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Title: Finite element analysis in metal forming processes
Author: Zhang, W.-C.
Awarding Body: University College of Swansea
Current Institution: Swansea University
Date of Award: 1987
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In metal forming processes such as extrusion and forging the deformation is due, primarily, to the plastic flow of the material. Nevertheless the deformation and the resulting stress distribution is influenced by an elastic effect albeit small. Attempts to solve elasto-plastic metal forming problems, using finite elements, have resulted in the emergence of two competing approaches, namely the solid mechanics based elasto-plastic schemes and rigid-plastic solution techniques such as the viscous flow formulation. This thesis is concerned with the viscous flow approach which generally appears to offer a cheaper solution in comparison to the traditional 'solid' approach. Before introducing elastic effects stress recovery techniques are considered in order to get accurate continuous stresses which also satisfy the equilibrium equations. The techniques developed for this purpose are equally applicable to standard displacement based solutions as well as viscous flow solutions. A multi-loop iterative finite element procedure, incorporating stress smoothing, is then established in an attempt to include elasticity effects. Numerical experiments have been carried out to investigate the consequences of including elasticity. Whilst the procedure works convergence difficulties were experienced when the effect of elasticity increases. Nevertheless the theoretical exposition together with the numerical results provides a valuable foundation from which most robust enhanced procedures for including elasticity can be developed. The above procedures all result in Eulerian steady state velocity solutions. In contrast a combined Eulerian-Lagrangian solution scheme is developed as a means of progressing the deformation of the material with respect to time. This technique is applied to axisymmetric superplastic forming in which the constitutive behaviour is a power law relation between stress and strain rate. A variety of analytical solutions are devised which enable the finite element superplastic formulation and a number of standard time marching schemes to be evaluated. Finally, the program is successfully applied to the free forming (bulging) of the aluminium and titanium alloys A1-Mg6-Mn1 and Ti-6A1-4V. In the forming case numerical results are compared to published experiment data.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available