Hem Bahadur Motra

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.

Influence of Specimen Dimensions and Orientation on the Tensile Properties of Structural Steel

Abstract For the measurement of tensile properties of materials, specimens with a rectangular cross-section are commonly used. However, the results are affected by the size of the specimen and the orientations. In this study, the rectangular cross-section specimens in both longitudinal (strain ratio r = 0°) and transverse (strain ratio r = 90°) directions were used to investigate the influence of specimen and orientation on the tensile properties of I-profile of IPE360 and IPE400 steel grade S235. For both I-profiles, four types of sixty dog bone samples with varying dimensions were tested. An electromechanical test machine together with contacting strain gauge and extensometer was used to perform standard tensile test procedures. The conclusion is drawn that specimen dimensions and orientation have a significant influence on the mechanical properties of both I-profile structural steel such as Youngs modulus of elasticity, upper and lower yield strength, tensile strength, post-necking elongation and strain hardening rate, which increase with increasing thickness or decreasing gauge length.

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.