Vibrational Properties Of Wood Research Articles

Effect of Moisture Sorption State on Vibrational Properties of Wood

Abstract The purpose of this study was to investigate the vibrational properties and corresponding anisotropicity in wood during different states of moisture sorption. Samples of maple (Acer spp.) and red oak (Quercus rubra Michx.f.) were moisture conditioned by the adsorption process from an ovendried state and by the desorption process from a water-saturated state. The dynamic modulus of elasticity (DMOE) and logarithmic decrement (δ) were examined as a function of grain orientation during moisture change processes and under constant moisture contents (MC). It was observed that regardless of species and grain direction, the DMOE and δ were lower and higher, respectively, during the moisture change process compared with those measured without a change in MC. The increase in δ value during adsorption was greater than that during desorption. These results suggest that wood in an unstable state shows lower elasticity and strength and higher damping properties than wood in an equilibrium state. Furthermore, results of this study demonstrate that a greater adsorption rate leads to greater destabilization during an adsorption process. The anisotropy in vibrational properties was found to vary between two species.

Effects of aging on the vibrational properties of wood

Abstract Vibrational properties of aged wood (121∼296 years old) were compared with those of recently cut “new” wood (8 years old). The aged wood showed higher sound velocity ( V L ) and lower mechanical loss tangent (tan δ L ) than the new wood. The ratio of Young's modulus and shear modulus ( E L / G L ) remained unchanged or increased slightly during the aging period. These results coincide with musicians’ empirical observations that the acoustic quality of wooden soundboards is improved by aging. In addition, the reduced tan δ L of the aged wood indicates the qualitative difference between the naturally aged and heat-treated wood. The experimental results were explained by using a cell wall model when we assumed the following: increase in the volume fraction of cellulosic microfibrils; reduction in the shear modulus of amorphous matrix substances, and; reduction in the loss tangent of the matrix. These assumptions appear reasonable when we consider the crystallization of cellulose, depolymerization of hemicelluloses, and cross-linking in the lignin complex during aging.

Effect of extractions on dynamic mechanical properties of white mulberry (Morus alba)

Vibrational properties of wood are affected by several parameters, of which extractives can be one of the most important ones. Wood for European musical instruments has been often studied, but traditional Middle Eastern ones had been left unnoticed. In this study white mulberry (Morus alba L.), the main material for long-necked lutes in Iran, was extracted by five solvents of various polarities (water included). Free-free bar forced vibrations were used to measure longitudinal (L) loss tangent (tanδ), storage (elastic) modulus (E′) and specific modulus (E′/γ) in the acoustic range. Their anisotropy between the 3 axes of orthotropy was determined by dynamic mechanical analysis. Native wood had a quite low E L′/γ but its tanδ was smaller than expected, and the anisotropy of tanδ and E′/γ was very low. Removal of extractives caused tanδ to increase and moduli to decrease. Acetone, the most effective solvent on damping despite a moderate extraction yield, increased tanδ L by at least 20% but did not modify E′/γ as much. When used successively, its effects masked those of solvents used afterwards. Anisotropy of E′/γ was nearly unchanged after extraction in methanol or hot water, while tanδ was much more increased in R than in T direction. Results suggest that in white mulberry, damping is governed more by nature and localization of extractives rather than by their crud abundance.

Extractives of muirapiranga (Brosimun sp.) and its effects on the vibrational properties of wood

The potential of muirapiranga (Brosimun sp.) as a substitute material for violin bows was estimated in terms of vibrational properties, and the influence of extractives on the vibrational properties was examined. The loss tangent of muirapiranga was somewhat higher and the specific dynamic Young’s modulus was rather lower than the respective values for pernambuco, which is regarded as the best material for violin bows. Therefore, muirapiranga is a poorer bow material in terms of vibrational properties. Impregnation of crude extractives from muirapiranga decreased the loss tangent of other wood specimens. The main compounds of the extractives were identified as xanthyletin and luvangetin. Impregnations of isolated xanthyletin and commercially available methoxsalen, which was tested as an analogue of luvangetin, markedly decreased the loss tangent of other wood specimens. Methoxsalen and xanthyletin differ from conventional loss tangent-decreasing substances, namely protosappanin B and hematoxylin, in terms of water insolubility and the absence of hydroxyl groups. From the similarity in molecular characteristics of loss tangent-decreasing substances found so far, restriction of molecular motion due to an impregnated substance in the wood matrix is suggested as one loss tangent-decreasing mechanism.

Effects of oriental lacquer (urushi) coating on the vibrational properties of wood used for the soundboards of musical instruments

In order to investigate the possibility of Oriental lacquer (urushi) as a coating for the wooden-soundboard of musical instruments, the effects of urushi coatings on the vibrational properties of wood were compared to those of conventional coatings. By coating, the dynamic Young’s modulus of wood decreased slightly in its fiber direction whereas that in the radial direction increased. The most remarkable changes due to coating were recognized in the internal friction of wood (Q-1), especially that in the radial direction. The effect of the urushi coating on the Q-1 of wood was relatively small and very close to those of polyurethane coating used for the soundboard of harp. The viscoelastic and mechanical properties of urushi lacquer films were also similar to those of the polyurethane lacquer film. These results suggested the possibility of urushi as a coating for the harp soundboard. The effects of coatings on the vibrational properties of wood were explained by using a model considering three layers, the uncoated wood, coating layer, and a layer consisting of lacquer and wood cell wall.

Effects of oriental lacquer(urushi)coating on the vibrational properties of wood used for the soundboards of musical instruments

Effects of oriental lacquer(urushi)coating on the vibrational properties of wood used for the soundboards of musical instruments

Vibrational properties of wood along the grain

The dynamic Young's modulus (E′L) and loss tangent (tan δL) along the grain, dynamic shear modulus (G′L) and loss tangent (tan δS) in the vertical section, and density (ρ) of a hundred spruce wood specimens used for the soundboards of musical instruments were determined. The relative acoustic conversion efficiency (\(\alpha ,{\text{ }}\sqrt {E'_{\text{L}} /{\kern 1pt} \rho /{\kern 1pt} \tan \delta _{\text{L}} } \)) and a ratio reflecting the anisotropy of wood (β, (E′L/G′L)(tan δS/tan δL)) were defined in order to evaluate the acoustic quality of wood along the grain. There was a positive correlation between α and β, and the variation in β was larger than that in α. It seemed logical to evaluate the acoustic quality of spruce wood by a measure of β. By using a cell wall model, those acoustic factors were expressed with the physical properties of the cell wall constituents. This model predicted that the essential requirement for an excellent soundboard is smaller fibril angle of the cell wall, which yields higher α and higher β. On the other hand, the effects of chemical treatments on the α and β of wood were clarified experimentally and analyzed theoretically. It was suggested that the α and β of wood cannot be improved at the same time by chemical treatment.

The Vibrational Properties of Wood. II

When the moisture content is reduced from the air-dried state, the internal friction of wood increases and the peak in tan δ-frequency curve shifts to the lower frequency. The Young's modulus and tan δ decreases and peak of tan δ shifts to the higher frequency with the increase of temperature at the absolutely dried state. The experimental activation energy was found to be about 1000 cal/mol. It is larger for the broad-leaved tree than for the needle-leef tree. The frequency character of tan δ can be explained by superposing both Eyring's and Newton's viscosity.

The Vibrational Properties of Wood I

When the moisture content is reduced from the air-dried state, the internal friction of wood increases and the peak in tan δ-frequency curve shifts to the lower frequency. The Young's modulus and tan δ decreases and peak of tan δ shifts to the higher frequency with the increase of temperature at the absolutely dried state. The experimental activation energy was found to be about 1000 cal/mol. It is larger for the broad-leaved tree than for the needle-leef tree. The frequency character of tan δ can be explained by superposing both Eyring's and Newton's viscosity.