ABSTRACT
Fiber-reinforced plastic (FRP) composites are being used for reinforcement of wood, concrete, and steel. Current research on wood reinforcement has focused on the use of fiber-reinforced strips or fabrics bonded to wood members. Although significant increases in stiffness and strength have been achieved by this reinforcing technique, there is a concern about the reliable performance of the FRP-wood interface bond, which can be susceptible to delamination. An inadequate interface bond strength and integrity can lead to premature failure of a reinforced wood member. Several adhesive systems have been used to reinforce conventional materials with composites; however, there are no long-term performance qualification methods for bonded interfaces of hybrid composites.
In this study, a comprehensive program to evaluate the durability of and obtain shear strength and fracture toughness data for FRP-wood bonded interfaces is presented. The potential in-service delamination of bonded interfaces is evaluated by a 3-cycle test of repeated wetting and drying, and the wet and dry interface strengths are evaluated through block-shear tests. The fracture toughness of the interface is measured by an innovative fracture mechanics test. Several key parameters on the durability of interface are investigated, such as coupling agent (primer) to promote bonding, open/closed assembly time, and clamping pressure. The present bond-interface characterization study can be used to qualify adhesives, establish service performance, and obtain apparent bond strength and fracture toughness for interfaces of FRP bonded to conventional materials.
This is the first study that provides practical guidelines for evaluating the inservice durability of the bond interface for composite-wood products, which are being used or developed for civil infrastructure applications. Moreover, this paper provides a method for obtaining fracture toughness data, which are needed to study delaminations of interfaces.
