Objective:

Develop a computational 3D finite element (FE) phase-field fatigue model for simulating stress fractures in bone. The aim is to simulate fatigue crack initiation and growth under daily loading conditions using a patient specific FE model.

Background:

Atypical femoral fractures (AFF) are stress fractures in the femoral shaft that mainly affect older osteoporotic patients on bisphosphonate (BP) therapy. This type of fatigue injury occurs due to repetitive daily loading and will lead to catastrophic failure when the crack has reached a critical size. Computational 3D FE models have shown that certain anatomical features in bone geometries (i.e., shaft bowing and neck-shaft angle) lead to a higher risk for AFF fractures, but no models exist that can simulate the fracture process itself.

Approach:

The candidate will develop phase-field fatigue FE models in 3D for simulating atypical femoral fractures. Available FE models of an AFF patient will be used as a starting point together with open-source code with the phase-field fatigue method implemented in Abaqus. Bone models of increasing complexity will be developed to simulate crack initiation and propagation under daily loading. The models will be used to explore what kind of fatigue mechanisms are prevalent, as well as estimate remaining load-carrying capacity and fatigue life for healthy and BP-treated bones that have been subjected to long-term repetitive loading.


a) Stress fracture in an AFF patient visualized with CT and high-resolution micro-CT. b) Available FE models from a previous study. c) Crack simulated with phase-field fatigue model.

Student background:

Knowledge in finite element modeling and solid mechanics. Knowledge of fracture mechanics is highly valued.

Important literature:

Kristensen, P. K., Golahmar, A., Martínez-Pañeda, E., & Niordson, C. F. (2023). Accelerated high-cycle phase field fatigue predictions. European Journal of Mechanics-A/Solids, 100, 104991.

Gustafsson, A., Schilcher, J., Grassi, L., Aspenberg, P., & Isaksson, H. (2016). Strains caused by daily loading might be responsible for delayed healing of an incomplete atypical femoral fracture. Bone, 88, 125-130.

For more info, please contact: Biomechanics group, Anna Gustafsson (anna.gustafsson@bme.lth.se) or Hanna Isaksson, hanna.isaksson@bme.lth.se