Discontinuous Deformation Analysis (DDA) and Distinct Element Method (DEM) have the same investigation objects: systems of highly discrete blocks; the same basic variables: block displacement related variables, and the same theoretical foundation: the momentum conservation law; with DDA applying the weak form: the minimum potential principle, and DEM utilizing the strong form: the Newton second law. While some differences exist in implementation, DDA and DEM both have to introduce artificial springs to enforce contact conditions, which, however, are violated to different degrees. Stiffness of artificial springs is hard to set, significantly spoiling their beauty and restricting more extensive applications.
