Performance of an auxetic honeycomb-core sandwich panel under close-in and far-field detonations of high explosive
Introduction
Increasing terrorist attacks and accidental explosions tend to increase the exposure of various civilian and military infrastructures to blast and impact loads [1], [2]. When a high explosive detonates, an extremely high amount of energy and pressure are released in a very short duration of time [3]. The intensive pressure and energy resulted from an explosion causes catastrophic damage and collapse of the infrastructures leading to significant human and economic losses [4], [5]. Therefore, the civil and military infrastructure are required to be protected to reduce casualties and economic loss from intentional and accidental explosions.
As blast pressure and energy are the major physical factors for damage and collapse of the infrastructures, damping of the blast pressure and dissipation of energy can be a solution to protect the civil and military infrastructures from detonation of high explosive. A large number of metamaterials with high energy absorption capacity have been developed for protective engineering. Among the different metamaterials, light weight honeycomb structures are extensively used to absorb blast and impact energies [6]. These lightweight honeycombs can be fabricated to have positive and negative Poison’s ratios.
The use of auxetic structures—the structures having negative Poisson’s ratio—to resist dynamic loads has gained the attention of several researchers in the recent years. The counterintuitive deformation mechanism of the auxetic materials is found to result in better physical properties such as higher energy absorption, improved indentation resistance and enhanced vibration damping [7], [8], [9]. However, an appropriate design of such auxetic materials and structure to resist dynamic loads effectively is a complex task [10].
Various auxetic structures are found to be used in protective engineering field for different applications. Al-Rifaie and Sumelka [11] developed a new shock absorbing uniaxial graded auxetic damper, and carried out parametric study to develop an efficient graded system for shock absorption. However, implementation of developed damper in real blast and impact shock absorption resulted from field explosion was not given the paramount importance, instead using simplified load functions. Yang et al. [12] studied auxetic composite honeycomb, re-entrant hexagon, and re-entrant arrowhead for their potential use in body protection with respect to shock absorption and comfort. Based on the structure, the same material was found to exhibit different Poisson’s ratio, and auxetics showed high potential for body protection with respect to reduction of impact force and comfortability to wear. An investigation on specific energy absorption and maximum displacement control of the composite panels comprising of 3D chiral auxetics subjected to blast load was conducted by Novak et al. [13]. A 10% lower maximum panel displacement with auxetic was reported. Imbalzano et al. [10] carried out a numerical study on the performance of re-entrant auxetic structure under blast load by varying the geometric parameters of auxetic unit cell. The performance of the auxetic structure was found to be affected by the parameters of unit cell. The geometry with larger value of equivalent negative Poisson’s ratio exhibited better performance to resist impulsive loadings. Furthermore, a higher number of layers of auxetic cells enhanced the energy absorption and decreased back face stress. A numerical investigation on blast resistance of composite panel with auxetic cellular core was conducted by Imbalzano et al. [14]. In this study, 3D re-entrant auxetic structure was modeled with beam elements to reduce the computation cost. The performance of composite panel was compared with an equivalent monolithic plate. The composite panel reduced backfacet displacemet by 30% and increased plastic energy absoprtion by 50% under blast loading. Qi et al. [15] designed and tested a protective structure for reinforced concrete panel by using auxetic honeycomb under close-in detonation. A numerical model was developed by Qi et al. [15] using a simplified method called blast impact impulse model (BIIM). Jin et al. [16] conducted a numerical investigation on dynamic behaviour of auxetic re-entrant honeycomb structure under blast load. It was concluded that graded auxetic core with higher density on upper part was better to resist blast load. Xiao et al. [17] investigated deformation and residual deflection of re-entrant auxetic core sandwiched panel under impact load by experimental and numerical approaches. A linear relationship between residual deflection and impulse was found in their study.
Linforth et al. [18] investigated energy absorption behaviour of the auxetic oval structure by quasi-static and dynamic compression tests. Increasing number of layers of the auxetic oval was found to result in better performance with respect to energy absorption. Furthermore, a hybrid auxetic oval was developed to mitigate fracture effects observed in the base auxetic oval. Parametric studies and optimisation of re-entrant honeycomb protective systems under blast load were conducted by Qi et al. [19]. The effects of boundary conditions, geometry and thickness of re-entrant hexagon honeycomb on blast resistance behaviour of the developed protective system were studied. Maximum displacement and energy absorption were found more sensitive to thickness than geometric parameters. In addition, boundary conditions showed insignificant effect on total energy absorption. Kalubadanage et al. [20] studied the behaviour of the large scale auxetic re-entrant honeycomb sandwich panels under near-field blast loadings by experimental and numerical approaches. Validated numerical models were developed in LS-DYNA using the BIIM method. Variation of blast load intensity led to different deformation pattern and negative Poisson’s ratio of re-entrant honeycomb cored sacrificial cladding systems. Furthermore, it was reported that quick densification of the auxetic core under close-in blast could form a high velocity projectile which may amplify the damage rather than mitigation.
The past researches are found to mainly focus on development of the protective systems by using auxetic structures. However, their actual efficacy to protect the infrastructure is rarely examined [21], [22]. Furthermore, only a particular dynamic loading scenario is found to be considered in the literatures. Thus, an in-depth insight on how parameters of dynamic blast load affect performance of protective system is lacking. This paper aims to investigate the effectiveness of a sacrificial protective system designed with re-entrant auxetic honeycomb sandwich panel (AHSP) to protect reinforce concrete (RC) structures from blast load. To examine the performance of AHSP under dynamic load with different characteristics, two different detonation scenarios (close-in and far-field) with equivalent positive impulses are considered in the research.
In this paper, performance of AHSP under close-in and far-field blasts was investigated by using comprehensive numerical modelling. Multi-material Arbitrary Lagrangian Eulerian (MM-ALE) algorithm in LS-DYNA was used to develop a comprehensive numerical model which simulates detonation of explosive, propagation of blast wave, and its interaction with the structure. In the numerical model, appropriate constitutive material laws, equation of states (EOS), boundary conditions, and rate effects were used. The performance of AHSP was compared with equivalent conventional honeycomb-cored sandwich pane (CHSP) having a positive Poisson’s ratio. Deformation pattern, energy absorption, blast overpressure damping, pressure reflection from deformed shape, and stress transmission to the base block characteristics of AHSP and CHSP were evaluated to quantify the performances.
Section snippets
Geometry and materials of sandwich panels
The geometry and material of auxetic honeycomb (AH) was adopted from Qi et al. [15]. An equivalent conventional honeycomb (CH) with a positive Poisson’s ratio was designed in such a way that it possessed the same mass and area with AH in an area of 500 mm × 550 mm. The thicknesses of top and inclined elements were 1 mm and 0.5 mm, respectively, in both AH and CH unit cells. Furthermore, the height of each unit cell was 24 mm. The details of AH and CH unit cells are shown in Fig. 1.
Two sandwich
Overview of field blast test
In the field blast test by Qi et al. [15], AHSP was subjected to a close-in blast and placed over a square reinforced concrete (RC) slab of sides 600 mm, and 100 mm depth. Two layers of 10 mm diameter steel reinforcing bars were provided in the concrete slab. Timber planks resting on a strong steel foundation were used to simply support the RC slab. The sandwich panel was covered with a high-strength steel (HSS) 9.4 mm thick cover plate. The dimensions of the HSS cover plate were the same with
Design of equivalent impulse blast load
A typical blast pressure–time history at a standoff distance is shown in Fig. 4. When a high explosive detonates, a very high pressure is released and it travels to the target (structure). After time tA of the explosion, pressure arrives at the target, and the pressure at target raises to Pso instantly. tA and Pso are called arrival time and peak positive overpressure, respectively. Within a duration of to (positive phase duration), the pressure at the target returns to ambient pressure (Po),
Numerical model development
In this study, LS-DYNA hydrocode was used to simulate the performance of sandwich panels under close-in and far-field blast loads. Multi-material Arbitrary Lagrangian Eulerian (ALE) formulation and Lagrangian formulation available in LS-DYNA were coupled together to simulate the performance of the designed honeycomb core protective structures under the blast loads. A brief description of ALE is given in Section 5.1. To minimise the computation cost, a quarter symmetry model was constructed.
Comparison with experiment results
The comparison of deformations of different parts from experiment and numerical simulation are shown in Fig. 8. The numerical model captured deformation pattern with a good accuracy. The detonation of the cylindrical charge created a dome-shaped depression on the cover plate in both experiment and simulation (see Fig. 8a). After close-in blast, AHSP showed concave spherical shape in the centre with some fracture of the material on the top plate. As compared in Fig. 8a, both the fracture and
Conclusions
In this paper, performance of a re-entrant auxetic honeycomb sacrificial protective structure was quantified for its efficacy to protect RC structure from close-in and far-field blast loads. MM-ALE formulation in LS-DYNA was used to develop a quarter-symmetric model. Validated constitutive material laws, appropriate boundaries, and strain rate effects were considered in the numerical model. The behaviours of AHSP were compared with the CHSP. In addition, to elucidate the mechanism of energy
Declaration of Competing Interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Acknowledgements
This research was funded through the ARC Discovery project DP170100851: A bio-inspired lightweight composite system for blast and impact protection; and the CRC-P for Advanced Manufacturing and Construction of Smart Building Modules. In addition, the Melbourne Research Scholarship for the opportunity to pursue doctoral degree at The University of Melbourne is appreciated by the first author.
Data availability
All the raw/processed data required to reproduce these findings were presented in this manuscript.
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