Phase-field cohesive zone models capture the nonlinear fracture behaviour of cortical bone: Calibration of material properties from fracture mechanics experiments.

In this work, an optimisation algorithm is employed to calibrate a quasi-brittle phase-field cohesive zone model against notched three-point bending experiments on bovine cortical bone using the force vs crack mouth opening displacement data. Calibration is performed both for individual specimens, to quantify parameter variability, and for groups of specimens from the same subject and crack propagation direction, to determine material parameters representative of the homogenised tissue. The proposed approach enables simultaneous identification of elastic modulus, strength and fracture toughness from a single specimen, yielding values consistent with ranges reported in the literature. Using the calibrated tissue material parameters, the model reproduces the experimental responses with good accuracy and captures key features of quasi-brittle fracture behaviour, including non-negligible crack advance prior to peak load. The good agreement suggests that a cohesive phase-field formulation provides a suitable framework for modelling fracture in cortical bone. This methodology can be applied to human bone in order to determine how fracture properties vary with age and disease, something that eventually could improve predictions of load-carrying capacity in subject-specific models.