Nicolò Grilli, PhD

Postdoctoral Research Associate

Solid Mechanics & Materials Engineering Group

Department of Engineering Science

University of Oxford

Education

  • PhD in Materials Science and Engineering, 2016
    École Polytechnique Fédérale de Lausanne and Paul Scherrer Institut
    Advisors: Prof. Helena Van Swygenhoven and Dr. Koenraad Janssens

  • MSc in Condensed Matter Physics, 2012
    Scuola Normale Superiore and University of Pisa

  • BSc in Physics, 2010
    Scuola Normale Superiore and University of Pisa

Skills

  • Finite element software: Abaqus, MOOSE framework, DAMASK crystal plasticity, COMSOL, Gmsh

  • Programming: Fortran, C++, Python, MATLAB, GitHub

Research Experience

  • University of Oxford, 2018-Present
    Development of constitutive models for crystal plasticity in alpha-Uranium
    Development of cohesive FEM model for fracture in alpha-Uranium
    Analysis of neutron diffraction experiments

  • Purdue University, 2016-2018
    Simulation of shocks in energetic materials using the crystal plasticity finite element method
    Fracture mechanics in energetic materials using phase field damage models
    MD-informed continuum models for chemical reactions in energetic materials

  • Paul Scherrer Institut, 2012-2016
    Development of dislocation-based constitutive models for the crystal plasticity finite element method
    Simulation of cyclic fatigue in FCC metals
    Simulation of dislocation patterning in copper, aluminium and stainless steel
    Model validation with Electron Channeling Contrast and Laue microdiffraction experiments

  • European Gravitational Observatory, 2011-2012
    Development of an electro-mechanical tiltmeter for the Virgo attenuators
    Development of a LVDT-based control system

  • National Enterprise for nanoScience and nanoTechnology, 2010
    Low-temperature electronic transport measurements in heterostructured nanowires

Metal fatigue during cyclic loading puts an endurance limit on most of today’s technology. It impacts the reliability of metallic components used for transportation, electronic devices and energy production because fatigue failure can occur without any apparent forewarning. Microstructure and material design requires constitutive models at the micrometre length scale, incorporating the physical processes in the material. This involves the study of dislocation dynamics and the formation of dislocation structures, which have been recognized as the key phenomena affecting the macroscopic fatigue behaviour of metals. We developed a continuum dislocation-based model, specific for cyclic fatigue at the micrometre length scale. It can predict the formation of 3D dislocation structures starting from a random initial dislocation distribution. The characteristic length scale and shape of dislocation structures are predicted using only physical parameters, such as the stacking fault energy, and without any fitting procedure. The model is implemented in the DAMASK crystal plasticity code.

Next

Fracture mechanics determine the behaviour, safety and effectiveness of energetic materials embedded in polymer binders. The damage induced in these materials during manufacturing, handling and transport can limit their safety and effectiveness. We have simulated brittle fracture using a continuum model based on the regularization of the crack surface using a phase field. The value of the phase field decreases from one in the unbroken state to zero in the broken state of the material. Dynamic simulations show the effect of wave propagation on the fracture mechanics. Dynamic crack propagation and branching have been reproduced. The value of the crack surface energy density is estimated by comparing simulations with dynamic tests. The effect of pre-existing damage, interface damage and impact velocity has been studied. At lower impact velocities the propagation of pre-existing cracks is dominant, while at higher impact velocities the interface damage becomes more important.

Next

The formation of dislocation structures in a polycrystal is simulated by extending the single slip continuum dislocation-based model to multiple slip load conditions. A method for the simulation of dislocation junction formation is introduced, which reproduces the behaviour of discrete objects, such as dislocations, in a continuum framework. Different dislocation densities are defined based on the projection of dislocation lines along the intersection between slip planes. This is different from the decomposition of the dislocation density into edge and screw components. Simulations of cyclic tension-compression experiments of polycrystalline 316L stainless steel are performed to validate the model. The simulated dislocation structures are compared to experimental results, obtained with the electron channeling contrast imaging technique, using a 2D orientation distribution function of the dislocation structures. The dominant orientation of dislocation walls is predicted by the new model; it turns out to be perpendicular to the intersection line between the two slip planes involved in their formation and at an angle of around 45 degrees from the loading axis.

Publications

  • DAMASK – The Düsseldorf Advanced Material Simulation Kit for modeling multi-physics crystal plasticity, thermal, and damage phenomena from the single crystal up to the component scale
    F Roters, M Diehl, P Shanthraj, P Eisenlohr, C Reuber, S L Wong, T Maiti, A Ebrahimi, T Hochrainer, H O Fabritius, S Nikolov, M Friák, N Fujita, N Grilli, K G F Janssens, N Jia, P J J Kok, D Ma, F Meier, E Werner, M Stricker, D Weygand, D Raabe
    Computational Materials Science 158, 420-478 (2019) link

  • The effect of crystal orientation on shock loading of single crystal energetic materials
    N Grilli, M Koslowski
    Computational Materials Science 155, 235-245 (2018) link

  • Effect of initial damage variability on hot-spot nucleation in energetic materials
    CA Duarte, N Grilli, M Koslowski
    Journal of Applied Physics 124, 025104 (2018) link

  • Dynamic fracture and hot-spot modeling in energetic composites
    N Grilli, CA Duarte, M Koslowski
    Journal of Applied Physics 123, 065101 (2018) link

  • Multiple slip dislocation patterning in a dislocation-based crystal plasticity finite element method
    N Grilli, KGF Janssens, J Nellessen, S Sandlöbes, D Raabe
    International Journal of Plasticity 100 (2018) 104-121 link

  • Laue micro-diffraction and crystal plasticity finite element simulations to reveal a vein structure in fatigued Cu
    A Irastorza-Landa, N Grilli, H Van Swygenhoven
    Journal of the Mechanics and Physics of Solids 104 (2017) 157-171 link

  • Effect of pre-existing immobile dislocations on the evolution of geometrically necessary dislocations during fatigue
    A Irastorza-Landa, N Grilli, H Van Swygenhoven
    Modelling Simul. Mater. Sci. Eng. 25 (2017) (5) link

  • Following dislocation patterning during fatigue
    A Irastorza-Landa, H Van Swygenhoven, S Van Petegem, N Grilli et al.
    Acta Materialia 112 (2016) 184-193 link

  • Crystal plasticity finite element modelling of low cycle fatigue in FCC metals
    N Grilli, KGF Janssens, H Van Swygenhoven
    Journal of the Mechanics and Physics of Solids 84 (2015) 424-435 link

  • New diagnostic approach to varicose veins. Haemodynamic evaluation and treatment
    R Delfrate, N Grilli
    Lorena Dioni Editore (2014) link

  • A sensitive and compact inclinometer for Virgo
    N Grilli, A Gennai, D Passuello
    EGO-Virgo internal report 23 (2013) link

Contact Me

nicolo.grilli@eng.ox.ac.uk

Department of Engineering Science

University of Oxford

Parks Road

Oxford

OX1 3PJ

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