Abstract
This study explored the suitability of fracture toughness properties for durability assessment of wood composite panels by observing changes in fracture toughness during crack propagation following cyclic exposure to moisture conditions. The main objective was to develop a new method for ranking the role of adhesives in the durability of wood-based composites. This new approach was compared to conventional mechanical performance tests, such as observing strength and stiffness loss after exposure. Comparing changes in fracture toughness as a function of crack length after moisture cycling shows that this approach can distinguish different adhesive systems on the basis of their durability, while conventional tests fail in this regard. The most and least durable adhesives (polyvinyl acetate and phenol formaldehyde) could be distinguished based on steady-state toughness alone, but this was not the case for the performance of two other adhesives (emulsion polymer isocyanate and phenol resorcinol formaldehyde). Further analysis of experimental R curves (toughness as a function of crack length) based on kinetics of degradation was able to rank all adhesives confidently. Probably, the failure of conventional tests in this context is that they are based on initiation of failure, while the fracture tests require consideration of fracture properties after a significant amount of crack propagation has occurred.
Acknowledgments
Financial support was provided by the National Science Foundation Industry/University Cooperative Research Center for Wood-Based Composites, Award No. IIP-1034975. We thank Momentive® Specialty Chemicals and Georgia Pacific Chemicals® for supplying all adhesives and veneer materials.
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