Influence of wood machining on tensile shear strength and wood failure percentage of one-component polyurethane bonded wooden joints after wetting

Abstract

This study determines the influence of mechanical surfacing on tensile shear strength (TSS) and wood failure percentage (WFP) of beech wood (Fagus sylvatica L.) at the wet stage according to prEN 302-1:2011 (tensile shear tests). The wood was planed, sanded and face milled, using different qualities of cutting edges and sanding grits. Roughness and wettability of the adherends were characterised, supplemented by environmental scanning electron microscopy images. The specimens were bonded by means of a one-component polyurethane adhesive and tested at the dry stage (pretreatment A1), at the wet stage (A4) and after re-drying (mA5). Results determined that the wettability and the wood structure’s integrity are considered more decisive for the TSS at the wet stage than surface roughness. Planing with very dull knives caused the lowest TSS and WFP after A4 and the most subsurface damage. Face milled and sanded batches revealed the best performance. The TSS and WFP decreased significantly from A1 to A4, but recovered after mA5.