Cortical bone exhibits an array of toughening mechanisms under deformation to inhibit crack propagation. Understanding how these toughening mechanisms and the individual microstructural constituents of cortical bone affect damage evolution has been an area of interest for research due to its engineering implications and potential influence on bio-inspired and bio-mimetic designs.

In the present study, phase field method is identified as an effective tool capable of handling the complex geometries of microstructural cortical bone, as well as for capturing the relevant extrinsic toughening mechanisms in the transverse orientation, though further refinement seems necessary. Two dimensional models were created based on the manual segmentation of Methenamine-Silver Nitrate stained anterior and posterior regions of human tibial cortical bone at 50% from the distal side, aged 60. For simplicity, only the interstitial tissue, osteonal tissue, and cement lines were considered.

The diffusive damage properties of compression were taken advantage of to initiate microcracks within cortical bone, allowing for naturally forming microcracks. Tension was then applied to the damaged model perpendicular to the crack growth to investigate how the existing microcracks alter the damage evolution of cortical bone in the transverse plane and to verify microcracking as an effective toughening mechanism. Further simulations were conducted with microcracks initiated under tension to differentiate between damage initiation of cortical bone under compression and tension, and with varying material properties to determine how an increased or decreased heterogeneity affects crack trajectory. When applicable, results were linked to the morphological data to identify trends, although the current data set is not statistically significant.

Results indicate an increased microcracking being beneficial for inhibiting crack growth and for increasing the final fracture displacement, validating microcracking as a toughening mechanism. A morphological comparison is made between the quantity of pores and its effect on creating a network of microcracks throughout the domain. Additionally, a possible link between heterogeneity and cement line interaction is identified.