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In this work, cellulose fibres extracted from bamboo culms were used to fabricate two types of cellular materials: rigid foams and fibrous networks. A relatively simple and low-technology fabrication method is presented, using natural binders and blowing agents to manufacture rigid foams, and fibrillation by partial hydrolysis in H2SO4 to manufacture fibrous networks. The compressive response is related to the internal microstructure and processing parameters. In the case of fibrous networks, the achievable relative density range is determined by the length of initial fibres and extent of external fibrillation. The compressive properties are dictated both by the density of the network and strength of the fibrous bridges, showing a linear stiffness-density relationship due to the length of fibres, and an inverse relationship at increased external fibrillation. The rigid foams showed an orthotropic internal microstructure but nearly isotropic compressive response, due to the influence of the interpenetrating void structure on the deformation and fracture mechanisms. The results show the potential of bamboo-fibre porous materials as low cost, lightweight structural materials.

T h e C o m p re s s iv e R esp o n se of Id e a liz e d C e rm e tlik e M a te ria ls Metals reinforced with a high volume fraction o f hard particles, e.g., cermets, have proper ties that are more akin to those o f granular media than conventional composites. Here, the mechanical properties and deformation mechanisms o f this class o f materials are investi gated through the fabrication and testing o f idealized cermets, comprising steel spheres in a Sn/Pb solder matrix. These materials have a similar contrast in the properties o f constituent phases compared to commercial cermets; however, the simpler microstructure allows an easier interpretation o f their properties. A combination o f X-ray tomography and multiaxial strain measurements revealed that deformation at large strains occurs by the development o f shear bands similar to granular media, with the material dilating under hydrostatic pres sure within these shear bands. Predictions o f finite element models with a random arrange ment of inclusions were in excellent agreement with the experimental results o f idealized cermets. These calculations showed that at large inclusion volume fractions, composites with a random arrangement o f inclusions are significantly stronger compared to their peri odic counterparts, due to the development o f a network o f force chains through the perco lated particles. 1 In tro d u c tio nThere are numerous examples of composites comprising a high volume fraction of a hard particulate phase in a ductile matrix; e.g., asphalt used in road construction, polymer bonded explo sives, and cermets, which are composed of ceramic particles in a ductile metal matrix. The primary reason for the widespread use of such composites is the compromise between strength and toughness. For example, cermets that contain 50-95% by volume ceramic particles (e.g., carbides, nitrides, and oxides) in a metal matrix (e.g., Mo, Ni, Co, Al) [1,2] typically have hardness in the range 500-2000 HV and fracture toughness ranging between 8 and 20Mpa m l/2 [3], The compromise between the strength of ceramics and toughness of metals makes them useful in applica tions such as cutting tools, high-pressure structural components [4], and materials for ballistic resistance in armor applications [5,6].The microstructure of cermets is typically complex, with a range of ceramic particle sizes and shapes distributed randomly in the metal matrix, see for example the micrograph of a WC/Co (tungsten carbide/cobalt) cermet with 90 vol. % WC particles in Fig. l(

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