In-situ characteristic elastic properties of bond-lines in laminated engineered wood products using microscopic digital image correlation

Adhesively laminated engineered wood products (EWPs), such as glue-laminated timber (GLT) and cross-laminated timber (CLT), have gained global popularity due to the increasing development of tall wood buildings. The mechanical performance of a bond-lines is crucial for the structural behavior of EWPs. In this study, a novel method was developed for evaluating in-situ elastic properties of a bond-line in adhesively laminated solid wood products. This method deployed the microscopic digital image correlation (DIC) technique capturing the strain distribution along the bond-line under axial (0°) and off-axis (45°) tensile loading. Three types of adhesives, namely polyurethane (PUR), emulsion polymer isocyanate (EPI), and phenol–resorcinol–formaldehyde (PRF), were used to make specimens. The modulus of elasticity (E) and modulus of shear (G) of a bond-line were accordingly calculated based on the strain along a bond-line and load applied on a specimen. For verification purpose, finite element (FEA) models on CLT and GLT beams were, considering the elastic properties of bond-lines and disregarding the elastic properties, developed to evaluate the effects of the elastic properties of a bond-line on the stress distribution. It was found that the proposed method could be used to accurately determine the in-situ characteristic elastic properties of bond-lines in EWPs. The elastic properties of a bond-line exhibited a large variability, but did not appear to have a significant impact on the overall stress distribution in a specimen. The E and G of bond-lines might be neglected in the structural analysis of large-sized laminated wood products such as GLT and CLT.