bluuebunny/crossref_metadata_2025_split huggingface dataset:
Forming response of retained austenite in a C‐Si‐Mn high strength TRIP sheet steel
Authors: Streicher Amy M. , Speer John G. , Matlock David K. 
Published: December 2016

TRIP sheet steels typically consist of ferrite, bainite, retained austenite, and martensite. The retained austenite is of particular importance because its deformation‐induced transformation to martensite contributes to excellent combinations of strength and ductility. While information is available regarding austenite response in uniaxial tension, less information is available for TRIP steels with respect to the forming response of retained austenite in complex strain states. Therefore, the purpose of this work was to study the austenite transformation behaviour in different strain paths by determining the amount of retained austenite before and after forming. Forming experiments were performed on a high strength 0.19C‐1.63Si‐1.59Mn TRIP sheet steel 1.2 mm in thickness in two different strain conditions, uniaxial tension (ε1 = ‐2ε2) and balanced biaxial stretching (ε1 = ε2). Specimens were formed to strains ranging from zero to approximately 0.2 effective (von Mises) strain. Specimens were tested both longitudinally and transverse to the rolling direction in uniaxial tension, and subtle mechanical property differences were found.The volume fraction of austenite, determined with X‐ray diffraction subsequent to forming, was found to decrease with increasing strain for both forming modes. Some modification in the crystallographic texture of the ferrite was observed with increasing strain, in specimens tested in the balanced biaxial stretch condition. This trend was not evident in the uniaxial tensile test results. Slight differences were found in the transformation behaviour of the austenite when formed in different strain conditions. More austenite transformed in specimens tested parallel to the rolling direction than transverse to the rolling direction in uniaxial tension. The amount of austenite transformed during biaxial stretching was determined to be greater than the amount transformed in uniaxial tension for specimens tested transverse to the rolling direction at an equivalent von Mises strain. The amount of austenite that transformed in biaxial tension, however, was comparable to the amount of austenite that transformed in specimens tested longitudinal to the rolling direction in uniaxial tension.
Influence of constant and variable restraining force on springback of TRIP700 and stainless steel grades
Authors: Greisert Carsten , Wesemannm Jürgen 
Published: December 2016

Newly developed high strength steels (HSS) like dual phase (DP) and transformation induced plasticity (TRIP) grades as well as austenitic grades like AISI 304 and AISI 301 show superior strength compared to the microalloyed grades with the same formability (e.g. HSLA340). However, due to the multiphase microstructure and the austenite martensite transformation during forming, a higher springback will appear.In this paper the influence of different process parameters of six high strength steels on springback after stamping is investigated. The material properties were determined with uniaxial tensile tests. A modified Duncan Shabel test was used to draw U‐profiles with a controlled restraining force. To investigate different process parameters, constant restraining forces of 1 and 5kN and die radii of 3, 6, 9, and 12 mm were applied. In a second step, a shape set process was used. A constant restraining force of 1kN was used until a draw depth of 80 % was reached. Then the restraining was increased to 5.5 kN. The springback and the sidewall force were measured and analysed. An increased restraining force and a reduced die radius increases the sidewall force and reduces the springback. This resulted in a significant decrease in springback. The tests with variable restraining forces, also known as shape set process have shown that it combines a good formability with a reduced springback.
Trials for Reducing Depth of Oscillation Marks in Continuous Casting
Authors: Kudoh Masayuki , Itoh Yoichi 
Published: December 2016

Improvement of surface defects in a continuously cast slab or billet is important for saving surface scarfing and for carrying out direct rolling. Deep oscillation marks, one type of the surface defects, sometimes cause surface cracking and positive segregation. In this study, the mechanism by which oscillation marks are formed was investigated by using a continuously cast simulator, which is a billet‐type machine. Then attempts were made to reduce the depth of oscillation marks by two methods in which electromagnetic force, which is the most effective means for reducing depth, was not used. The two methods were use of an adiabatic board for preventing solidification of a meniscus and the use of a board for suppressing the flow of flux.Overlapping of a molten metal on a meniscus resulted in formation of oscillation marks in tin. On the other hand, bending of a solidified shell also resulted in formation of oscillation marks in a tin‐lead alloy. The depth of the oscillation marks formed by the overlapping mechanism was greater than that formed by the bending mechanism. Both mechanisms depended on the strength of the solidified shell. Therefore, two trials to reduce the depth of oscillation marks formed by the overlapping mechanism were carried out. In one trial, an adiabatic board was inserted into the molten metal. Reduction in depth of the oscillation marks reduced up to about 86% was achieved when high viscosity flux was used. However, the adiabatic board was not effective when low viscosity flux was used. In the other trial, a board was inserted into a molten flux layer with a depth of 10 mm in depth in order to suppress the flow of the flux and to change the direction of flux flow, and the depth of oscillation marks was reduced by about 33%. Therefore, both of these methods are effective for reducing the depth of oscillation marks in a continuously cast billet.
DTA‐Measurements to Determine the Thixoformability of Steels
Authors: Püttgen Wolfgang , Bleck Wolfgang 
Published: December 2016

Semi‐solid metallurgy (SSM), also known as “thixoforming” or “thixoprocessing”, is of special interest as a new potential manufacturing technology for components in the automobile, machine and electronic industries. The aim of this technology is to produce complex shapes which cannot be produced with conventional processing methods.An important process step of semi‐solid processing (SSP) is the reheating and isothermal holding of the billet within the solid‐liquid range in order to obtain the required fraction liquid content and the desired globular microstructure. Aside from the investigation of billet heating and the development of a suitable tool design, the development and evaluation of adequate microstructures over a wide temperature area is very important. The focus of this paper is to determine the semi‐solid area of different steels through Differential Thermal Analysis (DTA) measurements. To determine a process window for handling the alloys in the semi‐solid state, the DTA‐results can be combined with microstructure parameters. Subsequent quenching experiments show the development of the microstructure parameters (e.g. grain size, phase distribution, volume fraction, shape factor, matrix character, contiguity, and particle density of the primary solid and liquid phases). A comparison of the slopes of the determined solid‐liquid areas for different steels show the width of the melting or freezing intervals to evaluate the possible process windows. DTA‐experiments performed at different heating rates show the influence of faster heating and cooling rates on the solidus‐liquidus interval. To evaluate the suitability for the thixoforming processes, this paper describes, and then compares, the semi‐solid intervals of different steel grades, which have been investigated in the Department of Ferrous Metallurgy at the RWTH Aachen University. The tool steel HS 6‐5‐3 and the cold work tool steel X210CrW12 have a wide semi‐solid area, which can be explained due to the dissolution of different carbides. In contrast to this, the steels C45, 42CrMo4, 16MnCr5, 34CrNiMo4, 100Cr6, X220CrVMo13‐4 and the Alloy 33 show a much smaller semi‐solid area.
Effect of Residual Elements on Hot‐Crack Susceptibility of Austenitic Stainless Steel
Authors: Scheller Piotr R. , Bleck Wolfgang , Flesch Roman 
Published: December 2016

After partial melting and solidification of cylindrical samples hot tensile tests were performed on austenitic stainless steels containing residual elements such as copper, tin and lead as well as calcium and magnesium. Using well controlled cooling conditions down to the testing temperature a radially solidified microstructure in the test zone of the samples was achieved. The testing material was prepared by remelting of base material from the industrial production and addition of single elements in the vacuum induction furnace. The maximum strength and the reduction of area were determined in the temperature range between liquidus and 1100°C.With regard to the reheating and hot rolling process some samples were thermally treated under industrial conditions. The ductility of the material at temperatures down to 950°C was tested and the effect of annealing was evaluated. Recommendations for material processing by continuous casting and hot rolling were derived from the tests performed.
Simulation of the Process Influencing Behaviour of Forming Machines
Authors: Großmann Knut , Wiemer Hajo 
Published: December 2016

In the design of sheet metal components and associated tools the use of forming process simulation based on finite element method is state of the art. The modelling of the forming process, however, neglects fundamental influences of the forming machine. But today, the machine behaviour influencing the process can be described with simulation tools sufficiently.The article presented here describes the current state of simulation for forming machines in regard to static and dynamic influences on the forming process. Furthermore, two examples and a proposal for enhancing the model are given.
Modelling of the High‐temperature Ductility Properties during Solidification of Austenitic Stainless Steel
Authors: Diederichs Roman , Trute Sebastian , Bleck Wolfgang 
Published: December 2016

Knowledge of the high‐temperature ductility properties of steel grades is essential for the processing of steel products due to the existence of critical temperature regions. Embrittlement in the liquid/solid two‐phase region and in the precipitation region can be distinguished. In these regions, material failure can occur due to cracking as soon as the appearing strains and stresses exceed the formability of the material at a given temperature. Therefore, the temperature ranges where reduced ductility occurs have to be identified to ensure appropriate processing of the materials in continuous casting or welding. These temperature regions are usually investigated by means of hot tensile testing after melting of the specimen in situ. As these experiments are time‐consuming and expensive, a mathematical estimation of the results would be a great advance.The presented research work outlines the possibility of a mathematical description of the most important characteristics in the relationship reduction of area versus testing temperature. Especially the zero ductility temperature and zero strength temperature, the critical solidification interval, the maximum ductility range and the region of the secondary ductility drop, including the beginning of the ductility drop and the minimum ductility, are investigated. Furthermore, the reduction of area values for given testing temperatures can be estimated on the base of the chemical composition and the parameters of the hot tensile tests. For this purpose, a model formulated by means of multiple regression analysis on the basis of published experimental data is proposed for the description of the high‐temperature ductility properties of austenitic stainless steel grades of the Cr‐Ni‐ and the Cr‐Ni‐Mo‐type.
Investigation of the Parameters Influencing the Accuracy of Rapid Steelmaking Slag Analysis with Laser‐Induced Breakdown Spectroscopy
Authors: Palagas C. , Stavropoulos P. , Couris S. , Angelopoulos G.N. , Kolm I. , Papamantellos D.C. 
Published: December 2016

Laser‐Induced Breakdown Spectroscopy (LIBS) is used for the analysis of steelmaking slags (EAF, Ladle Furnace (LF) and Vacuum Ladle Degasser (VLD)). In view of the potential industrial application of LIBS for rapid slag analysis, relatively simple criteria were employed in order to obtain calibration curves for the elements of interest. The LIBS experiments were performed on samples prepared after crushing and milling to a size less than 0.2 mm and on as delivered solidified slag samples. In general, the analysis of the solidified as delivered slag samples exhibited better results than the corresponding analysis of the pressed slag, mainly for the elements distributed in the matrix. Thus, for LIBS application, the time consuming sample preparation of the slag can be avoided. According to the results obtained, the potential of LIBS technique for in‐situ, multi‐element analysis of slag was examined at the 60t‐ EAF of Helliniki Halyvourgia SA (HH‐Greece). The most important parameters that influence slag analysis are the laser pulse energy, the number of accumulated laser shots, the laser beam focusing conditions and the gating conditions of the detector. LIBS accuracy was found to depend on both the distribution of elements in the slag and on their environment (i.e. if they are embedded in the matrix or in a specific crystallized phase) as well. LIBS limitations for quantitative slag analysis are also discussed.The accuracy of FeOn LIBS analysis for as delivered solidified EAF and VLD slags of the steel plant of Georgsmarienhütte was satisfactory showing a Regression Coefficient (RC) of 0.93 and 0.95 respectively. The accuracy of SiO2 and MgO analysis of VLD slags with RCs of 0.94 and 0.86 respectively was also satisfactory. In contrast, for the EAF slags the RC for MgO and SiO2, due to the observed non‐homogeneous crystallized phases have shown insufficient values, with 0.55 and 0.43 respectively. Similar results were gained for the FeOn, MgO and SiO2 analysis of the HH slags. Due to the higher intensity of scattering, the analysis of CaO, Al2O3 and Cr2O3 was of lower accuracy than for FeOn, MgO and SiO2.
Assessment of agricultural crops and natural vegetation in Scotland for energy production by anaerobic digestion and hydrothermal liquefaction
Authors: Biller Patrick , Lawson David , Madsen René B. , Becker Jacob , Iversen Bo B. , Glasius Marianne 
Published: December 2016

AbstractThe current paper investigates the use of natural vegetation and agricultural crops commonly found in Scotland as a source of bioenergy. Such biomass is shown to have a high moisture content upon harvest (∼80%) which renders them suitable for wet conversion technologies such as anaerobic digestion (AD) and hydrothermal liquefaction (HTL). Experimental investigations are carried out on 16 different types of biomass to assess their bio-crude yields via HTL and theoretical methane potential via AD based on compositional analysis. The different types of biomass vary significantly in biomass yield upon harvesting from 1.1 t/ha (dry matter) for bracken to a maximum of 17.5 t/ha for winter rye. These area specific yields are the most influential factor in the final energy yield per area. Area specific energy yields are found to average at 67 GJ/ha for AD and 53 GJ/ha for HTL. The respective conversion efficiencies of HTL and AD for different biomass feedstocks are also shown to be an important factor on the overall energy potential. AD averages a mass to energy conversion of 9.1 GJ/t compared to 7.2 GJ/t for HTL. A combination of AD and HTL is investigated by liquefying digestate from rye, but the results suggest this is not a viable option due to low bio-crude yields. However, analysis of the water phase post HTL allowed the calculation of theoretical methane potential from the HTL process water and suggests that this can yield additional energy. Overall, the work shows that utilisation of natural vegetation is a promising approach for bioenergy production.
Serious games and blended learning; effects on performance and motivation in medical education
Authors: Dankbaar Mary 
Published: December 2016

Introduction More efficient, flexible training models are needed in medical education. Information technology offers the tools to design and develop effective and more efficient training. The aims of this thesis were: 1) Compare the effectiveness of blended versus classroom training for the acquisition of knowledge; 2) Investigate the effectiveness and critical design features of serious games for performance improvement and motivation.
Methods Five empirical studies were conducted to answer the research questions and a descriptive study on an evaluation framework to assess serious games was performed.
Results The results of the research studies indicated that: 1) For knowledge acquisition, blended learning is equally effective and attractive for learners as classroom learning; 2) A serious game with realistic, interactive cases improved complex cognitive skills for residents, with limited self-study time. Although the same game was motivating for inexperienced medical students and stimulated them to study longer, it did not improve their cognitive skills, compared with what they learned from an instructional e‑module. This indicates an ‘expertise reversal effect’, where a rich learning environment is effective for experts, but may be contra-productive for novices (interaction of prior knowledge and complexity of format).
Discussion A blended design is equally effective and attractive as classroom training. Blended learning facilitates adaptation to the learners’ knowledge level, flexibility in time and scalability of learning. Games may support skills learning, provided task complexity matches the learner’s competency level.
A novel maturation index based on neonatal diffusion tensor imaging reflects typical perinatal white matter development in humans
Authors: Rasmussen Jerod M. , Kruggel Frithjof , Gilmore John H. , Styner Martin , Entringer Sonja , Consing Kirsten N.Z. , Potkin Steven G. , Wadhwa Pathik D. , Buss Claudia 
Published: December 2016

AbstractHuman birth presents an abrupt transition from intrauterine to extrauterine life. Here we introduce a novel Maturation Index (MI) that considers the relative importance of gestational age at birth and postnatal age at scan in a General Linear Model. The MI is then applied to Diffusion Tensor Imaging (DTI) in newborns for characterizing typical white matter development in neonates. DTI was performed cross‐sectionally in 47 neonates (gestational age at birth = 39.1 ± 1.6 weeks [GA], postnatal age at scan = 25.5 ± 12.2 days [SA]). Radial diffusivity (RD), axial diffusivity (AD) and fractional anisotropy (FA) along 27 white matter fiber tracts were considered. The MI was used to characterize inflection in maturation at the time of birth using GLM estimated rates of change before and after birth. It is proposed that the sign (positive versus negative) of MI reflects the period of greatest maturation rate. Two general patterns emerged from the MI analysis. First, RD and AD (but not FA) had positive MI on average across the whole brain (average MIAD = 0.31 ± 0.42, average MIRD = 0.22 ± 0.34). Second, significant regions of negative MI in RD and FA (but not AD) were observed in the inferior corticospinal regions, areas known to myelinate early. Observations using the proposed method are consistent with proposed models of the white matter maturation process in which pre‐myelination is described by changes in AD and RD due to oligodendrocyte proliferation while true myelination is characterized by changes in RD and FA due to myelin formation.
Optimal perturbation growth in axisymmetric intrusions
Authors: Sutherland Bruce R. , Caulfield C. P. 
Published: December 2016

The cylindrical lock-release laboratory experiments of Sutherland & Nault (J. Fluid Mech., vol. 586, 2007, pp. 109–118) showed that a radially advancing symmetric intrusive gravity current spreads not as an expanding annulus (as is the case for bottom-propagating gravity currents), but rather predominantly along azimuthally periodic radial ‘spokes’. Here, we investigate whether the spokes are associated with azimuthal perturbations that undergo ‘optimal’ growth. We use a nonlinear axisymmetric numerical simulation initialised with the experimental parameters to compute the time-evolving axisymmetric base state of the collapsing lock fluid. Using fields from this rapidly evolving base state together with the linearised perturbation equations and their adjoint, the ‘direct–adjoint looping’ method is employed to identify, as a function of the azimuthal wavenumber $m$, the vertical–radial structure of the set of initial perturbations that exhibit the largest total perturbation energy gain over a target time $T$. Of this set of perturbations, the one that extracts energy fastest, and so is expected to be observed to emerge first from the base flow, has azimuthal wavenumber comparable to the number of spokes observed in the experiment.
A method to retrieve the spectral complex refractive index and single scattering optical properties of dust deposited in mountain snow
Authors: SKILES S. McKENZIE , PAINTER THOMAS , OKIN GREGORY S. 
Published: December 2016

ABSTRACTDust deposition to snow can have regionally important climatic and hydrologic impacts resulting from direct reduction of surface albedo and indirectly from the initiation of snow albedo feedbacks. Modeling the radiative impacts of dust deposited in snow requires knowledge of the optical properties of both components. Here we present an inversion technique to retrieve the effective optical properties of dust deposited in mountain snow cover from measurements of hemispherical dust reflectance and particle size distributions using radiative transfer modeling. First, modeled reflectance is produced from single scattering properties modeled with Mie theory for a specified grain size distribution over a range of values for the imaginary part of the complex refractive index (k = 0.00001–0.1). Then, a multi-step look-up table process is employed to retrieve kλ and single scattering optical properties by matching measured to modeled reflectance across the shortwave and near infrared. The real part of the complex refractive index, n, for dust aerosols ranges between 1.5 and 1.6 and a sensitivity analysis shows the method is relatively insensitive to the choice of n within this range, 1.525 was used here. Using the values retrieved by this method to update dust optical properties in a snow + aerosol radiative transfer model reduces errors in springtime albedo modeling by 50–70%.