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Research Papers

# Numerical Evaluation of Stiffness and Energy Absorption of a Hybrid Unidirectional/Random Glass Fiber Composite

[+] Author and Article Information
Wensong Yang

Mechanical and Aerospace Engineering Rutgers,  The State University of New Jersey, 98 Brett Road, Piscataway, NJ 08854

Assimina A. Pelegri1

Mechanical and Aerospace Engineering Rutgers,  The State University of New Jersey, 98 Brett Road, Piscataway, NJ 08854pelegri@jove.rutgers.ed

1

Corresponding author.

J. Eng. Mater. Technol 133(4), 041018 (Oct 27, 2011) (8 pages) doi:10.1115/1.4005253 History: Received March 11, 2011; Revised July 13, 2011; Published October 27, 2011; Online October 27, 2011

## Abstract

A finite element method is employed to numerically evaluate the stiffness and energy absorption properties of an architecturally hybrid composite material consisting of unidirectional and random glass fiber layers. An ls-dyna finite element model of a composite hollow square tube is developed in which the position of the random fiber layers varies through the thickness. The assessment of the stiffness and energy absorption is performed via three-point impact and longitudinal crash tests at two speeds, 15.6 m/s (35 mph) and 29.0 m/s (65 mph), and five strain rates, $ɛ·$  = 0.1 s−1 , 1 s−1 , 10 s−1 , 20 s−1 , and 40 s−1 . It is suggested that strategic positioning of the random fiber microstructural architecture into the hybrid composite increases its specific absorption energy and, therefore, enhances its crashworthiness. The simulation data indicate that the composite structure with outer layers of unidirectional lamina followed by random fiber layers is the stiffest due to the considerable superior specific energy absorption of the random fiber micro-architecture. Moreover, it is illustrated that the specific energy absorption increases with the increased ratio of impact contact area over cross-section area. Of all the parameters tested the thickness of the unidirectional laminate on the specific energy absorption does not appear to have a significant effect at the studied thickness ratios.

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## Figures

Figure 1

Finite element model of (a) three-point impact and (b) energy absorption testing for a hybrid (2-ply) unidirectional/(3-ply) random glass fiber composite tube. Dimensions are 20 mm × 20 mm × 200 mm (width × depth × length) and 5 mm thickness.

Figure 2

Cross-sections of 12 different arrangements of the hybrid (2-ply unidirectional (2U), 3-ply (3 R) random) glass fiber composite tube. Red (lighter shade) and blue (darker shade) colors refer to unidirectional lamina and random chopped fiber lamina, respectively. Position of the unidirectional glass plies is marked as x/x notation, counting from the outer perimeter of the cross-section.

Figure 3

(a) The deflection curves of the four 2U3R_1/x hybrids, in addition to the (5 R) and 5(U) layups under low (15.6 m/s) velocity impact; (b) the impact forces of the same layups under low velocity impact. All-random (5 R) and all unidirectional (5U) layups form an envelope of values for the hybrid structure, with (5 R) presenting the highest deflections and (5U) the lowest deflections. Inverse trends are observed for the impact load.

Figure 4

(a) The deflection curves of the four 2U3R_1/x hybrids, in addition to the (5 R) and 5(U) layups under high (29.0 m/s) velocity impact; (b) the impact forces of the same layups under high velocity impact. All-random (5 R) and all unidirectional (5U) layups form an envelope of values for the hybrid structure. Deflection and impact force values are higher than the observed ones of 15.6 m/s (Figs.  33) but trends are similar.

Figure 5

Impact force versus displacement curves at different strain rates during 8 mm crashing in the fiber direction of the 2U3R_1/2 hybrid. Increase of the strain rate results in higher impact force values achieved at larger displacements.

Figure 6

Impact force versus displacement curves at different steel impactor contact area sizes during 8 mm crashing in the fiber direction of the 2U3R_1/2 hybrid. Strain rate of ε· = 20 s−1 during loading. Increase of the contact area results in higher impact force values achieved at larger displacements.

Figure 7

Impact force-deflection curves for four different unidirectional lamina thicknesses of the 2U3R_1/2 hybrid (overall thickness is 5 mm). The increased percentage of unidirectional fibers in the structure results in slightly higher impact forces in the begging of the 8 mm crash simulations at ε· = 20 s−1 . A traditional crash and release pattern is observed at the 4 mm–8 mm displacement range for the 56% of unidirectional fibers in the hybrid composite.

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