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Thesis (Ph.D.) -- University of Rhode Island, 2007 / Typescript. Includes bibliographical references (leaves 136-140).

Typescript (photocopy). / Digitized by Kansas Correctional Industries

The objective of this study is to provide an experimental performance assessment of cement borehole plugs subjected to dynamic loadings. This includes the study of dried-out plugs as well as of plugs that have remained wet throughout the testing period. Literature review indicates lack of quantitative data on plug performance under dynamic loading. Nevertheless, it shows that deep underground structures in competent rocks are safer than surface structures, openings at shallow depth, and openings in fractured rocks, when subjected to earthquakes and subsurface blasts. Flow test results indicate that wet cement seals are less permeable than Charcoal granite. Sealing performance is severely degraded when cement seals are allowed to dry. Dye injection tests show that the flow penetrates uniformly through the wet plugs, but occurs only along the plug/rock interface of the dried-out plugs. The permeability of wet and dried-out cement seals does not change significantly after the application of dynamic loads.

General anisotropic constitutive laws and relevant dynamic equations of motion for porous media are described. The accuracy of various discretization algorithms in space and in time was surveyed. Results of these models and algorithms were compared to the exact solutions. Appropriate models and algorithms for further studies of spinal motion segments were then determined. Poroelastic axisymmetric finite element models, simulating spinal motion segments were analyzed and studied. Material properties of the intervertebral disc were derived by fitting experimental data based on porous medium theory using one-dimensional mathematical models. Structural models for the normal and degenerative processes were simulated for investigation of nutritional supply routes in the disc. Detailed structural anaalyses and failure conditions in various spinal motion segments were studied. Results of finite element analyses were consistent with the experimental observations. Nonlinear elastic material behavior of the solid skeleton was assumed and relevant formulas in creep were derived and examined. Preliminary results indicated that the nonlinear poroelastic material law used here may be useful in future analysis of the disc in finite element models of spinal motion segments.

Thesis (B.S.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 1980. / MICROFICHE COPY AVAILABLE IN ARCHIVES AND ENGINEERING. / Bibliography: leaf 42. / by Eliot H. Frank. / B.S.

Not available / text

Submitted towards the Degree of Master of Technology in Mechanical Engineering at the Cape Peninsula University of Technology / A Small Punch Test is a non-destructive technique for evaluating mechanical behaviour. The main advantage of this testing technique is the fact that material can be extraxted from a component in service due to the small dimensions of the speciments.Typical test specimens cut from components are similar in size to a normal human fingernail.

During its service life, a structure may be subjected to various environmental and loading conditions. However, in general, the properties determined under one set of conditions may not be used to determine the behaviour of the material under a different set of conditions. For example, it is well known that concrete is a strain rate sensitive material; therefore, its properties determined under conventional static loading cannot be used to predict the performance of concrete subjected to high strain rates. The problem is serious because these high strain rate loadings are associated with large amounts of energy imparted to the structure in a very short period of time, and concrete is a brittle material. Since the strain rate sensitivity of concrete prohibits the use of its statically determined properties in assessing its behaviour under dynamic conditions, high strain rate tests are required. Impact tests were carried out on about 500 concrete beams. An instrumented drop weight impact machine was used. The instrumentation included strain gauges mounted in the striking end of the hammer (called 'the tup'), and also in one of the support anvils. In addition, three accelerometers were mounted along the length of the beam in order to obtain the beam response, and also to enable the inertial correction to the observed tup load to be made. Two different concrete mixes, normal strength with a compressive strength of 42 MPa, and high strength with a compressive strength of 82 MPa, were tested. The effect of two types of fibres, high modulus steel, and low modulus fibrillated polypropylene, in enhancing concrete properties was investigated. In addition, tests were also conducted on beams with conventional reinforcement. Hammer drop heights ranging from 0.15m to 2.30m were used. Static tests were conducted on companion specimens for a direct comparison with the dynamic results. In general, it was found that concrete is a very stain rate sensitive material. Both the peak bending loads and the fracture energies were higher under dynamic conditions than under static conditions. Fibres, particularly the steel fibres, were found to significantly increase the ductility and the impact resistance of the composite. High strength concrete made with microsilica, in certain circumstances, was found to behave in a far more brittle manner than normal strength concrete. High speed photography (at 10,000 frames per second) was used to study the propagation of cracks under impact loading. In general, the crack velocities were found to be far lower than the theoretical crack velocities. The presence of reinforcement, either in the form of fibres, or of continuous bars was found to reduce the crack velocity. A model was proposed based on a time step integration technique to evaluate the response of a beam subjected to an external impact pulse. The model was capable of predicting not only the experimentally observed non-linear behaviour of concrete under impact loading, but also the more pronounced brittle behaviour of high strength concrete. / Applied Science, Faculty of / Civil Engineering, Department of / Graduate