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Flatness of wood composite panels, such as Laminated Veneer Lumber, is often difficult to control during the manufacturing process. Out-of-plane deformation, or warpage, of wood veneers caused by changes in moisture content affects the ability to press flat panels. To understand wood panel warpage, experimental methods are developed to create and measure moisture-induced deformation of wood veneers on five species of various thicknesses. Three moisture induction methods are investigated and evaluated to determine the increase in moisture content. Experiments are developed to produce moisture gradients of two concentrations in the veneers to examine the effect on warpage behavior. Additionally, the surface area of applied moisture and veneer thickness is also investigated. Three-dimensional scanning technology is used to measure warpage of veneers. A procedure using a structured-light scanner is developed to analyze the surface curvatures to observe the effect of moisture-induced warpage. After moisture-induction treatment of the veneer, surface deformation data is measured using the scanner and the data is converted into a 3D solid body model that is used for curvature comb analysis. The results show that curvature comb analysis can be used to analyze the geometry of moisture-induce warpage. The method can be used to analyze the effect of moisture gradient variables on warpage behavior including concentration, veneer thickness, and surface area. The experimental methods developed can be used by future researchers to validate theoretical warpage prediction models.

The key to improving drying quality and reducing drying time and energy consumption lies in understanding and controlling moisture movement during drying. As wood dries, strains and stresses develop as a result of restraints imposed by moisture gradients and differential shrinkage in wood. So accurately measuring the moisture gradient in wood during drying will be helpful to improving drying quality. In this project, moisture gradients in red oak will be measured through four different techniques----bandsaw slicing, Forstner bit layering, flaking and razor blade slicing. The first two techniques are found in the literature. The last two are developed in this study. The results obtained with these four techniques were compared, and it was found that the newly developed techniques could get moisture gradients that were closer to the true value. The thickness of the slice was assumed to affect measuring the moisture gradient because of the environmental influences. So a thickness series was tested with the two new technique----flaking and razor blade slicing. The results showed that there was no slice or flake thickness effect on the moisture gradients.And an optimum slice and flake thickness was determined for the wood industries and research studies. Finally, the directional effect on transverse moisture movement during kiln drying was examined through measuring moisture gradients in the tangential and radial directions of wood. The results showed that moisture moved slightly faster in the radial direction than in the tangential direction during kiln drying and the moisture gradients in the tangential direction were slightly steeper than those in the radial direction.

All timber extracted from the forest contains a large amount of water, most of which must be removed before the timber can give satisfactory service in use. The process of drying (seasoning) removes the surplus moisture as economically and with as little damage to the wood as possible. The moisture gradient is a critical parameter in the drying process because high moisture gradients cause drying defects, yet small gradients prolong drying. Kiln drying is not expensive when compared to the sawing process, but the defects that can occur during drying (such as splits, checks, cracks, warp, staining, casehardening and excessive shrinkage) can greatly affect the overall drying cost. Drying schedules are used to control kiln drying to minimise the occurrence of drying defects. These schedules are primarily time based because there is a lack of moisture content measurement methods that provide an accurate and continuous measurement during the entire drying cycle. This research investigated the moisture gradient using both measurement and prediction techniques. Measurement of the moisture gradient involved using gravimetric methods to calibrate a newly developed dielectric moisture sensor (DMS) that inferred the moisture gradient from the measurement of the average and surface moisture contents. A combined constant drying-rate and diffusion model was used to predict the moisture content and moisture gradient of a single board during drying. Monte-Carlo simulation techniques were applied to the single board model to examine the moisture content and moisture gradient variation within a stack of timber based on the difference in the initial moisture content and morphological properties of the boards. The experimental work conducted with the DMS (only an early prototype version was available in time for these trials) was affected by difficulties caused through moisture ingress into the electronic components inside the kiln. The results obtained suggested that as drying progresses there is a significant reduction in the drying rate as the surface moisture content approaches the fibre saturation point (25-30% dry weight basis moisture content). The decreasing slope is an indication of both the reduced drying rate and a reduction in the sensitivity of the instrument at low moisture contents. Additional work is required to determine the effect of kiln temperature, humidity and wood density on the sensor calibration. The single board drying model was used to determine the constant drying-rate and diffusion coefficients by calibrating the model drying curves to fit measured gravimetric data over a wide range of temperatures, and using timber of various densities. The coefficients that were determined were then analysed to determine the effects on them of kiln temperature and board density for use in the stochastic simulation model. The stochastic model showed that an accurate prediction of the drying times, moisture content and gradient could be made at several different kiln settings. The predicted drying curves obtained from the model showed that a large amount of variation exists between the boards during the middle stages of the drying cycle. This variation is reduced to within 5% and 10% for 25 and 50 mm timber respectively upon completion of drying. The moisture content differences between the average and surface of 2%, for 25 mm timber, and 6%, for 50 mm timber were predicted by the model at the completion of the simulation. The largest differences were observed during the middle stages in the drying cycle.