“Wood-nacre”: Development of a Bio-inspired Wood-Based Composite for Beam and 3D-Surface Elements with Improved Failure Mechanisms

Abstract

Following the natural structure of the nacre, the material studied consists of a multitude of hexagonal tiles that are glued together in an offset manner with a ductile adhesive. This so-called “wood nacre” consists of macroscopic tiles of birch wood veneer with a thickness of 0.8 mm and a size of 20 or 10 mm in diameter in order to mimic the aragonite tiles and the ductile PUR-adhesive corresponds to the layers of collagen in between. E-modulus (MOE), bending strength (MOR) and impact bending strength of the samples were determined and compared with reference samples of birch laminated wood. The hierarchical layered structure of the tiles does not cause any relevant loss in stiffness. Like nacre, “wood nacre” also shows tough fracture behaviour and a high homogenization effect. However, strain hardening and high fracture toughness of the natural model could not be fully achieved. The reason for this is the insufficient ratio between the strength and stiffness of the veneer layers and the adhesive. By adjusting the size of the tiles, increasing the strength and surface roughness of the veneers, e.g. by densification, and using more ductile adhesives that can be applied in smaller layer thicknesses, it should be possible to better reproduce the natural ratios of nacre and thus achieve a significant improvement in the material properties of “wood nacre”. In addition to the mechanical properties, the high potential of the new material lies in the possibility of producing 3D shell-shaped elements for lightweight wood hybrid construction.