Henri Baillères

Natural vibration analysis of clear wooden beams: a theoretical review

Abstract In wood science, natural vibration analysis is being used to an increasing extent to characterise the longitudinal and the shear modulus of elacticity of various geometrical types of prismatic beams. A lateral or a axial percussion at one end of a beam set up on elastic support produces bending or longitudinal vibrations. Considering the hypothesis of the homogeneity of geometrical and mechanical properties of the beam, basic dynamics theorems can be applied to obtain the motion equations of longitudinal and transverse vibrations. The resolution of the differential equation for transverse motion leads to a search for solutions to the frequency equation. Because no exact analytical solution can be found, several approximate results are analysed. The application and validity range have to be defined to be able to achieve realistic results. The effects of the elastic support, the shear modulus and the height to length ratio are discussed. The conceptual bases help in understanding the analytical results and accuracy calculations can then be developed for practical applications. We present the most common theoretical models and define their validity range, application conditions, and accuracy levels with respect to measured values.

Comprehensive genetic dissection of wood properties in a widely-grown tropical tree: Eucalyptus

BackgroundEucalyptus is an important genus in industrial plantations throughout the world and is grown for use as timber, pulp, paper and charcoal. Several breeding programmes have been launched worldwide to concomitantly improve growth performance and wood properties (WPs). In this study, an interspecific cross between Eucalyptus urophylla and E. grandis was used to identify major genomic regions (Quantitative Trait Loci, QTL) controlling the variability of WPs.ResultsLinkage maps were generated for both parent species. A total of 117 QTLs were detected for a series of wood and end-use related traits, including chemical, technological, physical, mechanical and anatomical properties. The QTLs were mainly clustered into five linkage groups. In terms of distribution of QTL effects, our result agrees with the typical L-shape reported in most QTL studies, i.e. most WP QTLs had limited effects and only a few (13) had major effects (phenotypic variance explained > 15%). The co-locations of QTLs for different WPs as well as QTLs and candidate genes are discussed in terms of phenotypic correlations between traits, and of the function of the candidate genes. The major wood property QTL harbours a gene encoding a Cinnamoyl CoA reductase (CCR), a structural enzyme of the monolignol-specific biosynthesis pathway.ConclusionsGiven the number of traits analysed, this study provides a comprehensive understanding of the genetic architecture of wood properties in this Eucalyptus full-sib pedigree. At the dawn of Eucalyptus genome sequence, it will provide a framework to identify the nature of genes underlying these important quantitative traits.

Sound quality assessment of wood for xylophone bars

Xylophone sounds produced by striking wooden bars with a mallet are strongly influenced by the mechanical properties of the wood species chosen by the xylophone maker. In this paper, we address the relationship between the sound quality based on the timbre attribute of impacted wooden bars and the physical parameters characterizing wood species. For this, a methodology is proposed that associates an analysis-synthesis process and a perceptual classification test. Sounds generated by impacting 59 wooden bars of different species but with the same geometry were recorded and classified by a renowned instrument maker. The sounds were further digitally processed and adjusted to the same pitch before being once again classified. The processing is based on a physical model ensuring the main characteristics of the wood are preserved during the sound transformation. Statistical analysis of both classifications showed the influence of the pitch in the xylophone maker judgement and pointed out the importance of two timbre descriptors: the frequency-dependent damping and the spectral bandwidth. These descriptors are linked with physical and anatomical characteristics of wood species, providing new clues in the choice of attractive wood species from a musical point of view.

Comparison between modulus of elasticity values calculated using 3 and 4 point bending tests on wooden samples

Abstract Several data banks on wooden properties of different species contain mechanical characteristics of which the bending modulus of elasticity. This modulus can be calculated using different test methods, the more ordinary used are the 3 point and 4 point bending tests. The values obtained by one method cannot be directly compared with those of other methods. So the bending properties read in a data bank have to be converted before using them and correctly compared with other data from different references. The aim of this study is to make an analytic formula of a crossing coefficient between 3 point and 4 point bending concerning the longitudinal modulus of elasticity measured following the French standards (NF 1942; NF 1987). This formula includes a study of the shear force influence, and a study of supports and loading head indentation effect, in a 3 point bending test. The analytical study and the experiences have shown that the supports and loading head indentation effect are not negligible but have the same influence as the shear effect. The indentation is the result of the competition between two physical phenomena which are the wood stiffness and the load level applied on the piece of wood during a bending test. The practical result of this study is the development of a crossing analytic formula from a 3 point bending modulus of elasticity to a 4 point bending one, verified by the experimentation.

Use of the partial least squares method with acoustic vibration spectra as a new grading technique for structural timber

Summary This study develops a high performance grading process based on the analysis of acoustic vibrations in the audible frequency range. The unique feature of the method is that the spectrum is directly applied to obtain predictive variables for estimating the modulus of elasticity and modulus of rupture. A partial least squares regression was used. This powerful method represents a compromise between principal component regression and multi-linear regression. Partial least squares regression screens for factors which account for the variance in the predictor variables and achieves the best correlation between factors and predicted variable. The method is based on projections, similar to principle components regression, whereby a set of correlated variables is compressed into a smaller set of uncorrelated factors.

Analysis of Protein Expression along the Normal to Tension Wood Gradient in Eucalyptus gunnii

Abstract This paper examines the contribution of various xylem proteins to wood formation in Eucalyptus gunnii. Proteins were extracted from differentiating xylem harvested from a crooked tree, separated by high-resolution two-dimensional polyacrylamide gel electrophoresis, visualised by silver nitrate staining and analysed with a computer-assisted system for single protein spot quantification. Growth strain measurements allowed xylem samples to be classified quantitatively from tension wood to normal wood. Regression of lignin content on growth strain showed that a decrease in lignin content corresponded to decreasing growth strain values, i.e., presence of tension wood. Out of the 140 studied protein spots, 12 were significantly associated with growth strain: 7 being less abundant in tension wood and 5 being more abundant in tension wood. A clustered-correlation analysis was performed to study protein expression simultaneously along the gradient of gravistimulated stressed xylem tissue. Proteins were found to form “expression clusters”.

Key signal and wood anatomy parameters related to the acoustic quality of wood for xylophone-type percussion instruments

Wood percussion instruments have been part of culture since the earliest human societies. In making an instrument, the practical experience of musical instrument makers ensures its acoustic quality, especially with respect to selecting the most suitable wood species. The aim of this study was thus to gain further insight into the relationship between the physical properties and the perceptual classification of woods to be used in xylophone-type percussion instruments. A xylophone maker perceptually classified 58 tropical wood species, most of which are not usually used for musical instruments. Dynamic tests were then performed to record radiated signals. Key signal parameters pertaining to the acoustic quality of the material were extracted. Relationships between perceptual classifications, signal parameters, and wood anatomical characteristics were thus analyzed. It has been shown that percussive acoustic quality of wood, as determined empirically by the xylophone maker, can first be related to the temporal damping of the fundamental frequency. The samples tested in this study were not musically tuned; this could explain why no frequency descriptor was relevant. However, a draft anatomical portrait of a good acoustic wood could be drawn up. The organization of wood components in the tested species highlighted the importance of the regularity and homogeneity of the anatomical structures. The axial parenchyma seems to be the key trait. It should be paratracheal, and not very abundant if possible. The rays are another important feature; they should be short, structurally homogeneous, and not very numerous.

Quantitative assessment of total phenol contents of European oak (#Quercus petraea# and #Quercus robur#) by diffuse reflectance NIR spectroscopy on solid wood surfaces

Abstract Near infrared spectroscopy (NIRS) combined with multivariate analysis techniques was applied to assess phenol content of European oak. NIRS data were firstly collected directly from solid heartwood surfaces: in doing so, the spectra were recorded separately from the longitudinal radial and the transverse section surfaces by diffuse reflectance. The spectral data were then pretreated by several pre-processing procedures, such as multiplicative scatter correction, first derivative, second derivative and standard normal variate. The tannin contents of sawmill collected from the longitudinal radial and transverse section surfaces were determined by quantitative extraction with water/methanol (1:4, by vol). Then, total phenol contents in tannin extracts were measured by the Folin-Ciocalteu method. The NIR data were correlated against the Folin-Ciocalteu results. Calibration models built with partial least squares regression displayed strong correlation – as expressed by high determination correlation coefficient (r2) and high ratio of performance to deviation (RPD) – between measured and predicted total phenols content, and weak calibration and prediction errors (RMSEC, RMSEP). The best calibration was provided with second derivative spectra (r2 value of 0.93 for the longitudinal radial plane and of 0.91 for the transverse section plane). This study illustrates that the NIRS technique when used in conjunction with multivariate analysis could provide reliable, quick and non-destructive assessment of European oak heartwood extractives.

Evaluating growth strain of Eucalyptus globulus Labill. from SilviScan measurements

Abstract Longitudinal surface strain was measured or estimated using three different methods along the stems of nine trees of 10-year-old Eucalyptus globulus Labill. Wood samples were collected close to the location where the strain was measured or estimated. Microfibril angle (MFA), cellulose crystallite width (Wcryst), microdensity and Youngs modulus along the grain (EL) were determined using the SilviScan-2 technology at high spatial resolution. Relationships of measured strain and estimated strain to wood properties were established. The quality of the relationships depends on a particular wood property. Strain was more closely related to mean Wcryst than to any other wood properties. Its relationship with MFA was the next closest. Based on the results of regression analysis, we propose that Wcryst may be suitable for the prediction of surface strain at a moderate level of reliability. Adding measurement of MFA, microdensity and EL does not significantly improve the prediction quality. The strain measurement method also affects the results. The best relationships were obtained with longitudinal displacement measured by the CIRAD method. Strain measured by the strain gauge method gave weak relationships, possibly owing to variation in the cambium age of the specimens.

Correction of moisture effects on near infrared calibration for the analysis of phenol content in eucalyptus wood extracts

Abstract• Methods based on near infrared spectroscopy used to assess wood properties are susceptible to variations in physical parameters (temperature, grain size, etc.). As wood is a hygroscopically sensitive material, we studied the effects of moisture on near infrared absorbance and calibration to accurately determine the application potential of this technique under routine.• A collection of Eucalyptus urophylla × E. grandis hybrid wood pieces were analysed to obtain reference calibration of polyphenol contents in wood extracts via NIR spectra acquired under constant moisture conditions. Other specimens from the same source were assessed to obtain spectra for eight moisture contents spanning a broad variation range. The effects of moisture on absorption and on estimates based on a reference model were analysed.• An increase in moisture content prompted a rise in near infrared absorption over the entire spectrum and for water O-H absorption bands. The polyphenol content estimates obtained by assessing specimens against the reference calibration at variable moisture contents revealed prediction bias. Five correction methods were then tested to enhance the robustness relative to moisture.• In-depth calibration and external parameter orthogonalization (EPO) were found to be the most efficient methods for offsetting this factor.Résumé• Les méthodes basées sur la spectroscopie proche infrarouge pour estimer les propriétés du bois sont sensibles aux variations des paramètres physiques (température, granulométrie…). Le bois étant un matériau hygroscopique sensible, l’influence de l’humidité sur l’absorbance et l’étalonnage proche infrarouge a été étudiée afin de mieux considérer les possibilités d’applications dans des conditions réelles.• Un étalonnage de référence de la quantité de polyphénols présents dans les extraits a été établi à partir de spectres d’une collection de bois d’hybrides d’Eucalyptus urophylla × E. grandis à humidité constante fixée. D’autres spectres ont été obtenus sur des échantillons de même provenance mais à 8 teneurs en eau couvrant une large plage de variation. L’influence de l’humidité sur l’absorbance proche infrarouge puis sur l’estimation par le modèle de référence a été analysée.• Une augmentation de l’humidité élève la ligne de base du spectre d’absorbance et également les régions d’absorbance caractéristiques de la liaison O-H de l’eau. Les estimations de la quantité de polyphénols à partir de l’étalonnage de référence sur les échantillons à humidité variable révèlent un biais sur les prédictions.• Parmi les cinq méthodes de correction testées pour rendre l’étalonnage robuste vis-à-vis de l’humidité, l’étalonnage exhaustif et l’EPO (External Parameter Orthogonalisation) s’avèrent être les plus efficaces et permettent de s’affranchir de ce facteur.