bluuebunny/crossref_metadata_2025_split huggingface dataset:
Material characterization of high strength sound-deadening sheets and its application on a square cup drawing simulation
Authors: Park Hyeonil , Kim Se-Jong , Lee Jinwoo , Kim Daeyong 
Published: November 2019

Abstract
In this study, the mechanical properties of a high strength sound-deadening sheet (SDS) in the stretch deformation mode was characterized, and it successfully apply to the formability prediction of the square cup drawing tests. The high strength SDS was fabricated with dual phase (DP) 590 steel sheets as outer skins and polymeric adhesive layer as a core by a roll bonding process. Uniaxial and biaxial mechanical characteristics were evaluated by the uniaxial tension tests and the in-plane biaxial tension tests, respectively, while the forming limit was investigated by the punched dome tests. Then, based on the experimental data, the mechanical properties of SDS was characterized, viz., hardening curve, yield function and forming limit curve. Square cup drawing was carried out using the SDS, and its deformation and failure behaviour were successfully predicted via the finite element simulation performed by inputting characterized mechanical properties.
Hot stamping steel grades with increased tensile strength and ductility - MBW-K 1900, tribond 1200 and tribond 1400
Authors: Rosenstock D , Banik J , Gerber T , Myslowicki S 
Published: November 2019

Abstract
The use of hot formed 22MnB5 steel with an aluminium-silicon (AS) coating is well established for high strength automotive parts to combine weight reduction and passenger safety. Recent developments aim to increase the material strength for further weight saving and to improve the ductility. Especially an improved ductility makes hot formed parts suitable for additional applications, such as parts with higher energy absorption or even axially loaded parts. thyssenkrupp Steel Europe AG has developed new hot stamping grades. With an increased strength of about 1900 MPa, the MBW-K 1900 allows the application of even lighter parts compared to 22MnB5. Due to the increased strength level, delayed fracture has to be evaluated. Furthermore, the recommended parameters for processing MBW-K 1900 are regarded.
A high crash performance of a material implies a high strength, while the material still shows no cracking during folding or heavy bending of the automotive part. This is the basis for the development of tribond 1200 and tribond 1400. As a new concept for hot stamping, tribond 1200/1400 are composite materials, which bond two outer layers of a ductile 500 MPa steel grade with a high strength 1500 MPa steel core layer. Both grades are already well known as monolithic steels MBW 500 and MBW 1500 for hot stamping. An aluminium-silicon coating allows tribond 1200/1400 to be processed in the same way as AS coated 22MnB5. Nevertheless tribond 1200/1400 show a reduced susceptibility to hydrogen embrittlement in the 4-point bending test compared to 22MnB5. By their improved crash behaviour, tribond 1200/1400 enable the manufacturing of more kinds of hot formed parts such as longitudinal beams. An advanced simulation method takes the composite structure of tribond 1200/1400 into account to evaluate the crash behaviour.
Formability of AlSi and Zn coating during hot stamping
Authors: Venema Jenny , Botman Gerben , Phan Tu , Kop Theo 
Published: November 2019

Abstract
Hot stamping is widely used in the automotive industry due to the combination of high strength (±1500 MPa), low springback and good formability. The sheet is austenitized in a furnace transported to a press and formed at high temperatures (600-800°C). Forming at lower temperatures could be interesting with respect to multi-step hot stamping. Coatings are used to prevent scaling during the austitisation. AlSi is the most common protection. Zn coatings are also applied but are susceptible to microcracks. These microcracks can be avoided by using pre-cooling. In this investigation the formability and fracture of AlSi and Zn coating at several temperatures are investigated. Cross dies are formed and extensively analysed. At low temperatures the AlSi coating is very brittle and results in large amount of tool pollution. With respect to fracture and formability the Zn coating is stable in the whole temperature range and could be suitable for multi step hot stamping process.
Evaluation of the stress vs strain curve using a high temperature bulge test device
Authors: Boyer A , Laurent H , Oliveira M C 
Published: November 2019

Abstract
The increasing amount of hot and warm stamping parts in the automotive industry shows that high temperature forming is critical to reach the emission goal fixed by regulation authorities, due to its contribution in reducing the vehicle’s weight. Hot stamping and warm forming take advantage of the material softening with temperature to reduce the forming forces and springback. The use of different temperature conditions also enables exploring the phase transformation occurring with in-tool quenching in hot stamping boron steels or artificial aging in heat treatable lightweight aluminum alloys. These new forming conditions require either new material characterization methods or the current methods need to be adapted to high temperature conditions. The equibiaxial expansion test allows the evaluation of the mechanical behavior of materials on a large strain range. However, the use of high temperature conditions gives rise to difficulties when using Digital Image Correlation (DIC) systems. This study analyses the possibility of using a scanner laser to obtain the stress vs. strain curve from an equibiaxial test performed with an aluminum alloy of the 6xxx series, at 150°C. The aim is to validate an experimental procedure that can be used to evaluate the stress vs. strain curve from high temperature bulge tests performed with other metallic sheets, including quenchable boron steel.
Local ductility – key parameter for predicting formability of AHSS
Authors: Westhäuser S , Schneider M , Teschner M , Denks I A 
Published: November 2019

Abstract
In order to be able to make targeted use of the advantages of AHSS grades in forming processes it is necessary to determine local material properties. Hence, in addition to edge crack sensitivity measures, such as hole expansion ratio according to ISO 16630 (HERISO), it is currently intensively discussed whether measures, that assess the local ductility of the material, should also be specified in material specifications. One representative is given by the parameter true fracture strain (TFS) that is based on the measurement of the fracture area of a cracked flat tensile specimen. By means of 16 different cold- and hot-rolled steel batches, the relation between the parameters TFS and HERISO was investigated. The outcome is that these parameters do not correlate to a satisfying degree when considering all materials and consequently are regarded as representatives of different material properties. Thus, the issue of the reliability of the measures is considered separately. For the regarded steel grades, the overall scattering of TFS, i.e. neglecting the sample orientation, is found to be 13 – 44 % and the scattering of HERISO is within 5 – 35 %. The high scattering of TFS is mainly caused by the anisotropy of the materials. In case of parallel measurements of the same batch the relative standard deviations of TFS and HERISO are on the same level for cold-rolled strips, whereas in case of hot-rolled strips the relative standard deviation of HERISO is significantly higher. By investigating the influence of the tensile specimen shape for a bainitic hot-rolled strip numerically, it could be shown that the width-to-thickness ratio, that takes the hole fracture area into account, influences the TFS value directly.
Basics for inline measurement of tribological conditions in series production of car body parts
Authors: Hansen B , Hoebler M , Purr S , Meinhardt J , Merklein M 
Published: November 2019

Abstract
The quality of car body parts in series production is strongly dependent on the tribological behavior. Fluctuating material properties such as the sheet roughness and the amount of lubricant have an influence on the forming process. On the basis of large amounts of data it is possible to investigate the friction behavior in series production and to make process adjustments if required. Therefore, inline measurement systems have a great potential to detect the sheet roughness during the cutting process of blanks in the coil line. Furthermore, contactless systems are advantageous as they do not damage the surface. Nevertheless, the optical measuring is influenced by the lubricant layer on top of the surface. Therefore, the previously unknown impact of the lubricant on the measuring result is investigated.
Within this study, stationary optical roughness measurements have been conducted using different amounts of lubricant on hot-dip galvanized EDT steel. The results demonstrate the influence of different amounts of lubricant on the sheet roughness measurement. Hence, it is possible to correct the inline measuring results and gain knowledge of fluctuating surface roughness. In addition, strip drawing test has been carried out to investigate the effect of fluctuating tribological conditions.
Temperature dependency of material constitutive behaviour: a simple model
Authors: Atzema E H 
Published: November 2019

Abstract
The realisation that the temperature in the stamping process plays an important and underestimated role is gaining recognition. In the ASPECT project [1] the implications of temperature on friction and material behaviour are modelled and used to design a control algorithm. Although the influence of temperature on the process is mainly via friction the change in material behaviour cannot be neglected. Tata Steel have long been advocates of dislocation physics based constitutive models and in this conference the results of the current modelling approach with temperature influence in the dynamic stress are presented [2] as well. For even higher accuracy a temperature influence on the static hardening part of the model can be taken into account [3] but those are in differential equation form and need to be continuously evaluated in the FEA algorithm which means adaptations in the source code. In this paper a simplified approach based for temperature influence on static hardening is presented that can be written in a closed form and thus be supplied as (tabular) hardening law to any desired FEA code.
A plane stress yield surface using Bézier curve interpolation in two directions
Authors: Vegter H , Abspoel M , Mulder J 
Published: November 2019

Abstract
Current advanced yield criteria, like BBC2005, Yld2000 and Yld2004, offer significant flexibility and are proven to be convex. The number of coefficients of the function is fixed, which limits the number of experimental results that can be fitted independently. A common approach is to define an error function. The optimal anisotropy coefficients are established by minimizing the error function. The Vegter yield criterion is very flexible with respect to experimental results. It is in fact defined as a function that smoothly connects experimental results, while ensuring a continuous function for the derivative. Fitting is therefore a non-issue; the experimental results are the coefficients for the yield criterion. Second order Bézier curves are used for the interpolation between experimental results. Extreme values for these results can cause concavity in the definition of the yield locus. Although rarely an issue, convexity needs to be validated as part of the implementation of the yield criterion. Recently we have seen some cases of concavity that could be attributed to the cosine interpolation in the original Vegter yield criterion definition. Cosine interpolation is used between experimental results at different angles to the rolling direction. An improved method is proposed that uses Bézier interpolation not only between biaxial stress states in one orientation, but also between stress states with a different material orientation. The benefits are greater flexibility in defining experimental results and a coherent approach towards a 3D extension. The benefits of this new yield criterion will be demonstrated in a direct comparison with Yld2000 and Yld2004. The comparison will include the definition of the yield locus, showing actual cases, where in particular biaxial stress states like plane strain and shear are difficult to fit accurately. The comparison will also include improved accuracy in forming simulations.
Computationally efficient necking prediction using neural networks trained on virtual test data
Authors: Greve L , Schneider B , Andres M , Martinez J D , Eller T , Weg B v d , Hazrati J , Boogaard A H v d 
Published: November 2019

Abstract
The onset of localized necking under monotonic and non-monotonic loading can be well-predicted by the imperfection-based approach proposed by [1] (MK). However, a large number of virtual imperfections has to be investigated for an accurate necking prediction, making the MK approach computationally expensive and hence preventing the industrial application for full-scale vehicle models. To overcome these issues, a computationally efficient neural network (NN) model is proposed for replacing the MK model in the present work. An extended version of the MK model has been implemented into a User Material for an explicit crash solver. The model continuously computes the “distance to localized necking” as an important engineering quantity. Single shell element simulations are utilized for creating a comprehensive virtual test database for monotonic and non-monotonic loading for a 22MnB5 grade in an as-delivered state. A simple feed-forward NN model, featuring only one hidden layer, is trained and tested against the virtual data, where invariants of the stress and plastic strain tensors represent the input features of the NN and the “distance to necking” represents the output value of the NN. For comparison of the computational cost, the NN architecture has also been implemented in a User Material Routine for shell elements. The predictions of the NN and the MK model are in good agreement, where, due to the simple mathematical structure of the NN, the computational cost of the NN is significantly lower than for the MK implementation.
Springback characteristics of a martensitic steel for warm U-shape bending: Experiments and FE simulation
Authors: Sun Y , Cai Z , Politis D J , Luan X , Chen G , Wang L 
Published: November 2019

Abstract
Martensitic (MS) steel, a modern type of Ultra-high Strength Steel (UHSS), offers a significantly improved strength-to-weight ratio compared to conventional cold rolled steel grades. This is especially important for weight saving applications on crash-relevant automotive structures. However, it is challenging to conventionally cold form MS steel sheet into complex components due to the lower formability and excessive springback. In this present work, both experimental and finite element simulation methods have been used to investigate the springback characteristics of MS steel in U-shape bending at cold and warm stamping conditions. It was found that the amount of springback is greatly reduced by approximately 62.3% at elevated temperature compared to cold forming. Fast forming speeds were also found to be beneficial for reducing the springback. FE models were successfully developed for the U-shape forming process and close agreement between experimental data and FE simulation results has been achieved.
Predicting plasticity and fracture of severe pre-strained EN AW-5182 by Yld2000 yield locus and Hosford-Coulomb fracture model in sheet forming applications
Authors: Camberg A A , Tröster T , Bohner F , Tölle J 
Published: November 2019

Abstract
The objective of this contribution is to evaluate the capabilities of the Yld2000 yield locus and the Hosford-Coulomb fracture model under isothermal conditions for an EN AW-5182 H18 material in sheet metal forming applications. The calibration of the Yld2000 model is based on uniaxial tension tests in 0°, 45° and 90° in respect to rolling direction and additional layer compression tests. Subsequently, the calibrated plasticity model is evaluated under shear stress and plane strain dominant conditions. Stress state dependent fracture strains are obtained from various tensile tests as well as from FLD tests. The implemented failure prediction is based on a generalized incremental stress-state dependent fracture model (GISSMO) combined with a three-parameter Hosford-Coulomb fracture and instability curve. Finally, the plasticity and fracture models are validated at a cross die cup. It is shown that the models are capable to provide an accurate prediction of the onset of fracture and could be used for a non-isothermal extension in future work.
Descriptions of stress-strain responses of non-linear unloading and closure of stress-strain hysteresis loop based on the Yoshida-Uemori model
Authors: Yoshida F 
Published: November 2019

Abstract
This paper proposes models to describe a non-linear unloading-reloading stress-strain response and closure of a cyclic stress-strain hysteresis loop based on the Yoshida-Uemori (Y-U) model. The average stress-strain slope given by the non-linear model is consistent with the Y-U model of Young’s modulus degradation. The closure of a cyclic stress-strain curve is described by automatically changing one of the Y-U material parameters. An advantage of the above approaches is that no additional parameters are needed for modeling.
Predictive Analysis from numerical and experimental data in press hardening
Authors: Penter Lars , Link Patrick , Stoll Anke , Albert André , Ihlenfeldt Steffen 
Published: November 2019

Abstract
Machine learning, big data and deep learning are today’s catchphrases for how to improve reliability and productivity of your manufacturing equipment. Production companies implement a large number of sensors to record every activity within their production lines and learn as much as possible about their running processes in order to predict shifting product properties and to prevent stoppage due to failure. The successful application of machine learning algorithms to predict machine and process behavior depends on a reliable and balanced database. Since the foremost goal of every manufacturing business is to make sound parts and to avoid defects, there is a large amount of data available for smoothly running processes but only very little for failure production. One approach to solve this imbalance would be to link the production line data with simulation data. Simulation models allow for computing failure parts with no additional costs and therefore enable the exploration of the entire parameter space. We conducted press-hardening experiments with a variation of process parameters for a structural car body part on the press hardening line at Fraunhofer IWU. As an evaluation criterion, we measured the hardness of the final part at critical spots. In order to expand the experimental data, we applied FE simulations to the entire press hardening process chain. The paper explains limitations of the model and elaborates on its parameterization. As a final task, we applied a basic machine-learning algorithm to both experimental and numerical data as well as to their combination in order to evaluate the data space expansion through simulations. The results obtained through machine learning indicate significant differences in the prediction of part quality for solely experimental data and its combination with simulation data. This is especially true for press hardening because of non-linear system behavior and a large amount of uncertain and hard-to-identify parameters. We found that the most challenging parts of uniting measured and simulated data is not only to create simulations with appropriate accuracy, which allow for a meaningful extrapolation of the parameter space, but also to compare simulation and production data based on the same criterion and to have stable simulation models for the entire parameter range.
Effects of fracture area measurement method and tension test specimen type on fracture strain values of 980 class AHSS
Authors: Hance B M , Link T M 
Published: November 2019

Abstract
With increasing focus on “local formability” and fracture behavior of advanced high strength steels (AHSS), the effects of tension test specimen type and fracture area measurement method on fracture strain values were examined. Three 980 class AHSS and three standard tension test specimens with various widths were evaluated. Fractures types were grouped into three categories according to appearance and thickness profile “shape”—Type 1: Perpendicular to the tensile axis (across specimen width) with a V-shape thickness profile; Type 2: Irregular transition from Type 1 to Type 3 with a W-shape thickness profile; and Type 3: Angled across the specimen width with a U-shape thickness profile. All materials exhibited Type 1 fractures when tested with Subsize specimens. However, as the specimen width-to-thickness ratio increased, the fracture type changed from Type 1 to Type 2 or from Type 1 to Type 3. In contrasting the effects of specimen type and fracture area measurement method, specimen type (width) has a far greater impact on the consequent fracture strain value. For tension testing no clear universal relationship exists between the width-to-thickness ratio and the fracture strain. These observations suggest that, when reporting fracture strain values, the specimen type, the material thickness, and the fracture area measurement method must be indicated.
Control of the servo-press in stamping considering the variation of the incoming material properties
Authors: Kim Hyunok , Gu Jiahui C. , Zoller Laura 
Published: November 2019

Abstract
The variation of incoming material properties and the quality of emerging advanced high-strength steels significantly increases the costs for product design and production. It is not economical to tightly control material chemistry to eliminate the variation of material properties at steel mills. This paper introduces a methodology on how to implement a non-destructive evaluation (NDE) tool to measure the variation of the incoming material properties. The servo-controlled forming process was successfully optimized to adapt to variations in the incoming material properties in a lab-scale stamping cell with a 300-Ton mechanical servo press. Final stamping quality was obtained with three different batch materials by altering servo press parameters, such as the slide motion and blank holder force, to adjust for the variation of the material properties from one batch to another. Both a mid-strength (340-MPa tensile strength) steel and a high-strength steel (980-MPa tensile strength) were evaluated in this study. The study shows the effectiveness of an NDE tool to non-destructively measure the sheet material properties and the servo-press control to adjust the press parameters for the variation of the material properties.