Ph.D. / Materials science / The influence of resonant and sub-resonant frequency vibration on the longitudinal residual stresses in A-36 mild steel weldments has been studied. Residual stress analysis was carried out using sectioning, x-ray and blind-hole-drilling techniques. The hole-drilling method was modified to take into account the effect of local plastic yielding due to stress concentration and the machining stresses, with a resultant accuracy comparable to that obtained by the sectioning method. As a result of the vibratory treatments, residual stress redistribution occurred near the weld; the peak stresses were decreased by up to 30%. The resonant frequency vibration had a more pronounced stress redistribution as compared to the sub-resonant frequency vibration. Transmission electron microscopy studies indicated local plastic deformation as the mechanism by which this stress reduction occurred. Constant amplitude axial fatigue experiments on samples machined from regions adjacent to the weld showed that both the vibratory techniques did not induce any fatigue damage.

Thesis (M.Eng.)--Memorial University of Newfoundland, 2001. / Bibliography: leaves 178-182.

Thesis (M.Eng.)--Memorial University of Newfoundland, 2002. / Bibliography: leaf 103.

Thesis (Naval Engineers Degree and M.S. in Mechanical Engineering)--Massachusetts Institute of Technology, 2002. / Includes bibliographical references (leaf 47). Also available online.

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published_or_final_version / Mechanical Engineering / Master / Master of Philosophy

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Radiography is an extensively used NDT method, especially in nuclear, aerospace and automotive industries where optimal designs call for greater reliability. The rules corresponding to industrial radiography are defined in a system of radiographic standards. The standards related to the radiographic testing of metallic welded joints had been harmonised in all over the Europe and at the end in 1997, the standard &quot / EN 1435&quot / was established and published. Since then, this standard has become the most widely used standard where the radiographic applications are necessary. To eliminate the person based errors during application of the standard, moreover to save time, cost and effort in radiographic exposures, in this study it was aimed to write a computer program which is able to calculate all necessary parameters for a radiographic exposure related to this standard EN 1435. In the programming stage, Visual Basic 6.0 &amp / #61651 / was used. The program consists of many windows, each giving and controlling separate parameters related to the exposure. Besides giving all the needed parameters, the evolved program is able to prepare a report with these parameters. So, both radiography technicians and experts can use it. It is believed that this study constructs a basis for developing other computerised test procedures for any kind of non-destructive testing methods used in industry today.