Numerical modelling of damage process in cohesive-frictional materials

Abstract

This research is related to modeling of the damage process in cohesive-frictional materials. There are two primary areas of application that include modeling of fractured rock mass as well as some selected topics in biomechanics. For both these areas, the methodology involves a homogenization approach that incorporates volume averaging. The research in rock mechanics deals with the assessment of equivalent mechanical properties of the host rock intercepted by sets of fractures. The effect of fracture network orientation/spacing on the macroscopic strength characteristics is examined. The research in biomechanics has both a numerical and experimental component and is focused on analysis of hip fracture due to a sideways fall. Here, the cortical bone tissue is modeled as a transversely isotropic material and an experimental program is setup to define the anisotropic fracture criterion. In particular, a series of novel direct shear tests is performed on small prism-shaped samples and is accompanied by uniaxial tension and compression performed at different orientations relative to the loading direction. It is demonstrated that the conditions at failure in compression range are independent of confining pressure, while the strength itself is orientation dependent. The failure criteria are postulated using the critical plane approach and the microstructure tensor approach in tension and compression regimes, respectively, and a procedure for identification of material constants is proposed. The last part of this research deals with numerical simulation of fracture propagation in a femur bone subjected to loading conditions simulating a sideways fall. A specific experimental test is modelled, and the mechanical properties of cortical tissue are specified from a series of independent material tests conducted on samples extracted from the fractured femur. The analysis incorporates the newly developed failure criteria and the numerical results pertaining to the assessment of ultimate load and the evolution of fracture pattern are compared with the experimental data.