Thesis (M.C.E.)--University of Delaware, 2007. / Principal faculty advisor: Jennifer Righman McConnell, Dept. of Civil & Environmental Engineering. Includes bibliographical references.

Thesis (Ph. D.)--Lehigh University, 2000. / Includes vita. Includes bibliographical references (leaves 154-162).

Abstract Bioabsorbable materials enable temporary implantation without the need for subsequent implant removal. The aim of the present experimental study was to evaluate the suitability of a fibrous bioabsorbable implant made of poly-L/D-lactide (PLDLA) 96/4 fibres as an episcleral implant. The general tissue reactions were evaluated in subcutaneous tissues in rats in follow-up periods ranging from 3 days to 48 weeks. The episcleral tissue reactions were studied in rabbits with follow-up periods of one, three, five and 48 weeks. A silicone sponge implant was used as a control material and operations were performed using similar technique with both implants. Tissue reactions were located just around the implant area and consisted of an acute inflammatory reaction in the early follow-up periods, continuing as a foreign body inflammatory reaction. With episcleral implants there were no inflammatory cells seen within the sclera or in the retinal layers, and the structure of the retina and the cornea was also normal. The biocompatibility was good in the 48 week follow-up despite the relatively high surface area of the fibrous implant. The material had not degraded by 48 weeks. The indentation effect by the PLDLA implant (diameter of 3–3.5mm) was lower than that achieved with the silicone sponge implant (diameter 4mm). The depth of indentation decreased over time in both groups with comparable rates over the follow-up period of 5 months. The duration of the indentation effect was sufficient to be used for scleral buckling in retinal detachment surgery. In conclusion, the biocompatibility of a fibrous implant made of PLDLA 96/4 placed subcutaneously and episclerally was good in the follow-up lasting 48 weeks despite the relatively high surface area of the implant. The fibrous implant made of PLDLA 96/4 seemed to be well-tolerated by ocular tissues and the indentation effect was sufficiently long.

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This research into the properties of a 5"x5"x16lb W.F., A 36 Steel, rolled structural member was undertaken to determine the following: i - Yield stress distribution over the cross section of the member as determined by coupon tests. ii - Development of strain over the cross section of the member, as measured by electric strain gauges, when subjected to a) Axial loading, b) Bending Moment. iii - The effect of previous loading of a member as a column into the region of yielding on its subsequent behaviour as a beam loaded to failure. The following results were obtained: i - Yield stress, particularly the upper yield stress was not uniform over the cross section. ii - The strain distribution in the plastic range was not uniform and varied from cross section to cross section and even at closely adjacent points on the same cross section. iii - Failure of the member, due to inadequate lateral support when loaded as a column, occurred before complete yielding was achieved. The effect of this previous loading on the subsequent behaviour of the member as a beam loaded to failure was inconclusive. / Applied Science, Faculty of / Civil Engineering, Department of / Graduate

The collapse-behaviour of pipes was to be studied by use of Finite Element modelling.Existing analytical expressions for collapse were evaluated and especially the one used inDNV-OS-F101 was decided to be studied in comparison with FE-model results.Parameters that may influence the collapse capacity and are not included in the analyticalexpressions –flattening, peaking, eccentricity, local wall thickness variation, materialstress-strain curve, residual stresses - were defined and explained. A model was built inthe Finite Element software package Abaqus v6.9.1 and several articles on collapsetesting used to verify it. The aforementioned parameters were studied by use ofsensitivity studies and the results shown and discussed. Effective thickness definitions foruse in the DNV-formula and the DNV-yield stress criterion were discussed in the contextof the results. The results seemed to indicate that the transition between the elastic andplastic range of the material stress-strain curve was of great importance. The results werediscussed in the context of the different collapse-related parameters defined beforehandand some concluding remarks were made on possible further work related to thesefindings.

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