Ongoing research projects


Ongoing research projects in iMMC (July 2020)

This a short description of research projects which are presently under progress in iMMC.
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List of projects related to: fracture mechanics

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.

Study of the hardening properties, damage resistance and toughness of a new family of beta metastables titanium alloys
Researcher: Laurine Choisez
Supervisor(s): Pascal Jacques

The association of different plastic deformation modes (TRIP, TWIP) induces unmatched levels of mechanical properties in a new beta metastables titanium alloys family. A hardening beyond the theoretical limit is especially noticed, together with a uniform deformation 3 to 4 times higher than the one in a classic TA6V alloy and a yield stress superior of 30 percent to the one in a
TWIP alloy. A positive synergy is thought to exist between a high hardening and the damage resistance and toughness of such materials. My thesis will consist in the study of the damage resistance and the toughness of several beta metastables titanium alloys with different prevailing plastic deformation mechanisms in order to highlight the mechanism responsible of the post-necking deformation properties.

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.

Researcher: Vincent Destoop
Supervisor(s): Thomas Pardoen

made his PhD on the adhesion of tooth-filling materials to the dentine. He’s now working on composite materials to replace metals in aircraft applications. He takes part to projects studying the mechanical behavior of composite materials (mainly polymer matrix reinforced with long fibers) which are new candidate materials for modern planes. His investigations focus on their bulk, cracking, impact and adhesion properties.

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.

Researcher: Thaneshan Sapanathan
Supervisor(s): Aude Simar

completed a mechanical engineering degree and a PhD at Monash University (Australia) in 2010 and 2014, respectively. His thesis was entitled “Fabrication of axi-symmetric hybrid materials using combination of shear and pressure”. During his PhD, he worked on architectured hybrid materials fabrication using severe plastic deformation (SPD) processes. Two novel axi-symmetric SPD techniques were investigated to fabricate hybrid materials with concurrent grain refinements. After that, he started a research project at University of Technology of Compiègne (France) in which he investigated the weldability window for similar and dissimilar material combinations using numerical simulations for magnetic pulse welding. He also studied the interfacial phenomena, behavior of material under high strain rate deformation, modeling and simulation of the magnetic pulse welding/forming. Then, I was working as a postdoctoral research fellow at UCL on the topic of characterizations of aluminium to steel welds made by friction stir welds and friction melt bonding. At present, I am working as a FNRS reserch officer (Chargé de recherche) and investigating intermetallic induced residual stresses and mitigation of hot tear in innovative dissimilar joints.

Renforcement des capacités de RDI des organismes de recherche dans les domaines utiles aux PME
Researcher: Michaël Coulombier
Supervisor(s): Thomas Pardoen

graduated as a material science engineer from UCL in 2006. He finished his PhD in 2012 under the supervision of Prof. Thomas Pardoen (iMMC) and Prof. Jean-Pierre Raskin (ICTEAM) developing a lab on-chip technique for nano-mechanical characterisation of thin films. Since then he has been a research assistant in iMMC involved in various projects dealing with material science, nanomechanical testing and tribology.

Friction stir processing based local damage mitigation and healing in aluminium alloys
Researcher: Matthieu Baudouin Lezaack
Supervisor(s): Aude Simar

Al 7XXX alloys will be characterized before and after friction stir process (FSP) in order to identify the damage mechanisms. The performances of FSPed alloys will be studied by macromechanical testing. Up to now, a 150% increase in ductility was reached by FSP + heat treatments compared to the base 7475 Al material. Then a numerical model will catch the 7XXX aluminium behavior in a close future.

Fracture toughness of high entropy alloys
Researcher: Antoine Hilhorst
Supervisor(s): Pascal Jacques, Thomas Pardoen

High entropy alloys (HEAs) are a new family of metallic alloys. In contrast to conventional alloys, HEAs have multiple principal elements e.g. the equiatomic "Cantor" alloy CrMnFeCoNi. Alloys in this range of chemical composition have gathered attention only recently. From what was observed in conventional alloys, it was expected that HEAs microstructure be composed of several intermetallic phases but some systems are surprisingly single phase solid solution. Moreover, such single-phase alloys have excellent mechanical properties. For instance, CrMnFeCoNi possess a large fracture toughness, which increases with decreasing temperature, putting this alloy on par with the current best alloys used for cryogenic applications. As such, the objective of the thesis is to understand the underlying mechanisms responsible for the observed macroscopic behavior of such alloys.

The thesis aims to answer several questions such as: What are the mechanisms responsible for the increase in ductility, strength, and fracture toughness with decreasing temperature? What high-throughput methodology would be able to screen the vast range of possible chemical composition of HEAs for high performance alloys?

To understand the deformation mechanisms, several HEAs will be fully characterized from casting to mechanical testing. For the fracture toughness measurements, the essential work of fracture method will be employed as it is best suited for ductile thin sheets than compact tests. Diffusion multiples will be explored as a possible high-throughput method, as the presence of composition gradients allows the simultaneous characterization of a range of composition by techniques such as EDX, EBSD and nano-indentation.

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.

Electromechanical properties of thin films
Researcher: Farzaneh Bahrami
Supervisor(s): Thomas Pardoen

The production of Graphene/h-BN heterostructures and the investiong of their microelectromechanical properties, the production of origami and kirigami stacks of Graphene and h-BN, the raman spectroscopy, SEM, TEM AFM and nanoindentation will be used

Development and qualification of irradiation tolerant tungsten and novel toughness-enhanced composites for fusion applications
Researcher: Chao Yin
Supervisor(s): Thomas Pardoen

This research aims at investigation of the radiation damage and post-irradiation mechanical-thermal behavior of tungsten. Tungsten selected as the first wall armor and Tungsten-based composites for structural applications in DEMO are expected to receive doses up to 20 dpa (Fe) (for the EARLY DEMO) or even higher (full power DEMO) [1]. Under these conditions, the mechanical properties of the materials are known to degrade radically due to (i) neutron irradiation, (ii) heat transients, (iii) plasma gas uptake and (iv) nuclear transmutation. Thus, this investigation is called by the need to validate the performance of novel and baseline garde tungsten. This project will include the experiemental study of reference and irradiated materials carried out by mechanical test and microstructure investigation.

Deformation and failure of polymeric and metallic glasses
Researcher: Frederik Van Loock
Supervisor(s): Thomas Pardoen

My research work is focused on the deformation and fracture of (glassy) polymeric materials and polymer-based hybrid material concepts such as polymeric foams, adhesive joints, and fibre-reinforced polymer composites. Some current research topics include:
i) The development of a mesoscale constitutive finite element model based on the concept of shear transformation zones (STZs) for glassy materials (polymers and metals). The STZ model allows to predict the complex large deformation response of glassy polymers, including post-yield softening and non-linear unloading behaviour, by calibration of a few parameters via experiments on the polymer of interest. The model also sheds light on the interactions between discrete and elementary distortion mechanisms (and their collective organisation) during plastic deformation of polymeric glasses. Ongoing research with the STZ model includes ageing (and mechanical rejuvenation) of polymers, viscoelastic effects, and the effect of confinement due to the presence of fibres on the constitutive response of glassy polymers. The STZ modelling approach is also being used to study deformation and fracture of confined layers of metallic glasses.
ii) Fracture problems in polymers and fibre-reinforced polymer composites.
iii) The development of a thermochemical model for the in-situ polymerization of a thermoplastic matrix in a fibre-reinforced polymer composite (PhD work of Sarah Gayot).
iii) Fracture problems in solder joints subjected to thermal cycling (PhD work of Vincent Voet).