Project proposed for a postdoctoral researcher

Postdoctoral project on

Regularized Failure Models for Quasibrittle Materials

supervised by Milan Jirásek

Czech Technical University in Prague, Czechia, 2023-2025

Brief description

Many regularized formulations for modeling of fracture have been proposed over the past 30 years, including the increasingly popular phase-field models. Most of these techniques are tailored for tension-dominated failure scenarios. Their reliable extension to general models that can predict failure under general conditions and that are applicable not only to brittle but also to quasibrittle materials is still in its infancy. The proposed project will explore the paths to such extensions and address unresolved issues related to calibration and validation of regularized failure models under general triaxial stress states, effects of boundaries including nonconvex ones, structure and evolution of the localized process zone, regularization of plasticity model with non-associated flow, physical background of nonlocality, micro-macro scale transitions for interacting defects, etc.

Ideal candidate

Holder of a PhD degree in computational mechanics, solid mechanics, structural mechanics, mechanics of materials or a related field, with keen interest in both mathematical and numerical modeling of damage, fracture and failure. Good theoretical background in continuum mechanics, plasticity, fracture and damage mechanics, combined with appropriate programming and visualization skills (C, C++, Python, ParaView, etc.).

Research topics

Regularized models under multi-axial stress: For many regularized formulations, careful one-dimensional studies of the whole localization process from the onset of localization to complete failure have been performed, and usully it is clear how model parameters affect the shape of the resulting uniaxial stress-strain diagram and the macroscopic properties such as tensile strength and fracture energy. However, the failure process is often affected by stresses parallel to the final macroscopic crack, as recently emphasized by Bazant and coworkers, who compared a number of models from the literature and identified difficult failure tests that can be used as tough benchmarks. We can analyze these cases in more detail and develop full understanding of the reasons why certain models give poor results. The gained insight can then serve as basis for modifications and improvements of such models.
Effect of boundaries: We can look into the initiation and propagation of a localized damage (or plastic) process zone starting from a smooth boundary and from a V-notch or a notch with a sharp tip. How is the evolution of the process zone and the density of dissipated energy related to the specific enrichment used as a localization limiter?
Non-associated flow: Localization of inelastic processes is usually attributed to softening, and the corresponding localization conditions and constraints on parameters of efficient localization limiters have received much attention. For plasticity models, non-associated flow rules also have a destabilizing effect and can even lead to localization without softening. We can study the formation of localized bands due to non-associated plastic flow in general terms and also for specific models, such as the damage-plastic model for concrete.
Ideas proposed by the candidate are most welcome. The project should lead to good-quality publications but the topics to be addressed are not strictly defined by a fixed plan. Candidates who are able to suggest and convincingly describe their own research ideas will be preferred.

How to apply

The deadline for applications is 31 August 2023. Please follow the instructions in the official project announcement on Euraxess.

Last update: 23 May 2023