| 1. |
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| 2. |
- Frómeta, David, et al.
(författare)
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Fracture Toughness Evaluation of Thick Press Hardened 22MnB5 Sheets for High Crash Performance Applications in Trucks
- 2019
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Ingår i: Hot sheet metal forming of high-performance steel. - : Wissenschaftliche Scripten. ; , s. 113-121
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Konferensbidrag (refereegranskat)abstract
- The present work investigates the fracture toughness of a thick press hardened 22MnB5 steel sheet, in order to assess its applicability for truck safety parts. The fracture toughness is evaluated in the frame of the elastic plastic fracture mechanics (EPFM), in terms of essential work if fracture (EWF) and J-integral. Digital Image Correlation (DIC) measuring techniques are used to measure crack tip opening displacement and crack extension. It is shown that EWF presents some limitations for thick high strength metal sheet applications, making necessary the use of conventional EPFM procedures. Digital image analysis has shown to be very useful in fracture toughness characterization of thick press hardened steel sheets. The differences observed between different methodologies are discussed and results are compared to toughness values of different AHSS grades.
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| 3. |
- Gustafsson, David
(författare)
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Effect of shear cutting on metal fatigue
- 2024
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Lightweighting of automotive and heavy-duty vehicle components is an important task that does not need any further motivation or background. It can be read in a large part of the technical papers in the field. A common approach for finding lighter solutions is to increase the material grade while decreasing the material thickness. Often in combination with design changes. For perfectly smooth components this is not an issue, but when cut edges from manufacturing processes are present the situation changes. One topic to address is that increased material grade often means increased notch and surface damage sensitivity. This has implications both on forming and fatigue. The reason for selecting a higher strength material is to allow for higher stresses in design. It has however been shown that for a given stress level the fatigue performance of a higher strength material could be worse than for a lower strength counterpart if punched holes or trimmed edges are present. This means that in the search of lower weight there is a risk of increasing stresses, and at the same time selecting a material that is less suited to handle this increase. Hence, engineers and developers are put in a position where these effects must be quantified to find the most efficient solution. This quantification is a cumbersome and expensive task, often including a considerable amount of testing. Important sources of fatigue life reduction in this context are the residual stresses in the loading direction and the surface roughness in the cut edge. This thesis aims to present an overview of metal fatigue in the context of shear cut components. Necessary knowledge regarding the shear cutting process is provided along with a description of numerical methods and considerations for process simulations. These findings are then applied to the presented papers where the first introduces a simplified approach for numerical simulation of shear cutting to obtain residual stresses. In this approach the simplification mainly lies in the failure model calibration. The second paper studies the possibility of using the obtained residual stresses together with measured values of surface roughness to quantify fatigue life reduction of shear cut specimens.
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| 4. |
- Heshmati, Nader, et al.
(författare)
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Correlation between microstructure and fatigue properties of hot-rolled thick-plate complex-phase steel
- 2023
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Ingår i: Materials Science & Engineering. - : Elsevier BV. - 0921-5093 .- 1873-4936. ; 885
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Tidskriftsartikel (refereegranskat)abstract
- Complex-phase (CP) steels, with a multiphase microstructure, offer an excellent combination of high strength, ductility, and formability, making them an attractive alternative to conventional high-strength low-alloy (HSLA) steels in the automotive industry. However, the microstructure and fatigue property relation in CP steels is complex. This limits the full exploitation of CP steels in applications, such as heavy-vehicles, where excellent fatigue performance of thick-plates after punching holes is the critical parameter. In this work, we initiate the study of the relation between microstructure and fatigue properties of a commercial CP steel (800CP) and compare it with a conventional HSLA (500MC) steel. Fatigue property, tensile property, and fatigue crack growth rate (FCGR) testing are conducted and the performance of the two steels is rationalized using detailed microstructure characterization, before and after fatigue testing. FCGR testing shows that, despite a higher yield strength of the 800CP, both steels have a similar propagation rate due to a more tortuous crack propagation path and a higher quantity of secondary crack formation in the 800CP microstructure. The high cycle fatigue (HCF) testing shows that the fatigue limit in the 800CP is 25% higher. This increase in fatigue limit is attributed to the improved resistance to fatigue crack initiation in the 800CP due to its larger fraction of bainite.
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| 5. |
- Parareda, Sergi, et al.
(författare)
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Understanding the Fatigue Notch Sensitivity of High-Strength Steels through Fracture Toughness
- 2023
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Ingår i: Metals. - : MDPI. - 2075-4701. ; 13:6
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Tidskriftsartikel (refereegranskat)abstract
- This study presents an innovative approach for selecting high-strength materials for fatigue dimensioning parts, considering both fracture toughness and fatigue performance. Warm and hot forming processes enable the construction of high-strength parts above 1000 MPa with complex geometries, making them suitable for lightweight chassis in automotive and freight applications. This research reveals that high-strength steels can experience up to a 40% reduction in fatigue performance due to manufacturing defects introduced during punching and trimming. Fracture toughness has been proposed as a good indicator of notch sensitivity, with a strong correlation of 0.83 between fracture toughness and fatigue notch sensitivity. Therefore, by combining fracture toughness measurements and fatigue resistance obtained through the rapid fatigue test, it becomes possible to quickly identify the most fatigue-resistant materials to deal with defects. Among the nine materials analysed, warm-formed steels show promising characteristics for lightweight chassis construction, with high fatigue resistance and fracture toughness exceeding the proposed fracture threshold of 250 kJ/m2.
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| 6. |
- Parareda, Sergi, et al.
(författare)
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Warm Forming of Hot Rolled High Strength Steels with Enhanced Fatigue Resistance as a Lightweight Solution for Heavy Duty Vehicles
- 2022
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Ingår i: Hot Sheet Metal Forming of High-Performance Steel: proceedings. - : Wissenschaftliche Scripten.
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Konferensbidrag (refereegranskat)abstract
- Most solutions for a lightweight design are based on the implementation of AHSS, Al alloys or CFRP. However, not all these strategies are susceptible to be applied to truck chassis parts. These components require high fatigue resistance and thick sheets. Additionally, they are usually trimmed and punched, which is known to affect fatigue resistance. This work addresses the lightweight con-struction of truck parts through the warm forming of steel grades tailored to show high formability and fatigue behaviour. The fatigue limit was evaluated for different edge conditions (polished and punched) and rationalized using the cracking resistance described by fracture toughness. The con-sideration of both mechanical properties, fatigue, and fracture toughness, gives an innovative and useful tool to develop and select materials for fatigue dimensioned parts.
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| 7. |
- Pilhagen, Johan, et al.
(författare)
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Fracture toughness of a welded super duplex stainless steel
- 2014
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Ingår i: Materials Science & Engineering. - : Elsevier BV. - 0921-5093 .- 1873-4936. ; 606, s. 40-45
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Tidskriftsartikel (refereegranskat)abstract
- Fracture toughness testing was conducted on standard single-edge notched bend bar specimens of base and weld metal. The material was the SAF 2906 super duplex stainless steel. The aim was to evaluate the susceptibility for brittle failure at sub-zero temperatures for the base and weld metal. The base metal was tested between -103 and -60. °C and was evaluated according to the crack-tip opening displacement method. The fracture event at and below -80. °C can be described as ductile until critical cleavage initiation occurs, which caused unstable failure of the specimen. The welding method used was submerged arc welding with a 7. wt% nickel filler metal. The welded specimens were post-weld heat treated (PWHT) at 1100. °C for 20. min and then quenched. Energy-dispersive X-ray spectroscopy analysis showed that during PWHT substitutional element partitioning occurred which resulted in decreased nickel content in the ferrite. The PWHT weld metal specimens were tested at -72. °C. The fracture sequence was critical cleavage fracture initiation after minor crack-tip blunting and ductile fracture.
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| 8. |
- Sandström, Rolf, et al.
(författare)
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Analysis of the brittle fracture avoidance model for pressure vessels in European standard
- 2005
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Ingår i: International Journal of Pressure Vessels and Piping. - : Elsevier BV. - 0308-0161 .- 1879-3541. ; 82:11, s. 872-881
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Tidskriftsartikel (refereegranskat)abstract
- A procedure for design against brittle failure based on a fracture mechanics model is available in the recent European pressure vessel standard EN 13 445. In the present paper, this model is analysed in the light of more recent findings in fracture mechanics. In particular, results from the SINTAP project and the Eurocode 3 procedure for selection of steel to avoid brittle fracture are considered. Alternative models for the scatter in strength, fracture toughness-impact toughness correlations as well as their temperature dependence, thickness dependence and strain rate dependence are compared. Different approaches for the handling of residual stresses are discussed. When the effect of clasto-plastic corrections is taken into account both for primary and secondary stresses, the net effect is small. In relation to more recent findings, the models used as a basis for EN 13 445 seem somewhat conservative, in particular for thinner gauges.
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| 9. |
- Sandström, Rolf, et al.
(författare)
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New brittle fracture model for the European pressure vessel standard
- 2004
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Ingår i: International Journal of Pressure Vessels and Piping. - : Elsevier BV. - 0308-0161 .- 1879-3541. ; 81:11-okt, s. 837-845
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Tidskriftsartikel (refereegranskat)abstract
- A model for design against brittle failure based on recent fracture mechanics findings is proposed. The procedure is an update of that in the recent European pressure vessel standard EN 13445. The thickness dependence of the maximum permissible crack has been analysed with the help of research on non-destructive testing. Cracks with a quarter thickness depth are assumed to be readily detectable for larger gauges. For thinner gauges the cracks have to cover a larger fraction of the thickness to be safely observed. The model is verified by comparison to fracture mechanics test data for high strength steels. Results from individual wide plate tests are successfully reproduced by the model. Furthermore, T-100 values (the temperature where K-JC=100 MPa m(1/2) for test series are conservatively predicted by the model. The model adequately describes the influence of thickness and heat treatment on the T-100()() values.
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| 10. |
- Sieurin, Henrik, et al.
(författare)
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Austenite reformation in the heat-affected zone of duplex stainless steel 2205
- 2006
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Ingår i: Materials Science & Engineering. - : Elsevier BV. - 0921-5093 .- 1873-4936. ; 418:1-2, s. 250-256
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Tidskriftsartikel (refereegranskat)abstract
- The aim of the present work was to evaluate the amount of reformed austenite in the heat-affected zone (HAZ) of submerged arc welded (SAW) duplex stainless steel 2205. The model is based on calculations of the nucleation and growth of austenite. The present results are compared with other studies to evaluate the toughness properties and the probability of precipitation of brittle, intermetallic sigma phase. The results indicate that cooling the weld in air provides a satisfactory amount of reformed austenite and prevents formation of sigma phase.
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