Masters Theses

Abstract

"Strengthening of aluminum by formation of the voids and the nature of resultant strengthening, viz., the temperature and the strain rate dependence of its yield strength were studied. Aluminum wires with 99.999% purity and of 3.1 mm diameter were quenched and heat treated to form voids of the approximate density 10¹³-10¹⁴ voids/cm³ and were tested for their yield strength. Voids in selected samples were observed by transmission electron microscopy using the Hitachi HU-11A microscope. The yield strength of the void strengthened samples was measured at various temperatures from 77ºK to 593ºK using two strain rates, 3.33 x 10⁻²/sec and 1.67 x 10⁻³/sec and the tests at room temperature and at 77ºK were carried out using various strain rates. The results are examined with the help of a model presented here for the mechanism of void strengthening. The model follows directly from the Orowan stress with Ashby's improved criterion together viewed from the Coulomb's approach. Limitations of both approaches are also discussed. From the mode, it is shown that the mechanism of void strengthening and the effectiveness of voids as obstacles to the dislocation motion and therefore the extent of void strengthening is primarily dependent on the void density and is much less dependent on the void size. The results obtained are found to be consistent with the model at room temperature. The void strengthened aluminum samples as compared to annealed samples show following characteristics. 1. They are more susceptable to the instability of plastic flow at low temperatures. 2. Their temperature dependence of yield strength varies in different temperature ranges; and 3. They have higher strain rate sensitivity of yield strength. These observations are explained in terms of various reactions occuring simultaneously. In a separate part, an hypothesis is presented to suggest that a thermodynamic cycle may be operating in a rotating component under load and therefore its fatigue life is some function of the strain rate sensitivity of both the material and its bulk thermal conductivity"--Abstract, pages ii-iii .

Advisor(s)

Leighly, Hollis P., 1923-2004

Committee Member(s)

Frad, William A., 1909-1974
Avula, Xavier J. R.

Department(s)

Materials Science and Engineering

Degree Name

M.S. in Metallurgical Engineering

Publisher

University of Missouri--Rolla

Publication Date

1971

Pagination

viii, 102 pages

Rights

© 1971 Purshottam G. Manusmar, All rights reserved.

Document Type

Thesis - Open Access

File Type

text

Language

English

Subject Headings

Aluminum alloys -- MicrostructureStrains and stressesAluminum -- Effect of temperature on

Thesis Number

T 2689

Print OCLC #

6038980

Electronic OCLC #

879221308

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