Bridging crack model for fracture of spruce

An analysis is presented of how cracking in wood can be predicted using fracture mechanics. In situ, real-time, scanning electron microscopy was used as a tool to estimate the physical mechanism of fracture in softwoods using end-tapered double cantilever beam specimens. It was found that bridging behind the crack tip is the main toughening mechanism, which contributes to non-linear wood behavior in the presence of stress concentrations. A new bridging crack model is presented that mimics the observed cracking mechanism. Intrinsic flaw size is found to correspond to the fiber length of spruce.