Investigations on properties of bog oak
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Physical-mechanical investigations on bog oak samples (Quercus robur L.), which were cut from a stored log in the river Bug (Poland), were carried out. Lifetime of the log is 150 years. It was found under a 3 m thick layer of sand and slush in the soil, where it has been stored for 7100 ± 50 years. In contrast to the very dark (deep black) discolouration in the outer zone, the wood became lighter in direction to the pith. No essential changes in mechanical as well as sorption behaviour compared to recent wood were determined. In radial direction the swelling of the bog oak decreased towards to the outer zone, that correlates with the colour changes. The darker the wood, the lower the radial swelling. In tangential direction only a slight influence of the position in the trunk could be seen. The porosity was unchanged. Regarding the mechanical properties the known differentiation of the E- and G-Modulus in the principal axes was determined. Measurements with ultrasound and the device BP5 (frequency 50 kHz) showed a little reduction of the dynamic E-Modulus. The E-Modulus of the bog oak decrease particularly with increasing dark colouration.