Development and application of the BPM for the investigation of mechanical properties of frozen solid materials
Tsz Tung Chan, M.Sc.
Particle fluid system (PFS) exists in a great proportion in natural and engineering condition. Such system accounts for different problem such as mining and geotechnical engineering. Moreover, if temperature drops under freezing point, solid bonds can be formed between particles, which alternate the structure to a composite material. Resulting changes in mechanical properties, such as tensile and compressive strength, yield stress and stiffness. These properties are crucial in numerous applications.
Bonded Particle Method (BPM) is an extension of Discrete element method (DEM), which discrete nodes is connected by solid bonds to form a meshfree agglomerates. The goal of the project is to develop a numerical model based on BPM which can accompany a wide range of particle material, particle size, temperature range, strain, strain rate, etc. Moreover, the pore distribution, degree of saturation and mechanical properties of the frozen PFS are investigated in the experiment stage.
Aim of the project
In this project, a system which is capable to predict the mechanical respond of the frozen particle fluid system with the minimum data input is aimed to be developed.
In order to accomplish such goal, different target has to be accomplished prior to the development of such system. In the experiment stage, self-constructed climate chamber constructed by 3D printed part with computer radiator is coupled to the texture analyzer, which can ensure the failure of the specimen is purely related to mechanical load rather than thermal degradation. The specimen construction methods are differentiated with different types of PFS.
For the numerical simulation part, micro-mechanical and macro-mechanical properties have to be differentiated. As the size of the bond lies within the mesoscale range, both properties have to be identified in order to alternate the bond model. In addition, the bond model of bridge and capillary area has to be investigated. The bridge area refers to the individual bond between pairs of particle and capillary area refers to the bonds between two or more particles.
The project has been separated into two main parts. First is the experimental approach. Compressive test and three-point bending test are being performed in the climate chamber, which is capable to maintain the ambient temperature at -10°C to -2 °C. The experiment data are recorded and processed according to the standard for further processes. Different PFS are constructed with different types of engineering and natural particles, for natural particles, sand particle has been chosen and for engineering particles, polymer, glass and alpha alumina particles have been chosen. Such selection can ensure a wide range of particles are considered, Such as high rigidity (glass and ceramic particles), low rigidity (polymer particles), smooth surface (glass and polymer particles), rough surface (sand and ceramic particles). Specimen with a wide range of ice and air volumetric content have been created for the experiment. The specimen preparation methodologies are also investigated vastly in this process.
Second is the numerical simulation, the experiment data obtained in the experimental stage are used in the development of the solid bond model in the DEM simulation framework MUSEN. BPM is the extension of DEM, which is also available in this framework. In the experiment stage, uniaxial compression test of pure ice specimen is performed, in order to obtain the pure bond structure mechanical properties. The material respond of the ice structure in different temperature and strain rate will be formulated. Such material characteristic will be used as a reference in the bond model, which the solid bond model is developed with respected to temperature and strain rate. Experiment data are used to validate the result and further improving the bond model. Both the fracture behavior and the material respond are investigated in the process. In the further step, dynamic mechanical testes and simulation will be conducted such as high dynamic simulation or cyclic loading.
 Dosta, M., Dale, S., Antonyuk, S., Wassgren, C.R., Heinrich, S. and Litster, S. (2016): Numerical and experimental analysis of influence of granule microstructure on ist compression breakage. Powd. Techn., 299, pp. 87-97.
 Kozhar, S., Dosta, M., Antonyuk, S., Heinrich, S. and Schmidt, V. (2015): DEM simulations of amorphous irregular shaped micrometer-sized titania agglomerates at compression. Adv. Powd. Techn., 26, pp. 1021-1030.
Funding: German Research Foundation (DFG) via Project GRK 2462