A Modified Elastic Approach To The Theoretical Determination of The Hygroscopic Warping of Laminated Wood Panels
Keywords:Plywood, restrained swelling, swelling stresses, warping, wood composites
This paper deals with the hygroscopic warping of laminated wood and wood composites. The theoretical analysis includes elastic and inelastic approaches. Experiments were conducted on narrow cross-laminated yellow-poplar beams and on two-ply beams constructed from laminas of medium-density fiberboard and particleboard. The elastic strains and the swelling stresses that sustain warp under conditions of increasing moisture content were determined experimentally, using a specially designed restraining device.
In the case of the yellow-poplar laminates, it was found that in the transverse direction (tangential) only about 25% of the tree hygroscopic expansion is transformed into elastic strain under conditions of complete restraint. In the longitudinal direction, yellow-poplar behaves elastically. These results were used to modify the inputs for the elastic equation (inelastic approach), which greatly improved the accuracy of the theoretical warping predictions.
In the case of laminate composites, the elastic equation without modification produced good agreements with measured warp.
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