Fracture Toughness of Wood and Wood Composites during Crack Propagation
Keywords:
Fracture, fiber bridging, numerical modeling, <i>R</i> curves, IB testsAbstract
Mode I fracture toughness as a function of crack length of medium-density fiberboard (MDF), particleboard (PB), and Douglas-fir (DF) was measured using a new energy-based method. PB and MDF are examples of composites that develop fiber bridging during crack propagation, which causes their toughness to increase with crack length. Longitudinal cracks in DF also displayed fiber-bridging behavior, but only when the crack plane was normal to the tangential direction. MDF and PB experiments were performed for both in-plane and out-of-plane cracks. The toughness of the former was much higher than the latter. The in-plane crack toughness of MDF was higher than PB, but its out-of-plane toughness was lower. PB made using a new soy-based resin had an in-plane toughness similar to commercial PB but an out-of-plane toughness three times higher. Out-of-plane crack propagation is suggested as an improved method for measuring internal bond (IB) properties. When the fracture method was compared with conventional IB tests, both methods showed that the soy PB was better but the fracture method provided a clearer distinction.References
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