Video Extensometer Characterization of Mechanical Properties in Modified Fibreboard Layers

The resistance of screws to being pulled out of wood-based panels depends largely on the mechanical properties of the substrate. The properties of medium-density fibreboard (MDF) are locally reinforced in the area where the fastener is embedded. The aim of the study is to determine the effect of using polyurethane (PUR) adhesives as a reinforcing agent. The aim of the study is to determine the elastic properties of individual layers of MDF boards modified with a polyurethane agent (PUR 555.6) applied to the outer and inner layers of the material. Deformations during axial compression of multilayer samples were measured using a digital optical video extensometer with digital image correlation (DIC). The reinforced board showed a significant increase in stiffness in all main orthotropic directions. The stiffness of the inner layers increased by approximately 100%–160%, while that of the outer layers increased by 30%–60%. The shear modulus increased by 60%–70% in the inner layers and by up to 45% in the outer layers. The results confirm the effectiveness of the optical video extensometer method as a fast and reliable technique for determining the mechanical properties of modified layered wood composites.