| 1. |
- Caballero, Francisca G., et al.
(author)
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Advanced Heat Treatments and Complex Ferritic Structures for Bearing Steels
- 2019
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In: Metals. - : MDPI. - 2075-4701. ; 9:11
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Journal article (peer-reviewed)abstract
- Nanostructured bainitic steels exhibit an optimum strength/toughness combination as a consequence of their extremely fine structure. They have also demonstrated potential for wear-resistance applications. The aim of this work was to develop bearing steels by the multi-scale control of complex ferritic structures, designed using atomic transformation theory and processed by novel heat treatments. Based on the results, the new ball bearings outperformed conventional grades, approaching more expensive material options.
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| 2. |
- Frómeta, David, et al.
(author)
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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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In: Hot sheet metal forming of high-performance steel. - : Wissenschaftliche Scripten. ; , s. 113-121
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Conference paper (peer-reviewed)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. |
- Garcia-Llamas, Eduard, et al.
(author)
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Optimization of Thick 22MnB5 Sheet Steel Part Performance through Laser Tempering
- 2023
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In: Metals. - : MDPI. - 2075-4701. ; 13:2
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Journal article (peer-reviewed)abstract
- Press Hardening offers the possibility to obtain a wide range of mechanical properties through microstructural tailoring. This strategy has been successfully applied in thin sheet components, for instance, through differential cooling strategies. The application of these added value features to truck components implies adapting the process to the manufacture of thick sheet metal. This introduces an additional layer of complexity, but also opportunity, in a process where the final microstructure and, thus the mechanical performance is generated in the press shop. This work presents a study on optimizing the crash worthiness and impact energy absorption on a press hardened thick 22MnB5 steel sheet. Different microstructure design strategies have been studied, including ferrite-Pearlite (representative of a differential heating and austenitization strategy), in-die generated Bainite (representative of differential cooling) and Tempered Martensite (generated through laser tempering), keeping a fully hardened martensite as a reference condition. The material performance has been compared in terms of the monotonic properties, useful for anti-intrusion performance, and Essential Work of Fracture, a well-suited parameter to predict the crash failure behavior of high strength steels. The results show that laser tempering offers properties similar to Bainite-based microstructures and can be a successful replacement in components where the sheet thickness does not allow for the fine control of the in-die thermomechanical evolution.
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| 4. |
- Latorre, Núria, et al.
(author)
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Forming of mechanically interlocked aluminium and carbon fibre reinforced polymer parts with complex geometry
- 2024
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In: Material Forming - ESAFORM 2024. - : Materials Research Forum LLC. ; , s. 1640-1649
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Conference paper (peer-reviewed)abstract
- Forming of aluminium-CFRP hybrid structures into complex shapes is key to decrease environmental impact in automotive industry. However, challenges such as preserving joint integrity after forming operations must be assessed. Therefore, the authors of this work have cold stamped hybrid aluminium-CFRP panels into omega shaped profiles with and without a mechanical interlocking joining technology. The effect of lubricant application, of the CFRP positioning (inside or outside the omega profile), and of the number of mechanical joints were studied. It was concluded that it is possible to cold stamp aluminium-CFRP prepreg panels even with mechanical joints into complex profiles when lubricant is used. Moreover, the position of the CFRP prepreg has a strong impact on the flange springback of the stamped part.
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| 5. |
- Parareda, Sergi, et al.
(author)
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Fatigue resistance of press hardened 22MnB5 steels
- 2020
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In: International Journal of Fatigue. - : Elsevier. - 0142-1123 .- 1879-3452. ; 130
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Journal article (peer-reviewed)abstract
- In press hardened steels, fatigue behaviour is very sensitive to surface defects or irregularities, either intrinsic or introduced during trimming operations. This work addresses the understanding and prediction of fatigue resistance of press hardened steels from a fracture mechanics approach. The size of fatigue originating defects were evaluated and used to estimate the fatigue limit for different surface conditions (coated and uncoated), different coatings (Al-Si and Zn) and different edge condition (polished and mechanically trimmed). Good agreement was found between calculated and experimental values, which shows the potential of fracture mechanics to estimate the fatigue performance of press hardened steels.
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| 6. |
- Parareda, Sergi, et al.
(author)
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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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In: Hot Sheet Metal Forming of High-Performance Steel: proceedings. - : Wissenschaftliche Scripten.
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Conference paper (peer-reviewed)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. |
- Pujante, Jaume, et al.
(author)
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Hot Stamped Aluminium for Crash-Resistant Automobile Safety Cage Applications
- 2021
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In: Materials Science Forum. - : Trans Tech Publications. - 0255-5476 .- 1662-9752. ; 1016, s. 445-452
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Journal article (peer-reviewed)abstract
- Hot stamping, also known as press hardening in the context of sheet steel, has steadily gained relevance in the automotive industry, starting off as a specialist application and turning into a staple technique in the production of safety cage products in little more than a decade. However, despite the weight reduction offered by martensitic steels, further improvement could be obtained by substituting these components by high-performance aluminium. In this regard, the very same process of hot stamping could be employed to attain the required combination of shape complexity and mechanical properties at a reasonable cost for mass-market application, if the limitations imposed by cycle time and process window could be overcome. In this work, the feasibility of hot stamping of 6000-series aluminium alloy sheet is studied, first in dilatometry experiments and later in semi-industrial conditions in a pilot facility. A cycle time shortening strategy is employed, and compared to the conventional thermal cycle in terms of implementation and obtained results. In addition to basic characterization, aluminium thus processed is studied in terms of fracture toughness, in order to obtain data relevant to crashworthiness that can be readily compared with alternative materials.
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| 8. |
- Pujante, Jaume, et al.
(author)
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Investigations into wear and galling mechanism of aluminium alloy-tool steel tribopair at different temperatures
- 2012
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In: 15th Nordic Symposium on Tribology - NordTrib 2012. - Trondheim : Department of Geography, Norwegian University of Science and Technology.
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Conference paper (peer-reviewed)abstract
- Aluminium-based alloys present a number of interesting properties, such as lower density, corrosion resistance, thermal and electrical conductivity and good recyclability. For this reason, there is a strong trend in increasing the use of these alloys, particularly in the automotive industry [1, 2]. However, aluminium alloys show poor formability at room temperature, and the production of complex components requires a series of high temperature forming processes, such as warm and hot forging, extrusion and hot sheet metal forming [3]. Forming aluminium in these conditions subjects the tools to severe adhesive wear and galling, leading to increased energy needs, shorter tool life, lower part quality and increased cost.In this work, the wear mechanisms generated by aluminium alloys on forming tools have been studied by means of linear reciprocating sliding tests, performed in an Optimol SRV equipment. Balls of two different compositions (AA2017 and 99% pure aluminium) were slid against DIN 1.2344 (AISI H13) tool steel samples with various surface finishes at temperatures up to 450 ºC. The resulting wear tracks were studied by means of confocal microscopy and electron microscopy (SEM/BSE).The main results show that the observed wear mechanisms are extremely dependent on the system temperature, ranging from pure abrasive wear to formation of layers of compacted aluminium debris and gross aluminium transfer in the form of lumps. The choice of aluminium alloy can be very relevant on the wear behaviour of the system. On the other hand, tool surface finish has a limited effect on material transfer. [1] Miller W S, et al. Recent development of aluminium alloys for the automotive industry. Materials Science and Engineering A 280 (2000), pp 37-49 [2] Toros S, Ozturk F, Kacar I. Review of warm forming of aluminium-magnesium alloys. Journal of Materials Processing Technology 207 (2008), pp 1-12[3] Hanna M D. Tribological evaluation of aluminium and magnesium sheet forming at high temperatures. Wear 267 (2009), pp 1046-1050
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| 9. |
- Pujante, Jaume, et al.
(author)
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Wear Mechanisms in Press Hardening: An Analysis through Comparison of Tribological Tests and Industrial Tools
- 2023
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In: Lubricants. - : MDPI. - 2075-4442. ; 11:5
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Journal article (peer-reviewed)abstract
- Press hardened components have become widespread in the automotive industry in structural and crash-resistant applications, thanks to the combination of the complex shapes and high mechanical properties obtained. However, the press hardening of coated boron steel results in severe adhesive-based wear, with tool maintenance being required in as few as 3000 cycles. The current industrial implementation of press hardening is defined to work around this phenomenon. While this aspect has been studied by different authors, most of the literature deals with laboratory-scale tribosimulators, leaving an open question into how this knowledge transfers to macroscopic effects on the industrial process. In this work, wear in press hardening is studied by comparing the results obtained in laboratory conditions with a pilot-scale line, and finally, with wear mechanisms observed on industrial tools. The aim of this study is to consolidate the current knowledge about the micro-mechanisms involved, and to understand to what extent the existing tests reproduce the actual mechanisms observed in the press floor. The results show how material transfer mainly happens as an accumulation of dust compacted into initial defects on the tool surface. Moreover, this mechanism is effectively reproduced in laboratory tribosimulators and pilot environments, showing a similar morphology to wear on industrial tools. The work sheds light on the underlying causes of wear, and its potential mitigation strategies.
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