Adaptive Concurrent Multiscale Method for Fracture of Material and Size Effect Problem

An adaptive concurrent multiscale methodology (ACM$^2$) is introduced to enable strong interaction between both macroscopic and microscopic deformation fields. The method is formulated in finite element framework and is based on the balance between two sources of error, namely, numerical and homogenization errors. In finite element framework, the first type of error dictates element refinement in regions that are characterized by high deformation gradient, to improve the accuracy of numerical solution. In contrary, the second type of error indicates that the refining procedure should not exceed a critical level, that is determined by the size of the unit cell and represents the scale of material's microstructure. The method then aims at embedding unit cells in continuum region and through appropriate boundary conditions couple the deformation field in both regions. Upon this, the method is able to adequately combine different descriptions of material to assure accuracy with low computational cost. We will then show that our computational technique, in conjunction with the extended finite element method, is ideal to study the strong interactions between a macroscopic crack and the microstructure of heterogeneous media. In particular, the method enables an explicit description of micro-structural features near the crack tip, while a computationally inexpensive coarse scale continuum description is used in the rest of the domain. The present work also aim at investigating several examples of crack propagation in materials with random microstructures, and discussing the potential of the multiscale technique in relating microstructural details to material strength and toughness, and capturing the size effect

Numerical analysis of energy piles under different boundary conditions and thermal loading cycles

The thermo- mechanical behavior of energy piles has been studied extensively in recent years. In the present study, a numerical model was adapted to study the effect of various parameters (e.g. heating/cooling temperature, head loading condition and soil stiffness) on the thermo-mechanical behavior of an energy pile installed in unsaturated sandstone. The results from the simulations were compared with measurements from a thermal response test on a prototype energy pile installed beneath a 1-story building at the US Air Force Academy (USAFA) in Colorado Springs, CO. A good agreement was achieved between the results obtained from the prototype and the numerical models. A parametric evaluation were also carried out which indicated the significance of the stiffness of the unsaturated sandstone and pile’s head loading condition on stress-strain response of the energy pile during heating/cooling cycles

Numerical analysis of energy piles under different boundary conditions and thermal loading cycles

The thermo- mechanical behavior of energy piles has been studied extensively in recent years. In the present study, a numerical model was adapted to study the effect of various parameters (e.g. heating/cooling temperature, head loading condition and soil stiffness) on the thermo-mechanical behavior of an energy pile installed in unsaturated sandstone. The results from the simulations were compared with measurements from a thermal response test on a prototype energy pile installed beneath a 1-story building at the US Air Force Academy (USAFA) in Colorado Springs, CO. A good agreement was achieved between the results obtained from the prototype and the numerical models. A parametric evaluation were also carried out which indicated the significance of the stiffness of the unsaturated sandstone and pile’s head loading condition on stress-strain response of the energy pile during heating/cooling cycles