Displacement fields of wood in tension based on image processing: Part 2. Crack-tip displacements in mode-I and mixed-mode fracture

Near tip displacement fields for tensile loaded cracked rubber and wood wit h a crack parallel-, perpendicular-to-grain, and a parallel-to-grain crack inclined 30 degrees, 45 degrees, and 60 degrees to the load axis were obtai ned from digital image correlation (DIC). Theoretical displacements were al so obtained for rubber and wood using isotropic and orthotropic fracture th eory, respectively. The results showed that DIC can reveal fine details of the nature of displacements and the influences of crack tip in both rubber and wood. Experimental crack tip displacements for wood compare well with t heory; particularly, when load is perpendicular-to-grain. Some anomalies we re found in the tip displacements in the direction of the tracheids due to the unique nature of their behaviour not accounted for by theory. Mixed-mod e crack tip displacement fields for wood clearly showed the increasing infl uence of crack angle on the displacements, and the displacements perpendicu lar to crack compared very well with theory. The displacements parallel to crack showed some variations owing to the involvement of tracheids.