MAGMA GmbH

Aachen, Germany

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Aachen, Germany
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Andriollo T.,Technical University of Denmark | Thorborg J.,Technical University of Denmark | Thorborg J.,MAGMA GmbH | Hattel J.,Technical University of Denmark
Modelling and Simulation in Materials Science and Engineering | Year: 2017

In this paper a thorough analysis of the equivalent indenter concept applied to nano-indentation is carried out, motivated by the fact that previous works in the field have not considered the requirement of a consistent relation between contact depth and projected contact area. Dimensional analysis is initially used to prove that the shape of the axisymmetric equivalent indenter can be regarded as a material property, provided that size-effects are negligible. Subsequently, it is shown that such shape can effectively be employed to describe the nano-indentation unloading stage by means of Sneddon's elastic solution which is formally valid only for indentation into a flat surface. This allows for formulating the problem of extracting Young's modulus from the unloading curve as an optimization problem. However, it is proved that the latter does not have a unique solution, due to the particular mathematical structure of the underlying equations; hence, additional constraints are needed to set restrictions on the admissible equivalent indenter shapes. An example of such constraint is hidden in some apparent inconsistencies of the well-known Oliver-Pharr method, which is demonstrated to be based on an equivalent conical indenter whose semi-apical angle depends on the ratio between residual and total penetration. Specifically, this angle tends to 90° when the material exhibits extensive inelastic deformation, whereas it reduces to the one characteristic of the real indenter for a perfectly elastic material. This provides a new physical explanation for the relatively good accuracy of the method even in presence of a non-negligible residual contact impression on the sample. © 2017 IOP Publishing Ltd.


Spangenberg J.,Technical University of Denmark | Roussel N.,University Paris Est Creteil | Hattel J.H.,Technical University of Denmark | Thorborg J.,Technical University of Denmark | And 4 more authors.
RILEM Bookseries | Year: 2010

SCC is nowadays a worldwide used construction material. However, heterogeneities induced by casting may lead to variations of local properties and hence to a potential decrease of the structure's load carrying capacity. The heterogeneities in SCC are primarily caused by static and dynamic segregation. The present paper reports property maps for a beam based on particle distributions at the end of casting derived from numerical flow simulations. A finite volume based numerical model is used to predict particle distributions at the end of casting, which are then converted into property maps using semi-empirical relations from the literature. © RILEM 2010.


Andriollo T.,Technical University of Denmark | Thorborg J.,Technical University of Denmark | Thorborg J.,MAGMA GmbH | Tiedje N.,Technical University of Denmark | Hattel J.,Technical University of Denmark
Modelling and Simulation in Materials Science and Engineering | Year: 2016

In this paper, the thermo-elastic behavior of the graphite nodules contained in ductile iron is derived on the basis of recent transmission electron microscopy investigations of their real internal structure. The proposed model is initially validated by performing a finite element homogenization analysis to verify its consistency with the room-temperature elastic properties of ductile iron measured at the macro scale. Subsequently, it is used to investigate the formation of local residual stresses around the graphite particles by simulating the manufacturing process of a typical ferritic ductile iron grade, and the results are compared with preliminary measurements using synchrotron x-rays. Finally, the obtained accurate description of the stress & strain field at the micro scale is used to shed light on common failure modes reported for the nodules and on some peculiar properties observed in ductile iron at both micro and macro scale. © 2016 IOP Publishing Ltd.


Flender E.,Magma GmbH | Sturm J.,Magma GmbH
International Journal of Metalcasting | Year: 2010

Not many developments in recent decades have changed the understanding of the metalcasting process as fundamentally as casting process simulation has. The main intention of this paper is to provide an easy to read and attractive overview for foundrymen addressing the development, current state, and future of casting process simulation from the point of view of the European authors. Copyright © 2010 American Foundry Society.


Kotas P.,Technical University of Denmark | Tutum C.,Technical University of Denmark | Hattel J.,Technical University of Denmark | Snajdrova O.,Vitkovice Heavy Machinery A.S. | And 2 more authors.
International Journal of Metalcasting | Year: 2010

This work summarizes the findings of multi-objective optimization of a gravity sand-cast steel part for which an increase of casting yield via riser optimization was considered. This was accomplished by coupling a casting simulation software package with an optimization module. The benefits of this approach, recently adopted in the foundry industry worldwide and based on fully automated computer optimization, were demonstrated. First, analyses of filling and solidification of the original casting design were conducted in the standard simulation environment to determine potential flaws and inadequacies. Based on the initial assessment, the gating system was redesigned and the chills rearranged to improve the solidification pattern. After these two cases were evaluated, the adequate optimization targets and constraints were defined. One multi-objective optimization case with conflicting objectives was considered in which minimization of the riser volume together with minimization of shrinkage porosity and limitation of centerline porosity were performed. Copyright © 2010 American Foundry Society.


Kotas P.,Technical University of Denmark | Tutum C.C.,Technical University of Denmark | Thorborg J.,MAGMA GmbH | Hattel J.H.,Technical University of Denmark
Metallurgical and Materials Transactions B: Process Metallurgy and Materials Processing Science | Year: 2012

A methodology of how to exploit the Niyama criterion for the elimination of various defects such as centerline porosity, macrosegregation, and hot tearing in steel castings is presented. The tendency of forming centerline porosity is governed by the temperature distribution close to the end of the solidification interval, specifically by thermal gradients and cooling rates. The physics behind macrosegregation and hot tears indicate that these two defects also are dependent heavily on thermal gradients and pressure drop in the mushy zone. The objective of this work is to show that by optimizing the solidification pattern, i.e., establishing directional and progressive solidification with the help of the Niyama criterion, macrosegregation and hot tearing issues can be both minimized or eliminated entirely. An original casting layout was simulated using a transient three-dimensional (3-D) thermal fluid model incorporated in a commercial simulation software package to determine potential flaws and inadequacies. Based on the initial casting process assessment, multiobjective optimization of the solidification pattern of the considered steel part followed. That is, the multiobjective optimization problem of choosing the proper riser and chill designs has been investigated using genetic algorithms while simultaneously considering their impact on centerline porosity, the macrosegregation pattern, and primarily on hot tear formation. © The Minerals, Metals &Materials Society and ASM International 2012.


Hepp E.,MAGMA GmbH | Hurevich V.,MAGMA GmbH | Schafer W.,MAGMA GmbH
IOP Conference Series: Materials Science and Engineering | Year: 2012

The integrated modeling and simulation of the casting and heat treatment processes for producing austempered ductile iron (ADI) castings is presented. The focus is on describing different models to simulate the austenitization, quenching and austempering steps during ADI heat treatment. The starting point for the heat treatment simulation is the simulated microstructure after solidification and cooling. The austenitization model considers the transformation of the initial ferrite-pearlite matrix into austenite as well as the dissolution of graphite in austenite to attain a uniform carbon distribution. The quenching model is based on measured CCT diagrams. Measurements have been carried out to obtain these diagrams for different alloys with varying Cu, Ni and Mo contents. The austempering model includes nucleation and growth kinetics of the ADI matrix. The model of ADI nucleation is based on experimental measurements made for varied Cu, Ni, Mo contents and austempering temperatures. The ADI kinetic model uses a diffusion controlled approach to model the growth. The models have been integrated in a tool for casting process simulation. Results are shown for the optimization of the heat treatment process of a planetary carrier casting. © Published under licence by IOP Publishing Ltd.


Bjerre M.,Technical University of Denmark | Tiedje N.S.,Technical University of Denmark | Thorborg J.,Magma GmbH | Hattel J.H.,Technical University of Denmark
IOP Conference Series: Materials Science and Engineering | Year: 2015

In the present paper modelling the solidification of cast iron parts is considered. Common for previous efforts in this field is that they have mainly considered thin walled to medium thickness castings. Hence, a numerical model combining the solidification model presented by Lesoultet al. [1] with a 2D FE solution of the heat conduction equation is developed in an in-house code and model parameters are calibrated using experimental data from representative castings made of ductile cast iron. The main focus is on the influence of casting thickness and resulting local cooling conditions on the solidification pattern and the relation to formation of degenerate graphite. © Published under licence by IOP Publishing Ltd.


Andriollo T.,Technical University of Denmark | Thorborg J.,MAGMA GmbH | Tiedje N.S.,Technical University of Denmark | Hattel J.,Technical University of Denmark
IOP Conference Series: Materials Science and Engineering | Year: 2015

In the present paper a micro-mechanical model for investigating the stress-strain relation of ductile cast iron subjected to simple loading conditions is presented. The model is based on a unit cell containing a single spherical graphite nodule embedded in a uniform ferritic matrix, under the assumption of infinitesimal strains and plane-stress conditions. Despite the latter being a limitation with respect to full 3D models, it allows a direct comparison with experimental investigations of damage evolution on the surface of ductile cast iron components, where the stress state is biaxial in nature. In contrast to previous works on the subject, the material behaviour in both matrix and nodule is assumed to be elasto-plastic, described by the classical J2-flow theory of plasticity, and damage evolution in the matrix is taken into account via Lemaitre's isotropic model. The effects of residual stresses due to the cooling process during manufacturing are also considered. Numerical solutions are obtained using an in-house developed finite element code; proper comparison with literature in the field is given. © Published under licence by IOP Publishing Ltd.

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