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B.A. Latella Materials Division, Australian Nuclear Science and Technology Organisation (ANTSO), Menai, NSW 2234, Australia (Received 20 December 2005; accepted 17 February 2006)

The structure, composition, and mechanical response of Australian bamboo were investigated. The graded structure, composition, and mechanical properties were confirmed by depth profiles obtained using synchrotron radiation diffraction and Vickers indentation. The mechanical performance of bamboo was strongly dependent on age. Results indicated that young bamboo has a higher strength, elastic stiffness, and fracture toughness than its older counterpart does. In addition, the hardness of bamboo is both load dependent and time dependent as a result of an expanding interfacial damage zone and indentation creep, respectively. In addition to fiber debonding, crack deflection and crack-bridging are the major energy dissipative processes for imparting a high toughness in bamboo.

I. INTRODUCTION

Bamboo is a composite material consisting of long and parallel cellulose fibers embedded in a ligneous matrix. The density of the fibers in the cross-section of a bamboo shell varies along its thickness. These fibers are densely distributed in the outer surface region and sparsely distributed in the inner surface region with their volume fraction being a function of radius.1,2 In essence, bamboo is a functionally graded material, evolved according to the state of stress distribution in its natural environment.3–5 The physical and mechanical properties of bamboo are strongly dependent on its fibres.6 On a weightto-weight basis, tensile strength, Young’s modulus, compressive strength, and the interlaminar shear of bamboo compare very favorably with conventional materials such as low-carbon steel and glass-reinforced plastics.7–9 Due to these superior properties and other factors like low cost, easy availability, and lack of environmental harm caused during service, bamboo has been widely used for scaffolds in the construction industry.10–12 In addition, bamboo fibers are used as reinforcement for cements and concretes,13–16 rubbers,17,18 thermoplastics,19–21 thermosets,22,23 and even aluminium.24 Bamboos are regarded to be a “smart” natural material with an optimized distribution of fibers and bio-matrices,

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Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/JMR.2006.0238 J. Mater. Res., Vol. 21, No. 8, Aug 2006

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not just across the cross section but also along the culm length, in resisting environmental loads in nature.25 The structure of bamboo is composed of three basic tissues, namely epidermal, vascular, and ground. The thick epidermis tissue is the shell of the bamboo, the vascular tissue is the longitudinal fiber supporting the bamboo, and the ground tissue occupies the rest of the organ. In addition, cellulose fiber plays a vital role in providing the basic structural element and strength with most bamboo species, which are composed of 50–70 wt% cellulose.