Khawaja, H, and K Parvez. “Validation of Normal and Frictional Contact Models of Spherical Bodies by FEM Analysis”. The International Journal of Multiphysics 4, no. 2 (June 30, 2010): 175-185. Accessed October 16, 2025. https://www.themultiphysicsjournal.com/index.php/ijm/article/view/4-2-175.