Influence of the moisture content on the fracture energy and tensile strength of hardwood spotted gum sawn timber and adhesive bonds (gluelines)

This study aims to measure the fracture properties, including crack initiation and propagation, of Australia's native forest grown spotted gum ([SPG], Corymbia citriodora) sawn timber and associated adhesive bonds at different moisture content levels. The collected data were used as input values to develop a numerical model to understand the delamination of SPG glulam beams when exposed to a wetting and drying process. Thus, Mode I and Mode II fracture energies for crack propagation along radial and glueline directions were experimentally investigated under various moisture content levels (8%, 12% and 16%). Single-end notched beams and compact shear specimens were used to capture the Mode I and Mode II fracture energies, respectively. For crack initiation, the tensile strength perpendicular to the grain and the shear strength (taken as the maximum stress from the Mode II fracture tests) were also measured. In total, 200 experimental tests were performed. One-way analysis of variance statistical analyses showed that the fracture energies and shear strengths were independent of the range of moisture content levels investigated. In addition, the collected data were compared with the limited published fracture properties of other hardwood species.