Dillingen an der Donau, Germany
Dillingen an der Donau, Germany

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DiRienzo A.L.,University of Wyoming | Yakacki C.M.,University of Colorado at Denver | Frensemeier M.,Leibniz Institute for New Materials | Schneider A.S.,AG der Dillinger Huttenwerke | And 3 more authors.
Journal of the Mechanical Behavior of Biomedical Materials | Year: 2014

The focus of this study was to fabricate and investigate the mechanical behavior of porous poly(para-phenylene) (PPP) for potential use as a load-bearing orthopedic biomaterial. PPPs are known to have exceptional mechanical properties due to their aromatic backbone; however, the manufacturing and properties of PPP porous structures have not been previously investigated. Tailored porous structures with either small (150-250. μm) or large (420-500. μm) pore sizes were manufactured using a powder-sintering/salt-leaching technique. Porosities were systematically varied using 50 to 90. vol%. Micro-computed tomography (μCT) and scanning electron microscopy (SEM) were used to verify an open-cell structure and investigate pore morphology of the scaffolds. Uniaxial mechanical behavior of solid and porous PPP samples was characterized through tensile and compressive testing. Both modulus and strength decreased with increasing porosity and matched well with foam theory. Porous scaffolds showed a significant decrease in strain-to-failure (<4%) under tensile loading and experienced linear elasticity, plastic deformation, and densification under compressive loading. Over the size ranges tested, pore size did not significantly influence the mechanical behavior of the scaffolds on a consistent basis. These results are discussed in regards to use of porous PPP for orthopedic applications and a prototype porous interbody fusion cage is presented.© 2013 Elsevier Ltd.


Steinboeck A.,Vienna University of Technology | Graichen K.,Vienna University of Technology | Wild D.,AG der Dillinger Huttenwerke | Kiefer T.,AG der Dillinger Huttenwerke | Kugi A.,Vienna University of Technology
Journal of Process Control | Year: 2011

A temperature control method is developed for reheating steel slabs in an industrial furnace. The work was motivated by the need for mathematically simple furnace control schemes that feature accuracy, robustness, applicability to online control, and capabilities of non-steady-state operating scenarios, where the temperature goals and other properties of the slabs may vary considerably. The proposed hierarchical control concept computes desired heat inputs for each individual slab based on a discrete-time nonlinear model. Then, a quadratic program is solved to plan reference trajectories of furnace temperatures which optimally realize the desired heat inputs into the slabs. The iterative algorithm accounts for constraints on system inputs as well as states and may be used for open-loop control or as a feedforward branch in two-degrees-of-freedom control structures. The feasibility and the limitations of the approach are demonstrated by means of an example problem. © 2010 Elsevier Ltd. All rights reserved.


Steinboeck A.,Vienna University of Technology | Wild D.,AG der Dillinger Huttenwerke | Kiefer T.,AG der Dillinger Huttenwerke | Kugi A.,Vienna University of Technology
International Journal of Heat and Mass Transfer | Year: 2010

A mathematical model of the reheating process of steel slabs in industrial fuel-fired furnaces is developed. The transient temperature field inside the slabs is computed by means of the Galerkin method. Radiative heat transfer inside the furnace constitutes boundary conditions that couple the dynamic subsystems of the slabs. Constraining the heat fluxes to piecewise linear, discontinuous signals furnishes a discrete-time state-space system. Conditions for an exponential decrease of the open-loop control error are derived. Measurements from an instrumented slab in the real system demonstrate the accuracy of the model. The simple and computationally inexpensive model is suitable for trajectory planning, optimization, and controller design. © 2010 Elsevier Ltd. All rights reserved.


Steinboeck A.,Vienna University of Technology | Wild D.,AG der Dillinger Huttenwerke | Kiefer T.,AG der Dillinger Huttenwerke | Kugi A.,Vienna University of Technology
Mathematics and Computers in Simulation | Year: 2011

A flexible solution method for the initial-boundary value problem of the temperature field in a one-dimensional domain of a solid with significantly nonlinear material parameters and radiation boundary conditions is proposed. A transformation of the temperature values allows the isolation of the nonlinear material characteristics into a single coefficient of the heat conduction equation. The Galerkin method is utilized for spatial discretization of the problem and integration of the time domain is done by constraining the boundary heat fluxes to piecewise linear, discontinuous signals. The radiative heat exchange is computed with the help of the Stefan-Boltzmann law, such that the ambient temperatures serve as system inputs. The feasibility and accuracy of the proposed method are demonstrated by means of an example of heat treatment of a steel slab, where numerical results are compared to the finite difference method. © 2010 IMACS.


Kiefer T.,AG der Dillinger Huttenwerke | Graichen K.,Vienna University of Technology | Kugi A.,Vienna University of Technology
IEEE Transactions on Control Systems Technology | Year: 2010

This brief deals with the tracking control design of a helicopter laboratory experimental setup. In order to be able to realize highly dynamic flight maneuvers, both input and state constraints have to be systematically accounted for within the control design procedure. The mathematical model being considered constitutes a nonlinear mathematical mechanical system with two control inputs and three degrees of freedom. The control concept consists of an inversion-based feedforward controller for trajectory tracking and a feedback controller for the trajectory error dynamics. The design of the feedforward controller for a point-to-point flight maneuver is traced back to the solution of a 2-point boundary value problem in the Byrnes-Isidori normal form of the mathematical model. By utilizing special saturation functions, the given constraints in the inputs and states can be systematically incorporated in the overall design process. In order to capture model uncertainties and external disturbance, an optimal state feedback controller is designed on the basis of the model linearization along the desired trajectories. The proposed control scheme is implemented in a real-time environment, and the feasibility and the excellent performance are demonstrated by means of experimental results. © 2009 IEEE.


Steinboeck A.,Vienna University of Technology | Wild D.,AG der Dillinger Huttenwerke | Kugi A.,Vienna University of Technology
IFAC Proceedings Volumes (IFAC-PapersOnline) | Year: 2011

A Lyapunov-based MIMO state feedback controller is developed for slab temperatures in a continuous, fuel-fired reheating furnace. Following an early lumping approach, the computationally simple tracking controller is designed for a nonlinear, switched dynamic model that captures both conductive and radiative heat transfer. The controller modifies reference trajectories of furnace temperatures and is part of a cascade control scheme. Given some nonrestrictive conditions, exponential stability is ensured, even under non-steady state operating conditions. The capabilities of the controller are demonstrated by means of an example problem. © 2011 IFAC.


Speicher K.,Vienna University of Technology | Steinboeck A.,Vienna University of Technology | Wild D.,AG der Dillinger Huttenwerke | Kiefer T.,AG der Dillinger Huttenwerke | Kugi A.,Vienna University of Technology
IFAC Proceedings Volumes (IFAC-PapersOnline) | Year: 2013

An integrated model and an extended Kalman filter (EKF) of the product temperatures in hot rolling are presented The dynamical model takes into account the effect of all significant production steps on the temperature evolution of the plate, i.e., roll passes, descaling passes, and air cooling periods Consequently, the model structure is switching Based on this model, an EKF is developed that uses surface temperature measurements from pyrometers installed along the production line However, these pyrometers measure only at discrete points in time, when the plate passes the pyrometer Thus, the EKF has to cope with the switching model structure and with scarce measurements To test the performance of the developed EKF, experiments with supplementary pyrometer measurements were carried out so that the observed temperature can be compared to measurements which were not used as inputs of the filter Copyright © 2013 IFAC.


Bruckhaus R.,AG der Dillinger Huttenwerke | Fandrich R.,Stahlinstitut VDEh
Transactions of the Indian Institute of Metals | Year: 2013

Abstract: About 60 % of the crude steel in Europe is currently produced by the oxygen steelmaking process and 40 % by the electric steelmaking process. The product range is of decisive importance for the layout of the steelworks and the equipment for secondary metallurgical treatment. Regarding steelmaking worldwide, thin slabs are increasingly being produced in addition to conventional formats such as slabs, blooms, billets and beam blanks. In order to ensure long-term economic success, however, companies have continuously to develop sophisticated technologies for steel production. Challenges for the future remain in the production of high-purity steel grades, as well as the development of zero-error strategies with maximum productivity and flexibility. This paper summarizes current trends in the development of steelmaking processes. © 2013 Indian Institute of Metals.


Lohmar J.,RWTH Aachen | Bambach M.,RWTH Aachen | Hirt G.,RWTH Aachen | Kiefer T.,AG der Dillinger Huttenwerke | Kotliba D.,AG der Dillinger Huttenwerke
Steel Research International | Year: 2014

The industry scale production of heavy steel plates is performed in plate mills using reversing mill stands and roll schedules with 30 or more passes. Ideal pass scheduling is dependent on a precise prediction of the roll force in each pass. To obtain these forces process models based on the slab theory together with semi-empirical material models are most frequently used. The material parameters necessary to calibrate the models for a specific steel grade are conventionally generated on a lab scale via time-consuming and expensive compression tests. This paper will introduce a concept that allows obtaining the material model parameters directly from the rolling process on an industrial scale by an inverse modeling technique. In this context, the parameters of the material model are adjusted according to the current offset between measured and calculated roll forces. The adjustment is enabled by a non-linear optimization that aims for a minimum deviation between measured and calculated roll forces for each pass. Several results gathered in an optimization run with industrial data of about 2650 produced plates are presented. The concurrence between measurement and prediction using the optimal parameters is in detail shown for three different schedules. In summary, inverse modeling seems to allow utilizing data of past rolling processes to determine material model parameters with high accuracy. © 2014 Wiley-VCH Verlag GmbH & Co. KGaA.


Bambach M.,RWTH Aachen | Seuren S.,AG der Dillinger Huttenwerke
Journal of Materials Processing Technology | Year: 2015

In multi-pass rolling processes such as plate rolling, accurate predictions of roll force and torque over all roll passes are desired, so that the pre-calculated roll pass schedule can be put into practice without exceeding the limits of the roll stand. In this context, the grain size has two roles; the final grain size determines the product properties, and the evolution of grain size influences the force predictions. Since the grain size predicted after each roll pass enters the recrystallization kinetics and grain size evolution equations of the subsequent pass, a feed-back loop for the grain size calculation is created, which may become unstable so that the computed roll force and grain size become very sensitive to small variations in the input parameters. Although models for the evolution of grain size in multi-stage hot rolling have been applied in the industry for decades, their mathematical stability has not been given much attention, which poses difficulties for force and grain size predictions in cases subject to partial recrystallization. In this paper, the stability of a common semi-empirical model for static recrystallization and grain growth is investigated. The conditions under which instabilities occur are analyzed both for an industrial plate rolling pass schedule and for idealized load cycles. It is shown that complete recrystallization between roll passes leads to a stable grain size evolution, and that some states of partial recrystallization are unstable and hence problematic for force and grain size predictions. Instabilities in force and grain size predictions of an industrial pass schedules are analyzed by computing sensitivities using automatic differentiation of the model, showing that large amplification factors may occur if the states of partial recrystallization are treated by average strains and grain sizes. The instabilities are an inherent property of the closed-form equations for microstructure evolution for some states of partial recrystallization. However, the side effects of the instabilities can be reduced if the microstructure is not represented by average values of grain size and accumulated strain but by substructures generated by partial recrystallization. This way, the accuracy of roll force predictions can be considerably improved. © 2014 Elsevier B.V.

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