Investigation of mechanical properties and elucidation of factors affecting wood-based structural panels under embedment stress with a circular dowel II: detailed observation for plywood and OSB using DIC and CT scanning

Abstract

Although embedment properties are vital to timber engineering, the behavior and strain distributions in wood-based panels have not been clarified in detail. Our early studies suggested four possible causes of failure behavior and strain distribution: (i) two types of failure behavior (in-plane and out-of-plane failure); (ii) enlargement of the stress-spreading range with increasing load step; (iii) reduction of the stress-spreading range (normalized by dowel diameter) with increasing dowel diameter; and (iv) preferential stress spreading in the vertical and horizontal directions along the strong and weak-axis specifications, respectively. However, these hypotheses were not supported by actual observations. The present study aims to observe and clarify the surface strain distribution via digital image correlation and the internal failure behavior via computed tomography scanning. Most results of the wood-based panel specimens (plywood and oriented strand board) did not contradict the above hypotheses. The failure behaviors of plywood and oriented strand board are likely determined by the direction of the veneer fibers and the layer’s position, respectively. Within the strong axial layer of plywood, fibers on both sides of the dowel were densified by fibers dissociated immediately above the dowel, whereas the weak axial layer in plywood was deformed like a timber under partial compression perpendicular to the grain. In contrast, oriented strand board under an embedding stress exhibited a circularly distributed strain and a dispersed void area in its outer layer. Densification was observed only in the inner layer.