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http://hdl.handle.net/11375/17823
Title: | Rate Effects in Bulk Forming |
Authors: | Forster, James Allam |
Advisor: | Duncan, J. L. |
Department: | Mechanical Engineering |
Keywords: | industrial metalworking processes, metalworking processes, extrusion, loads and material flow characteristics,;deforming metals, tangential velocity, rotation |
Publication Date: | Dec-1978 |
Abstract: | <p> One of the major industrial metalworking processes is extrusion and it is of technological importance to be able to estimate the loads and material flow characteristics within the deforming metal. Hot metals and superplastic materials are particularly sensitive to the speed of the operation al though it is difficult to col".sider this in an analysis of the problem. </p> <p> This thesis reviews the analytical techniques available to the engineer to determine the loads in bulk forming processes and examines the way in which rate effects have been accommodated. The upper bound method, which is an approximate analytical technique, is reviewed in detail. The concept of a tangential shear zone of constant shear strain rate is introduced and used to enable strain rate effects to be considered within the upper bound technique. The work rate across each discontinuity is shown to be a function of the material strain rate sensitivity, the shear zone width and the tangential veloc i ty change. </p> A number of tangential velocity fields are proposed for the side extrusion process. These are examined and compared by minimizing the work rate using a computer optimization technique. The optimum solution for a simple tangential velocity discontinuity field is shown to give load estimates which are within 10% of those given by the more exact slip-line field method. </p> <p> Experiments, performed by the author on the side extrusion of two materials, which have very different strain rate sensitivities, are reported in detail. A characteristic difference in the extrudate geometry for the two materials is identified and shown to be a result of the difference in the materials strain rate sensitivity index. The experimental extrusion pressures for the two materials at different ram velocities are compared with theoretical values derived using the theory developed earlier in the thesis; the correlation is good. </p> <p> The shape of the tangential discontinuity between a uniform translational and uniform rotational field is examined and shown to be a circular arc. A number of new tangential velocity discontinuity fields are presented for a variety of common metalworking processes. These fields comprise straight and circular discontinuities and represent a new type of "mixed" field which predicts the rotation of the extrudate. </p> |
URI: | http://hdl.handle.net/11375/17823 |
Appears in Collections: | Open Access Dissertations and Theses |
Files in This Item:
File | Description | Size | Format | |
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Forster_James_A_1978Dec_Ph D.pdf | 101.57 MB | Adobe PDF | View/Open |
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