The vibrational properties of native and thermally modified wood in dependence on its moisture content

Abstract

The vibrational properties of spruce (Picea abies Karst.) and European beech (Fagus sylvatica L.) were investigated in this study in dependence on the relative humidity (RH). The RH was measured at 20 °C ranging from oven-dried to 85%. For the evaluation of the vibrational properties the dynamic modulus of elasticity E’ and the damping coefficient tan δ were measured at 7 climate steps. The same samples used for the vibrational tests were afterwards mildly thermally modified at 180 °C and measured at the same climate steps. Both wood species were compared and evaluated considering the property changes (E’, tan δ, sorption isotherms and volume swelling) due to the thermal modification. The chosen modification resulted in a marginal change in the vibrational properties of spruce, whereas the properties of beech were clearly changed. The vibrational properties of beech could be improved in the usual RH range (35–85%) due to this thermal modification. For spruce, it was concluded that a mild modification, conducted in this study, is not suitable for improving the vibrational properties. Further conclusions concerning the underlying causes as well as the use in musical instruments were drawn.

Identification of Damping of Spruce Wood (Picea abies) under Various Levels of Moisture Content Using Time-Scale Decomposition

“…An initial decrease in damping with increasing EMC and then an increase is also reported [5,6], where the damping factor for spruce with 12% EMC was 0.0042. Similar results were obtained by Buchelt et al [12], who determined lower EMC values at similar relative humidities. For example, the EMCs at 26%, 50%, 65%, and 85% RH were 3.2%, 7.8%, 11.6%, and 16.9%, respectively, while in our study at 20%, 44%, 76%, and 88% RH, the EMCs were 7.2%, 9.9%, 13.3%, and 19%, respectively.…”

“…Similar results were obtained by Buchelt et al [12], who determined lower EMC values at similar relative humidities. For example, the EMCs at 26%, 50%, 65%, and 85% RH were 3.2%, 7.8%, 11.6%, and 16.9%, respectively, while in our study at 20%, 44%, 76%, and 88% RH, the EMCs were 7.2%, 9.9%, 13.3%, and 19%, respectively.…”

“…When the wood is thermally modified, the damping is generally reduced, as confirmed by Zauer et al [8], who investigated the effects of thermal modification on the damping of beech wood. Mania and Skrodzka [9] and Danihelova et al [10] investigated the effect of thermal modification on the damping of spruce wood, Stanciu et al [11] investigated the effect of ammonia treatment; and Buchelt et al [12] investigated the influence of thermal modification on damping and on the modulus of elasticity at different moisture contents. The damping properties of different tree species used for musical instruments were studied by Wegst [13], Merhar and Humar [14], Sproßmann et al [15], and Gurau et al [16].…”

“…This article aims to present the determination of the damping of wood on the first three bending vibration modes using the wavelet transform, which has received little attention to date despite the extensive literature on WT. In contrast, many papers in the literature research the damping of wood under various conditions [3][4][5][6]9,12,14,15,17], using the predominant inaccurate methods being based on either the logarithmic decrement or the 3 dB method. The aim is also to compare the wavelet transform with the method of vibration envelope fitting as an improved version of the well-known logarithmic decrement for damping determination in the first vibration mode.…”