Mode I Fracture Toughness of Fiber Reinforced Composite-Wood Bonded Interface

Abstract

An experimental characterization of the opening-mode (Mode I) fracture toughness of bonded interfaces for hybrid laminates is presented. A bi-layer Contoured Double Cantilever Beam (CDCB) specimen, which is designed by the Rayleigh-Ritz method, is effectively used for the fracture toughness tests of the bonded interfaces. The bi-layer specimen consists of constant thickness adherends bonded to straight tapered sections of an easily machinable material, and it is contoured to achieve a constant rate of compliance change with respect to crack length. Using linear slope CDCB specimens, Mode I fracture tests for wood-wood and Fiber Reinforced Plastic (FRP)-wood bonded interfaces are performed to determine the critical loads for crack initiation and crack arrest, and from the critical loads measured, the critical strain energy release rates (GI,) are easily evaluated by making use of the experimentally verified constant compliance rate change over defined crack lengths. Based on finite element analyses, the predicted GI, values by the Jacobian Derivative Method correlate closely with experimental results. The FRP-wood bonded interface considered in this study exhibits a stable crack propagation behavior, and the Resorcinol Formaldehyde adhesive used offers a good potential for bonding FRP to wood sub-strates. The efficient CDCB specimen and experimental/analytical program presented in this paper can be used to evaluate the Mode I fracture toughness (Gkn) for hybrid material interface bonds, such as FRP-wood.