New Perspectives for LVL Manufacturing from Wood of Heterogeneous Quality—Part. 1: Veneer Mechanical Grading Based on Online Local Wood Fiber Orientation Measurement

Abstract

The grading of wood veneers according to their true mechanical potential is an important issue in the peeling industry. Unlike in the sawmilling industry, this activity does not currently estimate the local properties of production. The potential of the tracheid effect, which enables local fiber orientation measurement, has been widely documented for sawn products. A measuring instrument exploiting this technology and implemented on a peeling line was developed, enabling us to obtain the fiber orientation locally which, together with global density, allowed us to model the local elastic properties of each veneer. A sorting method using this data was developed and is presented here. It was applied to 286 veneers from several logs of French Douglas fir, and was compared to a widely used sorting method based on veneer appearance defects. The effectiveness of both grading approaches was quantified according to mechanical criteria. This study shows that the sorting method used (based on local fiber orientation and average density) allows for better theorical quality discrimination according to the mechanical potential. This article is the first in a series, with the overall aim of enhancing the use of heterogeneous wood veneers in the manufacturing of maximized-performance LVL by veneer grading and optimized positioning as well as material mechanical property modelization.

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

“…First, this part explains how the veneers' longitudinal modulus of elasticity was calculated in relation to Part 1 [2], taking into account possible variations in the relationship between modulus of elasticity and density. Then, the algorithm developed to optimize the longitudinal position of the veneers within the laminate according to their quality is presented.…”

“…This classification is generally practiced by the intervention of cameras integrated on the panel-making line. In the first part of the series of articles [2], it was shown that local modeling of elastic properties from local fiber orientation and average density could establish quality sorting criteria, giving sorting results significantly different from the standard sorting method. Now, distributing this high-quality heterogeneity of veneers using their local mechanical properties to obtain the best possible performance of the material is a major issue.…”

“…This article belongs to a group of papers, whose first one is [2], which is dedicated to the use of heterogeneous species, such as large French Douglas-fir, in LVL manufacturing. In this first paper, the determination of local veneer properties by fiber orientation measurement integrated into the peeling line and veneer density enabled the establishment of a criterion to classify them according to their expected mechanical quality.…”

“…First, a new strategy in the use of wood of heterogeneous quality for composing LVL products will be presented, enabling the quality of veneers to be optimized according to the requirement of bending stresses along the beam. This optimization is driven by a declination of a random veneer positioning panel manufacturing algorithm presented in [2]. Second, optimized panels were manufactured from a sample of veneers representative of the considered resource and were tested experimentally according to applicable standards [6,7].…”

“…Random beams from the same veneers were made numerically, simulating manufacturing without the view to optimizing panels. Finally, comparisons with beams from the different sorting methods from [2] were made so that the effects of grading could be estimated against the effects of optimized veneer placement.…”