| The present work consists of three parts. In the first part, void nucleation is studied both experimentally and computationally with the aim of identifying a macroscopic criterion for nucleation by particle cracking. Three types of circumferential notched cylindrical specimens made of a low alloy steel were used. The tensile tests were interrupted at various loads below the fracture load. The specimens were sectioned parallel to the loading axis and the locations of cracked and untracked titanium nitride inclusions were identified. Finite element calculations were carried out for each specimen geometry using conventional isotropic hardening plasticity theory. The ability of various potential void nucleation criteria to predict the onset of void nucleation by inclusion cracking is explored. In the second part, finite element analysis of the effect of particle fracture on the tensile response of particle-reinforced metal-matrix composites is carried out. The analysis is based on three-dimensional unit cell model. The reinforcement is characterized as an isotropic elastic solid and the ductile matrix as an isotropically hardening viscoplastic solid. An initial crack, perpendicular to the tensile axis, is assumed to be present in the particle. Quasi-statically growing cracks are analyzed. Resistance to crack growth in its initial plane and along the particle-matrix interface is modeled using a cohesive surface constitutive relation that allows decohesion. Variations of the size of initial crack present in the particle, particle morphology and stress state triaxiality are explored. Conditions governing the onset of cracking within the particle, the evolution of field quantities as the crack advances within the particle to the particle-matrix interface, and the dependence of overall tensile stress-strain response during continued crack advance are analyzed. In the third part, competition between particle cracking and debonding in metal-matrix composites is analyzed. The composite, containing a periodic array of particles, is represented in terms of a three-dimensional unit cell. The matrix is characterized as isotropically hardening elastic visco-plastic solid and the particle as an isotropic elastic solid. Particle cracking and debonding is modeled using cohesive zone framework. The effect of material and morphological properties on the competition between particle cracking and debonding is investigated. |
