Crack Propagation Fracture Toughness of Several Wood Species

    Volume 2, Issue 1

    ISSN: 2165-3984

    CODEN: ACEMOAD

    Published Online: 27 June 2013

    Page Count: 12


    Wilson, Elijah
    Wood Science & Engineering, Oregon State Univ., Corvallis, OR

    Mohammadi, Meisam Shir
    Wood Science & Engineering, Oregon State Univ., Corvallis, OR

    Nairn, John A.
    Wood Science & Engineering, Oregon State Univ., Corvallis, OR

    (Received 6 November 2012; accepted 1 May 2013)

    Abstract

    In materials with process zones, such as fiber-bridging zones in wood, it is crucial to characterize fracture toughness as a function of crack growth, known as the material's R curve. Here, a new fracture testing protocol developed to measure continuous R curves was used on six different species of solid wood—Douglas fir, Ponderosa pine, cedar, hemlock, balsa, and oak. Importantly, the new method uses monotonic loading, because unloading phases, as used in prior R curve methods, might damage the bridging fibers and alter subsequent toughness results. The crack length was recorded by a synchronized, automated imaging system. The solid wood R curves were measured for cracks running parallel to the wood grain direction with the crack plane normal to the radial direction (RL cracks) or normal to the tangential direction (TL cracks). The R curves for all species rose as a consequence of fiber bridging. TL toughness rose faster then RL toughness and therefore for long cracks TL toughness was higher for all species except cedar. The toughness trended upward as the density increased. Density had a much larger effect on fiber-bridging effects (i.e., the rise of the R curve) than it did on initiation toughness (i.e., the start of the R curve).


    Paper ID: ACEM20120045

    DOI: 10.1520/ACEM20120045

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    Author
    Title Crack Propagation Fracture Toughness of Several Wood Species
    Symposium , 0000-00-00
    Committee D07