Thesis supervisor: Majid Movahedi Rad
Location of studies (in Hungarian): Széchenyi István University Abbreviation of location of studies: SZE
Description of the research topic:
The focus of the proposed research work is on constitutive modelling of the influence of grain crushing on the mechanical response of cohesionless granular materials like sand, gravel or broken rock. Grain crushing causes a change of the grading of the grain sizes, the grain shape, the limit void ratios and the critical void ratio. It can also be accompanied by a change of the course of force chains and a reorientation of the grain skeleton into a denser state. Grain crushing becomes dominant within the localized zone while outside of the shear band the material remains almost undamaged under continuous shearing. Moreover grain crushing in shear zones can already be detected under low pressures. Thus the occurrence of grain crushing is not only a question of the stress level, but it is also influenced by different factors related to the grading of the grain sizes, the angularity of the grains and the loading history. The amount of grain damage under shearing can be rather different to the one under predominant isotropic loading. Only little experimental data is available in the literature, so that numerical simulations are a possibility to gain deeper insight into the mechanisms of grain crushing. In this context the question arises as to what state quantities are appropriate for modelling of the influence of grain crushing on the mechanical response. For mathematical description and the numerical modelling of the mechanical behaviour of granular materials different concepts are proposed in the literature. For instance the discrete modelling of individual grains and their interaction within the grain skeleton using DEM (Discrete Element Method) or the phenomenological modelling based on a continuum description are two examples. Although the application of DEM is usually limited to small-scale problems by the capacity of available computers, the results obtained from numerical simulations are very helpful to gain further insight into the micro-structure behaviour of granular materials under different loading conditions. Investigations of the micro-structure can also be helpful for developing more sophisticated macroscopic models, i.e. continuum models with an enhanced set of state variables. Enhanced continuum models take into account for instance the void ratio, particle rotation in addition to particle translation, couple stresses, characteristic lengths and the change of the grain size distribution as a result of grain crushing. The study of such state quantities with real experiments in the laboratory is difficult and limited to macroscopic considerations while the evolution of individual state quantities can be analysed in detail using DEM.
Deadline for application: 2019-04-30
2024. IV. 17. ODT ülés Az ODT következő ülésére 2024. június 14-én, pénteken 10.00 órakor kerül sor a Semmelweis Egyetem Szenátusi termében (Bp. Üllői út 26. I. emelet).
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