Woodpecker’s head inspired sandwich beam for improved impact resistance
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Date
2018
Authors
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Publisher
Universiti Teknologi Malaysia
Abstract
It is well recognized by structural engineers that sandwich structures in the presence of impact load experience more severe damages in their skins and cores. Thus, this study introduces a new sandwich beam inspired by the woodpecker head structure to enhance its impact resistance. A four-layered bio-inspired sandwich beam (BHSB) consisting of two carbon/epoxy composite skins, aluminum honeycomb core, and rubber core for improved impact resistance was developed and examined under repeated impact loadings. First, BHSB was compared experimentally and numerically (ABAQUS/Explicit 6.13) with a conventional sandwich beam (HSB) at different repeated impact energies (7.28 J, 9.74 J, 12.63 J, 13.5 J, 15.55 J, and 21.43 J). The BHSB was then optimized in terms of numerous stacking sequences ([0/±30], [0/±45], [0/±60], and [0/±90]), ply numbers (6, 9, and 12), aluminum honeycomb core thicknesses (20, 25, and 30 mm), and rubber core thicknesses (3, 6, and 9 mm). Failure mode maps for the developed beam were also constructed based on the low-velocity repeated impact event. The novel addition of rubber core to the sandwich beam reduced the damage area by 60-95 % compared to HSB at different impact energy levels. The damage mechanism of BHSB was only matrix cracking. The bottom skin of BHSB carried 12-20 times lower stresses than that of HSB. It is because the rubber core minimizes the propagation of stress during impact by a planar spreading mechanism allowing only little stress to develop in the bottom skin of BHSB. To assess overall performance, the newly proposed impact resistance efficiency indices for BHSB were found to be 2.35 to 25.22 times higher than HSB, indicating that BHSB resists more efficiently the impact loading. Based on these findings, a superior sandwich beam inspired by the woodpecker’s head configuration in resisting low-velocity impact load has been successfully produced. The optimization results showed that the best impact resistance of the new sandwich beam was found from the skin with the stacking sequence [0/±30], ply number of 12, aluminum honeycomb core thickness of 25 mm, and rubber core thickness of 9 mm. For design convenience, a series of equations was developed based on the observed results for easy failure mode prediction for various impact energies and numbers. In terms of main contributions, this study is the first to develop a sandwich beam based on woodpecker head structure, model repeated impacts loading for any sandwich structure, construct failure map based on real low-velocity data, produce failure map design equations for design convenience, and propose an overall impact performance index, Ie, for a fair impact resistance comparison.
Description
Thesis (Ph.D (Civil Engineering))
Keywords
Sandwich construction—Testing, Structural engineering—Research, Strains and stresses