Simulation of strain induced austenite-martensite transformation

Grain refinement due to phase transformation is an effective method for improving the mechanical properties of steel. An approach is proposed in the present work based on the FEM, for numerical simulation of the microstructure evolution as a result of hot rolling and subsequent cold torsion. Grain refinement in 304 stainless steel at four different technological schedules is considered. Results of numerical simulation are compared with experimental data. Coupling of the thermoplastic deformation with microstructure evolution is realized. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Prediction of temperature distribution and phase transformation on the run-out table in the process of hot strip rolling

In this paper a mathematical model based on the finite element method and the Scheil additivity rule is presented for predicting the temperature distribution and phase transformation behavior on the run-out table during the hot strip rolling of a low carbon steel. The model considers the austenite to ferrite and pearlite transformations, the temperature-dependent material properties of the cooling austenite as well as the austenite work hardening effect on the kinetics of austenite transformation. To determine the validity of the model predictions, the time-temperature histories of a low carbon steel rod in different cooling media were measured and also hot rolling experiments were performed. Good agreement between the predictions and the experimental results indicates the reliability of the model.     

Modelling of recrystallization behavior and austenite grain size evolution during the hot rolling of GCr15 rod

In this paper, four 3-D finite element models are developed to simulate the whole rod rolling process of GCr15 steel. The distribution and evolution of different field-variables, such as effective strain, effective strain rate and temperature, are obtained. Based on the simulated results and the microstructure evolution models of the steel, the paper designs a FORTRAN program to predict the evolution of recrystallization behavior and austenite grain size in rolled piece during the rolling. The surface temperatures of rolled piece calculated by FEM agree well with measured values. Comparison between calculated values and measured ones of grain size shows the validity of the program.     

A review of planning and scheduling systems and methods for integrated steel production

Iron and steel industry is an essential and sizable sector for industrialized economies. Since it is capital and energy extensive, companies have been putting consistent emphasis on technology advances in the production process to increase productivity and to save energy. The modern integrated process of steelmaking, continuous casting and hot rolling (SM–CC–HR) directly connects the steelmaking furnace, the continuous caster and the hot rolling mill with hot metal flow and makes a synchronized production. Such a process has many advantages over the traditional cold charge process. However, it also brings new challenges for production planning and scheduling. In this paper we first give a comparative analysis of the production processes and production management problems for the SM–CC–HR and the traditional cold charge process. We then review planning and scheduling systems developed and methods used for SM–CC–HR production. Finally some key issues for further research in this field are discussed.     

Deep Drawing Simulations Based on Microstructural Data

For the optimization of process chains in sheet metal forming it is required to accurately describe each partial process of the chain, e.g. rolling, press hardening and deep drawing. The prediction of the thickness distribution and the residual stresses in the blank has to be of high reliability, since the subsequent behavior of the semi-finished product in the following subprocesses strongly depends on the process history. Therefore, high-quality simulations have to be carried out which incorporate real microstructural data [1,2,3]. In this contribution, the ferritic steel DC04 is analyzed. A finite strain crystal plasticity model is used, for the application of which micro pillar compression tests were carried out experimentally and numerically to identify the material parameters of DC04. For the validation of the model, a two-dimensional EBSD data set has been discretized by finite elements and subjected to homogeneous displacement boundary conditions describing a large strain uniaxial tensile test. The results have been compared to experimental measurements of the specimen after the tensile test. Furthermore, a deep drawing process is simulated, which is based on a two-scale Taylor-type model at the integration points of the finite elements. At each integration point, the initial texture data given by the aforementioned EBSD measurements is assigned to the model. By applying this method, we predict the earing profiles of differently textured sheet metals. (© 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Material-based process-chain optimization in metal forming

The characteristics of a manufacturing product are influenced by a variety of different factors, such as the material properties of the base product. The prediction of properties that give optimal results in metal forming applications is a complex task but of high interest for the manufacturer. To realize such a prediction scheme, the process chain is split up into individual process steps and for each of them an inverse modeling is required. The specific aim of this work is to present an approach for the inverse problem formulation of a process step and to solve it using methods of machine learning. Moreover, the challenges that often arise due to the ill-posed nature of inverse problems will be discussed. The main focus is on the crystallographic texture of metals, which strongly affects the deformation behavior during a process step and highly influences the characteristics of the final product. (© 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Application of mathematical model for microstructure and mechanical property of hot rolled wire rods

A set of integrated mathematical models for predicting microstructures evolution during hot rolling and controlled cooling of high carbon wire rods has been developed through laboratory research work and industrial validation experiments. It consists of many sub-models such as critical strain, static and dynamic recrystallization of austenite, fraction of transformed austenite, interlamellar spacing of pearlite, microstructure–property relations. Based on the models, a simulating software is programmed which can run on PC computers. The physical metallurgy process during hot rolling and controlled cooling including the temperature distribution, the evolution of austenite grains, fraction of transformation austenite, final microstructure and mechanical properties were predicted. The predicted results are agree well with measured of the industrial tests.     

提高优质碳素结构钢(20#)钢板质量的研究

本文运用正交试验方法 ,确定优质碳素结构钢 (2 0 # )钢板热轧工艺参数 ,实现控制 ,提高2 0 #钢板的综合机械性能和冷弯工艺性能 ,提高产品质量     

FEM analysis for residual stress prediction in hot rolled steel strip during the run-out table cooling

With the increasing demand of higher quality hot rolled strips, flatness defects occurred on the strips during the cooling process on the run-out table have received significant attention and should be considered in the online shape control model. Non-uniform temperature distribution and cooling across the strip width are the main reasons why the strip becomes unflatten after cooling process although the strip is rolled flat at the finishing mill. A thermal, microstructural and mechanical coupling analysis model for predicting flatness change of steel strip during the run-out table cooling process was established using ABAQUS Finite Element Software. In this model, Esaka phase transformation kinetics model was employed to calculate the phase transformation, and coupled with temperature calculation by means of the user subroutine program HETVAL. An elasto-plasticity constitutive model of the material, in which conventional elastic and plastic strains, thermal strain, phase transformation strain and transformation induced plastic strain were taken into account, was derived and realized using the user subroutine program UMAT. The conclusion that the flatness of the steel strip will develop to edge wave defect under the functions of the different thermal and microstructural behaviors across strip width direction during the run-out table cooling procedure was acquired through the analysis results of this model. The calculation results of this analysis model agree with the actual measurements and observation, therefore this model has a high accuracy. To better control the flatness quality of hot rolled steel strip, the shape compensation control strategy of slight center wave rolling is proposed based on the analysis result. This control strategy has been verified by actual measurements, and applied in actual production.     

Simulating solid state sintering and compaction of metal powder in the finite strain regime

In many industrial applications (e.g. mills for crushing mineral goods, bearing rings) large ring-shaped workpieces with thick outer wear resistant layers can be found. The powder metallurgical production of these layers on a substrate ring using the hot isostatic pressing technology (HIP) has become the most prevailing production process in this field. Nevertheless using the HIP technology shows some important drawbacks like long process times, high logistic costs and maximum ring diameters of about 1.5 meters. A remedy to these problems is expected from the process integrated powder coating through radial axial rolling of rings. Herein, HIP is replaced by integrating the compaction and sintering of the metal powder into the rolling process of the substrate ring. For this purpose a constitutive material model is introduced in the following, which is able to describe sintering and compaction of metal powder in the finite strain regime. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Simulation and Measurements of Rolling Tire Dynamics

The simulation of rolling tires including stationary rolling, modal analysis, excitation with roughness of road surfaces and sound radiation is presented for state of the art industrial tire models. The target of this research, part of the german project “Leiser Straßenverkehr”, is the reduction of trafic noise, whereas the main source, namely the tire/road system, is investigated in contrast to other techniques like sound insulating walls. The needs and methods for the solution of the resulting large scale problems are discussed next to special properties of rotating structures, high frequency behavior of rubber material and approaches for the reduction of computational cost. For the validation of the model measurements of real tires and roads are used. These include shaker tests of the standing tire and acoustics of tires rolling on a drum. The same set–ups are applied to the simulation for the comparison of frequency response functions and sound pressure levels. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Microstructure analysis on IN 718 alloy round rod by FEM in the hot continuous rolling process

Based on physical metallurgy rules and experiential equations, models for microstructure analysis on IN 718 alloy in the round rod hot continuous rolling process has been developed using the finite element method (FEM) on the software ANSYS/LS-DYNA. The dynamic and metadynamic recrystallization models in and after deformation, the grain growth models in the compensated reheating process for IN 718 alloy are regressed, and corresponding processes are involved in these models. For a real rolling practice, the calculated central grain sizes were examined and are in good agreement with the measured ones. The element in the center of the workpiece is a typical one possessing the maximum of the effective strain, the temperature and the grain size in the rolling process. In the hot continuous rolling process, the relationship between the final grain size of the typical element and the inlet velocity of the first stand has been regressed by FE analysis, and the lower rolling speed is beneficial to the grain refinement.     

Theoretical and experimental investigation of anisotropic damage in textile-reinforced composite structures

In the present work, a phenomenological plane-stress damage-mechanics-based model for textile-reinforced composites is presented and its predictive capability is evaluated by carrying out a series of experimental tests. Damage variables are introduced to describe the evolution of the damage state and, as a subsequence, the degradation of material stiffness. For calculating the nonlinear stress and strain distribution of complexly loaded composites with a textile reinforcement, a special emphasis has to be placed on the interaction between the fiber failure due to the stress in the fiber direction and the matrix failure due to the transverse and shear stresses. This demands the formulation of realistic failure criteria taking into account the microstructural material behavior and different fracture modes. The new failure criteria, like the fracture mode concepts, consider these fracture modes, as well as further fracture types, in the reinforcement plane. The failure criteria are based on equations for failure surfaces in the stress space and damage thresholds in determining the stiffness degradation of the composite. The model proposed was used to characterize the strength and the failure behavior of carbon-fiber-reinforced composites. For this purpose, several unidirectional and bidirectional tests were performed to determine the specific properties of the material. The specimens were investigated by using acoustic emission techniques and strain-controlled tension and torsion tests.Russian translated published in Mekhanika Kompozitnykh Materialov, Vol. 40, No. 6, pp. 791–810, November–December, 2004.     

Numerical simulations of poly-crystalline shape-memory alloys based on a micromechanical model

Based on a micormechanical model we describe the material behaviour of specimens made of shape memory alloys by a finite element implementation. These materials undergo solid to solid phase transformations during loading and unloading which determine the characteristic pseudo-elastic or pseudo-plastic material response. Phase transitions, orientation distribution (pole figures) and the influence of pre-texture on the specimen, due to some previous treatment like rolling, are discussed. (© 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Thermomechanical modeling and simulation of aluminum alloys during extrusion process

The purpose of this work is to simulate the microstructure development of aluminum alloys during hot metal forming processes such as extrusion with the help of the Finite Element Method (FEM). To model the thermomechanical coupled behavior of the material during the extrusion process an appropriate material model is required. In the current work a Johnson–Cook like thermoelastic viscoplastic material model is used. To overcome the numerical difficulties during simulation of extrusion such as contact problem and element distortion an adaptive meshing system is developed and applied. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Dynamic modelling and simulation of a hot strip finishing mill

Hot rolling is an essential industrial process in the production of sheet steel, a widely used product in manufacturing and construction. A finishing mill performs a set of operations in a hot strip rolling mill, and is a complex unit including many processes and control loops. Its modelling is a challenging task due to the variety of phenomena that occur within the mill, and variable transport delays. Model validation is also challenging due to a scarcity of measurements. On the other hand, a dynamic model that adequately reflects the numerous interactions between the mill units can be very useful for tasks such as high performance control design or vibration analysis. In this study, a one-dimensional model has been developed and validated against real plant data. The end use of the model is intended to be looper control analysis, but the model is kept sufficiently general so that it can be used or easily extended for other applications.     

A hierarchical approach for one-dimensional cutting stock problems in the steel industry that maximizes yield and minimizes overgrading

In the steel industry, as hot steel products exit the producing facility, they are cut at primary saws (hotsaws) into shorter pieces. After these pieces cool, they are inspected for defects and either applied directly to customer orders or are further cut to ordered lengths at secondary saws (cold saws). In this case study, we will describe a hierarchical algorithm, DYNACUT_CS, that efficiently and effectively generates cutting patterns for material that is to be cut at cold saws. DYNACUT_CS strives to maximize yield over all the material cut and simultaneously tries to minimize overgrading (applying higher quality material than specified by the customer). An example will be given to illustrate how the algorithm works. This approach has been implemented for a variety of products at several different Bethlehem Steel Corporation facilities.     

Numerical Simulation of Spot-Weld Joints under Crash Loading

This paper compares FE simulations of spot-weld joints for dual-phase steel under different load cases by using damage models of Gurson-Tvergaard-Needleman (GTN) and its two extensions, GTN-Johnson-Cook and GTN-Hutchinson. Spot-weld specimens have three zones depending with different material properties: Base material, heat-affected zone and fusion zone. The characterization of the base material is straightforward. The other two zones are characterized with specifically heat-treated specimens. For each zone, flat smooth tensile, flat notched tensile and Iosipescu-shear specimen are used in order to obtain the damage behavior for different triaxiality values. GTN damage model parameters are calibrated with the help of smooth and notched flat tensile specimens. The parameters of the above mentioned extensions of GTN damage model are identified with the help of Iosipescu-shear specimen. Finally, the calibrated material models are used in the FE simulation of the spot-weld specimens under quasi static-load case (10 mm/min) for loading directions of 0°, 30°, 60°, 90°. The numerical force-displacement results are in good agreement with experimental results. (© 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)     

A multilevel network study of the effects of delinquent behavior on friendship evolution

A multilevel approach is proposed to the study of the evolution of multiple networks. In this approach, the basic evolution process is assumed to be the same, while parameter values may differ between different networks. For the network evolution process, stochastic actor-oriented models are used, of which the parameters are estimated by Markov chain Monte Carlo methods. This is applied to the study of effects of delinquent behavior on friendship formation, a question of long standing in criminology. The evolution of friendship is studied empirically in 19 school classes. It is concluded that there is evidence for an effect of similarity in delinquent behavior on friendship evolution. Similarity of the degree of delinquent behavior has a positive effect on tie formation but also on tie dissolution. The last result seems to contradict current criminological theories, and deserves further study.