Ongoing research projects

IMMC

Ongoing research projects in iMMC (December 2019)


This a short description of research projects which are presently under progress in iMMC.
Hereunder, you may select one research direction or choose to apply another filter:

Biomedical engineering

Computational science

Civil and environmental engineering

Dynamical and electromechanical systems

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Fluid mechanics

Processing and characterisation of materials

Chemical engineering

Solid mechanics


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List of projects related to: micromechanics




Characterization and physics based modeling of plasticity and fracture of Dual-Phase steels towards ultratough materials by microstructure optimization
Researcher: Karim Ismail
Supervisor(s): Thomas Pardoen, Pascal Jacques

The research work, in collaboration with company ArcelorMittal, is about the plasticity, the damage and the crack propagation resistance of dual-phase steels, which are commonly used in the automotive industry. A minimum level of fracture toughness is required to prevent the propagation during forming operations of small edge damage or cracked zones induced by cutting. Therefore, unravelling the relationship between fracture toughness, microstructure and damage mechanisms is essential to develop advanced steels with superior forming ability. Furthermore, reaching superior fracture toughness could open to other potential applications.
Experimental works as well as computational modeling are used to study the behavior of such steels. A model for the plastic behavior and for the damage mechanisms related to the microstructure has been developed. A finite element based unit cell approach is used to address the plastic behavior, locally as well as at the macroscopic scale. A particular focus is put on the effect of particle morphology and orientation that have not been much investigated and that considerably affect local mechanical fields, and hence damage and fracture behavior. A two-stage void coalescence process is suggested in elongated microstructures. The data extracted from the elastoplastic analysis are fed into a cellular automaton approach of the damage evolution. This model introduces a statistical description of the material while using relatively simple damage evolution laws. Furthermore, the essential work of fracture method is used to quantify the resistance to the propagation of a crack on thin sheets. Martensite morphology in the form of platelets seems to be a means to reach a high fracture toughness. Finally, damage mechanisms are observed post-mortem and hole expansion ratio tests will be performed.



Contributions to nonlinear micromechanical modeling of composite and porous materials under small and large deformation
Researcher: Marieme Imene El Ghezal
Supervisor(s): Issam Doghri

The goal of my research is to deliver models able to predict the effective mechanical behavior of materials made of at least two different phases and which can be used for complex loading tests like non-proportional loadings. The adopted technique is the Mean Field Homogenization (MFH). The development of such schemes strongly depends on the constitutive laws of the constituents. The range of materials concerned by this research is wide: elastic, viscoelastic, elasto-plastic (in the small strain regime) and hyperelastic-plastic in the finite strain regime. My research interests also include FE analysis of cellular materials, porous materials and composites involved mainly in the validation of the MFH schemes.



Micromechanical characterization of carbon fiber reinforced epoxy resins
Researcher: Jérémy Chevalier
Supervisor(s): Thomas Pardoen

Carbon fiber reinforced polymers (CFRP) are widely used in structural applications where weight is a critical factor. However, the lack of generic tools to accurately predict their failure must be compensated by heavy experimental campaigns to ensure the safety of the structures, increasing their cost. Hence, the goal of this thesis is to provide a precise understanding of the deformation and failure mechanisms of CFRP constituents in order to serve as a basis of a bottom-up approach.

Regarding the matrix, a detailed analysis of both the fracture and viscoplastic behavior is peformed to understand the underlying mechanisms responsible for its apparent mechanical behavior. In particular, a fracture criterion has been identified and validated under a large range of stress triaxialities, providing a unique failure mechanism for highly cross-linked epoxy resins. Regarding viscoplasticity, the so-called shear transformation zone (STZ) framework is used as a modelling approach to account for the nanoscale heterogeneity controlled mechanical response of glassy polymers. In parallel, macroscopic and insitu tests in a scanning electron microscope on a unidirectional composite are used to unveil the influence of the fibers on epoxy resins behavior when used as a matrix in CFRP. Lastly, nanoindentation is used both to characterize the microscale mechanical behavior of RTM6 and to perform push-out tests on single carbon fibers embedded in a polymer matrix to obtain direct a measurement of the interfaces properties.




Finite strain modelling of polymers and continuous fiber reinforced composites
Researcher: Muralidhar Reddy Gudimetla
Supervisor(s): Issam Doghri

The main thesis goal is to efficiently integrate the constitutive models of resin, fiber and fiber/matrix interface into a mulit-scale approach to predict the behavior of an uni-directional carbon-epoxy composite ply. This would require an efficient constitutive model for the resin/polymer which would address the experimentally observed features like strain-rate, temperature and pressure-dependency. So, an isotropic thermodynamically based fully coupled viscoelastic-viscoplastic model formulated under finite strain transformations was developed considering isothermal conditions, which is further extended to an anisotropic version suitable for structural composites. This model would be implemented in a multi-scale approach, with corresponding models for fiber and fiber/matrix interface, to predict softening/degradation in an uni-directional composite ply.



Viscoplasticity and strain localization in metallic thin films
Researcher: Guerric Lemoine
Supervisor(s): Laurent Delannay, Thomas Pardoen

Metallic thin films are widely used in the microelectronic industry and for surface functionalization. Owing to their very fine microstructure, thin films generally suffer of a lack of ductility and are prone to creep at room temperature. To avoid such detrimental effects in applications, their mechanical behaviors have to be characterized and modeled. Combining both experiments and simulations, my doctoral research focus on the rate dependent plasticity and the strain localization of metallic thin films. The Lab-on-chip technique is used to characterize the yield stress, the ductility, the hardening behavior and the strain rate sensitivity of Ni thin films. A localized necking model is also developed, dedicated to thin films and nano crystalline metals which aims at accounting for strain gradient plasticity effects, for grain size dependent strength, rate sensitivity and the possible contribution of creep/relaxation mechanisms. A dislocation-based crystal plasticity model has also been developed in order to study the mechanical and creep/relaxation behavior of the polycrystalline Pd thin films with high initial defect concentration, obtained by M-S Colla during her PhD thesis.



DeltaT
Researcher: Valentin Marchal-Marchant
Supervisor(s): Pascal Jacques

obtained his degree in engineering in materials science from the Université catholique de Louvain in 2011. Then, he accomplished his PhD under the supervision of prof. Pascal Jacques, on the study of Physical Vapor Deposition of thick copper films on steel.

His research is now focused on the development of thermoelectric materials and thermoelectric generators for energy harvesting and passive electromechanical systems. It aims at using common and non-toxic materials to generate electrical power from thermal gradients. Nowadays, attention is put on large scale applications owing to more than 7 years of research about thermoelectric materials leaded in IMAP.

The big challenge of this topic is the development of new tools and equipments for material production and assembly, and specific characterization methods. Such a wide range of different tasks can only be achieved thanks to the versatility of technical and scientific expertises of the IMAP team members as well as Lacami support.



Crystal plasticity modelling of thermomechanical fatigue in ITER relevant tungsten
Researcher: Aleksandr Zinovev
Supervisor(s): Laurent Delannay

Tungsten, selected as plasma-facing material for fusion reactors (such as ITER and DEMO), needs to possess high crack resistance and ductility under extreme operation conditions, such as high neutron flux and cyclic thermal load, which lead to material degradation. The objective of this project is to develop a finite element (FE) model capable to simulate mechanical behaviour of polycrystalline tungsten under tensile testing with the focus made on effect of test temperature and irradiation-induced defects. The input for the model is derived from experiments and lower-scale models, such as crystal plasticity (CP), molecular dynamics (MD) and dislocation dynamics (DD). A combination of FE and CP approach allows for investigation of mechanical behaviour of tungsten at the grain level.



The following scientific questions have to be addressed in the frame of this PhD project:

How does the heterogeneity of stress and strain within grains affect the cracking behaviour of tungsten under ITER-like heat loads? How can the impact of neutron irradiation defects be included in the CP model? What is the effect of texture on anisotropy of plastic deformation and fracture properties?



A macroscopic constitutive law, which describes plasticity of tungsten in the ITER-relevant temperature range, has already been constructed. Based on that, two papers have been published in peer-reviewed journals.




Coupled mechanical-electrical effects in highly strained Ge thin films
Researcher: Marie-Stéphane Colla
Supervisor(s): Thomas Pardoen

Graduated in chemical and materials science engineering at the Université catholique de Louvain in 2009 (Belgium). Then, under the supervision of Prof. Thomas Pardoen (iMMC) and Prof. Jean-Pierre Raskin (ICTEAM), she accomplished a PhD on the study of the mechanical properties of thin films, more specifically on the plasticity and creep of freestanding nanocrystalline Pd films. The lab-on-chip technique developed previously at the UCL was adapted to deform Pd thin films. After the PhD, she worked for more than two years at the CRM Group in Liège on the development of industrially viable thin film solar cells on steel. From June 2016 to September 2018, she is back at the UCL as a research engineer involved in projects dealing with the understanding of fracture behaviour of high strength steels under a wide range of strain rates.​ In 2018, she received a 'Chargée de recherches - FNRS grant' and is now working on coupled mechanical-electrical effects in highly strained germanium thin films. Germanium is a promising material for optoelectronic device owing to its compatibility with the standard complementary metal-oxyde-semiconductor (CMOS) technology and to the possibility to convert it into a direct bandgap semiconductor by straining it.



Characterization and modeling of surface mechanical properties at the micro-nanometer scale for the study of polymer and composite behavior in contact with industrial fluids
Researcher: Céline Vlémincq
Supervisor(s): Thomas Pardoen

Currently the characterization of the mechanical properties of polymers after ageing with fluids is long and costly, as it is essentially based on the macroscopic characterization of saturated samples. In this context, the objective of the project is to exploit the potential of local methods to evaluate the evolution of the surface mechanical properties, through nanoindentation and atomic force microscopy (AFM), and to establish assessment protocols for the quantification of the impact of fluids on mechanical properties. With these local methods, the aging time could be reduced from months to a few minutes.

To achieve this objective it will be necessary to establish a modeling strategy based on a micro-mechanical basis. The aim of the modeling approach is to link nano- and microscopic measurements to the elasto-viscoplastic properties and to understand the root causes of the fluid impact on physical mechanisms.



BIODEC, STOCC
Researcher: Audrey Favache
Supervisor(s): Thomas Pardoen

obtained a PhD degree in the domain of process control in 2009 at Université catholique de Louvain (Belgium), after having graduated there as chemical engineer in 2005. Since then, she is working as a "senior" researcher on several applied research projects in collaboration with the industry in the domain of mechanics of materials. More particularly, she is interested in the link between the mechanical properties of the individual components of a complex system and the global mechanical response of this system. She applied this approach to the framework of tribology and contact mechanics for understanding the scratch resistance of coatings and multilayered systems. Her work covers both experimental aspects and finite element simulations.



On a chip fracture mechanics test method
Researcher: Sahar Jaddi
Supervisor(s): Thomas Pardoen

The aim of this research is to develop a new testing method based on an-on-chip concept to measure the fracture toughness of freestanding submicron films. This device consists of two major components, a notched specimen and two actuators. When the test structure is released by etching the sacrificial layer, the two actuators contract, this in turn loads the specimen in traction. In order to define the stress intensity factor expression, which is given by this new model, analytical analysis and finite element simulations must be performed in addition to the experimental part, which is based on the microfabrication techniques. Silicon nitride, silicon oxide and metallic glass thin films will be studied during this work. The major goal of this model is to extract fracture toughness of 2D materials like graphene.