Use this URL to cite or link to this record in EThOS: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.637789
Title: Finite element modelling and adaptive remeshing in static and dynamic analysis of metal powder forming processes
Author: Khoei, A. R.
Awarding Body: University of Wales Swansea
Current Institution: Swansea University
Date of Award: 1998
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Abstract:
This thesis presents a general framework for the finite element simulation of powder forming processes. As the compaction process involves a very large reduction in volume, the behaviour of the powders is assumed to be that of a rate-independent elasto-plastic material. The process is therefore described by a large displacement finite element formulation for the spatial discretization. A generalized Newmark scheme is used for the time domain discretization and then the final nonlinear equations are solved by a Newton-Raphson procedure. A combination of a Mohr-Coulomb and elliptical cap model is utilised as a constitutive model to describe the nonlinear behaviour of powder materials in the concept of the generalized plasticity formulation for the description of cyclic loading. The finite element approach adopted is characterized by the use of 'interface' elements in which a plasticity theory of friction is incorporated to simulate sliding resistance at the powder-tool interface. The constitutive relations for friction are derived from a Coulomb friction law. Efforts have been made to develop an automatic and generally applicable adaptive procedure in the analysis of powder forming processes. A-posteriori Zienkiewicz-Zhu estimator using L2 norm of strain by a recovery procedure is proposed. The simulation of the deformation is shown as well as the distribution of stress and relative density. The results clearly indicate that the algorithm makes it possible to simulate the powder forming problems efficiently and automatically. It has been shown that the proposed adaptive finite element approach is capable of simulating metal powder compaction processes in an efficient and accurate manner. A method is presented for applying the mixed formulation to study the prediction of localization phenomena in a dynamic plasticity problems. This has focused on the performance of mixed u- π triangular and quadrilateral elements to study their efficiency in indicating localization for various mesh refinements. It has also been shown that if a correct approximation is used then both the uniform and non-uniform mesh refinements will converge to the correct answer and clearly indicate the localization phenomenon.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID: uk.bl.ethos.637789  DOI: Not available
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