| 1. |
- Abiri, Olufunminiyi, et al.
(författare)
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Comparison of Multiresolution Continuum Theory and Nonlocal Dame model for use in Simulation of Manufacutring Processes
- 2016
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Ingår i: International Journal for Multiscale Computational Engineering. - 1543-1649. ; 14:1, s. 81-94
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Tidskriftsartikel (refereegranskat)abstract
- Modelling and simulation of manufacturing processes may require the capability to account for localization behavior, often associated with damage/fracture. It may be unwanted localization indicating a failure in the process or, as in the case of machining and cutting, a wanted phenomenon to be controlled. The latter requires a higher accuracy regarding the modelling of the underlying physics, as well as the robustness of the simulation procedure. Two different approaches for achieving mesh-independent solutions are compared in this paper. They are the multiresolution continuum theory (MRCT) and nonlocal damage model. The MRCT theory is a general multilength-scale finite element formulation, while the nonlocal damage model is a specialized method using a weighted averaging of softening internal variables over a spatial neighborhood of the material point. Both approaches result in a converged finite element solution of the localization problem upon mesh refinement. This study compares the accuracy and robustness of their numerical schemes in implicit finite element codes for the plane strain shear deformation test case. Final remarks concerning ease of implementation of the methods in commercial finite element packages are also given.
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| 2. |
- Abiri, Olufunminiyi, et al.
(författare)
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Controlling Thermal Softening Using Non-Local Temperature Field in Modelling
- 2016
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Ingår i: Journal of Machining and Forming Technologies. - : Nova Science Publishers, Inc.. - 1947-4369. ; 8:1-2, s. 13-28
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Tidskriftsartikel (refereegranskat)abstract
- One of the aims of this work is to show that thermal softening due to the reduced flow strength of a material with increasing temperature may cause chip serrations to form during machining. The other purpose, the main focus of the paper, is to demonstrate that a non-local temperature field can be used to control these serrations. The non-local temperature is a weighted average of the temperature field in the region surrounding an integration point. Its size is determined by a length scale. This length scale may be based on the physics of the process but is taken here as a regularization parameter.
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| 3. |
- Abiri, Olufunminiyi, et al.
(författare)
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Non-local damage models in manufacturing simulations
- 2013
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Konferensbidrag (refereegranskat)abstract
- Localisation of deformation is a problem in several manufacturing processes. Machining is an exception where it is a wanted feature. However, it is always a problem in finite element modelling of these processes due to mesh sensitivity of the computed results. The remedy is to incorporate a length scale into the numerical formulations in order to achieve convergent solutions. Different simplifications in the implementation of a non-local damage model are evaluated with respect to temporal and spatial discretisation to show the effect of different approximations on accuracy and convergence.
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| 4. |
- Abiri, Olufunminiyi, et al.
(författare)
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Non-local damage models in manufacturing simulations
- 2015
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Ingår i: European journal of mechanics. A, Solids. - : Elsevier BV. - 0997-7538 .- 1873-7285. ; 49, s. 548-560
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Tidskriftsartikel (refereegranskat)abstract
- Localisation of deformation is a problem in several manufacturing processes. Machining is an exception where it is a wanted feature. However, it is always a problem in finite element modelling of these processes due to mesh sensitivity of the computed results. The remedy is to incorporate a length scale into the numerical formulations in order to achieve convergent solutions. Different simplifications in the implementation of a non-local damage model are evaluated with respect to temporal and spatial discretisation to show the effect of different approximations on accuracy and convergence.
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| 5. |
- Abiri, Olufunminiyi, et al.
(författare)
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Non-Local Modelling of Strain Softening in Machining Simulations
- 2017
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Ingår i: IOP Conference Series. - : Institute of Physics (IOP). - 1757-8981 .- 1757-899X. ; 225
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Tidskriftsartikel (refereegranskat)abstract
- Non-local damage model for strain softening in a machining simulation is presented in this paper. The coupled damage-plasticity model consists of a physically based dislocation density model and a damage model driven by plastic straining in combination with the stress state. The predicted chip serration is highly consistent with the measurement results.
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| 6. |
- Azizoğlu, Yağız, 1986-, et al.
(författare)
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Finite Element Analysis of cold pilgering using elastic roll dies
- 2017
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Ingår i: Procedia Engineering. - : Elsevier. - 1877-7058. ; 207, s. 2370-2375
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Tidskriftsartikel (refereegranskat)abstract
- A finite element model of cold pilgering with elastic roll dies have been developed and used to investigate the influence of roll die deformation on the material flow, contact region, roll separating force and tube dimensions. Full scale experiments were performed to validate the contact surface and tube dimensions. The results show that the influence of roll die flattening is not significant on the contact length. However, elastic deformation of roll die has strong influence on both the wall thickness reduction and roll separating force. Thus it is recommended to consider elasticity of roll dies when forces and tube dimensions are estimated.
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| 7. |
- Azizoğlu, Yağız, et al.
(författare)
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Finite element modeling of tube deformation during cold pilgering
- 2016
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Ingår i: MATEC Web of Conferences. - : EDP Sciences. ; , s. 1-8
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Konferensbidrag (refereegranskat)abstract
- A three-dimensional finite element model of cold pilgering of stainless steel tubes is developed in this paper. The objective is to use the model to increase the understanding of forces and deformations in the process. The focus is on the influence of vertical displacements of the roll stand and axial displacements of the mandrel and tube. Therefore, the rigid tools and the tube are supported with elastic springs. Additionally, the influences of friction coefficients in the tube/mandrel and tube/roll interfaces are examined. A sensitivity study is performed to investigate the influences of these parameters on the strain path and the roll separation force. The results show the importance of accounting for the displacements of the tube and rigid tools on the roll separation force and the accumulative plastic strain.
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| 8. |
- Azizoğlu, Yağız, et al.
(författare)
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Finite element modelling of cold pilgering of tubes
- 2015
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Ingår i: Proceedings of the 8th International Conference on Computational Plasticity - Fundamentals and Applications, COMPLAS 2015. - Barcelona : International Center for Numerical Methods in Engineering (CIMNE). - 9788494424465 ; , s. 716-726
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Konferensbidrag (refereegranskat)abstract
- Cold pilgering is a cold forming process used during manufacturing of seamless tubes. The tube with a mandrel inside is fed forward and rotated in stepwise increments, while the roll stand moves back and forth. The total plastic deformation of the tube is such that the cross-sectional area of the tube decreases and the length of the tube increases during the process. However, this is performed in many small incremental steps, where the direction of deformation in a material point changes at each stroke. Most published models of cold pilgering use simplified material models. In reality, the flow stress is dependent on temperature, strain rate, strain history and microstructure. In this work, temperature and strain rate distributions are computed, using a 3D thermo-mechanical FE model, and the influence of temperature and strain rate on the rolling force is investigated. The Johnson-Cook model is employed to describe the flow stress using isotropic hardening. The results show that strain rate and temperature have a significant influence on the roll separation force.
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| 9. |
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| 10. |
- Azizoğlu, Yağız, 1986-
(författare)
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Modeling of Cold Pilgering of Stainless Steel Tubes
- 2023
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Cold pilgering is a complex forming process used to produce seamless tubes in terms of modeling due to the complexity in kinematic of tools, friction condition and material behavior. The process development has mostly been based on simple formulas and costly full-scale tryouts. The aim in this study is to develop validated Finite element models of cold pilgering to support design of a robust process.A three-dimensional thermo-mechanical Finite element models of cold pilgering has been developed in the course of the work leading to this thesis. The commercial code MSC. Marcwas used in the simulations. General 3D models are needed to be able to capture asymmetric deformation in cold pilgering. Elastic deflections of tools and roll stand were included in the model via linear and nonlinear springs that were calibrated versus experiments. A temperature dependent Chaboche type plasticity model was employed in this simulation to mimic strain hardening and softening behavior under multidirectional loading. The model parameters were optimized using multi-directional compression and uni-directional tensile tests. Heat exchange between tools and lubricant was included in the simulation via heat convection films on the surfaces. The film parameters were calibrated using experimental data. Simulation predictions for hardening, rolling force, process temperature and geometry were compared with experiments for validation purposes. The predictions showed overall good agreement with validation experiments enabling the use of this model for understanding and improving the process.
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