Zarghaam Haider Rizvi

Advanced Meso-Scale Modelling to Study the Effective Thermo-Mechanical Parameter in Solid Geomaterial

The effects of coupled thermo-mechanical processes under consideration of micro-fracturing of the solid geomaterial on mechanical and thermal properties of geomaterials are investigated and subsequently simulated using advance Lattice Element Method (LEM). As a result of that extension, the alteration of effective parameter due to structural changes become numerically understandable. Hence, the simulation of the coupled processes on the meso-scale helps to develop and validate reliable identification method for real cases. The obtained results make it obvious that LEM has a large potential for fracture problems in geomaterials.

Dynamic Analysis by Lattice Element Method Simulation

Quantifying the fracture in materials and structures is daunting task and to add to this misery there is no unique approach or model to wrestle with this problem. The challenges to model this complexity that arise with failure are plentiful, beginning with mesh dependency for softening to various numerical hitches and instabilities, tracking procedures, multiple cracking with crack interactions etc. Formation of cracks in the dynamic framework come with additional challenges bringing inertial effects, crack branching etc. In this paper, lattice model for dynamic failure is presented. The concluding objective is to mimic crack origination and propagation in 2D brittle and quasi-brittle material prone to dynamic loading. The advantage of the lattice element models is in their effective demonstration of failure mechanisms. The presented model is established on Delaunay triangulated lattice of Bernoulli beams which act as interconnected links among the Voronoi cells used to calculate beam cross sections. The removal of elements exceeding the failure criteria serve for depiction of failure mechanisms in modes I, whereas the mass and the inertial properties are encompassed into lattice network. Representative numerical simulation is implemented comparing the outcomes for static and dynamic analysis.

A New Lattice Element Method (LEM) with Integrated Interface Elements to Determine the Effective Thermal Conductivity of Rock Solids Under Thermo-Mechanical Processes

In order to determine the change of thermal conductivity of rock solids under coupled thermo-mechanical processes and developed microstructure fractures, an application of a new lattice element method (LEM) with additional interface elements representing the bond between the particles is investigated. The thermo-mechanical loadings in many engineering applications, such as deep geothermal systems, can result in a change of mechanical and thermal properties of rock solids. In the proposed model, the change of thermal conductivity under mechanical loading, thermal expansion and developed fractures due to coupled thermo-mechanical processes are considered. The main advantage of the new model is that it considers the thermal expansion while increasing the compression stresses in particles contact zone, which captures the true stress-strain behavior of the rock sample under coupled processes. The numerical results are eventually compared to the experimental results obtained from multi-anvil apparatus in Laboratory of CAU Kiel. It is shown that the new model is able to estimate the change of thermal conductivity under coupled thermo-mechanical loadings and developed microcracks.