Modelling the effects of wood cambial age on the effective modulus of elasticity of poplar laminated veneer lumber

Key messageA modelling method is proposed to highlight the effect of cambial age on the effective modulus of elasticity of laminated veneer lumber (LVL) according to bending direction and veneer thickness. This approach is relevant for industrial purposes in order to optimize the performance of LVL products.ContextLVL is used increasingly in structural applications. It is obtained from a peeling process, where product’s properties depend on cambial age, hence depend on radial position in the log.AimsThis study aims to highlight how radial variations of properties and cambial age impact the mechanical behaviour of LVL panels.MethodsAn analytical mechanical model has been designed to predict the modulus of elasticity of samples made from poplar LVL panels. The originality of the model resides in the integration of different data from the literature dealing with the variation in wood properties along the radius of the log. The simulation of the peeling process leads to veneers with different mechanical properties, which are randomly assembled in LVL panels.ResultsThe model shows a correct mechanical behaviour prediction in comparison with experimental results of the literature, in particular with the decrease in MOE in LVL made of juvenile wood. It highlights that the bending direction and veneer thickness have no influence on the average MOE, but affect MOE dispersion.ConclusionThis paper proposed an adequate model to predict mechanical behaviour in the elastic domain of LVL panels based on the properties of raw wood material.ANR xyloforest, région Bourgogne franche-comt

Modeling the Influence of Knots on Douglas-Fir Veneer Fiber Orientation

This study presents a method for predicting the local fiber orientation of veneers made from peeled Douglas-fir logs based on the knowledge of the tree branch characteristics (location, radius, insertion angle, azimuth angle, and living branch ratio). This model is based on the Rankine oval theory approach and focuses on the local deviation of the fiber orientation in the vicinity of knots. The local fiber orientation was measured online during the peeling process with an in-house-developed scanner based on the tracheid effect. Two logs from the same tree were peeled, and their ribbons were scanned. The knot locations and fiber orientation were deduced from the scanner data. The first objective was to compare the fiber orientation model with measurements to enhance and validate the model for French Douglas-fir. The second objective was to link data measurable on logs to veneer quality.Région Bourgogne-Franche-Comté Ministère de l'Agriculture et de l'Alimentatio

How to model orthotropic materials by the Discrete Element Method (DEM): random sphere packing or regular cubic arrangement?

The discrete element method (DEM) is used for continuous material modeling. The method is based on discretizing mass material into small elements, usually spheres, which are linked to their neighbours through bonds. If DEM has shown today its ability to model isotropic materials, it is not yet the case of anisotropic media. This study highlights the obstacles encountered when modeling orthotropic materials. In the present application, the elements used are spheres and bonds are Euler-Bernoulli beams developed by André et Al. [1]. Two different modeling approaches are considered: cubic regular arrangements, where discrete elements are placed on a regular Cartesian lattice, and random sphere packed arrangements, where elements are randomly packed. As the second approach is by definition favoring the domain’s isotropy, a new method to affect orientation-dependent Young’s modulus of bonds is proposed to create orthotropy. Domains created by both approaches are loaded in compression in-axis (along the material orthotropic directions) and off-axis to determine their effective Young’s modulus according to the loading direction. Results are compared to the Hankinson model which is especially used to represent high orthotropic behavior such as encountered in wood or synthetic fiber materials. For this class of materials, it is shown that, contrary to cubic regular arrangements, the random sphere packed arrangements exhibit difficulties to reach highly orthotropic behavior (in-axis tests). Conversely, this last arrangements display results closer to continuous orthotropic material during off-axis tests.ANR xyloforest ; Région Bourgogne Franche-Comt

Effect of Forestry Management and Veneer Defects Identified by X-ray Analysis on Mechanical Properties of Laminated Veneer Lumber Beams Made of Beech

This study proposes an innovative model based on local grain angle measurements to predict the modulus of elasticity of LVL made from beech. It includes a veneers sorting method industrially compatible thanks to its low computational time. For this study 41 LVL panels were prepared from 123 beech sheets of veneers. Local grain angle was obtained with a two dimensional scanner and veneer density was measured. Several models based on these measurements have been developed and their ability to predict the modulus of elasticity of LVL panels have been compared. The model based only on local grain angle measurements have been proven more efficient than models taking into account the veneer density. The proposed method can be used to sort veneer during the peeling process and grade the production of LVL panels to optimize their mechanical properties even for low-quality veneer.ANR-10-EQPX-16 XYLOFOREST ; Région Bourgogne Franche-Comté ; Brugèr

New Perspectives for LVL Manufacturing from Wood of Heterogeneous Quality—Part 2: Modeling and Manufacturing of Variable Stiffness Beams

This paper presents a new strategy in the use of wood of heterogeneous quality for composing LVL products. The idea is to consider veneers representative of the resource variability and retain local stiffness information to control panel manufacturing fully. The placement of veneers is also no longer random as in the first part of this group of papers but optimized for the quality of veneers according to the requirement of bending stresses along the beam. In a four-point bending test arrangement, this means the high-quality veneer is concentrated in the center of the beam in the area between the loading points where the bending moments are the most important, and the low quality is located at the extremities. This initiates the creation of variable stiffness beams. This is driven by an algorithm developed and tested on representative veneer samples from the resource. Four LVL panels were manufactured by positioning the veneers in the same positions as in an analytical calculation model, which allowed the calculation of beam mechanical properties in four-point bending. The proposed optimization of LVL manufacturing from variable quality veneers should help for more efficient usage of forest resources. This optimization strategy showed notable gains for modeled and experimental mechanical properties, whether in terms of stiffness or strength. The analytical calculation of the local modulus of elasticity from modelized beams was satisfactory compared to the tests of the manufactured beams test results, allowing the reliability of the model for this property to be confirmed

Identification of local to global mechanical properties of clear wood peeled veneers from off axis tensile tests using full-field local displacement measurements

This study examines the influence of fiber orientation variability on the mechanical properties of wood, focusing on veneer clear wood specimens. The research is motivated by the need to develop high performance composite materials for sustainable transportation applications, particularly in reducing greenhouse gas emissions. The experimental protocol involves manufacturing veneers from beech wood, followed by producing the manufacturing of veneers from beech wood, followed by the production of small specimens with deliberate variations in fiber orientation. Non-destructive measurements of local fiber orientations and global density are conducted, along with tensile tests to determine local mechanical properties, i.e., Young's modulus, strength, and the shear modulus Advanced imaging techniques (DIC) and models for isotropic materials are employed for analysis.The resultsreveal that fiber orientation has a significant role in wood variability, with pronounced effects on Young's modulus and strength at low angles. Transversal and shear modulus appear lower than in the literature due to the cracks due to the manufacturing of veneer (peeling process).ANR-15-IDEX-00

Lathe check development and properties: effect of log soaking temperature, compression rate, cutting radius and cutting speed during peeling process of European beech (Fagus sylvatica L.) veneer

The depth of lathe checks and integrity of veneer have been shown to be critical factors affecting the bonding process but also affecting the mechanical properties of veneer-based products. This study shows how beech (Fagus sylvatica L.) veneer lathe checks interval and depths are affected by soaking temperature, compression rate, cutting radius and cutting speed during the peeling process in well-controlled conditions. Freshly felled European beech logs were soaked in a water tank at 50, 60, 70 or 80 °C. Following soaking, the logs were immediately peeled with laboratory scale lathe (SEM S500) to 3.5 mm thick veneer at a cutting speed of 1, 2 or 3 m s−1 and pressure rates of 0, 5, 10 or 15%. The correlation between lathe check depth and frequency was validated using “Système de Mesure d’Ouverture des Fissures” (SMOF) device, which enables to measure check properties reliably on veneer ribbons. In a well-controlled peeling process, the strong correlation between check depth and interval was shown. At higher temperature, shallower and more frequent checks are created compared to lower temperature. However, the effect of soaking temperature (between 50 and 80 °C) on veneer checking is much smaller than the effect of compression rate during peeling process, where the higher compression rate produced veneer with shallower and more frequent checks. The results of the study also show that the direction of lathe check propagation could be affected by the rays in beech veneer. Rays resist crack growth in tangential direction, but act as weak planes in radial direction.ANR-10-EQPX-16 XYLOFOREST ; Région Bourgogne Franche-Comt

Influence of veneer lathe checks on the mechanical properties of LVL

Laminated veneer lumber (LVL) is a high-performance engineered wood product made of several wood veneers bound together mostly in grain direction. Veneers are obtained thanks to peeling process. This cutting process induces lathe checks of the veneer with variable depth and spatial frequencies. In this work, we studied the influence of lathe checks on the mechanical properties of LVL thanks to a finite element model of LVL beams made of checked veneers. The checks were modelled as free spaces in the cross-section. Several typical check depths and frequencies were compared, with the beam tested edgewise or flatwise. The results show that the longitudinal modulus of elasticity and the shear modulus in flatwise bending are marginally affected by checking, while the shear modulus of the LVL beam is significantly reduced in edgewise bending if the check depth is important. This phenomenon is due to high shear deformations in the edgewise bending case, because checks are mainly horizontal in this state. Therefore, the check depth may also affect the resistance of LVL in edgewise bending, thus experimental testing of this assumption will be done

Évaluations préliminaires des performances de la densitométrie non ionisante du bois par ondes TeraHertz : Projet BOOST

Cette thèse s’inscrit dans le projet ANR BOOST dont l’objectif est de démontrer la possibilité de l’utilisation du bois dans l’industrie du transport. Cette industrie étant très automatisée et ayant besoin de produits standardisés, la forte variabilité du bois fait qu’il est nécessaire d’analyser finement ses propriétés, afin d’appréhender au mieux son comportement. La masse volumique fait partie de ces propriétés que l’on souhaite mesurer. Actuellement, dans un contexte industriel, la technologie rayons X est employée pour une mesure localisée en ligne. Cette méthode est parfaitement adaptée à des cadences industrielles, cependant ce type de rayonnement est ionisant et par conséquent dangereux pour la santé. C’est la raison pour laquelle une nouvelle méthode est étudiée, avec des rayonnements Thz qui eux ne sont pas ionisant. Néanmoins, ces rayonnements ne sont pas encore autant communément utilisés que les rayons X et leurs applications dans le bois et en particulier pour la mesure de sa masse volumique n’a pas encore été beaucoup étudié. L’objectif ici est donc de se servir de la masse volumique mesurée par rayons X comme référence afin de valider puis exploiter la nouvelle méthode