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Automatic determination of wood fibre failure percentage of plywood shear samples

: Plinke, B.

WOOD K PLUS, Kompetenzzentrum für Holzverbundwerkstoffe und Holzchemie, Wien:
Wood based materials. Wood composites and chemistry : International symposium, September 19-20, 2002, Vienna, Austria
Wien, 2002
International Symposium "Wood Based Materials" <2002, Wien>
Conference Paper
Fraunhofer WKI ()
Bildverarbeitung; Sperrholz; Oberflächenstruktur; Normung

Various wood species and glue types are used in plywood production all over Europe: The range comprises apparently light species such as Nordic birch as well as medium-coloured beech or dark exotic species and light glue types such as urea as well as dark phenolic. One of the main parameters of glue bond performance beside the shear strength is the percentage of wood fibre failure in shear strength samples. The EN 314 standard requires this wood fibre failure percentage to be estimated visually. A joint European research project (PLYWOOD G6RD-2000-00273) will improve the use of these standards and propose procedures for calibration and testing. A training image database with various types of shear samples for the training of operators and databases to support internal and external factory controls and production monitoring according to EN 326 will be supplied. One task is the automatic visual evaluation of scanned images of the fracture surfaces. A shear sample set (10 pieces) is mounted into a plastic sample holder. Digitized images of the sample set are created using a standard office scanner and processed using a computer program in a PC. Different image processing procedures such as thresholding, gradient filtering, smoothing, and a combination thereof, have to be applied, depending on glue type and wood species, and are included as options in the program. The image of each piece is converted into a binary image where wood and glue area are segmented and area sizes can be measured. This can be output in table form with the estimated wood fibre failure percentages for all pieces of the sample. The computer program and procedures for implementation and operation are currently under development and will be ready for use in the plywood industry within the next months.