Université de Liège

Coma Science Group

The simulation of the whole ductile fracture from the large-scale yielding to the localised crack initiation and propagation, is still challenging for scientists and engineers, especially under complex loading conditions. In this work, we develop a computationally efficient and energetically consistent damage to crack transition framework to address this issue. In addition, we provide an appropriate porous material model as well as the related calibration procedure.

Practically, an implicit non-local damage model represents the first diffuse damage stage, possibly beyond the softening onset. Once a crack insertion criterion is satisfied, a crack is introduced using a cohesive band model (CBM). This latter, contrarily to a cohesive zone model (CZM), accounts for 3D stress states during the crack opening which is mandatory in order to predict accurate results. The framework is implemented inside a Discontinuous Galerkin (DG) framework following the extrinsic CZM/DG formalism. Those choices ensure to the scheme interesting numerical properties demonstrated in this work: robustness upon failure, mesh-independence, energetic consistency and a reasonable trade-off between computational efficiency and simplicity.

The framework is first applied to a damage-enhanced elastic behaviour where the cohesive band thickness, the only introduced numerical parameter by the CBM, is determined from energetic considerations. It is then extended to the context of large strains and porous plasticity. Therewith, a micromechanics model including void nucleation, growth and coalescence, is presented. A suited crack insertion criterion is derived from a micro-mechanics coalescence model. In both cases, the numerical model is validated using experimental results from the literature.

Finally, the damage to crack transition model is validated with respect to an extensive experimental campaign studying a high-strength steel. The material and numerical models parameters are calibrated following micromechanics-based arguments. The framework, hence calibrated, is shown to be able to accurately predict the material behaviour until complete failure under different stress conditions and to include failure anisotropy. In particular, the complex experimental crack path on round bars and on grooved plates in plane strain is reproduced.

The full thesis can be downloaded at :
https://orbi.uliege.be/bitstream/2268/247753/1/phdThesis_LeclercJulien.pdf

A damage to crack transition framework for ductile materials

The University of Liège (ULiège) has developed an automated test for the detection of SARS-CoV-2, the virus responsible for Covid-19. The technique developed at ULiège allows to increase the daily capacity of detection of the coronavirus in Liège by 2000 tests. ULiège thus becomes one of the 5 reference centres for the detection of SARS-CoV-2 in Belgium. The technique could quickly be adopted by the 4 other reference centres (GSK, UCB, Janssen Pharmaceutica and KULeuven), as well as by other countries.

An automated test for the detection of Covid-19

The University of Liège inaugurated the first operational 7 Tesla MRI scanner in Belgium. Thanks to its ultra-high magnetic field, this imaging device will allow researchers to better understand the physiology and brain pathology of neurological diseases such as Alzheimer's disease, epilepsy, Parkinson's disease and multiple sclerosis. More information: https://www.news.uliege.be/en/irm7tesla

A better understanding of neurological diseases thanks to the 7 Tesla MRI Scanner

Despite advances in resting state functional magnetic resonance imaging investigations, clinicians remain with the challenge of how to implement this paradigm on an individualized basis. A group of researchers from the University of Liege and MIT have assessed the clinical relevance of resting state functional magnetic resonance imaging acquisitions in patients with disorders of consciousness by means of a systems-level approach.

Explore the wandering mind

Unravelling the roles of lysine acetylation in neural development by defining how protein (de)acetylation regulates cerebral cortical neurogenesis and the development of the inner ear.

This research is lead by Dr Laurent Nguyen and Dr Brigitte Malgrange from GIGA-Neurosciences (ULg).

Focus on the primary cilium

We now have the ability to read the genome very efficiently. We have, in the past ten years, come up with ways of reading out the genome sequences of cancers. You can sequence a person's gene, get their complete sequence. You can do that for an adult, for a new born baby, for an unborn baby, but that raises lots of issues.

Université de Liège

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