No description available.

No description available.

No description available.

Finite element models have been successfully used to analyze adhesive bonds in actual structures, but this takes a considerable amount of time and a high computational cost. The objective of this study is to develop a simple and cost-effective finite element model for adhesively bonded joints which could be used in industry. Stress and durability analyses of crack patch geometries are possible applications of this finite element model. For example, the lifetime of aging aircraft can be economically extended by the application of patches bonded over the flaws located in the wings or the fuselage. Special two and three- dimensional adhesive elements have been developed for stress and displacement analyses in adhesively bonded joints. Both the 2-D and 3-D elements are used to model the whole adhesive system: adherends and adhesive layer. In the 2-D elements, adherends are represented by Bernoulli beam elements with axial deformation and the adhesive layer by plane stress or plane strain elements. The nodes of the plane stress-strain elements that lie in the adherend-adhesive interface are rigidly linked with the nodes of the beam elements. The 3-D elements consist of shell elements that represent the adherends and solid brick elements to model the adhesive. This technique results in smaller models with faster convergence than ordinary finite element models. The resulting mesh can represent arbitrary geometries of the adhesive layer and include cracks. Since large displacements are often observed in adhesively bonded joints, geometric nonlinearity is modeled. 2-D and 3-D stress analyses of single lap joints are presented. Important 3-D effects can be appreciated. Fracture mechanics parameters are computed for both cases. A stress analysis of a crack patch geometry is presented. A numerical simulation of the debonding of the patch is also included. / Ph. D.

No description available.

Intact and fractured rock samples were studied in the laboratory in order to understand more fully the mechanism of closure of fractures subjected to high confining stresses and the resultant effect on specimen permeability. Confining stresses applied to the specimens ranged from 3.0 to 20.0 MPa, and the closure of fractures was observed by monitoring the change in the hydraulic conductivity of the specimens. Test results suggest that some resealing may occur due to crushing and realignment of mineral grains along a fracture surface. The closure of fractures is dependent upon the strength of the rock mass, the physical nature of the fracture, and the fluid pressure present in the fracture. Fracture closure is highly time dependent, and a number of nonlinear pressure flow relationships have been identified. These deviations are thought to represent two fundamentally different processes, the most important of which are turbulence in the flow and fracture expansion.

Submarine landslides, commonly triggered by earthquakes, significantly affect tsunami wave heights. Subaerial landslides can also generate tsunamis (if the land flows into a body of water) and may be catastrophic in nature, causing human casualties and direct property damage. This work focuses on landslides associated with shear band that develops beneath the slipping mass. Accordingly, we consider a landslide as a dynamic process when a shear band emerges along the potential failure surface. Within this band, the shear strength decreases due to the softening behaviour of the particulate material. Material above the band moves downwards, causing the band to propagate dynamically. This already produces a landslide velocity before the slide reaches the post-failure stage and begins separating from the substrata and generating tsunami. However, existing models of tsunamigenic landslides assume zero initial slide velocity. Previous analyses of the catastrophic shear band propagation in slopes of normally- and over-consolidated sediments have shown that a relatively short initial failure zone is sufficient to cause a full-scale landslide. For the shear band to propagate, the energy produced in the body by an incremental propagation of the shear band must exceed the energy required for the propagation. This consideration separates the shear band growth into progressive (stable) and catastrophic (dynamic) stages and treats the band growth as a true physical process rather than an instantaneously appearing discontinuity. This work considers a dynamic shear band problem formulated within the framework of the Palmer and Rice’s [1973] approach. We obtain the exact, closed-form solution for the shear band and landslide velocities as well as for the spatial and temporal distributions of strain and material velocity. This solution assesses when the slide fails due to the limiting condition near the propagating tip of the shear band. We also obtain a simple asymptotic solution, which is compared to the exact solution. In the case of submerged slopes, the obtained solutions are used in landslide and tsunami height analyses. Our results suggest that the conventional static approach to the slope stability analysis leads to a significant underestimation of the slide size (volume). In most cases, the volumes of catastrophic slides are roughly twice the volumes of progressive slides. For submerged slides, this dynamic effect further manifests itself in increasing the tsunami magnitude compared to the static case.

No description available.

published_or_final_version / Civil Engineering / Doctoral / Doctor of Philosophy

No description available.