Wood fracture characterization under mode I loading using the three-point-bending test. Experimental investigation of Picea abies L.

Abstract

Mode I fracture characterization was performed in wood using the single-edge-notched beam loaded in three-point-bending (SEN-TPB). A data reduction scheme based on equivalent linear elastic fracture mechanics concept was used to evaluate the Resistance-curve instead of classical methods. The method is founded on assessment of an equivalent crack from specimen compliance using beam theory and the existence of a stress relief region in the crack vicinity. Crack length monitoring is unnecessary during the loading process, providing a complete Resistance-curve which is essential for a clear identification of the fracture energy. Experimental results were obtained from fracture tests involving geometrically similar SEN-TPB specimens of different sizes. It was observed that the smallest tested specimen is inadequate to estimate the fracture energy due to fracture process zone confinement. Contrarily, the other two are suitable for such purpose. An inverse method was used to determine a bilinear cohesive law representative of wood material fracture. It was concluded that a unique cohesive law is able to mimic the fracture behaviour of considered specimen sizes.