Éditeur(s) : HAL CCSD American Geophysical Union
Résumé : International audience
Using first principle simulations we calculated the elasticity of chlorite. At a density ρ~ 2.60 g cm−3, the elastic constant tensor reveals significant elastic anisotropy: VP ~27%, VS1 ~56%, and VS2 ~43%. The shear anisotropy is exceptionally large for chlorite and enhances upon compression. Upon compression, the shear elastic constant component C44 and C55 decreases, whereas C66 shear component stiffens. The softening in C44 and C55 is reflected in shear modulus, G, and the shear wave velocity, VS. Our results on elastic anisotropy at conditions relevant to the mantle wedge indicates that a 10-20 km layer of hydrated peridotite with serpentine and chlorite could account for the observed shear polarization anisotropy and associated large delay times of 1-2 s observed in some subduction zone settings. In addition, chlorite could also explain the low VP/VS ratios that have been observed in recent high-resolution seismological studies.
ISSN: 0094-8276

hal-01053707
https://hal.archives-ouvertes.fr/hal-01053707
https://hal.archives-ouvertes.fr/hal-01053707/document
https://hal.archives-ouvertes.fr/hal-01053707/file/Mookherjee_et_al-2014-Geophysical_Research_Letters.pdf
DOI : 10.1002/2014GL059334

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
In this paper, we describe an outcrop to characterize the effect of fracture spacing and type on larger scale effective elasticity, which is measured for the first time in-situ with a Schmidt hammer. The outcrop is dominated by lime mudstones and belongs to the deformation zone of the St Clement fault, in southern France. Our results suggest that small spacing of faults, open fractures and styolites leads to lesser effective Young's modulus, whereas small sealed fracture spacing leads to greater effective Young's modulus. These relationships are compatible with theoretical models of effective elasticity. Using Amadei and Savage (1993) approach, we define a non-linear model that relates Schmidt hammer rebound to spacing by fracture type. A hemisphere with a radius of 40 to similar to 200 cm is the rheological volume characterized by the Schmidt hammer. Results of model inversion demonstrate that variations of Schmidt hammer rebound over the outcrop can be used to estimate fracture type and stiffness. Stiffness of sealed fractures is 2-3 orders of magnitude greater than the stiffness of faults, stylolites and open fractures. This result is consistent with an increase of the rate of interseismic stress build-up of major faults with sealing of fractures in their damage zone.
ISSN: 0191-8141

hal-00669954
https://hal.archives-ouvertes.fr/hal-00669954
DOI : 10.1016/j.jsg.2011.09.009

Éditeur(s) : HAL CCSD Elsevier
Résumé : The dense hydrous magnesium silicate called the D phase is the most likely candidate to recycle hydrogen into the lower mantle in subduction zones. As seismology represents the preferred method to detect this mineral in subduction zones, the single crystal elastic tensor has been calculated using first principle methods. A triple cell (View the MathML source) was used to account for an ordered ideal composition of the D phase to lower mantle pressures. The elastic tensor of the mineral at ambient conditions is predicted to be C11 = 387.7, C33 = 287.7, C44 = 100.4, C12 = 108.0, C13 = 51.1, C14 = − 14.6 in GPa with bulk modulus at zero pressure Ko = 163 GPa and a statistical error of about 4.0 GPa for all constants. The pressure derivatives of the elastic constants have been determined to pressure of 80 GPa. Our tensor correctly predicts the published experimental measurements of linear compressibility along the a- and c-axes, the logarithmic pressure derivative of the c/a axial ratio and bulk modulus at zero pressure. It contradicts the experimentally measured elastic tensor reported by (Liu, L.-G., Okamoto, K., Yang, Y.-J., Chen, C.-C., Lin, C.-C., 2004. Elasticity of single-crystal phase D (a dense hydrous magnesium silicate) by Brillouin spectroscopy. Solid State Commun. 132, 517–520), which fails to reproduce the experimental compressibility data. Using the elastic constants and density predicted to 85 GPa, the seismic anisotropy of P- and S-waves has been calculated as a function of pressure. The single crystal has high P-wave velocities and shear wave splitting in the basal plane below 20 GPa. At high pressures, the maximum P-wave velocities have threefold symmetry normal to a-axes in the basal plane, whereas the maximum shear wave splitting is parallel to a-axes with twofold symmetry. The D phase has high Vp and Vs anisotropy at ambient pressure, 17.6% for Vp and 19.9% for Vs. The Vp anisotropy decreases with increasing pressure to about 30 GPa, while it remains constant at 8% from 30 to 85 GPa. The Vs anisotropy decreases to 17% at 20 GPa and then increases to 22% at 85 GPa. The isotropic velocity ratios of S to P (Rs/p), bulk sound to S (Rphi/s) and density to S (Rρ/s) are calculated as a function of pressure. The Rs/p shows very little variation with pressure with low value of 0.6, whereas both Rphi/s and Rρ/s increase with pressure to peak values of 2.8 and 2.0 respectively at about 60 GPa. The presence of the D phase in subducted horizontal ‘stagnant' plates in the circum Pacific could contribute to a number of seismic observations, such as the observed velocity heterogeneity at depths between 500 and 1000 km and the fast S-waves travelling horizontally with horizontal polarization in this depth range. Further the lower density of the D phase compared with anhydrous minerals could influence buoyancy of the hydrated ‘stagnant' slabs. The transformation of the D phase to perovskite plus ferripericlase during thermal annealing may be responsible for horizontal slab seismogenesis.
ISSN: 0012-821X

hal-00406379
https://hal.archives-ouvertes.fr/hal-00406379
DOI : 10.1016/j.epsl.2007.04.053

Éditeur(s) : HAL CCSD Elsevier
Résumé : To contribute to the understanding of how opening-mode fractures (joints) form and open or close at depth in layered rocks, we present a 2D numerical study aiming to determine whether tensile stress can develop in pre-fractured elastic multilayers submitted to biaxial compressive strain conditions. First, we investigate the role of the elastic and geometrical properties of the layers on the development of tensile stress in models with five bonded layers and containing one open fracture in the central layer. Our results indicate that, in absence of elastic contrast (in Young's modulus) between the layers, no tensile stress develops in the models. However, when the fractured layer is stiffer than the two adjacent layers directly above and below, a lobe of horizontal tensile stress develops centered on the pre-existing fracture. The creation of this tensile stress is contingent upon the partial closing of the fracture. The levels of tensile stress and the thickness of the lobe of tensile stress increase logarithmically with an increase in the elastic contrast and are systematically larger for a larger Soft/Stiff ratio (ratio of the total thickness of the soft layers with the total thickness of the stiff layers). Second, we investigate the role of fracture interaction in the development of tensile stress in models containing a pair of open fractures. We observe that the levels of tensile stress in the region between the fractures are systematically higher than those observed in identical models containing a single fracture. This increase in tensile stress is very large for small elastic contrasts between the layers but diminishes when the elastic contrast increases. Furthermore, the spacing between the pre-existing fractures plays an important role in the stress distribution in the region between them. When the fracture spacing is equal to or lower than 1.15 times the height of the fractured layer for the experimental conditions chosen, the lobes of tensile stress centered on the fractures coalesce. This results in the formation of vast areas of tensile stress in models under remote compressive loading conditions. Such tensile areas are likely to allow the initiation and propagation of subsequent opening-mode fractures. The results obtained provide new insights into the formation of joints in layered rocks in compressive environments, with important consequences on fluid flow.
ISSN: 0040-1951

hal-00407576
https://hal.archives-ouvertes.fr/hal-00407576
DOI : 10.1016/j.tecto.2006.12.003

Éditeur(s) : HAL CCSD De Gruyter
Résumé : International audience
This study aims at better understanding the respective influences of specific gravity (γ), microfibril angle (MFA), and cell-wall matrix polymers on viscoelastic vibrational properties of wood in axial direction. The wide variations of properties between normal wood (NW) and compression wood (CW) are in focus. Three young bent trees (Picea abies, Pinus sylvestris and Pinus pinaster) that recovered verticality were sampled. Several observed differences between NW and CW were highly significant in terms of anatomical, physical (γ, shrinkage, CIELab colorimetry), mechanical (compressive strength), and vibrational properties. Specific dynamic modulus of elasticity (E'/γ) decreases with increasing MFA, and Young's modulus (E') can be satisfactorily explained by γ and MFA. Apparently, the type of the cell wall polymer matrix is not influential in this regard. The damping coefficient (tanδ) does not depend solely on MFA of NW and CW. The tanδ - E'/γ relationship evidences that, at equivalent E'/γ, the tanδ of CW is approx. 34% lower than that of NW. This observation is ascribed to the more condensed nature of CW lignins, and this is discussed in the context of previous findings in other hygrothermal and time/frequency domains. It is proposed that the lignin structure and the amount and type of extractives, which are both different in various species, are partly responsible for taxonomy-related damping characteristics.
ISSN: 0018-3830

hal-00808062
https://hal.archives-ouvertes.fr/hal-00808062
https://hal.archives-ouvertes.fr/hal-00808062/document
https://hal.archives-ouvertes.fr/hal-00808062/file/Changes_viscoelastic_vibrational_Bremaud_al.pdf
DOI : 10.1515/hf-2011-0186

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
Networks of localized conjugate compactive shear bands with large dihedral angles (corresponding to so-called shear-enhanced compaction bands) were generated in 3-layer plane strain finite-difference models. The central layer has elastic–plastic properties with a small positive internal friction coefficient, negative dilatancy factor, and the hardening modulus reducing during the deformation. The two other layers are elastic. The spatial organization of the networks in the central layer, resulting from the elastic–plastic instability of the 3-layer system, was shown to be dependent on the contrast of the elastic stiffness of the layers and on the friction between them. When the stiffness E of the elastic layers and/or the friction are small, the networks are rather symmetric (the bands of both orientation families are distributed homogeneously within the layer). An increase in E at high friction, results in the clustering of the bands of one orientation along a layer segment which is followed by another segment filled with the bands of the other orientation. Different network types are characterized by different band spacing which is smaller in the clustered networks. The intensity of inelastic deformation and hence of porosity reduction within the bands are also smaller in this case. The obtained band networks are very similar to those in nature where the same variability of the network organization is observed. Available geological and mechanical data confirm the conclusions from the modeling about the origin of this variability.
ISSN: 0040-1951

hal-01116201
https://hal.archives-ouvertes.fr/hal-01116201
DOI : 10.1016/j.tecto.2014.01.021

Éditeur(s) : HAL CCSD Springer Verlag (Germany)
Résumé : International audience
The anisotropy of vibrational properties influences the acoustic behaviour of wooden pieces and their dependence on grain angle (GA). As most pieces of wood include some GA, either for technological reasons or due to grain deviations inside trunks, predicting its repercussions would be useful. This paper aims at evaluating the variability in the anisotropy of wood vibrational properties and analysing resulting trends as a function of orientation. GA dependence is described by a model based on transformation formulas applied to complex compliances, and literature data on anisotropic vibrational properties are reviewed. Ranges of variability, as well as representative sets of viscoelastic anisotropic parameters, are defined for mean hardwoods and softwoods and for contrasted wood types. GA-dependence calculations are in close agreement with published experimental results and allow comparing the sensitivity of different woods to GA. Calculated trends in damping coefficient (tanδ) and in specific modulus of elasticity (E′/ρ) allow reconstructing the general tanδ-E′/ρ statistical relationships previously reported. Trends for woods with different mechanical parameters merge into a single curve if anisotropic ratios (both elastic and of damping) are correlated between them, and with axial properties, as is indicated by the collected data. On the other hand, varying damping coefficient independently results in parallel curves, which coincide with observations on chemically modified woods, either “artificially”, or by natural extractives.
Wood Science and Technology

hal-01096868
https://hal-agroparistech.archives-ouvertes.fr/hal-01096868
DOI : 10.1007/S00226-010-0393-8

Éditeur(s) : HAL CCSD Public Library of Science
Résumé : 51 pages; 15figures; 3 tables, accepted for publication in PloS ONE
International audience
We present a study about AFM imaging of living, moving or self-immobilized, bacteria in their genuine physiological liquid medium. No external immobilization protocol, neither chemical nor mechanical, was needed. For the first time, the native gliding movements of Gram-negative Nostoc cyanobacteria upon the surface, at speeds up to 900microns/h, were studied by AFM. This was possible thanks to an improved combination of a gentle sample preparation process and an AFM procedure based on fast and complete force-distance curves made at every pixel, drastically reducing lateral forces. No limitation in spatial resolution or imaging rate was detected. Gram-positive and non-motile R. wratislaviensis bacteria were studied as well. From the approach curves, Young modulus and turgor pressure were measured for both strains at different gliding speeds and are ranging from 20±3 to 105±5MPa and 40±5 to 310±30kPa depending on the bacterium and the gliding speed. For Nostoc, spatially limited zones with higher values of stiffness were observed. The related spatial period is much higher than the mean length of Nostoc nodules. This was explained by an inhomogeneous mechanical activation of nodules in the Nostoc. We also observed the presence of a soft extra cellular matrix (ECM) around the Nostoc. Both strains left a track of polymeric slime with variable thicknesses. For R. wratislaviensis, it is equal to few hundreds of nanometers, likely to promote its adhesion to the sample. While gliding, the Nostoc secretes a slime layer the thickness of which is in the nanometer range and increases with the gliding speed.
ISSN: 1932-6203

hal-00769765
https://hal.archives-ouvertes.fr/hal-00769765
https://hal.archives-ouvertes.fr/hal-00769765v3/document
https://hal.archives-ouvertes.fr/hal-00769765/file/REsubmission_In-situ_determination_Dhahri_Plos_One_R2_Hal.pdf

Éditeur(s) : HAL CCSD Springer Verlag
Résumé : International audience
Grain deviations and high extractives content are common features of many tropical woods. We aimed at clarifying their respective impact on vibrational properties, referring to African Padauk (Pterocarpus soyauxii Taub.), a species selected for its interlocked grain, high extractives content, and uses in xylophones. Specimens were cut parallel to the trunk axis (L), and local variations in grain angle (GA), microfibril angle (MFA), specific Young's modulus (E'L/ρ, where r stands for specific gravity) and damping coefficient (tanδL), were measured. GA dependence was analyzed by a mechanical model which allowed to identify the specific Young's modulus (E'3/ρ) and shear modulus (G'/ρ) along the grain (3), as well as their corresponding damping coefficients (tanδ3, tanδG). This analysis was done for native and then for extracted wood. Interlocked grain resulted in 0-25° GA and in variations of a factor 2 in E'L/ρ and tanδL. Along the grain, Padauk wood was characterized, as compared to typical hardwoods, by a somewhat lower E'3/ρ and elastic anisotropy (E'/G'), due to a wide microfibril angle plus a small weight effect of extracts; and a very low tanδ3 and moderate damping anisotropy (tanδG/tanδ3). Extraction affected mechanical parameters in the order: tanδ3 ≈ tanδG > G'/ρ >> E'3/ρ. That is, extractives' effects were nearly isotropic on damping but clearly anisotropic on storage moduli.
ISSN: 0043-7719

hal-00544382
https://hal.archives-ouvertes.fr/hal-00544382
https://hal.archives-ouvertes.fr/hal-00544382/document
https://hal.archives-ouvertes.fr/hal-00544382/file/Identification_anisotropic_vibrational_properties_Bremaud_al.pdf
DOI : 10.1007/s00226-010-0348-0

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
Porous thin films considered for applications like separation, sensing and microelectronic have to sustain mechanical stresses during their integration process or in working conditions. Thanks to recent progress in processing methods, it is now possible to precisely control the porosity and combine ordered mesopores with randomly-distributed macropores to achieve hierarchically porous materials. The mechanical properties of thin films containing different types of porosity (ordered meso, random macro and hierarchical) have been investigated by means of nanoindentation. In particular a method recently proposed by Li and Vlassak (H. Li, J.J. Vlassak, Journal of Materials Research 24 (2009) 1114-1126) is applied to account for the substrate effect. Residual indent impressions were imaged by Atomic Force Microscopy (AFM) to provide some insights in the mechanical behavior of the films. In addition, experimental indentation moduli are compared to theoretical predictions obtained via Finite Element (FE) analysis. The different porous structures have been modeled by FE to obtain the effective elastic properties from which the indentation modulus can be inferred. Finally, the experimental-model differences are discussed. © 2010 Elsevier Inc. All rights reserved.
ISSN: 1387-1811

hal-01683194
https://hal.univ-antilles.fr/hal-01683194
DOI : 10.1016/j.micromeso.2010.09.004

Éditeur(s) : HAL CCSD Springer Verlag (Germany)
Résumé : International audience
*Context Increased knowledge on diversity in wood properties would have implications both for fundamental research and for promoting a diversification of uses as material. *Aims The objective is to contribute to overcoming the critical lack of data on the diversity of wood dynamic mechanical/viscoelastic vibrational properties, by testing lesser-known species and categorizing sources of variability. *Methods Air-dry axial specific dynamic modulus of elasticity (E'/γ) and damping coefficient (tanδ) were measured on a wide sampling (1792 specimens) of 98 wood types from 79 species. An experimental device and protocol was designed for conducting systematic (i.e. rapid and reproducible) characterizations. *Results Diversity at the specimens' level corroborates the "standard" relationship between tanδ and E'/γ, which is discussed in terms of orientation of wood elements and of chemical composition. Diversity at the species level is expressed on the basis of results for normal heartwood, with specific gravity (γ) ranging from 0.2 to 1.3. Axial E'/γ ranges from 9 to 32 GPa and tanδ from 4×10-3 to 19×10-3. Properties distribution follows a continuum, but with group characteristics. The lowest values of tanδ are only found in certain tropical hardwoods. Results can also suggest alternative species for musical instruments making.
Annals of Forest Science

hal-00808242
https://hal.archives-ouvertes.fr/hal-00808242
https://hal.archives-ouvertes.fr/hal-00808242/document
DOI : 10.1007/s13595-011-0166-z

Éditeur(s) : HAL CCSD Springer Verlag
Résumé : International audience
The anisotropy of vibrational properties influences the acoustic behaviour of wooden pieces and their dependence on grain angle (GA). As most pieces of wood include some GA, either for technological reasons or due to grain deviations inside trunks, predicting its repercussions would be useful. This paper aims at evaluating the variability in the anisotropy of wood vibrational properties and analysing resulting trends as a function of orientation. GA dependence is described by a model based on transformation formulas applied to complex compliances, and literature data on anisotropic vibrational properties are reviewed. Ranges of variability, as well as representative sets of viscoelastic anisotropic parameters, are defined for mean hardwoods and softwoods and for contrasted wood types. GA-dependence calculations are in close agreement with published experimental results and allow comparing the sensitivity of different woods to GA. Calculated trends in damping coefficient (tanδ) and in specific modulus of elasticity (E′/ρ) allow reconstructing the general tanδ-E′/ρ statistical relationships previously reported. Trends for woods with different mechanical parameters merge into a single curve if anisotropic ratios (both elastic and of damping) are correlated between them, and with axial properties, as is indicated by the collected data. On the other hand, varying damping coefficient independently results in parallel curves, which coincide with observations on chemically modified woods, either "artificially", or by natural extractives.
ISSN: 0043-7719

hal-00804242
https://hal.archives-ouvertes.fr/hal-00804242
https://hal.archives-ouvertes.fr/hal-00804242/document
https://hal.archives-ouvertes.fr/hal-00804242/file/Anisotropy_wood_variational_properties_Bremaud_al_2011.pdf
DOI : 10.1007/s00226-010-0393-8

Éditeur(s) : HAL CCSD Springer Verlag
Résumé : Active mechanisms of re-orientation are necessary to maintain the verticality of tree stems. They are achieved through the production of reaction wood, associated with circumferential variations of three factors related to cambial activity: maturation strain, longitudinal modulus of elasticity (MOE) and eccentric growth. These factors were measured on 17 mature trees from different botanical families and geographical locations. Various patterns of circumferential variation of these factors were identified. A biomechanical analysis based on beam theory was performed to quantify the individual impact of each factor. The main factor of re-orientation is the circumferential variation of maturation strains. However, this factor alone explains only 57% of the re-orientations. Other factors also have an effect through their interaction with maturation strains. Eccentric growth is generally associated with heterogeneity of maturation strains, and has an important complementary role, by increasing the width of wood with high maturation strain. Without this factor, the efficiency of re-orientations would be reduced by 31% for angiosperms and 26% for gymnosperms. In the case of angiosperms, MOE is often larger in tension wood than in normal wood. Without these variations, the efficiency of re-orientations would be reduced by 13%. In the case of gymnosperm trees, MOE of compression wood is lower than that of normal wood, so that re-orientation efficiency would be increased by 24% without this factor of variations.
ISSN: 0931-1890

hal-01031825
https://hal.archives-ouvertes.fr/hal-01031825
DOI : 10.1007/s00468-005-0407-6

Éditeur(s) : HAL CCSD Springer Verlag/EDP Sciences
Résumé : International audience
Context and aim : This study aimed to examine the effect of the tension wood G‐layer on the viscoelastic properties of wood. Methods : Tension wood and opposite wood samples were obtained from six French Guianese tropical rainforest species (Sextonia rubra, Ocotea guyanensis, Inga alba, Tachigali melinoni, Iyranthera sagotiana and Virola michelii); the tension wood of the former three of these species had a Glayer, whilst the tension wood from the latter three had no Glayer. Tensile dynamic mechanical analysis (DMA) was performed on green never dried wood samples in the longitudinal direction with samples submerged in a water bath at a temperature (30°C) and frequency (1 Hz) representative of the conditions experienced by wood within a living tree. Then, DMA was repeated with samples conditioned to an air-dried state. Finally, samples were oven-dried to measure longitudinal shrinkage. Results : Tension wood did not always have a higher longitudinal storage (elastic) modulus than opposite wood from the same tree regardless of the presence or absence of a G‐layer. For the species containing a G‐layer, tension wood had a higher damping coefficient and experienced a greater longitudinal shrinkage upon drying than opposite wood from the same species. No difference was found in damping coefficients between tension wood and opposite wood for the species that had no G‐layer. Conclusion : It is proposed that the different molecular composition of the G-layer matrix has an influence on the viscoelasticity of wood, even if a biomechanical gain is not yet clear. This study shows that rheological properties and longitudinal shrinkage can be used to detect the presence of a G‐layer in tension wood.
ISSN: 1286-4560

hal-00677460
https://hal.archives-ouvertes.fr/hal-00677460
https://hal.archives-ouvertes.fr/hal-00677460/document
https://hal.archives-ouvertes.fr/hal-00677460/file/Clair2.pdf
DOI : 10.1007/s13595-011-0164-1

Éditeur(s) : HAL CCSD Oxford University Press (OUP)
Résumé : International audience
Energy dissipation is observed on seismic data when a wave propagates through a porous medium, involving different frequency regimes depending on the nature of rock and fluid types. We focus here on the role of partial fluid saturation in unconsolidated porous media, looking in particular at P-wave phase velocity and attenuation. The study consists in running an experiment in a sand-filled tank partially saturated with water. Seismic propagation in the tank is generated in the kHz range by hitting a steel ball on a granite plate. Seismic data are recorded by buried accelerometers and injecting or extracting water controls the partial saturation. Several imbibition/drainage cycles were performed between the water and gas residual saturations. A Continuous Wavelet Transform applied on seismic records allowed us to extract the direct P-wave at each receiver.We observe an hysteresis in phase velocities and inverse quality factors between imbibition and drainage. Phase velocities and inverse quality factors are then jointly inverted to get a final poro-visco-elastic model of the partially saturated sand that satisfactorily reproduces the data. The model formulation consists in generalizing the Biot theory to effective properties of the fluid and medium (permeability and bulk modulus) in order to properly explain the phase velocity variation as a function of the saturation. The strong level of attenuation measured experimentally is further explained by an anelastic effect due to grain to grain sliding, adding to Biot's losses. This study shows that fluid distribution at microscopic scale has strong influence on the attenuation of direct P-waves at macroscopic scale and confirms that seismic prospection may be a powerful tool for the characterization of transport phenomena in porous media.
ISSN: 0956-540X

hal-00779920
https://hal.archives-ouvertes.fr/hal-00779920
https://hal.archives-ouvertes.fr/hal-00779920/document
https://hal.archives-ouvertes.fr/hal-00779920/file/Barriere_et_al_HAL.pdf
DOI : 10.1111/j.1365-246X.2012.05691.x

Éditeur(s) : HAL CCSD Springer Verlag
Résumé :  
Growth strains were measured in situ in nine trees of three species from a French Guiana tropical rainforest in a clearly active verticality restoration process. The aim was to detect tension wood within the samples. Wood specimens were cut in the vicinity of the growth strain measurements in order to determine the microfibril angle and some mechanical and physical properties. As suspected, tensile growth strain was much higher in tension wood zones, as shown by the slightly higher longitudinal modulus of elasticity. Conversely, tension wood showed reduced compression strength. Longitudinal shrinkage was much higher in tension wood than in opposite wood. Clear relationships between the microfibril angle and longitudinal properties were noted in comparison (i) with those observed in gymnosperm compression wood and (ii) with expected relationships from the organization of wood fibres cell wall structure.
ISSN: 0043-7719

hal-01032114
https://hal.archives-ouvertes.fr/hal-01032114
DOI : 10.1007/s00226-010-0323-9

Éditeur(s) : HAL CCSD Springer Verlag
Résumé : International audience
Few studies have investigated the influence of environmental conditions on the within-treevariation in Eucalyptus wood traits. The genotype and environment effects and their interactionsinfluence the wood properties. Their evaluations are crucial to estimate the genotype values andto select with efficiency. Thus, the aim of this study was to better understand the effect ofground slope and wind speed on the spatial variation of basic density (ρ), stiffness (MOE) andmicrofibril angle (MFA) of Eucalyptus wood. Wood discs cut along the trunk were sampledfrom 150 six-year-old Eucalyptus grandis x E. urophylla hybrids growing in 3 contrastinggrowing conditions influenced by ground slope and wind regime. Near Infrared (NIR)calibrations previously developed for ρ, MOE and MFA were used to predict in our discs. 2-Dplots presenting the spatial variation of predicted wood traits were compared. The higher theground slope, the greater the magnitude of radial variation in ρ, principally in the medium zoneof the trunk. The spatial variation of wood stiffness seems to be sensitive to two environmentalconditions. The MFA radial decreases were more pronounced where the wind speed was higher.At the base and top of the trees, however, there was no significant effect of growing conditionson the radial variation of the wood properties considered here.
ISSN: 0931-1890

hal-01451896
https://hal.archives-ouvertes.fr/hal-01451896
https://hal.archives-ouvertes.fr/hal-01451896/document
https://hal.archives-ouvertes.fr/hal-01451896/file/Art_Gril_al_Spatial_variation_wood_density_2016.pdf
DOI : 10.1007/s00468-015-1327-8

Éditeur(s) : HAL CCSD
Résumé : The forests of French Guiana occupy a central part of the region’s potential resource base, but as yet remain almost completely unexploited. This stems from the forestry industry struggling to valorize wood stocks of a high diversity with an extremely heterogeneous distribution. Indeed, identifying essences for future propagation is an issue of both environmental and socio-economic importance for the region. Bagassa guianensis Aubl. and Cordia alliodora (Ruiz & Pav.) Oken. go against conventional models, in that they display the life history characteristics of rapid growth and wood of high quality, and thus are species of high potential for future plantations. Firstly, our study of growth characteristics reveals a defined strategy half way between long-lived species and pioneer species. It is the variability of basic density of wood which is a key trait allowing for such a development, favoring rapid growth in initial years whilst allowing for tree longevity. Secondly, the analysis of a range of wood properties (shrinkage, modulus of elasticity, durability) in relation to tree growth confirms the technologic quality of the two species. It also enables the emergence of new results like the effect of extractives on wood stability, the control of growth as a result of basic density variation, the evolution of leaf traits throughout tree development or the improvement of trunk maintenance thanks to interlocked grain. The knowledge gained in relation to the developmental traits of these two species, and to the quality of their wood allows for the elaboration of plantation projects and what will be required for their success. The results of this study can orientate future studies on novel species for commercialization in French Guiana.
La ressource forestière en Guyane occupe une place maîtresse au sein de la région et est encore majoritairement préservée, mais la filière bois parvient difficilement à valoriser la biodiversité locale en raison de l’hétérogénéité de la ressource. Identifier les essences à planter demain représente aujourd’hui un enjeu à la fois environnemental, économique et social pour la Guyane. Bagassa guianensis Aubl. et Cordia alliodora (Ruiz & Pav.) Oken. vont à l’encontre des modèles usuels en associant vitesse de croissance et qualité du bois et sont identifiées comme prometteuses pour la plantation. Dans un premier temps, l’étude de la dynamique de croissance des deux espèces révèle un modèle écologique singulier, à la fois pionnières et longévives. La variabilité de l’infradensité dans l’arbre est l’élément clé qui permet un tel développement, favorisant une croissance rapide dans les premières années tout en assurant la longévité de l’individu. Dans une seconde partie, l’analyse d’un large panel de propriétés du bois (retrait, module, durabilité) en lien avec le développement de l’arbre confirme les qualités technologiques des deux espèces et permet l’émergence de résultats novateurs tels que le rôle des extractibles sur le retrait, le contrôle de la croissance grâce aux variations d’infradensité, l’évolution des traits foliaires au cours de l’ontogénie ou encore la mise en place de contrefil dans l’arbre pour assurer son maintien. La connaissance acquise vis-à-vis du mode de développement de ces deux espèces et des facteurs influençant la qualité de leur bois permet aujourd’hui de définir avec plus de précision le cadre d’un projet de plantation et les conditions de son succès. Les résultats de cette étude permettent finalement d’orienter la recherche de nouvelles espèces d’avenir pour la plantation en Guyane.
https://tel.archives-ouvertes.fr/tel-01338281

tel-01338281
https://tel.archives-ouvertes.fr/tel-01338281
https://tel.archives-ouvertes.fr/tel-01338281/document
https://tel.archives-ouvertes.fr/tel-01338281/file/Th%C3%A8se%20Julie%20Bossu.pdf

Éditeur(s) : HAL CCSD Botanical Society of America
Résumé :  
Tree buckling risk (actual height/critical buckling height) is an important biomechanical trait of plant growth strategies, and one that contributes to species coexistence. To estimate the diversity of this trait among wide samples, a method that minimizes damage to the plants is necessary. On the basis of the rarely used, complete version of Greenhill's model (1881, Proceedings of the Cambridge Philosophical Society 4(2): 65-73), we precisely measured all the necessary parameters on a sample of 236 saplings of 16 species. Then, using sensitivity (variance) analysis, regressions between successive models for risk factors and species ranks and the use of these models on samples of self- and nonself-supporting saplings, we tested different degrees of simplification up to the most simple and widely used formula that assumes that the tree is a cylindrical homogeneous pole. The size factor had the greatest effect on buckling risk, followed by the form factor and the modulus of elasticity of the wood. Therefore, estimates of buckling risk must consider not only the wood properties but especially the form factor. Finally, we proposed a simple but accurate method of assessing tree buckling risk that is applicable to a wide range of samples and that requires mostly nondestructive measurements.
ISSN: 0002-9122

hal-01032059
https://hal.archives-ouvertes.fr/hal-01032059

Éditeur(s) : HAL CCSD Springer Verlag/EDP Sciences
Résumé : International audience
The vibration damping coefficient (tanδ) of wood is an important property for acoustical uses, including musical instruments. Current difficulties in the availability of some of the preferred species call for diversification, but this comes up against the lack of systematic damping coefficient data. * Keeping in mind the possible factors affecting tanδ, could we predict its variations between species, by using indicators that are either easily measured and/or readily available for many species? * Vibrational properties, equilibrium moisture content and colorimetric parameters were assessed on 94 wood types belonging to 76 species. Experimental results were then related to data on chemical contents and physical properties from the CIRAD database. The "standard" relationship between tanδ and specific modulus of elasticity (E'/ρ) explained only half of the variations. Deviations from this trend were correlated to extractives content, yet effects were not directly quantitative. Damping deviations were also correlated to colour and moisture-related properties, especially so with fibre saturation point. * By taking into account a combination of moisture-related properties, colour - or extractives content, and the "standard" relationship between tanδ and E'/ρ, we could propose simple predictive models which explain up to 89% of observed variations in tanδ between 48 species.
ISSN: 1286-4560

hal-00808338
https://hal.archives-ouvertes.fr/hal-00808338
https://hal.archives-ouvertes.fr/hal-00808338/document
https://hal.archives-ouvertes.fr/hal-00808338/file/Physico-chemical_indicators_Bremaud_al.pdf
DOI : 10.1051/forest/2010032