Process Zone Length and Fracture Energy of Spruce Wood in Mode-I from Size Effect

This article reports on the determination of fracture energy and fracture process zone length in Mode I fracture of European spruce wood loaded in tension perpendicular to the fiber direction based on Bazant's size effect law. Within the size effect model, fracture energy and fracture process zone length are correlated and represent unambiguous limit values for large structures or specimens. The model parameters were derived from an earlier experimental size effect study on specific single-edge notched beam specimens with a scale range of 1:32. The Mode I fracture energy range of 250-290 N/m, derived from the size effect law, is in agreement with fracture energies obtained for the same specimens based on external work to complete specimen failure. The elastically equivalent length of the fully developed fracture process zone ahead of the nominal crack tip was determined to be in the range of about 2 mm. The stated independent proof of the correlated fracture energy confirms the validity of the derived size of the fracture process zone. Furthermore, fracture process zone size obtained is in close agreement with a previous result for eastern Canadian spruce, a finding based on scanning electron microscopy