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Materials (Basel). 2012 Jun 19;5(6):1115-1124. doi: 10.3390/ma5061115.

Strain Measurements within Fiber Boards. Part I: Inhomogeneous Strain Distribution within Medium Density Fiberboards (MDF) Loaded Perpendicularly to the Plane of the Board.

Author information

1
Wood K plus-Competence Centre for Wood Composites and Wood Chemistry, Altenberger Straße 69, 4040 Linz, Austria. j.rathke@kplus-wood.at.
2
Department of Material Sciences and Process Engineering, Institute of Physics and Material Sciences, BOKU-University of Natural Resources and Life Sciences, Peter Jordan Straße 82, 1190 Vienna, Austria. gerhard.sinn@boku.ac.at.
3
Department of Material Sciences and Process Engineering, Institute of Wood Science and Technology, BOKU-University of Natural Resources and Life Sciences, Konrad Lorenzstraße 24, 3430 Tulln an der Donau, Austria. johannes.konnerth@boku.ac.at.
4
Wood K plus-Competence Centre for Wood Composites and Wood Chemistry, Altenberger Straße 69, 4040 Linz, Austria. ulrich.mueller@kplus-wood.at.

Abstract

Internal bond strength testing is a widely used approach for testing quality traits of wood based panels. Generally, failure of internal bond specimens is due to adhesion and/or wood failure in the specimen. It has been reported that a composite product with a large variation in the vertical density profile fails in the center part of the board which is either the middle of the core layer or the transition zone between core layer and face layer. The density in the failure zone is typically 50% lower than the maximum density in the face layers. The aim of this study was to analyze the strain distribution in a specimen under tension perpendicular to the panel plane. The results showed that a high variety of strain magnitude occurred in the specimen. The strain is either aligned with the tension direction or a tension zone is built in one of the edge zones leading to failure. Vector graphics of the specimen show the problematic test setup of internal bond strength measurement. Strain spots in the edges lead to the assumption of an uneven stress distribution due to the momentum which results from non-perfect alignment or irregularities in the test setup.

KEYWORDS:

electronic laser speckle interferometry; internal bond strength; medium density fiber board; strain distribution

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