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The fracture toughness of wood in teak, rubber wood and mango were computed in the LR and LT crack plane configurations. Teak wood has shown highest fracture toughness followed by rubber wood and mango wood. The crack plane orientation has large influence on the fracture properties. It was found that all the three species exhibit more fracture toughness in LT plane than in LR plane. The fracture toughness values of plywood and particleboard wood composites in flat and edge crack plane configuration were determined. The plywood samples showed higher fracture toughness values as compared with particleboards in both the crack plane orientations. Plywood exhibited higher values of toughness when loaded in the edge crack plane as compared with the flat crack configuration. Particleboard also exhibited the similar pattern being tough while loaded in the edge than in the flat. The greatest acoustic activity was observed near the end of the proportional limit and just before the sample failure. Acoustic activity (cumulative signal intensity) was found to be increasing with the application of increasing loads and also with time till the failure of the sample. For given the same amount of load, the notched samples have shown higher amount of acoustic signals and early onset of the emission of acoustic signals as compared to the wood samples having no notch. The compressive strength was found highest in the longitudinal direction followed by radial and tangential directions. In all the three directions, the compressive strength was found to increase with loading rate up to 10 mm per minute and then decreased. The rate of decrease in the longitudinal compressive strength was more as compared to other two compressive strengths. At higher loading rates (100 mm per min.), the difference between the radial and tangential compressive strengths were shown to be minimized and these were found merging in each other. This shows that at higher loading speed like sudden impacts, compressive strength of wood in radial and tangential directions becomes almost equal. The compression fracture of samples in longitudinal direction was observed to have a characteristic appearance. The fracture band was found to run perpendicular to the grain on the radial face and obliquely on the tangential face having an angle between 60 o to 70 o along the grain direction. The fracture band was about 1-2 mm wide and fibres have been observed as buckled but have remained continuous. Microscopic observations of the longitudinally compressed specimens revealed a characteristic fracture band of buckled fibres making S like shape. In some of the samples, branching macroscopic failure lines were also observed. Tangential view of the specimen tested in compression parallel to grain showed that extreme buckling at microscopic level resulted from separation of cells above and below buckling zone.

SEM micrographs of longitudinally compressed specimens of A. auriculaeformis in the LT plane having a characteristic fracture band making S- like shape with buckled wood fibres but remained continuous.


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  Last Updated on 03-08-2015