Using Crack Propagation Fracture Toughness to Characterize the Durability of Wood and Wood Composites Public Deposited

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  • We measured fracture resistance curves (or R curves) for laminated veneer lumber (LVL) made with Douglas fir veneer and polyvinyl acetate resin and for solid wood Douglas fir. The LVL and solid wood R curves were the same for initiation of fracture, but the LVL toughness rose much higher than solid wood. Because a rising R curve is caused by fiber bridging effects, these difference show that the LVL resin has a large affect on the fiber bridging process. We exploited this resin effect to develop a test method for characterizing the ability of a resin to provide wood composites that are durable to moisture exposure. The test method exposed LVL specimens to soaking/drying cycles and then monitored the rising portion of the LVL R curves as a function of the number of cycles. Douglas fir/polyvinyl acetate LVL lost about 30% of their toughness after 16 cycles. In characterizing toughness changes, it was important to focus on the magnitude and rate of the toughness increase attributed to fiber bridging. We suggest these properties are much preferred over other fracture or mechanical properties of wood that might be used when characterizing durability.
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  • Mirzaei, B., Sinha, A., & Nairn, J. A. (2015). Using crack propagation fracture toughness to characterize the durability of wood and wood composites. Materials & Design, 87, 586-592. doi:10.1016/j.matdes.2015.08.010
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  • 87
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  • Financial support was provided by the National Science Foundation Industry/University CooperativeResearch Center for Wood-Based Composites, Award No. IIP-1034975. We thank Momentive® Specialty Chemicals for supply all resins and veneer materials.
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