| 1. |
- Björklund, Oscar, et al.
(författare)
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Anisotropic fracture criteria for a dual-phase steel
- 2014
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- The main objective of this work is to examine the use of anisotropic fracture criteria in order to predict fracture in dual-phase steel. The introduction of a material directional function into the fracture criterion was used in order to account for anisotropy observed in experiments. Selected fracture criteria were fist calibrated by ordinary tensile and in-plane shear tests using specimens cut in three material directions. In order to validate the performance, two types of validation tests were conducted. First, plane strain (notched tensile) tests were carried out in three material directions. Second, Nakajima tests with a waist of 130 mm were conducted, also in three material directions. The fit to the calibration tests was improved with all material directional functions compared to the isotropic criterion. Overall best performance was achieved when a material direction function based on the structural tensors was introduced.
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| 2. |
- Björklund, Oscar
(författare)
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Ductile Failure in High Strength Steel Sheets
- 2014
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Developments in computer-aided engineering and the rapid growth of computational power have made simulation-driven process and product development efficient and useful since it enables detailed evaluation of product designs and their manufacturing processes. In the context of a sheet metal component, it is vital to predict possible failure both during its forming process and its subsequent usage. Accurate numerical models are needed in order to obtain trustworthy simulation results. Furthermore, the increasing demands imposed on improved weight-to-performance ratio for many products endorse the use of high-strength steels. These steels often show anisotropic behaviour and more complex hardening and fracturing compared to conventional steels. Consequently, demand for research on material and failure models suitable for these steels has increased.In this work, the mechanical and fracture behaviour of two high-strength steels, Docol 600DP and Docol 1200M, have been studied under various deformation processes. Experimental results have been used both for material characterisation and for calibration of fracture criteria. One major requirement as concerns the fracture criteria studied is that they should be simple to apply in industrial applications, i.e. it should be possible to easily calibrate the fracture criteria in simple mechanical experiments and they should be efficient and accurate. Consequently, un-coupled phenomenological damage models have been the main focus throughout this work.Detailed finite element models including accurate constitutive laws have be used to predict and capture material instabilities. Most of the fracture criteria studied are modifications of the plastic work to fracture. Ductile tensile and ductile shear types of fracture are of particular interest in sheet metal applications. For these fractures the modification of the plastic work relates to void coalescence and void collapse, respectively. Anisotropy in fracture behaviour can be captured by the introduction of a material directional function.The dissertation consists of two parts. The first part contains theory and background. The second consists of five papers.
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| 3. |
- Björklund, Oscar, et al.
(författare)
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Failure characteristics of a dual-phase steel sheet
- 2014
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Ingår i: Journal of Materials Processing Technology. - : Elsevier. - 0924-0136 .- 1873-4774. ; 214, s. 1190-1204
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Tidskriftsartikel (refereegranskat)abstract
- Failure in ductile sheet metal structures is usually caused by one, or a combination of, ductile tensile fractures, ductile shear fractures or localised instability. In this paper the failure characteristics of the high strength steel Docol 600DP are explored. The study includes both experimental and numerical sections. In the experimental sections, the fracture surface of the sheet subjected to Nakajima tests is studied under the microscope with the aim of finding which failure mechanism causes the fracture. In the numerical sections, finite element (FE) simulations have been conducted using solid elements. From these simulations, local stresses and strains have been extracted and analysed with the aim of identifying the fracture dependency of the stress triaxiality and Lode parameter.
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| 4. |
- Björklund, Oscar, et al.
(författare)
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Failure of high strength steel sheets : Experiments and modelling
- 2013
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Ingår i: Journal of Materials Processing Technology. - : Elsevier BV. - 0924-0136 .- 1873-4774. ; 213:7, s. 1103-1117
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Tidskriftsartikel (refereegranskat)abstract
- Failure in sheet metal structures of ductile material is usually caused by one of, or a combination of, ductile fracture, shear fracture or localised instability. In this paper the failure of the high strength steel Docol 600DP and the ultra high strength steel Docol 1200M is explored. The constitutive model used in this study includes plastic anisotropy and mixed isotropic-kinematic hardening. For modelling of the ductile and shear fracture the models presented by Cockroft–Latham and Bressan–Williams have been used. The instability phenomenon is described by the constitutive law and the finite element (FE) models. For calibration of the failure models and validation of the results, an extensive experimental series has been conducted including shear tests, plane strain tests and Nakajima tests. The geometries of the Nakajima tests have been chosen so that the first quadrant of the forming limit diagram (FLD) were covered. The results are presented both in an FLD and using prediction of force–displacement response of the Nakajima test employing element erosion during the FE simulations. The classical approach for failure prediction is to compare the principal plastic strains obtained from FE simulations with experimental determined forming limit curves (FLCs). It is well known that the experimental FLC requires proportional strains to be useful. In this work failure criteria, both of the instability and fracture, are proposed which can be used also for non-proportional strain paths.
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| 5. |
- Björklund, Oscar
(författare)
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Modelling of Failure in High Strength Steel Sheets
- 2012
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- In this theses the high strength steel Docol 600DP and the ultra high strength steel Docol 1200M are studied. Constitutive laws and failure models are calibrated and veried by the use of experiments and numerical simulations. For the constitutive equations, an eight parameter high exponent yield surface has been adopted, representing the anisotropic behaviour, and a mixed isotropic-kinematic hardening has been used to capture non-linear strain paths.For ductile sheet metals three dierent failure phenomena have been observed: (i) ductile fracture, (ii) shear fracture, and (iii) instability with localised necking. The models for describing the dierent failure types have been chosen with an attempt to use just a few tests in addition to these used for the constitutive model. In this work the ductile and shear fracture have been prescribed by models presented by Cockroft-Latham and Bressan-Williams, respectively. The instability phenomenon is described by the constitutive law and the nite element models. The results obtained are in general in good agreement with test results.The thesis is divided into two main parts. The background, theoretical framework, mechanical experiments and nite element models are presented in the rst part. In the second part, two papers are appended.
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| 6. |
- Björklund, Oscar, et al.
(författare)
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Prediction of fracture in a dual-phase steel subjected to non-linear straining
- 2014
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Ingår i: Journal of Materials Processing Technology. - : Elsevier. - 0924-0136 .- 1873-4774. ; 214:11, s. 2748-2758
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Tidskriftsartikel (refereegranskat)abstract
- In this work, selected fracture criteria are applied to predict the fracture of dualphase steel subjected to non-linear strain paths. Furthermore, the effects of manufacturing history are studied. Four fracture criteria were calibrated in three tests using standard specimens. The fracture criteria were first validated in the circular Nakajima test. A second validation test case was included in order to validate fracture prediction for non-linear strain paths. In this test a sheet metal component was manufactured and subsequently stretched until it fractured. All fracture criteria included in this study predict fracture during the Nakajima test with reasonable accuracy. In the second validation test however, the different fracture criteria show considerable diversity in accumulated damage during manufacturing which caused substantial scatter of the fracture prediction in the subsequent stretching. This shows that manufacturing history influences the prediction of fracture.
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| 7. |
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| 8. |
- Franzen, Oscar, et al.
(författare)
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The Short Non-Coding Transcriptome of the Protozoan Parasite Trypanosoma cruzi
- 2011
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Ingår i: PLoS Neglected Tropical Diseases. - : Public Library of Science (PLoS). - 1935-2727 .- 1935-2735. ; 5:8, s. e1283-
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Tidskriftsartikel (refereegranskat)abstract
- The pathway for RNA interference is widespread in metazoans and participates in numerous cellular tasks, from gene silencing to chromatin remodeling and protection against retrotransposition. The unicellular eukaryote Trypanosoma cruzi is missing the canonical RNAi pathway and is unable to induce RNAi-related processes. To further understand alternative RNA pathways operating in this organism, we have performed deep sequencing and genome-wide analyses of a size-fractioned cDNA library (16-61 nt) from the epimastigote life stage. Deep sequencing generated 582,243 short sequences of which 91% could be aligned with the genome sequence. About 95-98% of the aligned data (depending on the haplotype) corresponded to small RNAs derived from tRNAs, rRNAs, snRNAs and snoRNAs. The largest class consisted of tRNA-derived small RNAs which primarily originated from the 3' end of tRNAs, followed by small RNAs derived from rRNA. The remaining sequences revealed the presence of 92 novel transcribed loci, of which 79 did not show homology to known RNA classes.
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| 9. |
- Frykholm, Oscar, et al.
(författare)
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Interaction design in a complex context : medical multi-disciplinary team meetings
- 2012
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Ingår i: The 7th Nordic Conference on Human-Computer Interaction: Making Sense Through Design. - New York, NY, USA : ACM. - 9781450314824 ; , s. 341-350
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Konferensbidrag (refereegranskat)abstract
- In order to improve collaboration on, and visualisation of, patient information in medical multi-disciplinary team meetings, we have developed a system that presents information from different medical systems to be used as a support for the decision process. Based on field studies, we have implemented a high-fidelity prototype on tablet-sized displays, and tested it in a realistic setting. Our evaluation proved that more patient information can efficiently be displayed to all meeting participants, compared to the current situation. Interaction with the information, on the other hand, proved to be a complicated activity that needs careful design considerations; it should ultimately be based on what roles the meeting participants have, and what tasks they should complete. Medical decision-making is a complex area, and conducting interaction design in this area proved complex too. We foresee a great opportunity to improve medical work, by introducing collaborative tools and visualisation of medical data, but it requires that interaction design becomes a natural part of medical work.
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| 10. |
- Hammarfjord, Oscar, et al.
(författare)
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Surgical treatment of recurring ameloblastoma, are there options?
- 2013
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Ingår i: British Journal of Oral & Maxillofacial Surgery. - : Elsevier BV. - 0266-4356 .- 1532-1940. ; 51:8, s. 762-766
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Tidskriftsartikel (refereegranskat)abstract
- Our aim was to evaluate the treatment given to patients with intraosseus ameloblastomas with special emphasis on recurrence and the outcomes of primary and secondary resection. Forty-eight patients who were treated for intraosseous ameloblastoma at 8 centres across Sweden met the inclusion criteria. They showed typical distribution of age, sex, site of lesion, and characteristic presenting features. Eleven of the 48 were initially treated with radical resection and none recurred. Twenty-two of the remaining 37 who were initially treated by conservative resection presented with recurrences. Sixteen of the 22 then had conservative secondary resections, which resulted in further recurrence in 6 patients. Initial radical resection is therefore superior to conservative management as far as recurrences are concerned. We argue, however, that a conservative surgical approach is adequate for many intraosseous ameloblastomas with limited extension, because relapse can be followed by radical resection if clinically indicated in selected cases.
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