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Jianjun Chen - One of the best experts on this subject based on the ideXlab platform.
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prediction of Edge crack in cold rolling of silicon steel strip based on an extended gurson tvergaard needleman damage model
Journal of Manufacturing Science and Engineering-transactions of The Asme, 2015Co-Authors: Jianjun ChenAbstract:Edge Cracking is commonly observed in cold rolling process. However, its failure mechanism is far from fully understanding due to the complex stresses and plastic flow conditions of steel strip under the rolling condition. In this paper, an extended Gurson–Tvergaard–Needleman (GTN) damage model coupled with Nahshon–Hutchinson shear damage mechanism was introduced to investigate the damage and fracture behavior of steel strip in cold rolling. The results show that extended GTN damage model is efficient in predicting the occurrence of Edge crack in cold rolling, and the prediction is more accurate than that of the original GTN damage model. The Edge Cracking behavior under various cold rolling process parameters is investigated. It comes to the conclusion that Edge crack extension increases with the increase of the reduction ratio, tension and the decrease of the roller radius and friction coefficient. The influence of shear damage becomes more significant in rolling condition with a larger reduction ratio, smaller roller radius, lower friction force, and tension.
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the initiation and propagation of Edge cracks of silicon steel during tandem cold rolling process based on the gurson tvergaard needleman damage model
Journal of Materials Processing Technology, 2013Co-Authors: Jianjun ChenAbstract:Abstract Edge Cracking is a commonly observed phenomenon during the cold rolling process of silicon steel, which may cause the rupture of strips in the rolling mill. In this paper the initiation and propagation of Edge cracks under the tandem cold rolling condition were investigated by using the Gurson–Tvergaard–Needleman damage model. The damage parameters were obtained from the tensile tests data and the SEM analyses. Different cold rolling experiments were carried out by a non-reversing two-high rolling mill and the experimental results agreed well with the finite element calculation results. Parametric studies were carried out and revealed that the crack propagation increases with the increasing of total reduction, friction coefficient, and unit tension. A bigger work roll is beneficial to reduce the Edge crack growth as well.
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the initiation and propagation of Edge cracks of silicon steel during tandem cold rolling process based on the gurson tvergaard needleman damage model
Journal of Materials Processing Technology, 2013Co-Authors: Jianjun ChenAbstract:Abstract Edge Cracking is a commonly observed phenomenon during the cold rolling process of silicon steel, which may cause the rupture of strips in the rolling mill. In this paper the initiation and propagation of Edge cracks under the tandem cold rolling condition were investigated by using the Gurson–Tvergaard–Needleman damage model. The damage parameters were obtained from the tensile tests data and the SEM analyses. Different cold rolling experiments were carried out by a non-reversing two-high rolling mill and the experimental results agreed well with the finite element calculation results. Parametric studies were carried out and revealed that the crack propagation increases with the increasing of total reduction, friction coefficient, and unit tension. A bigger work roll is beneficial to reduce the Edge crack growth as well.
X.m. Chen - One of the best experts on this subject based on the ideXlab platform.
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Edge Cracking mechanism in two dual-phase advanced high strength steels
Materials Science and Engineering: A, 2014Co-Authors: Zhenke Teng, X.m. ChenAbstract:Abstract One of the manufacturing issues restricting the applications of advanced high-strength steels is Edge Cracking during forming. Computer simulations using the conventional forming limit curve (FLC) as a failure criterion often fail to predict Edge Cracking. A new failure criterion is needed to assess the Edge stretchability in simulations and applications, subsequently understanding the fracture mechanism in the microstructural scale is a prerequisite. In this study, the Edge fracture mechanisms of two selected dual-phase steels (designated as DP980 and IBF980) with identical chemistry but different Edge Cracking behaviors are studied by controlled Edge tension tests and scanning electron microscopy (SEM). The results show that the Edge Cracking behaviors are essentially fractures propagated from pre-existing microcracks introduced by the shearing process. The dominant Edge fracture mechanism is decohesion between the martensite and ferrite phases. This study employs the interfacial strength between ferrite and martensite as an index to predict the material Edge Cracking resistance. The interfacial strength is calculated to be 1070 MPa for IBF980 and 854 MPa for DP980 using void-nucleation models. This result indicates that IBF980 has a higher resistance to Edge Cracking and subsequently a higher local formability, which is consistent with the higher hole expansion ratio values observed. Refining the martensite particle size and minimizing banded martensite structures are effective approaches to increase the local formability.
Frómeta Gutiérrez David - One of the best experts on this subject based on the ideXlab platform.
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Fracture resistance of advanced high-strength steel sheets for automotive applications
'Springer Science and Business Media LLC', 2021Co-Authors: Frómeta Gutiérrez David, Lara Antoni, Grifé Laura, Dieudonné Thomas, Dietsch Pascal, Rehrl Johannes, Suppan Clemens, Casellas Padró Daniel, Calvo Muñoz JessicaAbstract: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 (wei), 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.Peer ReviewedPostprint (published version
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On the measurement of fracture toughness to understand the Cracking resistance of advanced high strength steel sheets
2021Co-Authors: Frómeta Gutiérrez DavidAbstract:Automotive designers are constantly facing new challenges to meet the more and more stringent safety and CO2 emission legislations. Concerning the latter, vehicle lightweighting has become one of the main goals of the automotive industry, not only to reduce fuel consumption in fuel-powered cars but also to enhance the battery range in electric vehicles. At the same time, weight reduction cannot be attained at the expense of passenger’s safety in case of a crash. Hence, it is important to select the best-suited strategies to find the optimum balance between weight reduction and crashworthiness. In this sense, Advanced High Strength Steels (AHSS) have been positioned as one of the most effective solutions to this demand. AHSS present very high strength and high crash performance, which allows reducing vehicle mass while maintaining the safety of the occupants. These outstanding mechanical properties have promoted their widespread implementation for structural and crash-relevant automobile components. However, the application of AHSS have introduced new challenges related to their limited ductility and Cracking resistance. Premature Cracking during Edge forming operations (Edge Cracking) or the occurrence and propagation of cracks under impact loading are some of the common Cracking related issues in processing and implementation of AHSS. To face these problems, the development of new approaches to properly characterize the Cracking resistance of AHSS has become unavoidable since conventional failure criteria based on uniaxial tensile properties and forming limit curves fail to describe Cracking related phenomena. In this thesis, a fracture mechanics-based approach is proposed to rationalize and understand the crack initiation and propagation resistance of AHSS. Results have been correlated with Edge Cracking resistance and crash behaviour of a broad range of advanced high strength sheet steels. Fracture toughness is evaluated in the frame of fracture mechanics through different testing methods, such as the essential work of fracture, the J-integral and the Kahn-type tear tests. The relationship between the obtained fracture toughness parameters as well as the limitations of the different methods have been discussed. High-resolution video extensometry and Digital Image Correlation (DIC) techniques were used to investigate the fracture behaviour of the different steels. Edge Cracking resistance is characterized by standard hole expansion tests and DIC-assisted hole tension tests. Crashworthiness is assessed through laboratory impact resistance tests. The influence of microstructural constituents on the crack propagation resistance of AHSS is also assessed. The results show that fracture toughness, in particular the specific essential work of fracture (we), is a suitable material property to understand the Cracking behaviour of AHSS and rank the material’s resistance to different crack-related failures, such as Edge fracture or crack propagation during a crash event. These conclusions are based on the good correlation established between we and the results from Edge Cracking and impact resistance tests. On the other hand, the experimental observations show that we can be used to discern the role of microstructural constituents on the fracture behaviour of AHSS. It is pointed out that proper microstructural design cannot be only focused on tensile properties since they do not inform about Cracking resistance. According to all the experimental findings, the fracture toughness is considered as a relevant material property for AHSS design and performance classification. In line with this, a new classification system, considering global ductility and fracture toughness, is proposed for a more comprehensive description of the overall formability and fracture behaviour of AHSS.Los diseñadores de automóviles se enfrentan constantemente a nuevos desafíos para cumplir con las cada vez más estrictas legislaciones de seguridad y emisiones de CO2. Con respecto a esto último, el aligeramiento de los vehículos se ha convertido en uno de los principales objetivos de la industria automotriz, no solo para reducir el consumo en los automóviles de combustión interna, sino también para mejorar la autonomía de los vehículos eléctricos. Al mismo tiempo, la reducción de peso no se puede lograr a expensas de la seguridad del pasajero en caso de accidente. Por lo tanto, es importante seleccionar las estrategias más adecuadas para encontrar el equilibrio óptimo entre reducción de peso y resistencia al impacto. En este sentido, los aceros avanzados de alta resistencia (AHSS) se han posicionado como una de las soluciones más efectivas. Los AHSS presentan una elevada resistencia y un buen comportamiento en caso de impacto, lo que permite reducir el peso del vehículo manteniendo la seguridad de los ocupantes. Estas excepcionales propiedades mecánicas han contribuido a su extensa implementación en componentes estructurales y de seguridad en el automóvil. Sin embargo, estos aceros también han introducido nuevos problemas relacionados con su limitada ductilidad y resistencia la fisuración, como la aparición prematura de fisuras durante el conformado (Edge Cracking) o la generación de fisuras durante el impacto. Para hacer frente a estos problemas, se ha hecho inevitable el desarrollo de nuevos enfoques para caracterizar la resistencia a la fisuración de los AHSS, ya que los criterios convencionales basados en ensayos de tracción y curvas límite de conformabilidad no son adecuados. En esta tesis doctoral se propone un enfoque basado en la mecánica de la fractura para explicar este tipo de fracturas relacionadas con la resistencia a la iniciación y propagación de grietas en el material. Con este fin, se investiga la correlación entre las mediciones de tenacidad de fractura y la resistencia al Edge Cracking y el comportamiento en caso de impacto en una amplia gama de chapas de acero avanzado de alta resistencia. La tenacidad de fractura se evalúa en el marco de la mecánica de la fractura mediante distintos métodos como el trabajo esencial de fractura, la integral J o los ensayos tipo Kahn y se discute la relación entre los parámetros obtenidos, así como las limitaciones de los diferentes métodos. Se utilizan técnicas de video de alta resolución y correlación de imágenes digitales para investigar el comportamiento de fractura de los diferentes aceros. La resistencia Edge Cracking se caracteriza mediante ensayos de expansión de orificios (hole expansion tests). La resistencia al impacto se evalúa mediante ensayos de impacto de laboratorio. Finalmente, se analiza brevemente la influencia de la microestructura en la resistencia a la propagación de grietas de los AHSS. Los resultados muestran que la tenacidad de fractura, en concreto el trabajo esencial de fractura (we) es una herramienta útil para comprender fenómenos de fisuración en los AHSS. Estas conclusiones se basan en la buena correlación establecida entre we y los resultados de las pruebas de resistencia al impacto y al Edge Cracking. Por otro lado, las observaciones experimentales muestran el gran potencial del parámetro we para discernir el efecto de la microestructura en la resistencia a la fractura de los AHSS. Se destaca que el diseño microestructural no debe centrarse sólo en las propiedades de tracción, ya que éstas no aportan información sobre la resistencia a la propagación de fisuras. De acuerdo con esto, la tenacidad de fractura se considera una propiedad del material relevante para el diseño y clasificación de los AHSS y se propone un nuevo método de clasificación para una descripción más completa de la conformabilidad y la resistencia a la fractura de los aceros AHSS
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On the measurement of fracture toughness to understand the Cracking resistance of advanced high strength steel sheets
2021Co-Authors: Frómeta Gutiérrez DavidAbstract:Tesi en modalitat de compendi de publicacions, amb una secció retallada per drets de l'editor. Sotmesa a embargament des de la defensa fins al dia 1 d'agost de 2021Automotive designers are constantly facing new challenges to meet the more and more stringent safety and CO2 emission legislations. Concerning the latter, vehicle lightweighting has become one of the main goals of the automotive industry, not only to reduce fuel consumption in fuel-powered cars but also to enhance the battery range in electric vehicles. At the same time, weight reduction cannot be attained at the expense of passenger’s safety in case of a crash. Hence, it is important to select the best-suited strategies to find the optimum balance between weight reduction and crashworthiness. In this sense, Advanced High Strength Steels (AHSS) have been positioned as one of the most effective solutions to this demand. AHSS present very high strength and high crash performance, which allows reducing vehicle mass while maintaining the safety of the occupants. These outstanding mechanical properties have promoted their widespread implementation for structural and crash-relevant automobile components. However, the application of AHSS have introduced new challenges related to their limited ductility and Cracking resistance. Premature Cracking during Edge forming operations (Edge Cracking) or the occurrence and propagation of cracks under impact loading are some of the common Cracking related issues in processing and implementation of AHSS. To face these problems, the development of new approaches to properly characterize the Cracking resistance of AHSS has become unavoidable since conventional failure criteria based on uniaxial tensile properties and forming limit curves fail to describe Cracking related phenomena. In this thesis, a fracture mechanics-based approach is proposed to rationalize and understand the crack initiation and propagation resistance of AHSS. Results have been correlated with Edge Cracking resistance and crash behaviour of a broad range of advanced high strength sheet steels. Fracture toughness is evaluated in the frame of fracture mechanics through different testing methods, such as the essential work of fracture, the J-integral and the Kahn-type tear tests. The relationship between the obtained fracture toughness parameters as well as the limitations of the different methods have been discussed. High-resolution video extensometry and Digital Image Correlation (DIC) techniques were used to investigate the fracture behaviour of the different steels. Edge Cracking resistance is characterized by standard hole expansion tests and DIC-assisted hole tension tests. Crashworthiness is assessed through laboratory impact resistance tests. The influence of microstructural constituents on the crack propagation resistance of AHSS is also assessed. The results show that fracture toughness, in particular the specific essential work of fracture (we), is a suitable material property to understand the Cracking behaviour of AHSS and rank the material’s resistance to different crack-related failures, such as Edge fracture or crack propagation during a crash event. These conclusions are based on the good correlation established between we and the results from Edge Cracking and impact resistance tests. On the other hand, the experimental observations show that we can be used to discern the role of microstructural constituents on the fracture behaviour of AHSS. It is pointed out that proper microstructural design cannot be only focused on tensile properties since they do not inform about Cracking resistance. According to all the experimental findings, the fracture toughness is considered as a relevant material property for AHSS design and performance classification. In line with this, a new classification system, considering global ductility and fracture toughness, is proposed for a more comprehensive description of the overall formability and fracture behaviour of AHSS.Los diseñadores de automóviles se enfrentan constantemente a nuevos desafíos para cumplir con las cada vez más estrictas legislaciones de seguridad y emisiones de CO2. Con respecto a esto último, el aligeramiento de los vehículos se ha convertido en uno de los principales objetivos de la industria automotriz, no solo para reducir el consumo en los automóviles de combustión interna, sino también para mejorar la autonomía de los vehículos eléctricos. Al mismo tiempo, la reducción de peso no se puede lograr a expensas de la seguridad del pasajero en caso de accidente. Por lo tanto, es importante seleccionar las estrategias más adecuadas para encontrar el equilibrio óptimo entre reducción de peso y resistencia al impacto. En este sentido, los aceros avanzados de alta resistencia (AHSS) se han posicionado como una de las soluciones más efectivas. Los AHSS presentan una elevada resistencia y un buen comportamiento en caso de impacto, lo que permite reducir el peso del vehículo manteniendo la seguridad de los ocupantes. Estas excepcionales propiedades mecánicas han contribuido a su extensa implementación en componentes estructurales y de seguridad en el automóvil. Sin embargo, estos aceros también han introducido nuevos problemas relacionados con su limitada ductilidad y resistencia la fisuración, como la aparición prematura de fisuras durante el conformado (Edge Cracking) o la generación de fisuras durante el impacto. Para hacer frente a estos problemas, se ha hecho inevitable el desarrollo de nuevos enfoques para caracterizar la resistencia a la fisuración de los AHSS, ya que los criterios convencionales basados en ensayos de tracción y curvas límite de conformabilidad no son adecuados. En esta tesis doctoral se propone un enfoque basado en la mecánica de la fractura para explicar este tipo de fracturas relacionadas con la resistencia a la iniciación y propagación de grietas en el material. Con este fin, se investiga la correlación entre las mediciones de tenacidad de fractura y la resistencia al Edge Cracking y el comportamiento en caso de impacto en una amplia gama de chapas de acero avanzado de alta resistencia. La tenacidad de fractura se evalúa en el marco de la mecánica de la fractura mediante distintos métodos como el trabajo esencial de fractura, la integral J o los ensayos tipo Kahn y se discute la relación entre los parámetros obtenidos, así como las limitaciones de los diferentes métodos. Se utilizan técnicas de video de alta resolución y correlación de imágenes digitales para investigar el comportamiento de fractura de los diferentes aceros. La resistencia Edge Cracking se caracteriza mediante ensayos de expansión de orificios (hole expansion tests). La resistencia al impacto se evalúa mediante ensayos de impacto de laboratorio. Finalmente, se analiza brevemente la influencia de la microestructura en la resistencia a la propagación de grietas de los AHSS. Los resultados muestran que la tenacidad de fractura, en concreto el trabajo esencial de fractura (we) es una herramienta útil para comprender fenómenos de fisuración en los AHSS. Estas conclusiones se basan en la buena correlación establecida entre we y los resultados de las pruebas de resistencia al impacto y al Edge Cracking. Por otro lado, las observaciones experimentales muestran el gran potencial del parámetro we para discernir el efecto de la microestructura en la resistencia a la fractura de los AHSS. Se destaca que el diseño microestructural no debe centrarse sólo en las propiedades de tracción, ya que éstas no aportan información sobre la resistencia a la propagación de fisuras. De acuerdo con esto, la tenacidad de fractura se considera una propiedad del material relevante para el diseño y clasificación de los AHSS y se propone un nuevo método de clasificación para una descripción más completa de la conformabilidad y la resistencia a la fractura de los aceros AHSS.Postprint (published version
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New tool to evaluate the fracture resistance of thin high strength metal sheets
'IOP Publishing', 2020Co-Authors: Frómeta Gutiérrez David, Lara Antoni, Grifé Laura, Parareda Oriol Sergi, Casellas Padró DanielAbstract: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.Peer ReviewedPostprint (published version
J. A. Szpunar - One of the best experts on this subject based on the ideXlab platform.
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The effect of reheating conditions and chemical composition on δ ferrite content in austenitic stainless steel slabs
Journal of Materials Science, 2000Co-Authors: F. Czerwinski, J. A. SzpunarAbstract:The specimens, selected from different locations of as-cast 304 stainless steel slab, were annealed according to the temperature profiles, which simulated the industrial re-heating process before hot rolling. Annealing, following thermal cycles with maximum temperatures between 1230 and 1270°C for a total time of 1 h, reduced the δ ferrite content, increased the size of the individual ferrite island and changed its shape to a more spherical one. An increase of annealing time to 1.5 h caused a drastic reduction in δ ferrite content and its further spheroidization. Moreover, the size of the individual ferrite islands was decreased. While after 1 h of annealing, the δ ferrite content depended on a particular thermal cycle and its maximum temperature; after a longer annealing time of 1.5 h, the δ ferrite content was very similar for all the thermal cycles applied. A statistical analysis of over 2200 industrial data, describing the slab chemical compositions and Edge quality of the hot rolled plates was conducted. Generally, the alloying elements suppressing the δ ferrite formation improved the plate Edge quality. In particular, carbon and nitrogen exerted the strongest influence, and the higher sum of both elements led to a lower probability of the Edge Cracking.
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The Edge-Cracking of AISI 304 stainless steel during hot-rolling
Journal of Materials Science, 1999Co-Authors: F. Czerwinski, A. Brodtka, A. Zielinska-lipiec, J. H. Sunwoo, J. A. SzpunarAbstract:The hot-rolled plates of AISI 304 stainless steel, containing Edge cracks of different intensities, were examined. The austenitic matrix of the steel contained small amounts of δ ferrite inhomogeneously distributed across the width and the thickness of the plate. A correlation was found between ferrite content and Edge Cracking: the higher the ferrite content the longer the Edge cracks. Among the chemical elements present in the steel, the most critical effect on δ ferrite content was exerted by carbon and nitrogen. The longest Edge cracks were observed for plates with the lowest content of carbon and nitrogen. A possible contribution of steel chemistry and heating temperature to changes in the steel phase composition and the probability of Edge Cracking is discussed.
Zhenke Teng - One of the best experts on this subject based on the ideXlab platform.
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Edge Cracking mechanism in two dual-phase advanced high strength steels
Materials Science and Engineering: A, 2014Co-Authors: Zhenke Teng, X.m. ChenAbstract:Abstract One of the manufacturing issues restricting the applications of advanced high-strength steels is Edge Cracking during forming. Computer simulations using the conventional forming limit curve (FLC) as a failure criterion often fail to predict Edge Cracking. A new failure criterion is needed to assess the Edge stretchability in simulations and applications, subsequently understanding the fracture mechanism in the microstructural scale is a prerequisite. In this study, the Edge fracture mechanisms of two selected dual-phase steels (designated as DP980 and IBF980) with identical chemistry but different Edge Cracking behaviors are studied by controlled Edge tension tests and scanning electron microscopy (SEM). The results show that the Edge Cracking behaviors are essentially fractures propagated from pre-existing microcracks introduced by the shearing process. The dominant Edge fracture mechanism is decohesion between the martensite and ferrite phases. This study employs the interfacial strength between ferrite and martensite as an index to predict the material Edge Cracking resistance. The interfacial strength is calculated to be 1070 MPa for IBF980 and 854 MPa for DP980 using void-nucleation models. This result indicates that IBF980 has a higher resistance to Edge Cracking and subsequently a higher local formability, which is consistent with the higher hole expansion ratio values observed. Refining the martensite particle size and minimizing banded martensite structures are effective approaches to increase the local formability.
