Analysis of tapered ENF specimen and characterization of bonded interface fracture under Mode-II loading

An engineering approach for evaluating the shear-mode (Mode-II) fracture toughness of wood–wood and wood-composite bonded interfaces is presented. A tapered beam on elastic foundation model is developed to analyze and design a linear tapered end-notched flexure (TENF) specimen for fracture tests of bonded interfaces. The elastic foundation model is verified numerically by finite element analysis and experimentally by compliance calibration tests, which demonstrate that the present model can accurately predict the compliance and compliance rate-change of the specimen, and with proper design, an approximate constant rate of compliance change with respect to crack length can be achieved. The proposed TENF specimen can be used for Mode-II fracture toughness evaluations with reasonable confidence in the linearity of compliance crack-length relationship. The fracture of wood–wood and wood-composite bonded interfaces under Mode-II loading is experimentally evaluated using the proposed TENF specimen, and the corresponding values of critical strain energy release rate are obtained. The modeling technique and testing method presented can be efficiently used for characterization of Mode-II fracture of bonded bimaterial interfaces.