New Swedish research attacks the huge data issues in trying to analyze distortion during drying for laminated, engineered wood products. In order to create a 3D computational model, researchers need to input data not only about moisture, temperature and the mechanical loading, but also the orientation of the wood fibres and the position the board held within the log.
During several years, research groups at Chalmers University and Lund University have now developed a three-dimensional FE model for moisture-related distortions of timber and laminated timber products. The research group included Sigurdur Ormarsson, Jonas Lindemann, John Ericsson, Ola Dahlblom and Hans Petersson.
Based on simulations and experimental verification on spruce, it has been found that the shape stability of different timber products can be much improved by gluing pieces of wood together in an optimal way. The results clearly show that warping of the products is strongly influenced by the radial variation in material data (spiral grain, shrinkage coefficients, etc.), the original location of the separate pieces within the log and how those pieces are oriented in products.
In the study’s conclusion, the authors comment it is difficult for researchers to convey their results and efforts to the industry. “The final step,” they say, “is often publication in technical reports or in some international (academic) journals.
This means that it is often very difficult for the industry to use or implement the research results. The main goal with the user interface presented in this paper is to encapsulate a distortion model… into software that can be used in industry by users with limited experience with FE-modeling. The developed software enables users to easily create the laminated products of wood that are of interest for them. Effects of different material properties, sawing patterns, internal orientations of the laminates, drying schedules, boundary conditions, etc., on the distortion and stiffness of the product can be easily studied.
With this software, the user first selects one of the pre-defined product types: single board, face-glued beams, edge-glued panels, horizontal stack, vertical stack or combined product. When a log with a sawing pattern has been created, the product can be created by dragging the boards onto the products defined in the product folder. The product can be made of boards in which the product inherits ring patterns and log properties from the different logs. The user can switch between ends of a log, and all individual components in the product can be rotated and moved in the product editor.
The user can then define the drying schedule, climate conditions, mechanical loading and boundary conditions, as well as other variables, and view the results in real time by moving a track ball to show distortion and deformations. Moisture data includes the three dimensional moisture flow and distortion model created by the authors in earlier research. All distortions and deformations have been numerically enhanced by a factor of five to make them more visible as they occur in the model.
For more information, contact: Sigurdur Ormarsson at Sigurdur.Ormarsson@sem.chalmers.se.
The small figures on either side of the beam show the top member of the two figures oriented differently (rings down or rings up). The beam, by way of illustration, has twisted during curing.
A screen shot of the software in action shows a few of the tools available: a drop-down menu for product selection, a view of assembled components the user can switch around, flip or change, below that a view of the log that can be switched end-for-end, a data box and a cut-away view of the log being analyzed.