Damping of spruce wood at different strain amplitudes, temperatures and moisture contents

Wood has a very high specific strength due to its low density and reasonable strength. However, wood is dimensionally unstable due to variable water content. Its strength varies as well; it decreases with increased water content. Another important mechanical property of wood is its damping capacity which influences significantly the acoustic properties of wood. This capacity is a complex function of temperature and moisture content. The change of damping under load and varying moisture content is rarely studied, although sufficient knowledge of it would drive targeted material substitution of environmentally harmful materials with wood. The amplitude-dependent damping of old (similar to 130 years old) and new (< 10 years after felling) spruce wood was measured using dynamic mechanical analysis (DMA) which is a characterisation method that was applied to study the behaviour of both spruce woods under different moisture contents and at different temperatures. The damping of both woods showed a strain-independent and a strain-dependent range. The temperature-dependent damping curves were very similar. Only in old spruce wood a significant dependency on moisture was observed.