Bioinspired Design of Building Materials for Blast and Ballistic Protection

Advances in Civil Engineering, Aug 2016

Nacre in abalone shell exhibits high toughness despite the brittle nature of its major constituent (i.e., aragonite). Its specific structure is a major contributor to the energy absorption capacity of nacre. This paper reviews the mechanisms behind the performance of nacre under shear, uniaxial tension, compression, and bending conditions. The remarkable combination of stiffness and toughness on nacre can motivate the development of bioinspired building materials for impact resistance applications, and the possible toughness designs of cement-based and clay-based composite materials with a layered and staggered structure were discussed.

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Bioinspired Design of Building Materials for Blast and Ballistic Protection

Bioinspired Design of Building Materials for Blast and Ballistic Protection Yu-Yan Sun,1 Zhi-Wu Yu,1 and Zi-Guo Wang2 1School of Civil Engineering, Central South University, Changsha 410004, China 2College of Resources and Planning Sciences, Jishou University, Zhangjiajie 427000, China Received 27 March 2016; Revised 9 July 2016; Accepted 11 July 2016 Academic Editor: Chiara Bedon Copyright © 2016 Yu-Yan Sun et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Abstract Nacre in abalone shell exhibits high toughness despite the brittle nature of its major constituent (i.e., aragonite). Its specific structure is a major contributor to the energy absorption capacity of nacre. This paper reviews the mechanisms behind the performance of nacre under shear, uniaxial tension, compression, and bending conditions. The remarkable combination of stiffness and toughness on nacre can motivate the development of bioinspired building materials for impact resistance applications, and the possible toughness designs of cement-based and clay-based composite materials with a layered and staggered structure were discussed. 1. Introduction Abalone nacre is the inner layer of abalone shell, which can help to maintain the integrity of the shell under external loads and thus protect the mollusk. Although composed of at least 95% of aragonite by weight, nacre exhibits high toughness which is 1000 times that of the aragonite without compromising strength [1]. Moreover, the ratio of compressive strength to tensile strength of nacre ranges from 1.5 to 3, which is much smaller than those of the conventional monolithic ceramics (range: 8–15) and plain concrete (range: 9–15) [2]. The outstanding mechanical performance of nacre is generally considered to be due to the hierarchical structure of nacre at the nano- and microlevels. Inspired by the structure of nacre, man-made composite materials have been developed with enhanced toughness, such as bioinspired glass and technical ceramic [3–7]. However, very limited work has been carried out to apply this natural principle to the toughness design of building materials such as cement-based and clay-based materials. This paper discussed the effects of the hierarchical structure on the mechanical behavior of nacre based on the existing publications. Learning the underlying mechanisms of the performance of abalone nacre would help to design nacre-like building materials that combine strength and toughness. When the building was subjected to seismic, impact, or blast loading, these materials can help reduce the incidences of failures and enhance public safety. 2. Abalone Nacre2.1. Structure Features Abalone nacre is a material of hierarchical structure formed by aragonite tablet layers and thin biological organic interlayers, as shown in Figure 1. Each tablet layer consists of polygonal aragonite tablets which are about 5–8 μm in diameter and 0.5 μm in thickness; the spacing between the neighboring tablets is about 5 nm [2]. Moreover, tablets in adjacent layers are slightly staggered rather than stacked randomly or exactly [8]. Transmission electron microscopy (TEM) shows that the surfaces of the aragonite tablets are not flat but significantly wavy, their roughness can reach amplitudes exceeding 200 nm when the average thickness of the tablets was 450 nm, and the waviness of the tablets is highly conformal so that the tablets of adjacent layers fit perfectly together [9]. Figure 1: The structure of abalone nacre at different length scales: (a) the inside view of an abalone shell, (b) SEM image showing the fractured surface of nacre, and (c) the asperities on the surface of aragonite tablets. At the nanoscale, the organic interlayer is about 20–50 nm thick, which is porous and possesses holes of about 50 nm in diameter [2]. Aragonite bridges (Figure 2(a)) connect the aragonite tablet layers through the interlayer [10], and aragonite asperities on the surface of the tablets (Figure 1(c)) form nanoscale islands that are around 30–100 nm in diameter, 10 nm in amplitude, and 60–120 nm apart [11]. Moreover, at the periphery of some tablets, dovetail-like features (Figure 2(b)) generated by the waviness of the interface can be observed in two-dimensional cross sections of nacre [8]. Furthermore, rotated nanograins with an average grain size of 32 nm within the aragonite tablets were found by Li et al. [12] using in situ dynamic atomic force microscope (AFM). Figure 2: Schematic illustrations of (a) aragonite bridges (marked by arrows) between tablets and (b) dovetail-like features at the periphery of tablets. 2.2. Mechanical Responses The outstanding mechanical properties of nacre were first demonstrated by Currey [13] and have been intensively studied over the past two decades. Sarikaya [14] conducted bending tests on r (...truncated)


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Yu-Yan Sun, Zhi-Wu Yu, Zi-Guo Wang. Bioinspired Design of Building Materials for Blast and Ballistic Protection, Advances in Civil Engineering, 2016, 2016, DOI: 10.1155/2016/5840176