| 1. |
- 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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| 2. |
- 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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| 3. |
- 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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