| 1. |
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| 2. |
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| 3. |
- Casellas, Daniel, et al.
(författare)
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A fracture mechanics approach to develop high crash resistant microstructures by press hardening
- 2017
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Ingår i: 6th International Conference Hot Sheet Metal Forming of High-Performance Steel CHS2. - Warrendale, PA : Association for Iron & Steel Technology, AIST. - 9781935117667 ; , s. 101-107
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Konferensbidrag (refereegranskat)abstract
- Crashworthiness is a relevant engineering property for car parts. However it is not easy to measure at laboratory scale and complex impact tests have to be carried out to determine it. Crash resistance for high strength steel is commonly evaluated in terms of cracking pattern and energy absorption in crashed specimens. Accordingly, the material resistance to crack propagation, i.e. the fracture toughness, could be used to rank crashworthiness. It has been proved in a previous work by the authors, so the measure of fracture toughness, in the frame of fracture mechanics in small laboratory specimens, would allow determining the best microstructure for crash resistance parts. Press hardening offers the possibility to obtain a wide range of microstructural configurations, with different mechanical properties. So the aim of this work is to evaluate the fracture toughness following the essential work of fracture methodology for ferrite-pearlite, bainite, ferrite-bainite, martensite and martensite-bainite microstructures. Results showed that bainitic microstructures have high fracture toughness, similar to TWIP and CP steels, which allows pointing them as potential candidates for obtaining high crash resistance in parts manufactured by press hardening.
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| 4. |
- Casellas, Daniel, et al.
(författare)
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Fracture resistance of tailor tempered microstructures obtained by different press hardening conditions
- 2015
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Ingår i: Hot Sheet Metal Forming of High-Performance Steel 5th International Conference. - Auerbach : Verlag Wissenschaftliche Scripten. - 9783957350237 ; , s. 221-229
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Konferensbidrag (refereegranskat)abstract
- Tailored tempering can produce different amounts of martensite, upper and lower bainite and ferrite depending on the press hardening conditions are usually obtained. The tensile properties of such microstructures are quite well known, but the intrinsic fracture properties, as fracture toughness, have not yet been characterized. This is mainly related the experimental difficulty to measure fracture toughness in thin sheets. Recently, the authors have proposed to measure it through the application of the Essential Work of Fracture methodology. The knowledge of facture toughness would give valuable information to increase their applicability in automotive components and would also allow a further understanding of fracture and crack propagation mechanisms in B steel hardened at different cooling conditions. Thus the aim of this paper is to determine the fracture toughness in microstructures of a 22MnB5 steels obtained by tailored tempering. Results indicate that the EWF methodology can be applied to measure fracture toughness and the energy for crack initiation in ferrite-pearlite and ferrite-bainite microstructures. Fracture initiation energy is the same in ferrite-pearlite and ferrite-bainite microstructures, which will indicate that ferrite has a clear effect on fracture initiation. Moreover, fractography results reveal the effect of inclusion content on fracture energies
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| 5. |
- Casellas, Daniel, et al.
(författare)
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Fracture Toughness to Understand Stretch-Flangeability and Edge Cracking Resistance in AHSS
- 2017
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Ingår i: Metallurgical and Materials Transactions. A. - : Springer. - 1073-5623 .- 1543-1940. ; 48A:1, s. 86-94
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Tidskriftsartikel (refereegranskat)abstract
- The edge fracture is considered as a high risk for automotive parts, especially for parts made of advanced high strength steels (AHSS). The limited ductility of AHSS makes them more sensitive to the edge damage. The traditional approaches, such as those based on ductility measurements or forming limit diagrams, are unable to predict this type of fractures. Thus, stretch-flangeability has become an important formability parameter in addition to tensile and formability properties. The damage induced in sheared edges in AHSS parts affects stretch-flangeability, because the generated microcracks propagate from the edge. Accordingly, a fracture mechanics approach may be followed to characterize the crack propagation resistance. With this aim, this work addresses the applicability of fracture toughness as a tool to understand crack-related problems, as stretch-flangeability and edge cracking, in different AHSS grades. Fracture toughness was determined by following the essential work of fracture methodology and stretch-flangeability was characterized by means of hole expansions tests. Results show a good correlation between stretch-flangeability and fracture toughness. It allows postulating fracture toughness, measured by the essential work of fracture methodology, as a key material property to rationalize crack propagation phenomena in AHSS.
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| 6. |
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| 7. |
- Crescenti, Marc, et al.
(författare)
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The continuous fibre injection process (CFIP): A novel approach to lightweight design of multi-material structural components
- 2024
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Ingår i: Material Forming - ESAFORM 2024. - : Materials Research Forum LLC. ; , s. 1630-1639
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Konferensbidrag (refereegranskat)abstract
- The combination of different materials enables to achieve highly efficient structures in terms of lightweight and mechanical performance, as well as in terms of manufacturing costs. However, the weakest points of these structures use to be the joints. For this reason, in the last years, many studies have dealt with joining technologies for dissimilar materials. The Reinforce3D’s Continuous Fibre Injection Process (CFIP) technology delivers a unique method to join dissimilar materials. CFIP is based on injecting continuous fibers, such as carbon fibers, simultaneously with liquid resin into tubular cavities within the part. Then the resin is cured and the final composite part is obtained. This work focuses on the characterization of the mechanical properties of CFIP-made specimens and describes the potential lightweight benefits of the technology. Mechanical tests were performed under tensile and bending conditions following standardized methods. The lightweight potential is addressed by developing a representative case study by implementing finite element and topology optimization methods. The results of this case study were finally compared with a monomaterial equivalent component (aluminium) demonstrating the improvement that CFIP provides in terms of lightweight while keeping the strength.
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| 8. |
- Frómeta, D., et al.
(författare)
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A new cracking resistance index based on fracture mechanics for high strength sheet metal ranking
- 2021
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Konferensbidrag (refereegranskat)abstract
- Driven by current safety and weight reduction policies in the automotive sector, the development of new high strength sheet metal products has experienced unprecedented growth in the last years. With the emergence of these high strength materials, new challenges related to their limited ductility and higher cracking susceptibility have also raised. Accordingly, the development of new fracture criteria accounting for the material's cracking resistance has become unavoidable. In this work, a new cracking resistance index (CRI) based on fracture mechanics is proposed to classify the crack propagation resistance (i.e. the fracture toughness) of high strength metal sheets. The index is based on the fracture energy obtained from tensile tests with sharp-notched specimens. The procedure is very fast and simple, comparable to a conventional tensile test, and it may be used as routine testing for quality control and material selection. The CRI is investigated for several advanced high strength steel (AHSS) sheets of 0.8-1.6 mm thickness with tensile strengths between 800 and 1800 MPa. The results show that the proposed index is suitable to rank high strength steel sheets according to their crack propagation resistance and it can be correlated to the material's crashworthiness and edge cracking resistance.
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| 9. |
- Frómeta, D., et al.
(författare)
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Assessing edge cracking resistance in AHSS automotive parts by the Essential Work of Fracture methodology
- 2017
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Ingår i: Journal of Physics, Conference Series. - : Institute of Physics (IOP). - 1742-6588 .- 1742-6596. ; 896
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Tidskriftsartikel (refereegranskat)abstract
- Lightweight designs and demanding safety requirements in automotive industry areincreasingly promoting the use of Advanced High Strength Steel (AHSS) sheets. Such steelspresent higher strength (above 800 MPa) but lower ductility than conventional steels. Their greatproperties allow the reduction of the thickness of automobile structural components withoutcompromising the safety, but also introduce new challenges to parts manufacturers. Thefabrication of most cold formed components starts from shear cut blanks and, due to the lowerductility of AHSS, edge cracking problems can appear during forming operations, forcing thestop of the production and slowing down the industrial process.Forming Limit Diagrams (FLD) and FEM simulations are very useful tools to predict fractureproblems in zones with high localized strain, but they are not able to predict edge cracking. Ithas been observed that the fracture toughness, measured through the Essential Work of Fracture(EWF) methodology, is a good indicator of the stretch flangeability in AHSS and can help toforesee this type of fractures.In this work, a serial production automotive component has been studied. The componentshowed cracks in some flanged edges when using a dual phase steel. It is shown that theconventional approach to explain formability, based on tensile tests and FLD, fails in theprediction of edge cracking. A new approach, based on fracture mechanics, help to solve theproblem by selecting steel grades with higher fracture toughness, measured by means of EWF.Results confirmed that fracture toughness, in terms of EWF, can be readily used as a materialparameter to rationalize cracking related problems and select AHSS with improved edgecracking resistance.
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| 10. |
- Frómeta, D., et al.
(författare)
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Evaluation of edge formability in high strength sheets through a fracture mechanics approach
- 2019
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Ingår i: Proceedings of the 22nd International ESAFORM Conference on Material Forming. - : American Institute of Physics (AIP).
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Konferensbidrag (refereegranskat)abstract
- Edge fracture prediction in high strength cold formed components still being a challenge for automotive part manufacturers. Even though several experimental methodologies have been proposed in the last years to assess edge formability, the material properties governing edge cracking sensitivity of high strength sheet materials are not clearly defined. This work investigates the correlation between the fracture toughness of various 1000 MPa Dual Phase and Complex Phase steel grades and their edge fracture resistance, evaluated by means of hole expansion tests according to ISO 16630. The good linear correlation observed between these parameters shows that fracture toughness is a reliable indicator of edge cracking resistance in advanced high strength steel sheets. However, it is well known that edge formability does not only depends on the material properties but also on the edge quality. In order to evaluate the effect of the edge condition on edge formability, additional hole tension tests are performed in some of the investigated steel grades with different punch to die clearances. It is shown that steels with greater fracture toughness present higher strain at fracture and lower cutting clearance sensitivity. According to these results, the fracture toughness is proposed as a relevant material property to understand the edge formability of high strength metal sheets.
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| 11. |
- Frómeta, D., et al.
(författare)
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Fracture Resistance of Advanced High-Strength Steel Sheets for Automotive Applications
- 2021
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Ingår i: Metallurgical and Materials Transactions. A. - : Springer. - 1073-5623 .- 1543-1940. ; 52:2, s. 840-856
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Tidskriftsartikel (refereegranskat)abstract
- The fracture resistance of different advanced high-strength steel (AHSS) sheets for automotive applications is investigated through conventional tensile tests, fracture toughness measurements, and hole expansion tests. Different fracture-related parameters, such as the true fracture strain (TFS), the true thickness strain (TTS), the fracture toughness at crack initiation (wie), the specific essential work of fracture (we), and the hole expansion ratio (HER), are assessed. The specific essential work of fracture (we) is shown to be a suitable parameter to evaluate the local formability and fracture resistance of AHSS. The results reveal that fracture toughness cannot be estimated from any of the parameters derived from tensile tests and show the importance of microstructural features on crack propagation resistance. Based on the relation fracture toughness-local formability, a new AHSS classification mapping accounting for global formability and cracking resistance is proposed. Furthermore, a physically motivated fracture criterion for edge-cracking prediction, based on thickness strain measurements in fatigue pre-cracked DENT specimens, is proposed.
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| 12. |
- 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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| 13. |
- Frómeta, D., et al.
(författare)
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Fracture toughness measurements to understand local ductility of advanced high strength steels
- 2019
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Ingår i: 38 th International Deep Drawing Research Group Conference. - : Institute of Physics (IOP).
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Konferensbidrag (refereegranskat)abstract
- The determination of the material parameters that best predict the local ductility of high strength sheet materials has become the focus of active research. Even though several correlations have been proposed, they can sometimes be not accurate enough and discussion is still open on this topic. This paper investigates the suitability of different fracture toughness measurements for local ductility prediction in multiple advanced high strength steels (AHSS). Fracture toughness is characterized by means of essential work of fracture and Khan tear tests. The results show that the essential work of fracture, we, correlates well with different local formability (HER, critical bending angle from V-bending tests and local strain at fracture from uniaxial tensile tests) and crash resistance parameters (energy absorbed in axial impact tests). It confirms that fracture toughness, measured in the frame of fracture mechanics, is a relevant material property to rationalize cracking issues associated to the local ductility of AHSS. On the other hand, it is also shown that Khan tear tests, which are conventionally used to evaluate the fracture resistance of thin metal sheets, can overestimate crack propagation resistance and offer a poor prediction ability for local formability and crash performance.
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| 14. |
- Frómeta, D., et al.
(författare)
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Identification of fracture toughness parameters to understand the fracture resistance of advanced high strength sheet steels
- 2020
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Ingår i: Engineering Fracture Mechanics. - : Elsevier. - 0013-7944 .- 1873-7315. ; 229
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Tidskriftsartikel (refereegranskat)abstract
- The fracture toughness of four advanced high strength steel (AHSS) thin sheets is evaluated through different characterization methodologies, with the aim of identifying the most relevant toughness parameters to describe their fracture resistance. The investigated steels are: a Complex Phase steel, a Dual Phase steel, a Trip-Aided Bainitic Ferritic steel and a Quenching and Partitioning steel. Their crack initiation and propagation resistance is assessed by means of J-integral measurements, essential work of fracture tests and Kahn-type tear tests. The results obtained from the different methodologies are compared and discussed, and the influence of different parameters such as specimen geometry or notch radius is investigated. Crack initiation resistance parameters are shown to be independent of the specimen geometry and the testing method. However, significant differences are found in the crack propagation resistance values. The results show that, when there is a significant energetic contribution from necking during crack propagation, the specific essential work of fracture (we) better describes the overall fracture resistance of thin AHSS sheets than JC. In contrast, energy values obtained from tear tests overestimate the crack propagation resistance and provide a poor estimation of AHSS fracture performance. we is concluded to be the most suitable parameter to describe the global fracture behaviour of AHSS sheets and it is presented as a key property for new material design and optimization.
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| 15. |
- Frómeta, D., et al.
(författare)
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Microstructural effects on fracture toughness of ultra-high strength dual phase sheet steels
- 2021
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Ingår i: Materials Science & Engineering. - : Elsevier. - 0921-5093 .- 1873-4936. ; 802
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Tidskriftsartikel (refereegranskat)abstract
- The influence of microstructure on the fracture toughness of two industrially processed 1000 MPa dual-phase (DP) steel grades is investigated. Crack initiation and propagation resistance are evaluated by means of the essential work of fracture (EWF) methodology and the main damage and fracture mechanisms are investigated. The results are discussed in terms of the proportion and distribution of the different microstructural constituents, which is assessed by scanning electron microscopy (SEM), high-resolution electron backscatter diffraction (HR-EBSD) and nanoindentation hardness measurements. The investigations show that the strain-induced transformation of retained austenite to martensite (TRIP effect), may be detrimental to cracking resistance, even though it increases tensile properties. This phenomenon is attributed to a “brittle†network effect generated by the presence of hard fresh martensite islands in the fracture process zone. The connectivity of the hard secondary phases and the proportion of soft phase (ferrite) also have a major role in fracture toughness. The DP steel with the larger volume fraction of ferrite and homogeneously distributed martensite islands shows significantly higher crack propagation resistance. The contribution of necking to the ductile fracture process is evaluated by means of thickness measurements in fractured DENT specimens and the correlation between the specific essential work of fracture (we) and tensile properties is investigated. It is concluded that the global formability and cracking resistance of high strength DP steels can be balanced through microstructural tailoring. © 2020 The Author(s)
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| 16. |
- Frómeta, D., et al.
(författare)
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New tool to evaluate the fracture resistance of thin high strength metal sheets
- 2020
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Ingår i: International Deep-Drawing Research Group (IDDRG 2020) 26-30 October 2020, Seoul, South Korea. - : Institute of Physics (IOP).
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Konferensbidrag (refereegranskat)abstract
- Fracture toughness has become a key property to predict the fracture performance of high strength metal sheets (edge cracking resistance, crash failure behaviour, local formability, etc.). However, the measurement of the fracture toughness of thin sheets still being challenging, mainly because of complex, expensive and time-consuming specimen preparation. In this work, an innovative tool to readily assess the fracture resistance of thin advanced high strength metal sheets is presented. The device consists of a special cutting tool (punch and die) designed to introduce sharp notches in sheet specimens through a simple shearing process. This new method avoids the need for fatigue pre-cracking procedures and allows measuring the fracture toughness of thin metal sheets with easy and cheap specimen preparation. It has been used in this work to evaluate the crack propagation resistance of four different advanced high strength steel sheets. The obtained toughness values are in good agreement with those measured with fatigue pre-cracked specimens and they show to be suitable to predict edge formability of AHSS sheets.
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| 17. |
- Frómeta, D., et al.
(författare)
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On the correlation between fracture toughness and crash resistance of advanced high strength steels
- 2019
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Ingår i: Engineering Fracture Mechanics. - : Elsevier. - 0013-7944 .- 1873-7315. ; 205, s. 319-332
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Tidskriftsartikel (refereegranskat)abstract
- Automotive industry players have devoted large efforts to identify the material parameters governing the crash resistance of Advanced High Strength Steels (AHSS). Such knowledge is essential to improve impact performance prediction and optimize new steel development. Nevertheless, there is still an open discussion about which are the most relevant properties on AHSS crashworthiness. In this work, the authors investigate the correlation between the fracture toughness of different AHSS and their crash failure behaviour. Fracture toughness is measured in the frame of fracture mechanics, through the essential work of fracture methodology. Two fracture resistance parameters are characterized: the fracture toughness at cracking initiation, wei, and the essential work of fracture, we. Toughness values are compared with the results of axial impact tests, which are evaluated according to the energy absorbed and the cracking behaviour observed in crash boxes. Results show that fracture toughness permits to describe different crash events in terms of crack initiation and crack propagation and allows ranking AHSS impact resistance; steels with higher we present better crash performance. Therefore, fracture toughness is proposed as a key material property to predict the crash resistance of AHSS and as a relevant design parameter for crash resistant parts.
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| 18. |
- Garcia-Llamas, Eduard, et al.
(författare)
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Optimization of Thick 22MnB5 Sheet Steel Part Performance through Laser Tempering
- 2023
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Ingår i: Metals. - : MDPI. - 2075-4701. ; 13:2
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Tidskriftsartikel (refereegranskat)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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| 19. |
- Golling, Stefan, et al.
(författare)
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Determination of the essential work of fracture at high strain rates
- 2017
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Ingår i: 6th International Conference Hot Sheet Metal Forming of High-Performance Steel CHS2. - Warrendale, PA : Association for Iron & Steel Technology, AIST. - 9781935117667 ; , s. 261-269
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Konferensbidrag (refereegranskat)abstract
- During the last decades, the use of ultra-high strength steel (UHSS) has increased as its favorable ratio between strength and mass allows the design of lighter body-in-white while maintaining passenger safety. Modeling impact loads of components made of UHS steel requires reliable descriptions of the material deformation and fracture behavior.Traditional stress or strain based fracture criteria are used in finite element modeling. A different approach in modeling fracture in components uses the fracture energy as a model parameter.Fracture toughness is difficult to measure in thin sheets; a method termed Essential Work of Fracture (EWF) provides the possibility to determine the fracture toughness in sheet metal. With knowledge of the fracture toughness the understanding of fracture behavior and crack propagation in ultra-high strength steel can be increased. The obtained EWF is related to the fracture energy and can be used in numerical models as a material parameter.In the present work results from preliminary testing are shown and a discussion on cross-head speed and strain rate in the critical specimen cross section is given. The use of digital image correlation provides information about the displacement field in the vicinity of the notch and hence about the strain- and strain rate distribution. Furthermore, the difficulties in reliable measurement of force and elongation in high speed tensile testing machines are elucidated. Issues encountered during the development of the high-speed DENT specimen are not limited to the specific geometry presented in this paper.The present work aims at the development of a test specimen to obtain the Essential Work of Fracture (EWF) at high test speed. This work contributes to the overall goal to model fracture behavior and crack propagation, dependent on the strain rate. For the investigation, a high-speed tensile testing machine equipped with an in-house developed load cell and an optical elongation measurement system was used with a high-speed camera to obtain data for digital image correlation.
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| 20. |
- Golling, Stefan, et al.
(författare)
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Influence of microstructure on the fracture toughness of hot stamped boron steel
- 2019
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Ingår i: Materials Science & Engineering. - : Elsevier. - 0921-5093 .- 1873-4936. ; 743, s. 529-539
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Tidskriftsartikel (refereegranskat)abstract
- The automotive industry's desire for weight reduction while maintaining crashworthiness demands development of materials and material properties within the economic framework of consumers. The industrial process of hot stamping provides a technique to utilize steel in an efficient way. In hot stamping, microstructural characteristics of a steel blank are influenced by controlling the cooling rate. Hot stamping has become a prevalent method for lightweight solutions in car bodies without sacrificing passenger safety. The process of hot stamping applies sequential forming and quenching in a single production step. During the cooling of the blank, various microstructures can be formed depending on the cooling rate or holding temperature. Special tooling allows the application of different cooling rates within the same blank. Thus, the microstructure and mechanical properties can be influenced in designated areas of a blank.Fracture toughness properties of sheet metal are necessary to better understand fracture initiation and crack propagation during crash loading as well as improve crashworthiness predictions. This paper focus on fracture toughness of low-alloyed boron steel sheet common in the automotive industry. A heat treatment process is used to form different microstructures, predominately consisting of one single phase or mixed microstructures with two distinct phases. The fracture toughness of the present microstructures is evaluated using the Essential Work of Fracture methodology. Results are discussed in terms of the different microstructures obtained and the consequent part performance.Results show a strong connection between microstructure and fracture toughness. The bainitic grade shows favorable fracture toughness while a mixed microstructure of bainite and martensite shows a very brittle fracture behavior. A post heat treatment in the form of paint bake curing shows a negligible effect on fracture toughness of martensite.
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| 21. |
- Golling, Stefan, et al.
(författare)
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Investigation on the Influence of Loading-Rate on Fracture Toughness of AHSS Grades
- 2018
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Ingår i: Materials Science & Engineering. - : Elsevier. - 0921-5093 .- 1873-4936. ; 726, s. 332-341
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Tidskriftsartikel (refereegranskat)abstract
- The automotive industry is striving for light body-in-white structures while maintaining or improving passenger safety. The aim of this paper is to investigate the influence of the loading rate on the fracture toughness of thin steel sheet metal of three advanced high strength steels. Although steel is a heavy material it plays a significant role for lightweight solutions in car bodies. Three different advanced high strength steel (AHSS) grades, namely dual-phase (DP), quench-partitioning (Q&P) and TRIP-assisted bainitic-ferritic (TBF), are investigated in the present paper. For crash relevant components it is of importance to know the material response under high loading velocities i.e. high strain rates. A standard tensile test system is used for low loading rates, a high-speed tensile testing setup is used to obtain high loading rates. The fracture toughness of the three AHSS grades is evaluated using the methodology of the Essential Work of Fracture (EWF). The tensile specimen used in the present work is the double edge notched tensile (DENT) geometry with a pre-developed crack. High-speed imaging is applied to verify the validity of the evaluation method Essential Work of Fracture at high rates of loading. Results from this work show that knowledge of fracture toughness would improve the understanding of fracture and crack propagation mechanisms for third generation high strength steels used for automotive components
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| 22. |
- Gonçalves, L. A., et al.
(författare)
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Numerical simulation of a rapid fatigue test of high Mn-TWIP steel via a high cycle fatigue constitutive law
- 2023
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Ingår i: International Journal of Fatigue. - : Elsevier Ltd. - 0142-1123 .- 1879-3452. ; 168
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Tidskriftsartikel (refereegranskat)abstract
- The generation of reliable data in the high cycle fatigue domain is crucial to support further metallurgic developments of fatigue optimized steel grades. Commonly employed for this aim, traditional standardized characterization methods are expensive and time-consuming. Thus, to circumvent these limitations, different accelerated fatigue testing methodologies have been proposed. In this work, the rapid fatigue test based on stiffness evolution is numerically reproduced using the finite element method for a specific grade of twinning-induced plasticity steel. A high cycle fatigue constitutive law grounded on the continuum damage mechanics framework is employed for this purpose. To adequately capture the material non-linear behavior observed in the experiments, a novel hardening–softening stress–strain curve for damage is proposed. The entire load history in the fatigue domain is modeled. A cycle-jump algorithm is used to improve the computational efficiency of the simulations. It is shown that a reduction of about 55% in the analysis elapsed time is reached by using this algorithm, while the result accuracy is maintained. Finally, the good agreement between numerical and experimental results, revealed by a maximum relative error smaller than 6.0%, evidences the potential of the present constitutive formulation to model the behavior of metals in the high cycle fatigue domain.
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| 23. |
- Grifé, Laura, et al.
(författare)
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Influence of pre-strain on fracture toughness of 3rd generation advanced high strength steels
- 2024
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Ingår i: Material Forming - ESAFORM 2024. - : Materials Research Forum LLC. ; , s. 1206-1214
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Konferensbidrag (refereegranskat)abstract
- The present work investigates the influence of pre-strain on the fracture toughness of 3rd Generation Advanced High Strength Steels (AHSS). Specifically, a Carbide Free Bainitic (CFB) and a Quenching and Partitioning (Q&P) steel have been studied, the properties of which are crucial for lightweight vehicle construction. Fracture toughness, which is a key parameter for crash performance applications, is assessed using the Essential Work of Fracture methodology. The study investigates the pre-straining states of uniaxial tension, plane strain, and equibiaxial tension in 1.5 mm Q&P and 1.4 mm CFB sheet-form steels of 1180 MPa tensile strength. Overall, Q&P steel demonstrates superior fracture toughness compared to CFB steel. Remarkably, the specific essential work of fracture (we) remains unaffected by pre-straining across different strain states. Nevertheless, pre-straining exerts a notable influence on the non-essential plastic work (βwp) due to the plastic energy consumed during pre-deformation. These results suggest that prestrain has little or no influence on the fracture properties of AHSS, which is relevant for the design and manufacturing of high crash-performance and safety-related components.
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| 24. |
- Jonsén, Pär, 1971-, et al.
(författare)
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A Novel Method for Modelling of Cold Cutting of Microstructurally Tailored Hot Formed Components
- 2019
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Ingår i: Hot sheet metal forming of high-performance steel. - : Wissenschaftliche Scripten. ; , s. 645-652
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Konferensbidrag (refereegranskat)abstract
- In the last decade, hot metal forming of advanced high strength steel (AHSS) have improved passenger safety and open possibilities for lightweight design. Hot metal forming can be applied to locally tailor the microstructure of components and gradual vary mechanical properties to improve crash resistance behaviour and optimized weight for e.g. safety related parts. Sometimes post punching or trimming must be done on hardened parts. Such conditions induce damage and fractures in the trimmed edge. Another issue is that high pressures are required in cutting operations due to the high yield stress of press hardened parts, which accelerate wear and produce premature fracture in tools. Optimizing cutting operations to minimize damage and wear are essentials and numerical simulations of cutting operations can be of good assistance. One of the main challenges in the numerical modelling consists of numerically be able to treat the extremely large deformation occurring in the cutting zone. A second challenge is to find suitable failure models. In this work, the punching process of soft and hard microstructures obtained by press hardening is experimentally studied, but also modelled with a combination of smoothed particle Galerkin (SPG) method and finite element method (FEM). Laboratory punching tests with different clearance values were carried out using sheets of different fracture strengths. All experimental cases are numerically modelled. Validation is conducted by comparing numerical results with experimental measurements of punch force and displacement. In addition, morphology of the final cutting edges from both real and virtual are compared. Numerical results show good agreement against experimental measurements. Furthermore, the combined method gives robust-ness and stability as it can handle large deformations efficiently.
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| 25. |
- Jonsén, Pär, et al.
(författare)
-
Fracture mechanics based modelling of failure in advanced high strength steels
- 2017
-
Ingår i: 6th International Conference Hot Sheet Metal Forming of High-Performance Steel CHS<sup>2</sup>. - Warrendale, PA : Association for Iron & Steel Technology, AIST. - 9781935117667 ; , s. 15-23
-
Konferensbidrag (refereegranskat)abstract
- In the last decade, the favorable properties of the press hardening process for advanced high strength steel (AHSS) have increased the demands concerning passenger safety and lightweight design. AHSS show excellent mechanical properties from e.g. tensile test measurements, but it has previously been shown that results from tensile elongation or energy calculation of un-notched and smooth specimen are not appropriate to classify the crash behavior of steel grades. This is because they completely underestimate the post-uniform region from start of necking to failure. Another issue, the mechanical behavior of a notched or cracked component is different than a smooth and un-notched component. If the mechanical behavior in some loading is dominated by crack propagation, it should be rationalized in terms of the materials crack propagation resistance. Therefore, the evolution of the material property that controls crack propagation, i.e. the fracture toughness, is an interesting approach to evaluate loading and deformation of AHSS. Process modelling including fracture toughness depending properties gives valuable information and additional understanding of fracture behavior and crack propagation mechanisms in AHSS components. Fracture toughness in thin sheets can be readily measured through the application of the Essential Work of Fracture (EWF) methodology. The damage evolution law can be specified in terms of fracture energy (per unit area) or in terms of equivalent plastic failure strain as a function of triaxiality and lode angle. In this work, DENT test samples have been experimentally evaluated and finite element simulations of the DENT tests have been performed. By this approach the numerical study includes mechanical response of AHSS specimen including sharp cracks. In the numerical model, the J-integral was evaluated using the virtual crack-tip extension (VCE) method. From the comparison of the numerical and experimental results of load-displacement for different ligament length cases it is obvious that there are in agreement. Also, the numerically obtained value of fracture toughness Jc, is in agreement with the experimentally measured value of essential work of fracture we. When finite element based fracture mechanics is applied to practical design, the fracture toughness can be used as design criteria. One appealing property of the evaluation of the J-integral is that it can be evaluated from the far field solution, which facilitates computation as many numerical errors arise close to the crack tip. Evolution of stress- and strain field, plastic zone, J-integral value and other mechanical properties is interesting to study with the combination of experimental and numerical investigations.
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| 26. |
- Lara, A., et al.
(författare)
-
Effect of Sandblasting on Low and High-Cycle Fatigue Behaviour after Mechanical Cutting of a Twinning-Induced Plasticity Steel
- 2018
-
Ingår i: MATEC Web of Conferences. - : EDP Sciences.
-
Konferensbidrag (refereegranskat)abstract
- In the last years, car bodies are increasingly made with new advanced high-strength steels, for both lightweighting and safety purposes. Among these new steels, high-manganese or TWIP steels exhibit a promising combination of strength and toughness, arising from the austenitic structure, strengthened by C, and from the twinning induced plasticity effect. Mechanical cutting such as punching or shearing is widely used for the manufacturing of car body components. This method is known to bring about a very clear plastic deformation and therefore causes a significant increase of mechanical stress and micro-hardness in the zone adjacent to the cut edge. To improve the cut edge quality, surface treatments, such as sandblasting, are often used. This surface treatment generates a compressive residual stress layer in the subsurface region. The monotonic tensile properties and deformation mechanisms of these steels have been extensively studied, as well as the effect of grain size and distribution and chemical composition on fatigue behaviour; however, there is not so much documentation about the fatigue performance of these steels cut using different strategies. Thus, the aim of this work is to analyse the fatigue behaviour of a TWIP steel after mechanical cutting with and without sandblasting in Low and High-Cycle Fatigue regimes. The fatigue behaviour has been determined at room temperature with tensile samples tested with a load ratio of 0.1 and load amplitude control to analyse High-Cycle Fatigue behaviour; and a load ratio of -1 and strain amplitude control to determine the Low-Cycle Fatigue behaviour. Samples were cut by shearing with a clearance value of 5%. Afterwards, a part of the cut specimens were manually blasted using glass microspheres of 40 to 95 microns of diameter as abrasive media. The results show a beneficial effect of the sandblasting process in fatigue behaviour in both regimes, load amplitude control (HCF) and strain amplitude control (LCF) tests, when these magnitudes are low, while no significant differences are observed with higher amplitudes. low-cycle fatigue, high-cycle fatigue, mechanical cutting, sandblasting, high manganese steel, TWIP steel.
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| 27. |
- Lara, A., et al.
(författare)
-
Sheared edge formability characterization of cold-rolled advanced high strength steels for automotive applications
- 2022
-
Ingår i: IOP Conference Series: Materials Science and Engineering. - : Institute of Physics (IOP).
-
Konferensbidrag (refereegranskat)abstract
- Edge cracking has become a limiting factor in the use of some advanced high strength steels (AHSS) for high-performance automotive applications. This fact has motivated the development of a multitude of experimental tests for edge formability prediction over the last years. In this sense, the Hole Expansion Test (HET) according to ISO16630 has been established in the automotive industry as a standard procedure for edge cracking sensitivity ranking. However, whereas it may be useful for rapid material screening, the results are often not accurate and reliable enough. Consequently, alternative methods based on Digital Image Correlation (DIC) have been proposed aimed at improving the prediction of edge cracking occurrence during forming and obtaining useful strain data that can be implemented in forming simulations. This paper explores the applicability of different DIC-based methods, such as Half-Specimen Dome Tests, Sheared Edge Tensile Tests, and KWI hole expansion tests with a flat nosed punch, for characterizing the edge formability of three cold-rolled AHSS sheets. The results obtained from the different testing methods are compared and validated with a laboratory-scale demonstrator. Finally, the limitations and advantages of the different methods are discussed.
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| 28. |
- Latorre, Nuria, et al.
(författare)
-
A mechanical interlocking joint between sheet metal and carbon fibre reinforced polymers through punching
- 2023
-
Ingår i: IOP Conference Series: Materials Science and Engineering. - : Institute of Physics (IOP).
-
Konferensbidrag (refereegranskat)abstract
- The joint between different lightweight materials plays a significant role in multi-material design of structural components for the automotive industry, aiming to reduce the vehicle's weight without compromising performance or safety. Yet, conventional mechanical joining technologies between metals and Carbon Fibre Reinforced Polymers (CFRP) result in either a hole being drilled in the composite material, leading to damages which reduce the load bearing capacity, or the weight of the part being increased due to the incorporation of fasteners. At the same time, alternative mechanical joining methodologies involve complex and costly processing, hindering their industrial application. This work presents a new, simple, cost-efficient and non-weight penalizing mechanical joining technology between a metal sheet and fibre reinforced polymer prepregs consisting of a single-step punching process. In this process, the metallic sheet is completely perforated, while the prepreg is not. The punch pushes the carbon fibres through the metallic hole, with no, or minimal fibre breakage, generating a mechanical interlock. The shear strength and the absorbed energy of the co-cured joint increase with the incorporation of the mechanical interlocking joint.
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| 29. |
- Latorre, Núria, et al.
(författare)
-
A punching process to join metal sheets and fibre reinforced polymer composites by mechanical interlocking
- 2023
-
Ingår i: Composites. Part A, Applied science and manufacturing. - : Elsevier. - 1359-835X .- 1878-5840. ; 175
-
Tidskriftsartikel (refereegranskat)abstract
- In the multi-material lightweight design of structural components for the automotive industry, the joint between different materials plays a significant role in reducing vehicle weight without compromising performance or safety. Conventional technologies to mechanically join metals and carbon fibre reinforced polymers result in either drilling a hole in the composite material or increasing the weight of the part because of the fasteners employed. This work presents a new, simple, cost-efficient and non-weight penalizing mechanical joining technology for metal sheets and fibre reinforced polymer prepregs. It consists of a single-step punching process where the metallic sheet is completely perforated, but the prepreg is not. The punch pushes the carbon fibres through the hole in the metal sheet with no or minimal fibre breakage, generating a mechanical interlock which, in turn, increases the shear strength and absorbed energy of the co-cured joint.
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| 30. |
- Latorre, Núria, et al.
(författare)
-
Forming of mechanically interlocked aluminium and carbon fibre reinforced polymer parts with complex geometry
- 2024
-
Ingår i: Material Forming - ESAFORM 2024. - : Materials Research Forum LLC. ; , s. 1640-1649
-
Konferensbidrag (refereegranskat)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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| 31. |
- Ortiz, L., et al.
(författare)
-
Measuring the fracture toughness of single WC grains of cemented carbides by means of microcantilever bending and micropillar splitting
- 2021
-
Ingår i: International journal of refractory metals & hard materials. - : Elsevier. - 0263-4368. ; 98
-
Tidskriftsartikel (refereegranskat)abstract
- The main goal of this work is to obtain a reliable value of the fracture toughness of single grains of tungsten carbide (WC). It is attempted by testing microcantilever and micropillar samples shaped out, by means of focused ion beam milling, of individual WC particles embedded within a WC-Co cemented carbide grade. Experimental testing included the use of a nanoindenter for inducing microcantilever bending and micropillar splitting, as well as sampling WC grains with basal and prismatic orientations. Experimental results are compared with those previously assessed through implementation of the indentation microfracture technique. Bending of notched microcantilevers yielded more consistent results than those measured out of micropillar splitting tests. In this regard, the average value of fracture toughness for single WC grains, within the two-phase interpenetrated network existing in cemented carbides, is found to be 5.6 ± 0.8 MPa·m1/2. Such a relatively high value – coherent with local plastic features evidenced in nanoindentation imprints - is in satisfactory agreement with results indirectly estimated from other macromechanical tests.
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| 32. |
- Parareda, Sergi, et al.
(författare)
-
A damage-based uniaxial fatigue life prediction method for metallic materials
- 2023
-
Ingår i: Materials & design. - : Elsevier. - 0264-1275 .- 1873-4197. ; 231
-
Tidskriftsartikel (refereegranskat)abstract
- Determining the fatigue behaviour of metallic materials using standardised testing methods is costly and time-consuming. Therefore, several methods have been proposed to shorten the testing time and improve the fatigue optimisation of materials and components. This work presents a new fatigue testing method based on fatigue damage monitoring that allows determining the fatigue resistance in a short time and with few specimens. The presented method, named as the stiffness method, monitors the inelastic strains as an indicator of fatigue damage evolution. Strain measurements were carried out by digital image correlation techniques and showed to effectively follow damage evolution during fatigue tests. Results are convincing and more evident to obtain and discuss than other monitoring techniques, like temperature dissipation. In addition, the method overcomes the main limitations of the existing fast testing methods by avoiding the utilisation of complex apparatus, like infrared cameras or acoustic emission sensors. The approach has been validated in ten different metallic materials, as titanium and aluminium alloys, carbon steels, and stainless steels. The estimated fatigue limit was compared with values obtained following standardised tests, showing excellent agreement. Results allow pointing out the stiffness method as an efficient and effective tool for rapidly determining the fatigue behaviour of metallic materials.
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| 33. |
- Parareda, Sergi, et al.
(författare)
-
A rapid testing method for assessing mode I fatigue delamination of carbon fibre-reinforced polymer
- 2024
-
Ingår i: International Journal of Fatigue. - : Elsevier. - 0142-1123 .- 1879-3452. ; 187
-
Tidskriftsartikel (refereegranskat)abstract
- Characterising fatigue delamination in composite materials following standardised testing protocols is often associated with high costs and significant time investment. Therefore, it can be helpful to have a testing strategy to reduce the testing time and easily assess the fatigue delamination of multiple materials and conditions. This work shows how to apply one of the new rapid testing techniques known as the stiffness method on composite materials. The method has been developed to predict the fatigue delamination of composite materials by monitoring the fatigue damage through the compliance of the specimen. The obtained data in terms of displacement and force is used to obtain the fracture toughness, fatigue crack onset, fatigue crack threshold, and crack propagation parameters by using a reduced number of specimens and a few testing hours. The testing procedure has been developed on carbon fibre-reinforced polymer used in aerospace structures. The obtained results in a short time are promising, reporting a deviation below 10% compared to the values obtained in the standardised fatigue delamination tests.
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| 34. |
- Parareda, S., et al.
(författare)
-
Effect of heat treatment conditions on the fatigue resistance of press hardened 22MnB5 steel evaluated through rapid testing technique
- 2021
-
Konferensbidrag (refereegranskat)abstract
- Fatigue strength is considered as a crucial parameter for automotive applications subjected to cyclic loads during their long service life, as chassis parts. The high yield stress of press hardened steels poses them as good candidates for lightweight solutions with improved fatigue resistance. However, their high strength leads to an increase in notch sensitivity which can ruin the whole part's integrity. This behaviour was observed in previous works on press hardened steels, where their high fatigue strength was significantly affected by the surface conditions and by heat treatment conditions. Nevertheless, press hardening steels are still good candidates to manufacture complex geometry parts reaching high performance.Aiming at increasing the existing knowledge on the fatigue behaviour of press hardened steels, this paper analyses the fatigue performance of boron steel (22MnB5) under different time austenitizing times. Fatigue resistance is evaluated using a novel rapid fatigue testing technique based on the stiffness evolution. The method permits a fast and reliable determination of the fatigue limit. Based on results obtained with this rapid testing method, the most suitable heat treatment to mitigate fatigue notch sensitivity and then achieving the best fatigue performance for chassis applications is discussed.
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| 35. |
- Parareda, Sergi, et al.
(författare)
-
Fatigue resistance evaluation of high Mn-TWIP steel through damage mechanics : a new method based on stiffness evolution
- 2022
-
Ingår i: International Journal of Fatigue. - : Elsevier. - 0142-1123 .- 1879-3452. ; 156
-
Tidskriftsartikel (refereegranskat)abstract
- The work presented here deals with the implementation of a new methodology that allows fast and reliable determination of the fatigue strength. It is based on monitoring the specimen stiffness changes at different stress levels, as an indicator of the evolution of fatigue damage. This new rapid fatigue test uses techniques available in many laboratories, as the DIC (Digital Image Correlation) technique and common extensometers. Moreover, the obtained data are easier to handle than infrared cameras or acoustic emission systems data, and the experimental procedure to determine the fatigue limit is more evident than in the self-heating method.Experiments have been conducted in TWIP (Twinning Induced Plasticity) steel, a material used for lightweighting the structural parts of vehicles. With their excellent energy absorption capacity, TWIP steels can satisfy the part requirements in terms of crash performance, while their high tensile strength can deal with the cyclic loads acting on chassis parts. Therefore, many efforts focus on improving the fatigue strength of TWIP steels through pre-straining and/or surface treatments. However, finding the best way to improve the fatigue resistance requires time and resources that often hinder the development of the material. For this reason, a TWIP steel has been selected to check the new rapid fatigue test. The prediction made using the proposed approach is validated by comparison with conventional staircase results and fatigue crack growth standardised tests. The good agreement allows proposing the new method as a fast and efficient way to determine the fatigue resistance in metals.
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| 36. |
- Parareda, Sergi, et al.
(författare)
-
Fatigue resistance of press hardened 22MnB5 steels
- 2020
-
Ingår i: International Journal of Fatigue. - : Elsevier. - 0142-1123 .- 1879-3452. ; 130
-
Tidskriftsartikel (refereegranskat)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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| 37. |
- Parareda, Sergi, et al.
(författare)
-
Fracture toughness to assess the effect of trimming on the fatigue behaviour of high-strength steels for chassis parts
- 2023
-
Ingår i: IOP Conference Series-Materials Science and Engineering. - : Institute of Physics (IOP).
-
Konferensbidrag (refereegranskat)abstract
- High-strength steels are widely used in vehicle body-in-white, offering a good balance between crashworthiness and lightweight design. The increased requirements of heavier electric vehicles, in terms of fatigue resistance and crashworthiness, highlight that chassis parts have remarkable lightweighting potential. However, applying these grades in chassis parts is not straightforward, as the forming processes, like trimming, may introduce surface defects that compromise the fatigue resistance of the component. This work presents a material selection strategy for the applicability of high-strength steels in chassis parts of electric vehicles. The proposed approach allows the evaluation of the key parameters of the chassis parts in a simple way. The crash performance is evaluated through fracture toughness using the essential work of fracture (EWF) methodology. The method is applied to thin high-strength steel sheets employing double-edge notched tensile specimens (DENT). On the other hand, fatigue performance is investigated in terms of fatigue resistance for both notched and unnotched specimens. The results for different complex-phase and dual-phase steels show a good agreement between the EWF and the fatigue notch factor. The method could help apply high-strength steel to chassis parts, as designers will have a tool to focus the expensive fatigue tests on the best material candidates.
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| 38. |
- Parareda, S., et al.
(författare)
-
Increasing fatigue performance in AHSS thick sheet by surface treatments
- 2018
-
Ingår i: MATEC Web of Conferences. - : EDP Sciences.
-
Konferensbidrag (refereegranskat)abstract
- Advanced High Strength Steels (AHSS) have been widely applied in the automotive industry as an affordable solution for car lightweighting, mainly in parts subjected to crash requirements. Heavy duty vehicle (HDV) can also benefit from the expertise learned in cars, but parts must be designed considering fatigue resistance, especially on trimmed areas, and stiffness. Mechanical surface treatments, as blasting or shot peening, help increasing fatigue life of AHSS in trimmed areas and will allow weight reduction in HDV through gauge downsizing. The expected decrease in stiffness through thickness reduction can be improved by design changes. However, scarce information about the effect of mechanical surface treatments on AHSS are available. Thus, the aim of this work is to evaluate the increment in fatigue life of two different steel grades (350 MPa, and 500MPa of yield strength) in thick sheet by means of mechanical surface treatment - sandblasting. High Cycle Fatigue [HCF] tests were conducted at alternating load [R=-1]. Residual stresses were measured by an X-ray tensometry prior fatigue tests. Also the surface roughness [Rz] and form is measured using an optical non-contact 3D microscope. On the other hand, the fracture surfaces of the test specimens were observed via scanning electron microscope (SEM) in order to determine the crack initiation points. The evaluation of fatigue life in terms of SN curves is also discussed, analysing how the sandblasting process modifies the surface roughness and introduce compressive residual stresses on the external layer of the material. Both phenomena enhance the fatigue strength of the evaluated steel grades.
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| 39. |
- Parareda, Sergi, et al.
(författare)
-
Understanding the Fatigue Notch Sensitivity of High-Strength Steels through Fracture Toughness
- 2023
-
Ingår i: Metals. - : MDPI. - 2075-4701. ; 13:6
-
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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| 40. |
- Parareda, Sergi, et al.
(författare)
-
Warm Forming of Hot Rolled High Strength Steels with Enhanced Fatigue Resistance as a Lightweight Solution for Heavy Duty Vehicles
- 2022
-
Ingår i: Hot Sheet Metal Forming of High-Performance Steel: proceedings. - : Wissenschaftliche Scripten.
-
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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| 41. |
- Pittner, János
(författare)
-
Endothelial Nitric Oxide in the Control of Glomerular Hemodynamics
- 2002
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The afferent arteriole of the kidney is a unique vascular segment: it is the effector of the renal hemodynamic autoregulation. The use of the isolated, perfused juxtamedullary nephron preparation makes it possible to visualize the afferent arteriole while preserving its tissue surroundings and the functional integrity of the nephron.The author has developed a method to measure and evaluate fluorescence signals from the afferent arteriolar endothelium in this preparation and has measured endothelial intracellular calcium levels and endothelial nitric oxide production during various conditions in this model. Albumin, a common ingredient of perfusion media, has been shown to have considerable capacity to scavenge nitric oxide. Scavenging properties of the perfusion media are important in setting a "working level" of nitric oxide in the wall of the afferent arteriole. To examine the role of nitric oxide in renal autoregulation, different luminal pressures in the entire autoregulatory pressure range have been used and the endothelial calcium and luminal pressure were found to be inversely related. Nitric oxide production of the endothelium was enhanced by increases in perfusion pressure. Applying existing models of the production and diffusion of nitric oxide in blood vessels and by inserting measured vascular parameters, a mathematical model was created to describe pressure profile, shear stress, nitric oxide production and diffusion relationships and vascular reactivity in the afferent arteriole.In conclusion, nitric oxide, a major physiological dilator, plays a paramount role in renal autoregulation and afferent arteriolar vasoreactivity. Effective vessel wall nitric oxide levels are modulated by the luminal scavenging. Shear stress enhances the production of nitric oxide, by stimulating the endothelial nitric oxide synthase through non-calcium mediated mechanisms.
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| 42. |
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| 43. |
- Pujante, Jaume, et al.
(författare)
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Hot Stamped Aluminium for Crash-Resistant Automobile Safety Cage Applications
- 2021
-
Ingår i: Materials Science Forum. - : Trans Tech Publications. - 0255-5476 .- 1662-9752. ; 1016, s. 445-452
-
Tidskriftsartikel (refereegranskat)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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| 44. |
- Pujante, Jaume, et al.
(författare)
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Investigations into wear and galling mechanism of aluminium alloy-tool steel tribopair at different temperatures
- 2012
-
Ingår i: 15th Nordic Symposium on Tribology - NordTrib 2012. - Trondheim : Department of Geography, Norwegian University of Science and Technology.
-
Konferensbidrag (refereegranskat)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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| 45. |
- Pujante, J., et al.
(författare)
-
Microstructural and mechanical study of press hardening of thick boron steel sheet
- 2017
-
Ingår i: Journal of Physics, Conference Series. - : Institute of Physics (IOP). - 1742-6588 .- 1742-6596. ; 896
-
Tidskriftsartikel (refereegranskat)abstract
- Press hardening has become a staple in the production of automotive safetycomponents, due to the combination of high mechanical properties and form complexity itoffers. However, the use of press hardened components has not spread to the truck industrydespite the advantages it confers, namely affordable weight reduction without the use of exoticmaterials, would be extremely attractive for this sector.The main reason for this is that application of press hardened components in trucks impliesadapting the process to the manufacture of thick sheet metal. This introduces an additionallayer of complexity, mainly due to the thermal gradients inside the material resulting inthough-thickness differences in austenitization and cooling, potentially resulting in complexmicrostructure and gradient of mechanical properties.This work presents a preliminary study on the press hardening of thick boron steel sheet.First of all, the evolution of the sheet metal during austenitization is studied by means ofdilatometry tests and by analysing the effect of furnace dwell time on grain size. Afterwards,material cooled using different cooling strategies, and therefore different effective cooling rates, isstudied in terms of microstructure and mechanical properties. Initial results from finite elementsimulation are compared to experimental results, focusing on the phase composition in throughthickness direction.Results show that industrial-equivalent cooling conditions do not lead to gradientmicrostructures, even in extreme scenarios involving asymmetrical cooling.
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| 46. |
- Pujante, Jaume, et al.
(författare)
-
Wear Mechanisms in Press Hardening: An Analysis through Comparison of Tribological Tests and Industrial Tools
- 2023
-
Ingår i: Lubricants. - : MDPI. - 2075-4442. ; 11:5
-
Tidskriftsartikel (refereegranskat)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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| 47. |
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| 48. |
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| 49. |
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| 50. |
- Sandin, Olle, et al.
(författare)
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Numerical modelling of shear cutting using particle methods
- 2023
-
Ingår i: IOP Conference Series: Materials Science and Engineering. - : Institute of Physics (IOP).
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Konferensbidrag (refereegranskat)abstract
- The use of Advanced High Strength Steel (AHSS) allows for lightweighting of sheet steel components, with maintained structural integrity of the part. However, AHSS grades show limitations in edge crack resistance, primarily influenced by sheared edge damage introduced by the shear cutting process. Numerical modelling of the shear cutting process can aid the understanding of the sheared edge damage, thus avoiding unforeseen edge cracking in the subsequent cold forming. However, the extreme deformations of the blank during the shear cutting process are likely to cause numerical instabilities and divergence using conventional Finite Element modelling. To overcome these challenges, this work presents the use of a particle-based numerical modelling method called the Particle Finite Element Method (PFEM). PFEM accurately solves some of the challenges encountered in shear cutting with the standard Finite Element method, such as large deformation, angular distortions, generation of new boundaries and presents an efficient way of transfer historical information from the old to the new mesh, minimising the results diffusion. The present work shows prediction of cut edge morphology of AHSS using a PFEM modelling scheme, where the numerical results are verified against experiments. With these results, the authors show new possibilities to obtain accurate numerical prediction of the shear cutting process, which promotes further advances in prediction of edge damaged related to shear cutting of AHSS.
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