Calibration of a combined XFEM and mode I cohesive zone model based on DIC measurements of cracks in structural scale wood composites

A combined experimental and numerical approach to characterize a fracture process in wood composites of Norway Spruce is presented. Processed results of crack growth during wedge split tests in TL (tangential - longitudinal), and RL (radial-longitudinal) planes for mode I (opening) are used as a basis for numerical fracture characterization of wood composites. A non-linear plane stress finite element model with extrinsic (monotonically decreasing) traction-separation law for fracture behaviour is used to model the experiment conditions. The data for the numerical model are validated against independent experimental measurements from two sources: displacement fields from DIC (Digital Image Correlation) and force-displacement logging history. The procedure of finding the optimal combination of model parameters resulting in the minimal error between experimental and numerical crack growth history is implemented. The model parameters are initial elastic compliance, damage initiation stress, crack separation at failure, shape coefficient for exponential softening law, and initial crack length for each experiment in both series. The space of the optimal sets of numerical parameters is established to be readily used in engineering applications. The mechanism of fracture process zone development in fibre composite is captured experimentally and numerically.