| 1. |
- Larsson, Mats, 1953, et al.
(författare)
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Some observations on failure prediction in sheet metal forming
- 2007
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Ingår i: Proceedings of The 6th European LS-DYNA Users' Conference, May 29-30, 2007, Göteborg, Sweden. ; , s. 5.93-5.102
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Konferensbidrag (refereegranskat)abstract
- This paper presents results from a FE-study on failure prediction in ductile metal sheets. The studied material, a DP600 dual phase steel, is used throughout the study. The effects of variation of element sizes, material parameters, and friction are shown and discussed. Also results from simulations of in-plane and out-of-plane tests are compared and discussed
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| 2. |
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| 3. |
- Mattiasson, Kjell, 1948, et al.
(författare)
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On the prediction of plastic instability in metal sheets
- 2007
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Ingår i: Proceedings of NUMIFORM'07, The 9th international conference on numerical methods in industrial forming processes, June 17-21, 2007, Porto, Portugal, AIP Conference proceedings 908. - 9780735404168 ; 1, s. 129-134
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Konferensbidrag (refereegranskat)abstract
- The current report presents some results from a study on the prediction of necking failure in ductile metal sheets. In particular methods for creating Forming Limit Curves (FLCs) are discussed in the present report. Three groups of methods are treated: Experimental methods, Theoretical/analytical methods, and the Finite Element Method (FEM). The various methods are applied to two different materials: An aluminum alloy and a high strength steel. These materials do both exhibit a distinct necking behavior before fracture, and they do both exhibit only a small strain rate dependence. As can be expected, the resulting FLCs from the various experimental, theoretical, and numerical methods show a substantial scatter. The reasons for these deviating results are analyzed, and some conclusions are drawn regarding the applicability of the different methods.
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| 4. |
- Mattiasson, Kjell, 1948, et al.
(författare)
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On the role of strain rate in in FE-simulation of sheet forming processes
- 2008
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Ingår i: Proceedings of NUMISHEET 2008, Editor Pavel Hora. - 9783909386802 ; , s. 223-228
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Konferensbidrag (refereegranskat)abstract
- Strain rate dependency of the sheet material is known to have a delaying effect on theformation of necks in the material. This phenomenon is especially strong in highly ductile steel alloys. Thestrain rate effect is rarely considered in commercial simulations of forming processes. However, if thepurpose of the simulation is to predict strain localization and necking, the strain rate effect has to beconsidered. In the current paper a simple inverse approach is suggested for the determination of thematerial’s strain rate dependency. The method assumes that the FLD0, the limit strain at plane strain, isknown from some experiment. The material’s strain rate dependency is then determined from simulations ofa plane strain test in a trial-and-error process. As a faster alternative to performing full FE simulations, theuse of a simple M-K model, consisting of two finite elements, is suggested. Three different functionsdescribing the strain rate hardening effect have been evaluated. The strain rate parameter determined bymeans of the simplified M-K model has been used in full FE simulations of press forming operations. TheFE model is shown to be capable of predicting necking strains in an accurate way.
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| 5. |
- Mattiasson, Kjell, 1948, et al.
(författare)
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Theoretical and experimental sheet metal failure evaluation
- 2007
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Ingår i: Proceedings of IDDRG'07, The international deep drawing research group, May 21-23, 2007, Györ, Hungary. ; , s. 185-194
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Konferensbidrag (refereegranskat)abstract
- In the present paper some results from an ongoing study on the prediction of necking and fracture in connection to sheet metal forming are presented. The materials used in this study do all show a distinct necking behavior before fracture. In fact, the formation of an incipient neck is here used to define the limit strains. Three groups of methods for defining limit strains are used in this study. These are: experimental methods, theoretical/analytical methods, and Finite Element methods. The various methods are briefly described in the report. Unfortunately, there is a considerable scatter in results between the various groups of methods, and also within the separate groups. These discrepancies are analyzed, and explanations for them are given where possible
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| 6. |
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| 7. |
- Sigvant, Mats, 1969, et al.
(författare)
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THE DEFINITION OF INCIPIENT NECKING AND ITS IMPACT ON EXPERIMENTALLY OR THEORETICALLY DETERMINED FORMING LIMIT CURVES
- 2008
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Ingår i: Proceedings of IDDRG'08, The International Deep Drawing research Group, June 16-18, Olofström, Sweden, Edited by Nader Asnafi.
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Konferensbidrag (refereegranskat)abstract
- In the current paper various methods for Forming Limit Curve (FLC)evaluation are presented and discussed. The capabilities of modern optical systems for strain measurement are demonstrated. A method for limit strain evaluation, based on the onset of instability, is described in detail. The method can be applied for the evaluation of experimental strains, as well as of strains from Finite Element (FE) simulations. Three different approaches have been applied for the determination of FLCs for a DP600 steel. The method used for limit strain evaluation is shown to have a considerable influence on the level of the resulting FLC. Also results from FE-simulations of the same tests are presented. Theimportance of always questioning how a certain FLC has been evaluated is emphasized.
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| 8. |
- Banabic, Dorel, 1943, et al.
(författare)
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Influence of constitutive equations on the accuracy of prediction in sheet metal forming simulation
- 2008
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Ingår i: Proceedings of NUMISHEET 2008, Editor Pavel Hora. - 9783909386802 ; , s. 37-42
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Konferensbidrag (refereegranskat)abstract
- During the last three decades, numerical simulation has gradually extended itsapplicability in the field of sheet metal forming. Constitutive modelling is one of the domains closely relatedto the development of numerical simulation tools. The paper is focused on the development of newphenomenological yield criteria developed in the CERTETA research centre able to describe the anisotropicresponse of sheet metals. The numerical tests presented in the paper prove the capability of the equivalentstresses to model the inelastic response of a large variety of materials (steel and aluminium alloys). The lastsection of the paper is devoted to a comprehensive testing of the new yield criterion as implemented in thefinite-element code AUTOFORM 4.1. With this aim in view, the authors have chosen the bulging and crossdeep drawing benchmarks. The test proves the capability of the yield criterion to describe the effects of theplastic anisotropy of the sheet metals subjected to industrial forming processes.
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| 9. |
- Mattiasson, Kjell, 1948, et al.
(författare)
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An evaluation of some recent yield criteria for industrial simulations of sheet forming processes
- 2008
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Ingår i: International Journal of Mechanical Sciences. - 0020-7403. ; 50, s. 774-787
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Tidskriftsartikel (refereegranskat)abstract
- The present paper deals with material modeling in connection with sheet metal forming analyses. One purpose of the report is to discuss the special needs and demands of industrial analysts. With this in mind, in particular, the demands put on the yield condition are analyzed. Two recent yield criteria for anisotropic metal sheets, in the literature denoted Yld2000 and BBC2000, respectively, are found to be very well suited for industrial use. They do both belong to a group of yield criteria called the ‘‘Hosford family’’. Practical issues with regard to these yield criteria, such as procedures for determining the parameters being part of the models, implementation issues, and numerical efficiency, are thoroughly discussed. A version of the above criteria, using a reduced set of parameters, is proposed, and is shown to offer a significantly reduced computing time at the cost of some loss of accuracy.
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| 10. |
- Mattiasson, Kjell, 1948, et al.
(författare)
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Issues in connection to the prediction of strain localization in metal sheets
- 2008
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Ingår i: International Journal of Material Forming. - : Springer Science and Business Media LLC. - 1960-6206 .- 1960-6214. ; 1:SUPPL. 1, s. 245-248
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Tidskriftsartikel (refereegranskat)abstract
- The current paper deals with the prediction of strain localization in metal sheets. Especially the effect of strain rate dependency on the necking phenomenon is treated. The ability of FEM to predict strain localization during simulations of sheet forming operations is investigated. An approach for the determination of the strain rate material parameters, based on an experimentally determined FLD0, is suggested. The current approach is demonstrated for three sheet materials, and from the results the approach can be judged as promising.
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