Experimental Characterization of Enhanced Hybrid Composite Structures for Improved Crashworthiness

[+] Author and Article Information
Luciana Arronche

Mechanical and Aerospace Engineering,
University of California,
Davis, CA 95616

Israel Martínez

Departamento de Ingeniería Mecánica,
Universidad de Guanajuato,
Guanajuato, Mexico

Valeria La Saponara

Mechanical and Aerospace Engineering,
University of California,
Davis, CA 95616
e-mail: vlasaponara@ucdavis.edu

Elias Ledesma

Departamento de Ingeniería Mecánica,
Universidad de Guanajuato,
Guanajuato, Mexico
e-mail: elias@ugto.mx

1Corresponding author.

Manuscript received April 27, 2012; final manuscript received August 28, 2012; accepted manuscript posted January 28, 2013; published online July 19, 2013. Assoc. Editor: Martin Ostoja-Starzewski.

J. Appl. Mech 80(5), 050902 (Jul 19, 2013) (9 pages) Paper No: JAM-12-1168; doi: 10.1115/1.4023495 History: Received April 27, 2012; Revised August 28, 2012; Accepted January 28, 2013

In this work, two hybrid composite structures were designed, modeled, and tested for improved resistance to impact. They were inspired by bistable composite structures, which are structures composed of two parts: a so-called “main link” and a so-called “waiting link.” These links work together as a mechanism that will provide enhanced damage tolerance, and the structure exhibits a bistable stress/strain curve under static tension. The function of the main link is to break early, at which point the waiting link becomes active and provides a redundant load path. The goal of the current study was to design, manufacture, and test a similar concept for impact loading and achieve greatly improved impact resistance per unit weight. In the current project, the main link was designed to be a brittle composite material (in this case, woven carbon/epoxy) exposed to impact, while the waiting link was chosen to be made with a highly nonlinear and strong composite material (in this case, polyethylene/epoxy), on the opposite surface. Hence, the structure, if proven successful, can be considered an enhanced hybrid concept. An explicit finite element (FE) commercial code, LS-DYNA, was used to design and analyze the baseline as well as two proposed designs. The simulations' methodology was validated with results published in the literature, which reported tests from linear fiber-reinforced composites. The plots were obtained via the ASCII files generated from the FE code, processed using matlab®, and compared to experimental impact tests. An instrumented drop-weight testing machine performed impact tests, and a high-speed camera validated the specimens' displacement under impact. It is shown that the FE model provided qualitative behavior very consistent with the experiments but requires further improvements. Experimentally, it is shown that one of the two enhanced hybrid models leads to up to a 30% increase of returned energy/weight when compared to its baseline and, therefore, is worthy of further investigations.

Copyright © 2013 by ASME
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References

Figures

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Fig. 1

Sketch of bistable structure (Winkelmann et al. [13])

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Fig. 2

Experimental load/displacement curve of bistable composite structure under quasi-static tension. Here, the specimen has CFRP main links and Spectra® FRP waiting links and is one of the specimens discussed in Ref. [13] and shown in Fig. 3.

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Fig. 3

Hybrid bistable composite specimens for static tension tests (width ∼25.4 mm) (Winkelmann et al. [13])

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Fig. 4

Experimental results for energy, force, and displacement from Heimbs et al. [19]

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Fig. 5

LS-DYNA model results of (a) force versus time, (b) energy versus time, and (c) displacement versus time. Input data were built using the problem in Ref. [19].

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Fig. 6

Energy plot for experimental data and FE simulation, from Chandekar et al. [20]

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Fig. 7

Results of the simulation of [20] under a nominal impact energy of 32.7 J, using the current methodology

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Fig. 8

Candidate model I type

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Fig. 13

(a) CAD/CAM drawing for foam milling; (b) machined foam

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Fig. 12

Contacts defined between impactor and impacted surface in the FE model

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Fig. 11

Energy versus time, for the baseline, under 80 J impact. This model used LS-DYNA real constants.

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Fig. 10

Energy versus time, for the baseline, under 80 J impact. This model used the LS-DYNA CONTACT_ TIEBREAK_ SURFACE_ TO_ SURFACE.

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Fig. 9

Candidate model II type

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Fig. 14

Manufactured candidates: (a) model I, (b) model II, with and without the foam core. The grid in the background has 25.4 mm × 25.4 mm squares (1 in. × 1 in.).

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Fig. 15

(Left) impact test machine with (right) fixture detail. Specimen width ∼140 mm.

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Fig. 16

Inelastic curve, from Rydin and Kharbari, [21]. Copyright © 1995, SAGE Publications.

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Fig. 18

Finite element mesh of model I

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Fig. 19

Buckling and contact early contact release, around ∼0.2 ms

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Fig. 20

Impact after 0.25 ms. For model II, contact release is immediately after impact.

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Fig. 21

Inelastic energy curve for baseline and enhanced specimens

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Fig. 22

Inelastic energy curve with returned energy normalized by weight

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Fig. 17

FE model of baseline specimen impacted at (a) 40 J and (b) 100 J. The plot for 80 J is shown in Fig. 10. (c) Corresponding inelastic energy curve.

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