| 1. |
- Frómeta, D., et al.
(author)
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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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In: Engineering Fracture Mechanics. - : Elsevier. - 0013-7944 .- 1873-7315. ; 229
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Journal article (peer-reviewed)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. |
- Gonçalves, L. A., et al.
(author)
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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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In: International Journal of Fatigue. - : Elsevier Ltd. - 0142-1123 .- 1879-3452. ; 168
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Journal article (peer-reviewed)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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| 5. |
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| 6. |
- Frómeta, D., et al.
(author)
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A new cracking resistance index based on fracture mechanics for high strength sheet metal ranking
- 2021
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Conference paper (peer-reviewed)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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| 7. |
- Frómeta, D., et al.
(author)
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Evaluation of edge formability in high strength sheets through a fracture mechanics approach
- 2019
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In: Proceedings of the 22nd International ESAFORM Conference on Material Forming. - : American Institute of Physics (AIP).
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Conference paper (peer-reviewed)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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| 8. |
- Frómeta, D., et al.
(author)
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New tool to evaluate the fracture resistance of thin high strength metal sheets
- 2020
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In: International Deep-Drawing Research Group (IDDRG 2020) 26-30 October 2020, Seoul, South Korea. - : Institute of Physics (IOP).
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Conference paper (peer-reviewed)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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| 10. |
- Lara, A., et al.
(author)
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Effect of Sandblasting on Low and High-Cycle Fatigue Behaviour after Mechanical Cutting of a Twinning-Induced Plasticity Steel
- 2018
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In: MATEC Web of Conferences. - : EDP Sciences.
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Conference paper (peer-reviewed)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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