NUMERICAL ANALYSIS OF STRAIN LOCALIZATION IN CEMENTED AGGREGATE MIXTURES

Abstract

This thesis deals with the numerical analysis of strain localization in cemented aggregate mixtures. The main objective is to develop a framework for describing localization phenomenon and to implement it in a finite element algorithm. An attempt is also made to establish a formulation for the description of the localized deformation in saturated cemented materials. The proposed framework combines a plasticity formulation (for homogeneous deformation), bifurcation criterion and homogenization technique (for localized deformation). The formulation of the homogenization technique is derived by estimating the average mechanical properties of a medium intercepted by the strain localization zone (shear band). The mechanical response of the homogenized system depends on the properties of the constituents (matrix and interface) and the respective volume fractions. The constitutive model for the interface is established by incorporating the degradation of both asperities orientation and cohesion. The implementation of the proposed framework in a finite element code requires an appropriate definition of an internal length parameter as well as a proper integration procedure and solution technique. These aspects are covered in the second part of this thesis. A number of numerical examples are provided for illustrating the performance of the proposed formulation. First, a series of problems involving compression-shear as a predominant failure mode are analyzed. The emphasis is placed on studies with regard to mesh-sensitivity and the influence of boundary constraints. Subsequently, the problems involving tension-shear fracture mode are studied. These include the analysis of notched specimens under tension and three-point bending. The predicted trends are, in general, consistent with experimental observation. The mathematical description of localized deformation in saturated cemented materials is also presented. The onset of localization results in the generation of an excess pore pressure gradient in the constituents (matrix and interface). An appropriate formulation for the description of deformation coupled with pore fluid diffusion is proposed. This coupling effect is studied through the analysis of three limited cases, involving: exchange of fluid between the matrix and interface, undrained response in both constituents and drained response of the interface.