Differences in wood material responses for radial and tangential direction as measured by dynamic mechanical thermal analysis

Wood is a complex cellular structure with different properties in the radial and tangential direction. Many researchers have measured dynamic properties in the longitudinal direction and a few in the radial direction but very little data can be found in the literature on dynamic mechanical properties in the tangential direction. The purpose of the work presented in this paper was to investigate the dynamic mechanical behaviour in the radial and tangential directions of wood (Pinus sylvestris). Testing was done in tension at 1 Hz with a Dynamic Mechanical Thermal Analyser. Properties in radial and tangential direction were different. The radial direction showed a higher elastic modulus and lower loss factor levels at temperatures between -120 degreesC and 80 degreesC. The tangential direction had on average a higher peak temperature than the radial direction for a loss factor peak around -80 degreesC. It is the opposite of synthetic composites where the stiffer direction has a higher peak temperature. A loss factor peak at around 0 degreesC was seen, most significantly in the tangential direction. This peak has scarcely been reported in the literature before. The distance between annual rings did not significantly affect the dynamic behaviour in the tangential direction. (C) 2001 Kluwer Academic Publishers.