Modelling and simulation of continuous metal foaming processBelkessam, Omar; Fritsching, Udo
doi: 10.1088/0965-0393/11/6/001pmid: N/A
Metal foams have recently gained a lot of technical interest, e.g. within the automotive industry, due to their reduced weight and interesting material properties. In this paper, a computational model is presented, which allows the simulation of static and dynamic metal foam production processes. The metal foaming process is based on a procedure whereby a pre-compacted material consisting of a base metal plus a foaming agent is heated up to a certain foaming temperature. The heating process leads to partial metal melting as well as to the release of the reacting propellant gas and consequently to the material foaming in the semi-solid state.Mathematical models of the different relevant physical subprocesses and effects during the metal foaming process are derived in this paper. For investigation of the conventional static metal foaming process, the geometry of a foamable material (round disc) is selected first and the foaming process is computed by means of one- and two-dimensional models. In addition to the computed foam geometry, further foam characteristics like global density, temperature distribution and time evolution of the species concentrations taking part in the decomposition chemical reaction have been determined within the foaming process from numerical simulation. Finally, the simulation of a new dynamic (continuous) metal foaming process within specifically designed nozzles is accomplished. The numerical results obtained are compared with experiments.
Internal atomic stress near 5 tilt grain boundary in aluminium under tensionKitamura, Takayuki; Umeno, Yoshitaka; Tsuji, Nagatomo
doi: 10.1088/0965-0393/11/6/002pmid: N/A
It is important to clarify the mechanical properties of inhomogeneous structures from the viewpoint of atomic scale to understand the mechanical behaviour of microscopic materials. Thus, the mechanical properties of local regions with inhomogeneous and non-uniform structure have been intensively investigated on the basis of the atomic stress and the elastic constant. In this study, in order to examine the mechanical behaviour of local regions under external load, we conduct atomic tensile simulations on a 5-(013) tilt grain boundary in aluminium using the many-body effective medium theory potential function. The structure of the grain boundary consists of two types of atomic layers, one of which has a higher elastic constant near the grain boundary and the other has a lower one. Although the grain boundary consists of identical atomic species, the local region near the grain boundary displays the mechanical properties similar to those of a composite material.
Simple model for localization in -PuSöderlind, Per; Landa, Alex
doi: 10.1088/0965-0393/11/6/003pmid: N/A
First-principles methods are employed to study the effect of localization of the 5f electrons in -Pu. First, a full-potential linear muffintin orbitals (FPLMTO) method was applied to a model system, , where Puloc are Pu atoms with localized (nonbonding) 5f electrons and Puit atoms with itinerant (bonding) 5f electrons. Within the FPLMTO, this system was treated as an ordered compound, either in the Cu3Au or the CuAu structure to model -Pu which crystallize in a face-centred-cubic structure. A more realistic alloy treatment of our model system was provided by the KorringaKohnRostocker method within Green's function formalism in which compositional disorder is treated by means of the coherent potential approximation. With these two approaches best agreement with the experimental lattice constant for -Pu were achieved for a 6768% fraction of itinerant (Puit) atoms. This corresponds to a little less than four itinerant 5f electrons/atom in -Pu which agrees well with some proposed theoretical models, but disagree with at least an other theoretical suggestion. We show that a good lattice constant (by construction), good bulk modulus, and full mechanical stability for -Pu follows from our model. The main problem with the present approach and some other presented models, trying to capture localization in -Pu, is that the contribution to the total energy from the localized 5f electrons cannot be calculated accurately and therefore one parameter (usually the lattice constant) needs to be fitted to experiment.
Through-process modelling of the impact of intermediate annealing on texture evolution in aluminium alloy AA 5182Engler, Olaf
doi: 10.1088/0965-0393/11/6/005pmid: N/A
The control of plastic anisotropy during the formation of a metallic sheet requires detailed knowledge on its microstructure and, especially, crystallographic texture. During the thermo-mechanical production of an aluminium sheet the material experiences a complex history of temperature, time and strain paths. Thus, for a comprehensive through-process modelling of the evolution of texture, the individual models for simulating rolling and recrystallization textures have to be combined, which makes great demands on the accuracy of the respective models. This paper explores the potential of such coupled texture simulations by using an aluminium alloy AA 5182 sheet produced with and without intermediate annealing. Besides a qualitative appraisal of the modelled textures, a quantitative measure is applied to scrutinize the quality of the texture simulations.
Computational study of core structure and Peierls stress of dissociated dislocations in nickelSzelestey, Peter; Patriarca, Marco; Kaski, Kimmo
doi: 10.1088/0965-0393/11/6/006pmid: N/A
We study the core structure and determine the Peierls stress (PS) of dissociated ½ 110 dislocations in FCC nickel by atomistic molecular dynamics simulations, using an EAM potential. Different pictures for the behaviour of edge and screw dislocations of this type emerge from the results of the simulations. On the one hand, the edge dislocation is observed to dissociate along a path that corresponds to the crystallographic Burgers vector of partials. The separation distance between partials is found to be a multiple of the lattice constant. Under the action of an external stress, the partials move in phase and behave globally as a rigid complex. Correspondingly, the PS for a single partial is close to the effective PS for the extended dislocation. On the other hand, in the screw dislocation, the separation distance is smaller and close to a half-integer of the lattice constant. The strong core overlap produces a significant reduction of the lateral Burgers vector in the dissociation process. Under a stress, the partials move out of phase and the separation distance undergoes some modulations. In this case, the effective PS is found to be smaller than the PS for partials.
Molecular dynamics study of pyrolytic carbon interphase in CF/CI preformYe, Yajing; Zhang, Litong; Cheng, Laifei; Wang, Junjie; Yin, Kailiang
doi: 10.1088/0965-0393/11/6/007pmid: N/A
The pyrolytic carbon interphase in the CF/CI preform was investigated. Two models of the carbon interphase were built on the atomic scale by using Cerius2 materials simulation software. The microstructures and bulk or Young's moduli of the two models were investigated by carrying out molecular dynamics annealing simulation in a circulation temperature from 300 to 2073K. After this, the slippages of the graphite laminas at the edge of the interphase were found. The Young's and bulk moduli of model 1 were reduced more than 10%, the bulk and Young's moduli in direction X of model 2 reduced 20.5% and 16%, respectively, whereas the Young's moduli increased in directions Y and Z by 3.9% and 24.8%. The reasons for these reductions were analysed and the improvement in the properties of these composites caused by these changes was also revealed.