Issue 35

T. Haiyan, Frattura ed Integrità Strutturale, 35 (2016) 472-480; DOI: 10.3221/IGF-ESIS.35.53 476 it is directly correlated to energy released by acoustic emission events. Vmax and RMS under different condition are shown in Tab. 2. (a) Double cantilever beam test (b) Compression test Figure 3 : Illustration for double cantilever beam test (a) and compression test (b) . Category of damage Bending and collapse of cell wall Delamination splitting Crack on fibre bundle Tearing and fracture on cell wall Vmax mV < 2 < 64 < 0.5 < 53 dB < 11 < 79 < 1 < 61 RMS mV < 34 < 90 < 11 < 81 dB > 34 > 90 > 11 > 81 Table 2 : Acoustic emission characteristics of wood with different damage. M ECHANICAL CHARACTERISTICS OF BAMBOO STRUCTURE Test samples he ninth and twentieth joint of three-year moso bamboo were cut down and split into bars (200 mm×10mm) after air-seasoning. Then the bamboo was made into 60 tensile samples which was wide and thick on two ends and thick and thin in the middle. 60mm×5mm×1.5mm was the size of major section for testing. As the sample was cut from different radial position of bamboo, fibre bundle contained in the cross section was also different. 12.5% of the test sample was water and the experiment was carried out at 25 °C. Simplified mechanical model and testing principle Bamboo materials cut from parts between joints can be considered as evenly distributed and continuous fibre reinforced composite material, if they have small thickness. Bamboo fiber bundle is characterized by high strength and high modulus, while ground tissue of bamboo is just the opposite. Meanwhile, the fragment from the starting point to emergence of facture in stress-strain curve is a straight line, as shown in Fig. 4. Therefore, parallel model composing of two elements (bamboo fiber and ground tissue) can be used to describe mechanical behavior of bamboo. Deformation of two elements is assumed to be the same when carrying load. F c , F f , F m , σ c , σ f and σ m are used to express force and stress that act on composite material, fiber and ground tissue. ε c , ε f , ε m , E c , E f and E m are used to express corresponding strain and elasticity modulus. Cross sectional area of bamboo fiber, ground tissue and composite material is set as A f , A m and A c respectively. Usually, content of two elements is expressed with volume fraction V , i.e., load acting on bamboo samples is shouldered by bamboo fiber and ground tissue. Then we have: c f m F F F   (2) or T