Ballistic impact experiments of metallic sandwich panels with aluminium foam core

https://doi.org/10.1016/j.ijimpeng.2010.03.006Get rights and content

Abstract

Metallic sandwich structures with aluminium foam core are good energy absorbers for impact protection. To study their ballistic performance, quasi-static and impact perforation tests were carried out and the results are reported and analysed in this paper. In the experiments, effects of several key parameters, i.e. impact velocity, skin thickness, thickness and density of foam core and projectile shapes, on the ballistic limit and energy absorption of the panels during perforation are identified and discussed in detail.

Introduction

As a novel composite structure, a sandwich panel with cellular core (frequently metallic foams) has excellent energy dissipating performance and advantage in weight saving, and thus can be used as an energy absorber in a wide range of applications under extreme loading conditions such as ballistic impact. The cellular microstructures offer them with the ability to undergo large plastic deformation at nearly constant nominal stress, and thus can absorb a large amount of kinetic energy before collapsing to a more stable configuration or fracture [1], [2], [3]. Investigations into the ballistic loading on composite structures have been extensively conducted on the polymer or glass/carbon fabric based laminates [4], [5], [6], [7], [8], [9], [10], [11], [12], [13], and comparably less attention has been paid on sandwich structures.

Most of the existing work on sandwich panels has focused on structures with conventional honeycomb or PVC foam cores. Goldsmith and Sackman [14] tested the effects of several parameters, e.g. impact velocity, boundary conditions and bonding strength between the honeycomb core and aluminium faces, on the energy dissipation during perforation. Mines et al. [15] examined the low velocity perforation behaviour of sandwich panels with polymeric composite skins and honeycomb core. They suggested that higher impact velocities tend to increase the energy absorption, which is attributed to an increase in the core crush stress and skin failure stress at high strain rates. Similar experiments have been carried out by Roach et al. [16], [17] on PVC foam core panels, where the role of core and the relationship between the energy absorbed and delamination area were studied as well. Hoo Fatt and co-workers [18], [19] developed analytical solutions for the ballistic limit of a honeycomb core sandwich plate subjected to normal impact by projectiles with different shapes, in which the overall bending and stretching of the plates were considered. Kepler [20], [21] experimentally and theoretically investigated the perforation performance of PVC foam core panels and three main damage modes were identified and formulated mathematically. Wen et al. [12] and Reid and Wen [13] developed analytical models to calculate the ballistic limit and energy dissipation for the panels of this type. More recently, Villanueva and Cantwell [22] conducted the high velocity impact on the composite and fibre-metal laminate sandwich structures with aluminium foam core. Three main failure patterns were distinguished and it was found that the panels with aluminium foam core offer considerably higher specific perforation energy than their plain composite counterparts with similar composite volume fractions. Hanssen et al. [23] carried out experimental tests and numerical simulations of the bird strike on sandwich panels made from aluminium foam core with aluminium faces. There is no perforation observed from the tests. Zhao et al. [24] tested the perforation behaviour of aluminium foam core sandwich panels with the aluminium alloy faces using a split Hopkinson pressure bar, and recorded the piercing force–displacement history. However, no detailed parametric studies have been reported yet.

In this study, a large number of perforation tests were conducted on the sandwich panels with aluminium foam core and two identical aluminium face-sheets, which were subjected to quasi-static loading and impact at velocities ranging from 70 m/s to 250 m/s. The experimental set-ups and procedure are presented in Section 2. Then in Section 3, the specimen perforation process recorded and the failure/damage patterns observed are described in detail. Based on the impact and exit velocities measured in the tests, the effects of face thickness, core thickness and relative density and the projectile shapes on the ballistic limit and energy absorption are analysed in Section 4. In addition, an empirical equation is derived to describe the influence of impact velocity on the perforation energy.

Section snippets

Specimens, projectiles and material properties

The square sandwich panels tested consisted of two aluminium face-sheets with identical thickness and an aluminium foam core. The face-sheets were made of Al-5005H34 and had four thicknesses i.e. 0.6 mm, 1.0 mm, 1.5 mm and 2.0 mm, respectively. The CYMAT™ closed cell aluminium foam (Al–Si(7–9%)–Mg(0.5–1%)) cores had five relative densities, that is, 5%, 10%, 15%, 18% and 20%. The cores were machined into 120 mm × 120 mm plates with two different thicknesses (25 mm and 50 mm). The face-sheets were glued

Experimental observations

A high speed video camera was also used to record impact and perforation process and response of the sandwich structures for six samples. Fig. 8(a) and (b) shows typical photographic sequences of the front face and back face, respectively, recorded at 20,000 frames/s during perforation by a hemispherical nosed projectile at 187 m/s. The perforation process took approximately 0.45 ms.

Depending on the impact energy level, the specimens after tests exhibit two damage modes: (1) full perforation and

Results and analysis

Two key quantitative results are analysed in detail in this section, which are critical for evaluating the penetration resistant behaviour and energy dissipating performance of the sandwich structures: (1) ballistic limit (Vb), which is defined as the velocity when the projectile is either stuck in the back face or exits with a negligible velocity; and (2) perforation energy (Ep), which is essentially the energy absorbed by the structure during perforation.

If the mass of any small

Conclusions

Quasi-static and impact perforation tests were carried out to test the ballistic performance and energy absorption of metallic sandwich panels. The sandwich specimens consisted of two aluminium alloy skins and a core made from aluminium foam, and impacted by three projectiles with different shapes: flat ended, hemispherical nosed and conical nosed. The perforated specimens showed similar damage patterns: the front face exhibits a circular crater without global deformation. A localised tunnel is

Acknowledgements

The reported research is financially supported by Australian Research Council (ARC) through a Discovery Grant, which is gratefully acknowledged. The third author (G. Lu) wishes to thank the National Science Foundation of China under grants 90305015 and 10632060 for the support of his visit to Tsinghua University, China.

References (29)

Cited by (199)

View all citing articles on Scopus
1

Current address: Bioengineering Center, Wayne State University, Detroit, MI 48201, USA.

View full text