The fracture toughness of medium density fiberboard and other fiber bridging composites

Graduation date: 2009In many composites, fiber bridging develops as part of the fracture process. Fiber bridging invalidates many toughness evaluation methods such as the ASTM E399 and complicates the identification of crack length, which is a necessary parameter in energy methods. In order to measure the toughness of fiber bridging composites, an energy method was developed, which required the use of digital image correlation (DIC) to measure crack growth. The method showed the mode I fracture toughness of medium density fiberboard (MDF) to be highly dependent on panel density and crack growth orientation. Simply applying the ASTM E399 method on MDF showed the same dependence on crack growth orientation but produced significantly lower values of toughness. The R-curves produced by the developed energy method were used to aid in the development of numerical models of the fracture process in MDF using the material point method (MPM). Specifically, bilinear (triangular) and cubic traction laws were used to simulate the behavior of fiber bridging. The simulations provide a fiber bridging interpretation of the experimental results