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- 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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- 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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- 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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- 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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- 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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- 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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