Mixed-mode interfacial fracture toughness of wood and adhesives

Abstract

This paper presents the results of a combined experimental and theoretical study of the fracture of wood/ adhesive interfaces. Thermoplastic and thermosetting adhesives are considered in this study as well as combinations of the two applied in sequence. Mode mixity dependence of interfacial fracture toughness is measured using Brazil-nut sandwich specimens. Interfacial fracture energies, Gc, between wood and adhesives are measured over a wide range of mode mixity. Two types of woods: pine and cedar in combination with three types of adhesives: a Polyurethane adhesive, a Resorcinol based adhesive and a Phenol-Resorcinol-Formaldehyde adhesive are investigated in this study. The results show that interfacial fracture toughness generally increases with the increase in mode mixity. The trends in the overall fracture energies are also predicted using fracture mechanics models. The mode mixity dependence of interfacial fracture toughness will also be explained using a crack-shielding model that accounts for the crack profiles and the contact between mating asperities. The goal of this research is to more fully understand the interfacial toughness of wood and adhesive interfaces that exist in these types of repairs. The results can be used as a guide to design wood-based structures and furniture.