Ph.D. and PostDoc Applications - Déantús - Platform 2 - Process-Structure Modelling
Apply here for the Déantús Process-Structure Modelling Ph.D. and Postdoc projects at the School of Mechanical and Materials Engineering, University College Dublin.

Deadline: 31st August 2017

The Déantús Advanced Manufacturing Research Centre will draw together research expertise from academia and industry to deliver innovation in additive manufacturing (AM) techniques and processes. Déantús Platform research combines novel metrology, modelling, data analytics and control theory to achieve significantly enhanced AM processing efficiency for metals and ploymers. Platform research highlights include (a) new process-structure-property models of AM, (b) novel materials, metrology and in-process data collection, (c) new technology for smart injection moulding, and (d) the application of novel cognitive computing methods to data interpretation and decision support for AM equipment operators.

Platform 2, Process-Structure Modelling, will develop and validate new models for the simulation of powder flow, metal melting, melt flow, metal solidification, and microstructure evolution, as well as constitutive models of resulting mechanical properties. In Platform 2, models of powder flow, melt flow, and solidification will combine discrete element modelling, continuum two-phase flow computational fluid dynamics, and plasticity models. To predict microstructure formation and identify columnar-equiaxed transitions, cellular automata (CA) will be applied for front tracking (FT). To couple the fluid solidification and microstructure evolution processes, a common software architecture OpenFOAM will be utilised. For mechanical property prediction, the phase field method (PFM) will be used, in combination with strain gradient crystal plasticity finite element models. Platform 2 will deliver a process-structure¬property through process model for the first time.

Four Ph.D. candidate positions and one PostDoc position are advertised:

PhD1: DEM model of powder flow and melting
Supervisors: Prof. Alojz Ivanković, Dr. Philip Cardiff, Prof. Željko Tukovic
Description: The powder particles behaviour will be simulated using Discrete Element Method (DEM), where Newton's equations of translational and rotational motion for constituent particles of the powder bed (PB) are simultaneously solved. (ii) Modelling of the PB melting including: (a) PB irradiation by a laser beam whereby the photon energy is transformed into thermal energy by absorption, (b) Powder melting, formation of a melt pool and melt pool dynamics driven by capillary and Marangoni forces, evaporation pressure, and the wetting ability of the powder particles and the previous layer; (iii) Coupling of the above into a strongly coupled fluid-solid-interaction model within a single computational framework. Development of powder flow model based on existing DEM software (LIGGGHTS), which can handle transport of powder particles with complex geometric shapes; Development of a two-phase CFD model of powder melt with trapped air in the OpenFOAM computational framework, where the Volume-Of-Fluid approach will be used to describe melting and wetting phenomena; Interaction (multi-physics) procedures for coupling DEM powder flow, heat transfer and CFD melt flow based on CFDEM (coupling between LIGGGHTS and OpenFOAM).

PhD2: Thermo-mechanical behaviour characterisation; Static, fracture, fatigue characterization of post-build components
Supervisors: Prof. Alojz Ivanković, Dr. Philip Cardiff, Prof. Željko Tukovic
Description: The AM process model requires a calibrated and validated thermo-mechanical viscoplastic constitutive model, including strain-rate effects, across a wide range of temperatures and for the complex thermal history of the powder-material mix. The successful establishment of a process-structure-property capability requires fracture and fatigue (including high temperature fatigue) characterization of the candidate AM materials and components. Isothermal, large-strain, high temperature tensile tests, up to at least 1000 degC. Static fracture tests in Mode I and Mode II, and fatigue tests in Mode I and Mode II. The above will be conducted under a range of temperatures and strain-rates.

PhD3: Develop surface and microstructural computational models of AM processing.
Supervisors: Prof. David Browne
Description: Develop models of surface melting of powders and free surface of molten alloy using Smoothed Particle Hydrodynamics formulation. Develop model of nucleation of solid and high resolution microstructural evolution using Phase Field methods. Coupling of length scales to meso-scale models of solidification and CFD. Simulations of surface
and microstructural evolution using the new models.

PhD4: Develop meso-scale computational models of evolving columnar and equiaxed dendritic crystals during AM processing
Supervisors: Prof. David Browne
Description: Develop Front Tracking (FT) models of the formation of columnar zones, and competing equiaxed zones leading to columnar-to-equiaxed transition during solidification of melt pool in AM. Devise a model, based on Cellular Automata (CA), of the nucleation and growth of individual columnar and equiaxed grains during alloy solidification. Extension of both FT and CA models to treat multiple passes in powder bed fusion added manufacturing. Coupling to macro-scale CFD models. Simulation of multi-pass AM processes.

PostDoc1: Multi-scale modelling and coupling for AM processes
Supervisors: Prof. Alojz Ivanković, Dr. Philip Cardiff, Prof. Željko Tukovic
Description: In the first instance, a two-scale model will be developed for coupling the macro-scale melt flow from above with the meso-scale FT-predicted columnar and equiaxed grain growth; Subsequently, the next scale of refinement will be included, where multi-scale coupling of macro-scales thermal CFD, meso-scale granular zones and micro-scale AC and PFM will be developed, resulting in a three-scale system. Finally, both hierarchical and embedded coupling procedures will be developed to achieve: high local accuracy using the embedded approach (where required); and efficiency using the hierarchical approach. Computational platform to encompass and interface all algorithms for multi-physics, multi-scale AM modeling: Development of a common computational platform within OpenFOAM, with customised data interfaces to deliver the first holistic multi-scale coupling of macroscopic SPH/DEM/CFD with mesoscopic FT, microscopic CA, PFM, CPFE and macroscopic dislocation mechanics based on J2 plasticity to directly predict key AM microstructure attributes, and global mechanical and damage/fracture/fatigue properties, local and global residual stresses of AM components.
Model(s)’ verifications: Material parameters will be calibrated using the experimental results from WP4. Each computational procedure within the platform will be ‘locally’ validated. Finally, AM processes conducted in Platform 1 as well as in related targeted projects will be simulated and the structure-property predictions from Platform 2 will be rigorously verified both in terms of measured properties and geometrical quality. Process-Structure-Property map:
(i) Simulations will be conducted under a range of processing conditions to create a map of Process-Structure-Property relationships. This will directly feed into the platform 3 for optimisation and AM process control

For more information about the projects PhD1, PhD2 and PD1, feel free to contact alojz.ivankovic@ucd.ie;
for more information about the projects PhD3 and PhD4, feel free to contact david.browne@ucd.ie.

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