Acoustoelastic birefringence effect in wood I: effect of applied stresses on the velocities of ultrasonic shear waves propagating transversely to the stress direction

The velocity changes of ultrasonic shear waves propagating transversely to the applied stress direction in wood were investigated. The wave oscillation directions were parallel and normal to the uniaxially applied stress direction. The velocities of the shear waves for both oscillations decreased as the compressive load increased, and increased as the tensile load increased. The velocity of the normally oscillated shear wave showed smaller change against the stress applied than that of the parallel oscillated wave. The initial birefringence due to the orthotropy of wood was observed without any stress. Velocity changes in the two principally oscillated shear waves were proportional to the stress within the stress range tested. The acoustoelastic birefringence effect was obtained from the velocity difference between the two shear waves. The relative difference between the two velocities (called acoustic anisotropy) was given as a function of the applied stress. The acoustoelastic birefringence constants were obtained from the relationships between the acoustic anisotropy and the applied stress.     

Acoustoelastic effect of wood II: Effect of compressive stress on the velocity of ultrasonic longitudinal waves parallel to the transverse direction of the wood

The changes in the velocity of ultrasonic waves propagating in wood parallel to the direction of applied stress are discussed. The ultrasonic mode was longitudinal waves traveling along the direction of applied stress with the compressive load applied parallel to the transverse direction of the wood. The ultrasonic velocities were measured by the sing-around method. The experimental results indicated the existence of an acoustoelastic phenomenon in the transverse direction of the wood. The percent change in the ultrasonic velocity was given as a function of the applied stress. The change in the velocity depended on the species and structural direction of the wood. That is, in the radial direction of hardwood, the ultrasonic velocity increased with increases in compressive stress at the initial stress level of less than 2MPa; it then gradually decreased with increases in stress. A change in velocity from an increase to a decrease was considered a unique phenomenon for wood. In contrast, in the radial direction of softwood and the tangential direction of hardwood, the ultrasonic velocity decreased with increases in stress from the beginning of loading. This phenomenon is also generally observed in metallic materials. The relations between velocity and stress at the initial stress level and between velocity and strain in the range of large deformation are represented by essentially straight lines. The acoustoelastic constants of wood were obtained from these relations at the initial stress level. The absolute values of the constants in the transverse direction of wood were larger than those for metals and were larger than those for the longitudinal direction of wood reported in our previous paper.This research was presented at the 1st Meeting of the Research Society of the Acoustoelastic Measurements in the Japan Society of Non-Destructive Inspection at Osaka, October 1996 and at the 47th Annual Meeting of Japan Wood Research Society at Kochi, April 1997     

Acoustoelastic birefringence effect in wood III: ultrasonic stress determination of wood by acoustoelastic birefringence method

Stress conditions produced in wood were analyzed by means of the acoustoelastic birefringence method. Bending load was applied against a wood beam specimen. Under loading, ultrasonic shear waves were propagated through the breadth direction of the wood beam specimen. The velocities of shear waves polarized in the longitudinal or tangential direction of the wood beam specimen were measured with the sing-around method. Bending stresses were determined by dividing the difference between the acoustic anisotropy and the texture anisotropy by the acoustoelastic birefringence coefficient. Shear stresses were also determined. These stress distributions of the beam specimen were in good agreement with those obtained by the strain gauge method and mechanical calculation.     

Acoustoelastic birefringence effect in wood II: influence of texture anisotropy on the polarization direction of shear wave in wood

Ultrasonic shear waves were propagated through the breadth direction of a wood beam which was subjected to a bending load such that it was in a plane-stress state. The oscillation direction of the shear waves with respect to the wood beam axis was varied by rotating an ultrasonic sensor, and the relationship between the shear wave velocity and the oscillation direction was examined. The results indicate that when the oscillation direction of the shear wave corresponds to the tangential direction of the wood beam, the shear wave velocity decreases sharply and the relationship between shear wave velocity and rotation angle tends to become discontinuous. When the oscillation of the shear waves occurs in the anisotropic direction of the wood beam instead of in the direction of principal stress, the shear wave velocity exhibits a peak value. In addition, the polarization direction was found to correspond to the direction of anisotropy of the wood beam according to the theory of acoustoelastic birefringence with respect to plane stress. This indicates that when the acoustoelastic birefringence method is applied to stress measurement of wood, it is appropriate to align the oscillation direction of the shear wave with the principal axial direction of anisotropy in order to carry out ultrasonic measurement.     

Effect of moisture content on the ultrasonic acoustic properties of wood

We determined the ultrasonic velocity and en-ergy attenuation value of three tree species (basswood, elm, and fir) 1 per tree in different moisture content levels, using RSM-SY5 ultrasonic testing inst...     

Osmotic stress in wood — part II: on the computation of drying stresses in wood

Summary Plastic stress arising in wood during drying is calculated according to the theoretical model developed earlier. The mechanism of stress reversal and the type of resudual stress corresponding to different values of material constants are shown. The results are in qualitative agreement with experimental evidence.List of symbols A coefficient of swelling below the fibre saturation point - C concentration of moisture in wood; weight of moisture per weight of dry wood - C ₀ uniform concentration of moisture in wood at the beginning of drying - C ₁ equilibrium concentration of moisture at the boundary during drying - C =C-C ₁ - non-dimensional concentration - D diffusivity - D ₀ first term in the expansion of diffusivity as function of concentration: D=D ₀(1+D ₁ C+...) - D ₁ secondterm in the expansion (see D ₀) - E Young's modulus - e _ij deviator of tensor of strain: - e _ij ^P deviator of plastic strain: - e _ij ^E deviator of elastic strain - F fibre saturation point (concentration at which the function (c) changes slope) - F =F-C ₁ - g(x,t) function which assumes the value 1 in the elastic zone and 0 in the plastic zone - k von Mises' yield stress - L half width of the sample - M total moisture content - P plastic power - S _ij deviator of stress - S _kk =S ₁₁+S ₂₂+S ₃₃ - S _ij ^E =2 e _ij - T _ij tensor of stress - T _kk =T ₁₁+T ₂₂+T ₃₃ - T non-zero component of stress in a beam or plate - non-dimensional stress - actual stress rate in an elastic zone, fictitious stress rate in a plastic zone - t time - t increment of time - x y z spatial coordinates - X increment of spatial coordinate - Y - Y ₀, Y ₁ terms in the expansion of Y(C): Y(C)=Y ₀(1+Y ₁ C+...) - non-dimensional Y - , (c) coefficient of osmotic expansion (dependent on concentration) - _ij tensor of strain - _kk =₁₁+₂₂+₃₃ - =_yy=_zz non-zero component of strain in the case of a plate or beam - modified strain - elastic constants of an isotropic body - non-dimensional spatial coordinate - Poisson's ratio - non-dimensional time     

Erratum to: Mechanical properties of wood in an unstable state due to temperature changes,and analysis of the relevant mechanism III: Effect of quenching on stress relaxation of chemically modified woods

In order to understand the mechanism of destabilization occurring when wood is quenched, we applied chemical modifications, and controlled the number of moisture adsorption sites in wood. The degree of destabilization was evaluated according to the fluidity (1-E _t/E ₀), increase in fluidity, and relative fluidity in relation to the nonmodified wood, and was discussed by comparing these quantities with the hygroscopicity or swelling of wood. We found that destabilization of chemically modified wood was lower than that in nonmodified wood, and the amount of adsorbed water controlled the magnitude of flow of wood. Moreover, according to the analysis of water state by the Hailwood-Horrobin equation, it was shown that the function of dissolved water to the fluidity is almost identical for both chemical modifications, whereas hydrated water has more effect on acetylated wood than on formaldehydetreated wood. We speculate that the motion of water molecules due to quenching accompanied with the redistribution of energy resulting from the exchange of their potential energy and movement to attain a new balance, and the introduced acetyl groups and cross-linking restrict the water molecule movement. An erratum to this article is available at .     

Mechanical properties of wood in an unstable state due to temperature changes,and analysis of the relevant mechanism IV: effect of chemical components on destabilization of wood

In order to investigate the effects of chemical components and matrix structure on the destabilization of quenched wood, we examined the physical and mechanical properties of steam-treated wood, hemicellulose-extracted wood, and delignified wood, which were treated at different levels. For steam-treated and hemicellulose-extracted wood,the relative relaxation modulus of the quenched sample was lower than that of the respective control sample. For delignified wood, the relative relaxation modulus fell with weight loss and reached a minimum value at a certain weight loss, and subsequently increased significantly. The hygroscopicity of all treated samples changed slightly by steaming, whereas increased with removing the component. More-over, the average volumetric swelling per 1% MC at 100% relative humidity (RH) was less than at 75% RH and 93% RH for component-removed wood. It was clear that a void structure existed. As a result, the destabilization evaluated by the fluidity (1 - E _t/E ₀) of steam-treated wood was influenced by the amount of adsorbed water. For component-removed wood, destabilization increased temporarily at lower weight loss because of nonuniform cohesive structure. At high weight loss, destabilization will decreased because capillary-condensed water gathered in the voids and obstructed the motion of adsorbed water. However, the destabilization of all treated wood changed less than that of chemically modified wood.     

Volatile composition analysis by solid-phase microextraction applied to oak wood used in cooperage (Quercus pyrenaica and Quercus petraea): effect of botanical species and toasting process

The purpose of this study was to investigate the sorption of selected volatile substances from oak wood-chip samples (Quercus pyrenaica Willd. and Quercus petraea L.) subjected to different toasting levels, namely, without toasting, with medium toasting, and with strong toasting, through the use of solid-phase microextraction (SPME). The main volatile compounds identified as a function of the toasting level and botanical species were furfural, hexanal, α-pinene, d-limonene, decanal, vitispirane, ethyl hexanoate, cis-3-methyl-γ-octalactone (“oak lactone” or “whisky lactone”), α-terpineol, p-xylene, and nonanal. Considering the data obtained from the toasted woods (medium and strong intensity) in comparison with those of nontoasted woods, it can be pointed out that the average peak area and the number of compounds identified in the gas chromatogram decreased during the toasting process. In general, regarding the compounds analyzed, quantitative differences were found between the two oak wood species under study. High values of volatile compounds were found in Quercus pyrenaica oak wood chips. In addition, for the number of compounds identified in oak wood extracts and directly extracted from solid oak wood chips by SPME, it is concluded that the best extraction process for volatile compounds from oak wood is the use of oak wood-chip liquid extracts.     

Heat treatment of wet wood fiber: A study of the effect of reaction conditions on the formation of furfurals

Abstract

Furan monomers are produced when wood is heated at high temperatures. To understand the process conditions for production of furfural (FF) and hydroxymethylfurfural (HMF) from wood, samples of milled aspen wood were subjected to autohydrolyzis by microwave heating in a sealed Teflon reactor. The experiments were designed to simulate temperature and pressure variables of a fiberboard press and their effect on production of furans from the hemicelluloses that have the potential for promoting self-bonding of the wood fibers. The effect of a Lewis acid catalyst, AlCl₃·6H₂O on the formation of FF and HMF was also studied. The hydrolysates were analyzed for the liberated wood sugars and dehydration products, FF and HMF. The FF and HMF yields under autohydrolyzis conditions increased with increase in severity factor, CS. Under catalyzed hydrolyzis conditions, the FF yield decreased, while the HMF yield increased with increase in severity factor. Under catalyzed hydrolyzis conditions the FF yield decreased presumably due to degradation reactions including resin formation. The increase in HMF yield with increasing severity factor was most likely due to hydrolyzis of glucan from cellulose. These results suggest that FF and resin yields could be enhanced with the addition of a Lewis acid catalyst to the wood particles, but that process variables need to be controlled in order to avoid or minimize degradation of the wood cellulose.     

蜜源-糖醋液对苜蓿盲蝽的引诱作用研究

蜜源-糖醋液是一种广谱性引诱剂,对多种害虫均有引诱作用。为了筛选蜜源-糖醋液对苜蓿盲蝽引诱的最佳配比,利用正交试验设计方法设计了9种不同配比的蜜源-糖醋液,研究其对苜蓿盲蝽的诱集效果。结果表明:不同配比的蜜源-糖醋液的引诱量之间存在显著性差异,当糖、醋、酒精、枣蜜的配比为20∶15∶5∶2时,蜜源-糖醋液对苜蓿盲蝽的诱集量最大,为每3d引诱(94±32.79)头;蜜源-糖醋液对雌、雄苜蓿盲蝽均有引诱作用,且诱集到的雌虫数量高于雄虫。不同时期,相同配比的蜜源-糖醋液的引诱量也存在明显差异;而且随着时间的延长,引诱数量呈下降趋势,尤其是10d之后的引诱量显著降低。     

Piezoelectric behavior of wood under combined compression and vibration stresses II: Effect of the deformation of cross-sectional wall of tracheids on changes in piezoelectric voltage in linear-elastic region

This study investigated and clarified the relation between the piezoelectric voltage and microscopic fracture of hinoki (Chamaecyparis obtura Endl.), in particular the deformation of the cross-sectional wall of the tracheid in linear-elastic regions under combined compression and vibration stresses. The piezoelectric voltage-deformation (P-D) curve consisted of a linear region starting from the origin followed by a convex curved region. The linear region of theP-D curve was only about 60% of that of the load-displacement (L-D) curve. By applying combined stresses to a specimen, the cross-sectional walls of the tracheid were deformed mainly at the radial walls. When a tracheid was regarded approximately as a hexagonal prism, the elastic buckling stress of the radial wall was estimated from scanning electron microscope images and our method based on a modification of the Gibson and Ashby method. As a result, it was estimated that the elastic buckling stress was only about 80% of the stress at the proportional limit of theP-D curve. It is found that there are two consecutive regions before the proportional limit of theP-D curve: One is the region up to the spot where the radial cell wall generates the elastic buckling, and the other is the region starting from the end of the aforementioned region up to the proportional limit of theP-D curve.Part of this paper was presented at the 47th annual meeting of the Japan Wood Research Society, Kochi, April 3–5, 1997     

上海绿地群落冠层的UVB屏蔽作用

文章选择上海绿地典型植物群落类型进行UVB屏蔽效率测定,分析绿地类型、植物配置方式对屏蔽效率的影响作用,并对群落优势种高度、枝下高等特征与群落屏蔽效率相关关系进行了初步研究。研究结果表明:(1)所测定植物群落中UVB屏蔽效率较高的为毛竹群落、水杉群落、香樟群落、女贞群落、朴树群落和雪松群落,UVB屏蔽效率最高为98.4%的女贞群落,最低为17.1%的红叶李群落(2)所测定群落UVB平均屏蔽效率为76.9%,即群落内2m高处UVB辐射值仅为全光照旷地20.2%。(3)植物群落内UVB辐射通量与群落郁闭度呈极显著负相关关系,相关系数为0.749,而与群落优势种平均高度和平均冠幅相关性不显著。       

Contribution of lignin to the reactivity of wood in chemical modifications I: influence of delignification on acetylation

In order to examine the contribution of wood components to the acetylation of wood, we acetylated wood meal that had been partially delignified. The results were analyzed in terms of the reaction kinetics. The first-order rate equation was successfully adjusted to the weight gain data. The rate constant for acetylation initially increased with progress of lignin elimination and then turned to decrease; the apparent activation energy showed the reverse tendency and ranged from about 90 to 130 kJ/mol. These results suggest that lignin elimination brings not only separation of lignin but also drastic change of the chemical and/or physical structure in the residual lignin, and this affects the reactivity of wood meal as a whole. The ultimate weight gain estimated by the regression of the rate equation showed a minimum when lignin was moderately eliminated, which was explained in terms of enhanced reactivity of lignin and lower accessibility for holocellulose than predicted. The equilibrium moisture content had a maximum when lignin was moderately eliminated. This tendency is the opposite of that observed for the ultimate weight gain, and suggests that the sites for acetylation do not always correspond to those for moisture adsorption. Part of this report was presented at the 54th Annual Meeting of the Japan Wood Research Society, Sapporo, August 2004     

Study of hydration behavior of wood cement-based composite II: effect of chemical additives on the hydration characteristics and strengths of wood-cement composites

The influence of the 30 chemical additives on the hydration characteristics of birch wood-cement-water mixture was determined by measuring the maximum hydration temperature (T _max) and the time (t _max) required to reach the temperature. The chemical additives were tested and divided into two types depending on the pattern of exothermic reaction peak within the 24-h observation period. The wood-cement-water mixtures with additions of each of the 11 type I chemical additives showed a two-peak temperature-time curve similar to that for neat cement. CaCl₂, FeCl₃, and SnCl₂ reached the highestT _max above 50°C. When the 19 type II chemical additives were included, the mixtures offered only one peak hydration temperature-time curve. Among them, the 10 chemical additives caused an obvious temperature increase at the beginning of the hydration reaction. The most significant effect was with the addition of diethanolamine, where the mixture produced aT _max above 50°C. The strength values (modulus of rupture, internal bond strength) of word-cement board were tested with separate additions of the 10 chemical additives arranged by the highestT _max. There was a good positive correlation betweenT _max and the strength values. In addition, the composite chemical additives were preliminarily examined to determine if they accelerated the hydration reaction of blast-furnace slag cement. The results revealed that composite chemical additives evidently accelerated the hydration reaction and the setting of blast-furnace slag cement mixed with wood. Blast-furnace slag cement can thus be considered for use as an acceptable inorganic bonding material for wood-cement panel manufacture.Part of this report was presented at the 49th Annual Meeting of the Japan Wood Research Society, Tokyo, April 1999     

激素、钙、水杨酸和铵诱导马尾松、黑松抗松材线虫病的研究

诱抗试验结果表明：（１）ＩＢＡ、乙烯、ＩＢＡ＋乙烯对马尾松的诱抗效果达６０％，而ＩＢＡ＋乙烯对黑松苗的诱抗效果为１２５％。（２）Ｃａ２＋＋ＩＢＡ对黑松苗的诱抗效果为３６６７％。（３）除Ｓａ＋ＩＢＡ对黑松苗的诱抗效果为１６７％外，其余Ｓａ的各处理效果均不明显。（４）铵的单用、混用或与Ｃａ２＋混用对马尾松诱抗效果均可达６６８％～１００％。     

Contribution of lignin to the reactivity of wood in chemical modifications II: influence of delignification on reaction with vaporous formaldehyde

Participation of lignin in the reaction between vapor-phase formaldehyde and wood was examined by using gradually delignified wood meal. A fi rst-order rate equation was successfully applied to the weight gain data. From the estimated reaction parameters such as rate constant, k, and ultimate weight gain, a, the reactivity toward formaldehyde was discussed among wood components, and compared with that for acetylation. k decreased monotonously with progress of the elimination of lignin, suggesting that the reaction rate of lignin is dominant over that of whole wood, and the decrease in the ratio of lignin retarded the reaction of wood as a whole. On the other hand, a increased with decreasing lignin content. This may be attributable to the enhanced reactivity of the remaining lignin due to some structural changes and to the increase in the number of reactive sites in polysaccharides as a result of their exposure accompanying the elimination of lignin. The dependencies of k and a on the lignin content were not similar to the case for acetylation, probably because of the difference in the reaction phase. In vapor-phase formaldehyde treatment, the remaining lignin reacts as it is, whereas in liquid-phase acetylation it would undergo rearrangement or swelling of the structure in the reaction solution.     

Relative contribution of edge and interior zones to patch size effect on species richness: An example for woody plants

In order to understand the capacity of habitats to conserve species, many authors have searched for a species–area relationship (SAR) to evaluate the effect of patch size on species richness in habitat fragments. However, a range of different processes may underlie or obscure this relationship. For woody plant species in forest fragments, as for other taxa, considering forest edges separately in the investigation of SAR is particularly relevant. The objective of our study was to evaluate edge influence on SAR in a fragmented forest landscape in south-western France. To achieve this objective, we considered SAR in two separate spatial portions of the forest fragment: the edge and the forest interior. We also considered SAR for different ecological groups of species based on their shade tolerance and their mode of dispersal, as species can respond differently to habitat reduction depending on their ecological characteristics. In 40 woodlands in an agricultural landscape, we observed the presence/absence of all woody species along parallel walking transects 20-m wide to inventory the total number of species in each woodlot. Vegetation surveys resulted in the identification of 53 woody species, with a total of 23 trees and 30 shrubs, and a number of species per woodlot ranging from 18 to 44. The species richness found in a given woodlot was significantly correlated with its area. When considering the edge and the interior parts of the woodlot separately we found a steeper increase in species richness with area for the part we considered as the edge, compared with the increase found in the interior part of the forest. Our results confirm the contribution of forest edge to forest fragment SAR. Results also underlined the importance of two additional processes that may contribute to SAR: a possible extinction debt of shade-tolerant species in forest edge zones and colonisation by light-demanding species in forest interior zones probably due to disturbances. This approach underlines the importance of taking the edge effect into account when studying the influence of patch size on species richness and the dynamic of species richness pattern.     

Differences of tensile strength distributions between mechanically high-grade and low-grade Japanese larch lumber III: effect of knot restriction on the strength of lumber

It is well known that the presence of knots in structural lumber is one of the most important strengthreducing factors. For practical purposes, visual grading including knot restriction is an effective method for nondestructive evaluation of strength. Edge knot restriction for not only visually graded lumbers but also mechanically graded lumbers is specified in the Japanese agricultural standards for glued laminated lumber. We conducted experimental studies on differences of tensile strength distributions between mechanically high-grade and low-grade Japanese larch (Larix kaempferi, carriere) lumbers daily used for manufacturing glued laminated timbers in Nagano, Japan. We then examined the additional visual grading of mechanically graded lumbers for nondestructive evaluation. We visually graded the prepared mechanically graded lumber by focusing on the knots' area ratio of grouped knots. We confirmed that the higher visual grade related to the stronger tensile strength, similar to our present knowledge; but the effects of knot restriction were reduced when the length of the lumber increased in view of nonparametric 5th percentiles of tensile strength. The differences in the strength/elasticity ratio between mechanically high-grade and low-grade lumber were negligible. It was clear that the length effect on the ratio in visually graded high-grade lumber was smaller than that of visually graded low-grade lumber. It was thus concluded that knot restriction should have little effect on the tensile strength of mechanically graded lumber.