Assessment of the error of fiber orientation measurement obtained by laser scanning on several European hardwood and softwood species

Scanner measurements allow knot detection and machine strength grading on sawn timber. In particular, laser scanners measure fiber orientation by means of the so-called tracheid effect explained by the fact that the wood fibers conduct concentrated light better in the direction of fibers than across. The LaBoMaP has developed a fiber orientation scanner effective on softwood and hardwood species. In the present work, the fiber orientation measurement error is assessed on several European hardwood and softwood species. A method to measure the intensity of the tracheid effect according to the species and wood cutting plane (radial-longitudinal or tangential-longitudinal) is also proposed, and several underlying artefacts of the tracheid effect are discussed. Results showed that fiber orientation measurement was possible on hardwood species with the LaBoMaP laser scanner, especially on oak

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

Measurement of fiber orientation by laser light scattering on dry and rough sawn green hardwoods

Scanner measurements allow knot detection and machine strength grading on sawn timber, which answers the construction and sawmilling industry needs at high production rates. In particular, laser scanners measure fiber orientation by means of the so-called tracheid effect on wood surface where elliptically scattered laser light can be observed. Many studies showed that a red laser scanner is very effective on softwood species like spruce but ineffective on many hardwood species like oak. However, the LaBoMaP has recently developed a fiber orientation scanner, utilizing another kind of laser, effective on hardwood species, especially oak. Other studies showed that measurement quality is better on sanded and planed wood than on rough sawn timber. Besides, the influence of moisture content on tracheid effect is also known. In practice, light ellipses are biggest on fresh wood than on dry wood. In the present work, a method is proposed to measure the intensity of tracheid effect on fresh sawn hardwoods, according to the species, and the error of the fiber orientation measurement is also assessed. To achieve this, clean fresh wood test pieces were first scanned at 0° orientation and ellipse geometrical parameters were compared to that obtained on an isotropic surface. In a second time, test pieces were scanned at different orientations from 0° to 90°. Measurement error was defined as the difference of scanned fiber angle mean on each iteration and test piece orientation between these same iterations. Comparisons of results between species and moisture content will be presented at the conference

Influence of wood anatomy on fiber orientation measurement obtained by laser scanning on five European species

Abstract In order to obtain high production rates of sawn timber, the sawmilling industry can use laser scanning, allowing knot detection and machine strength grading. In particular, laser scanners measure grain angle using the so-called tracheid effect on wood surface where an elliptic scattering of the laser light can be observed. This paper aims to describe the light scattering obtained by a laser beam projection on wood surface and to assess the accuracy of such fiber orientation measurement on five European species. Firstly, fiber orientation measurement error was assessed by rotating samples. Secondly, the description of the scattering effect was done considering ellipse axis ratios and areas. This was studied according to several parameters such as wood surface machining, moisture content, and orthotropic planes of symmetry. Fiber orientation measurement was successfully performed on all the tested species. The measurement error was below 1.6°, except for oak longitudinal–radial (LR) plane showing an error up to 3.1°. For most of the species, the error was higher in LR plane because of the influence of medullary rays. Despite the observation of major variabilities in laser light scattering, it was possible to measure the grain angles with a good accuracy for all investigated species

Performance of strength grading methods based on fibre orientation and axial resonance frequency applied to Norway spruce (Picea abies L.), Douglas fir (Pseudotsuga menziesii (Mirb.) Franco) and European oak (Quercus petraea (Matt.) Liebl./Quercus robur L.)

Key message Machine strength grading of sawn timber is an important value adding process for the sawmilling industry. By utilizing data of local fibre orientation on timber surfaces, obtained from laser scanning, more accurate prediction of bending strength can be obtained compared to if only axial vibratory measurements are performed. However, the degree of improvement depends on wood species and on board dimensions. It is shown that a model based on a combination of fibre orientation scanning and axial vibratory measurement is very effective for Norway spruce ( Picea abies L.) and Douglas fir ( Pseudotsuga menziesii (Mirb.) Franco). For European oak ( Quercus petraea (Matt.) Liebl./ Quercus robur L.) boards of narrow dimensions, axial vibratory measurements are ineffective whereas satisfactory results are achieved using a model based on fibre orientation. ContextMachine strength grading of sawn timber is an important value adding process for the sawmilling industry.AimsThe purpose of this paper has been to compare the accuracy of several indicating properties (IPs) to bending strength when applied to Norway spruce (Picea abies L.), Douglas fir (Pseudotsuga menziesii (Mirb.) Franco) and European oak (Quercus petraea (Matt.) Liebl./Quercus robur L.).MethodsThe IPs were determined for a set of data comprising scanned high-resolution information of fibre orientation on board surfaces, axial resonance frequency, mass and board dimensions.ResultsWhereas dynamic axial modulus of elasticity (MoE) gave good prediction of bending strength of Norway spruce (R2 = 0.58) and Douglas fir (R2 = 0.47), it did not for narrow dimension boards of oak (R2 = 0.22). An IP based on fibre orientation gave, however, good prediction of bending strength for all three species and an IP considering both dynamic axial MoE and local fibre orientation for prediction of bending strength gave very good accuracy for all species (Norway spruce R2 = 0.72, Douglas fir R2 = 0.62, oak R2 = 0.59). Comparisons of results also showed that scanning of fibre orientation on all four sides of boards resulted in more accurate grading compared to when only the two wide faces were scanned.ConclusionData of local fibre orientation on wood surfaces give basis for accurate machine strength grading. For structural size timber of Norway spruce and Douglas fir, excellent grading accuracy was achieved combining such data with data from vibratory measurements. The improvements achieved enable substantial increase of yield in high-strength classes.Conseil régional Bourgogne Franche Comté, ANR ClaMe

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

Contactless moisture content measurement on green veneer based on laser light scattering patterns

The wood structure anisotropy and moisture content variation within the volume create different patterns of light scattering inside the wood. The objective of this study was to assess the suitability of a laser method for online measurement of green veneer moisture content based on the so-called tracheid effect. Beech and poplar veneers with thicknesses of 1, 2 and 3 mm were subsequently laser scanned and weighed to obtain various humidities. The results show that the measured laser scattering profile, such as the major axis, minor axis and ellipse area on the veneer surface, increases with moisture. The laser scattering profile provides a reliable and precise prediction of the moisture content. Out of the three ellipse parameters evaluated, the ellipse area provides the best prediction of the moisture content of the green veneer for both beech and poplar.This study was performed thanks to the partnership built by BOPLI: a shared public–private laboratory between Bourgogne Franche-Compté region, LaBoMaP and the company Fernand BRUGERE. The authors would also like to thank the Xylomat Technical Platform from the Xylomat Scientific Network funded by ANR-10-EQPX-16 XYLOFOREST. Finally, the authors would like to thank Fernand BRUGERE and the Carnot Institute ARTS for funding this research

An innovative method based on grain angle measurement to sort veneer and predict mechanical properties of beech laminated veneer lumber

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

Panel Shear of Plywood in Structural Sizes - Assessment Improvement Using Digital Image Correlation

This paper introduces a new test configuration for the determination of panel shear properties in structural sizes. This original test configuration has been successfully applied to calculate the shear properties of beech plywood. A numerical model has been developed to evaluate the influence of such a novel setup in comparison to the common standard. The research includes the mechanical characterization of a total of 36 samples using Digital Image Correlation (DIC) to measure the in plane displacements. The use of DIC has been proven to be efficient to measure the shear properties and also acts as a tool to ensure that the solicitation was adequate during the test. Finally, the results highlight the interest to actually perform the proposed test instead of using the alternative density-based equivalencies provided by the standards.ANR-10-EQPX-16 XYLOFOREST LabMixte BOPLI (ENSAM & Région Bourgogne-Franche-Compté

Board localization within logs using image analysis approaches for traceability and quality assessment in sawmills

Board localization within logs using image analysis approaches for traceability and quality assessment in sawmillsEffiQuAss project ANR‐21‐CE10‐0002‐0