A Computational Framework for Capturing and Tracking Failure Patterns in Earthen Structures
thesisposted on 01.07.2016, 00:00 by David A. Weed
Within a finite element context, the embedded strong discontinuity approach for strain localization has been used extensively to model localized deformation and fracture in geomaterials. As a fracture propagates, any changes in orientation will inhibit sliding and force the surfaces, in some locations, to open. Some previous models feature only a single sliding degree of freedom. As the surfaces slip in such models, an artificial hardening occurs, creating a geometric locking effect. To this end, we implement a formulation, which, in addition to sliding, possesses an opening degree of freedom. We develop a traction-separation model that allows for coupled opening and shearing displacement in tension, as well as frictional sliding in compression. This thesis compares the single degree of freedom formulation with the model containing both degrees of freedom. We show that the locking effect is alleviated. In addition, a combined implicit-explicit integration scheme for increasing the robustness of softening problems is featured. Additionally, a new method for embedding predefined interfaces within an arbitrary finite element mesh is proposed and demonstrated. The algorithm for generating these predefined surfaces is detailed and subsequently applied to masonry structures composed of earthen materials to demonstrate its efficacy. Within a given finite element, the initiation of fracture or slippage may occur simultaneously along a predefined interface and in the bulk of the element. In order to determine which surface is critical, we feature a criteria which aids in determining the correct surface upon which all further slippage due to fracture will occur. This interface method is cast in the framework of an enhanced strain finite element which is capable of capturing softening along an embedded strong discontinuity.