Three-dimensional micromechanical damage models, fiber pullout models and fracture toughness of discontinuous steel fiber reinforced cementitious composites

The primary goal of the present dissertation research is to investigate the local micromechanics and effective elasticity of randomly located and randomly oriented steel fiber reinforced concrete. A micromechanical damage model is presented to predict the overall elastic behavior in the composites. The effective elastic constitutive behavior of steel fiber reinforced concrete containing randomly located and randomly oriented composites is proposed. The homogenization procedure is performed to derive the three governing ensemble volume average equations based on aligned particle-reinforced composites. Subsequently, the orientation average process over the three elastic governing constitutive field equation for aligned particle-reinforced composites is performed to obtain the constitutive relations and the elastic stiffness of steel fiber reinforced composites with randomly oriented particles. Here, the so-called "effective" or "overall" properties of a heterogeneous composite are obtained by some volume and orientation averaging process over a "Representative Volume Element" (RVE) featuring a "mesoscopic" length scale which is much larger than the characteristic length scale of microscopic particles (inhomogeneities or inclusions) but smaller than the characteristic length scale of a macroscopic specimen. The effective elastic stiffness fourth rank tensor is explicitly derived for randomly located and randomly oriented particles. The effects of volume fraction of particles, particle shape, and elastic properties of constituents on the overall elastic constants of the composite are presented.;Chapter 2 presents the effective elastic properties of two-phase composites containing randomly located and randomly oriented particles.;Chapter 3 presents the effective elastic damage behavior of cementitious composites.;Chapter 4 presents the various definitions of fracture toughness.;In Chapter 5, we present a crack bridging model derived from the micromechanical analysis of a single fiber pull-out based on a constant shear model.;In Chapter 6, we derive a crack bridging model accounting for linear slip-hardening interfacial shear stress for randomly oriented and randomly located discontinuous steel fiber-reinforced cementitious composites, based on a micromechanical analysis of a single fiber pull-out. (Abstract shortened by UMI.).