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Addis Ababa University Libraries Electronic Thesis and Dissertations: AAU-ETD! >
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Thesis - Mechanical Engineering >
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http://hdl.handle.net/123456789/1520
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| Title: | THERMAL STRESSES AND CREEP ANALYSIS OF BOILER TUBES |
| Authors: | Chanyalew, Taye |
| Advisors: | Dr. Alem Bazezew |
| Copyright: | 2004 |
| Date Added: | 20-Oct-2008 |
| Publisher: | Addis Ababa University |
| Abstract: | An analysis is developed for the calculation of creep deformation of an axisymmetric boiler
tube subjected to axisymmetric load. The stresses and the permanent strains at a particular
time and at the steady state condition, resulting from loading of the tube under constant
internal pressure and elevated temperature were evaluated when accounts is taken to the
secondary creep characteristics of a given material. In this thesis first the formulation of an
analytical theory of creep for tubes according to the Bailey creep theory [41] was discussed.
Bailey theory was proposed for an idealized homogeneous material loaded uniaxially. The
theory takes into account the initial elastic strain, the transient creep strain, and the
minimum creep rate strain. Next, more general solution by finite element method are
presented and discussed for a class of problems in which no prior analytical solution may
exists; like the cases of cracked and/or pitted boiler tubes. The method of solution is an
extension of the direct stiffness method. The body is replaced by a system of discrete
triangular cross-section ring elements interconnected along circumferential nodal circles.
The equations of equilibrium for the body are derived from the principle of minimum
potential energy. The creep behavior of the body is formulated in terms of creep laws in
current use. Starting with the elastic solution of the problem, creep strains are treated as
initial strains to determine the new stress distributions at the end of time interval. The
procedure is repeated until either the final time is reached or until the stress distribution is
not changed i.e. when a steady stated condition is reached. Calculated results according to
arbitrarily selected boiler tube data are shown at the end. |
| Description: | A thesis submitted to the School of Graduate Studies of Addis Ababa University in partial
fulfillment of the Degree of Masters of Science in Mechanical Engineering
(Applied Mechanics stream) |
| URI: | http://hdl.handle.net/123456789/1520 |
| Appears in: | Thesis - Mechanical Engineering
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