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Document Type

Thesis - University Access Only

Award Date

1989

Degree Name

Master of Science (MS)

Department

Mechanical Engineering

First Advisor

Bashir A. Sayar

Abstract

One of the primary areas of experimental stress analysis for the last century has been the determination of theoretical stress concentration factors for different combinations of holes and notches on samples under static loading (tension and compression). Although the values for the theoretical stress concentration factor for static loading, Kt, are readily available, data on the dynamic stress concentration factor, Kf, are very limited, especially for samples in bending. This research will present experimental values for the dynamic bending fatigue stress concentration factor, Kf, for a variety of combinations of circular holes, or semicircular notches located across the section and along the edges of flat, trapezoidal specimens. The Krouse flat-sheet fatigue machine with a 40-pound connecting rod and 1725 RPM speed, was used for this experimental research to provide dynamic bending to specimens. The testing materials were SAE 1010 cold-worked, cantilever-type specimens with ultimate strength of 65,000 Psi, yield strength of 55,000 Psi, and Brinell hardness of 128 BHN. This investigation shows that specimens with one 1/8 inch diameter hole on one side require lower numbers of cycles for failure than comparable whole specimens. The number of cycles leading to failure is reduced even more for specimens with one hole on each side, spaced across the short dimension of the specimens. The decrease in the lives of specimens is related to the spacing between the two holes, which is significantly greater than the hole diameter. Two holes on one side of the specimens tend to induce a much higher stress magnitude and as a result, a higher stress concentration, or lower fatigue life. This increase is partly due to the fact that ligament width is smaller than the diameter of the hole, and also due to the unsymmetrical nature of the holes. The results further show that specimens with two holes on each side tend to become stronger in comparison to those already analyzed, although not as strong as a virgin specimen. This strengthening process could be explained by the fact that the four-hole specimens will experience a lower stress magnitude due to the wide spread of the pairs of holes. The results further show that specimens with three holes across will have a less severe change in strength in comparison to the four-hole specimen. The uniform and large distance between the holes in comparison to the hole diameter is responsible for this reduction as opposed to closely located holes on either side in the four-hole system. Experiments also reveal that the specimens with one semicircular notch on one side show a decrease in the life of the specimen in comparison to unnotched specimens.

Library of Congress Subject Headings

Steel -- Stress corrosion

Steel -- Testing

Steel -- Fatigue

Format

application/pdf

Number of Pages

111

Publisher

South Dakota State University

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