| Abstract: | A multiscale computational framework for multiphase composites considering damage is developed in this research. In micro-scale, micromechanics based homogenization methods are used to estimate effective elastic moduli of graded Ti₂AlC/Al composites (GCMeCs) considering existence of damage (micro-voids). Then, in macro-scale, these properties are implemented in finite element model by using user material subroutine (UMAT) in Abaqus for numerical analysis of plate. In meso-scale, detailed 3D RVEs are created based on the microstructure of composites. Effective thermal and elastic properties are obtained from the corresponding FE models of 3D RVEs and compared with experimental results and micromechanics based homogenization methods. Two constitutive models are used to model plastic-damage behavior of two IPCs regarding their different material properties of constituent phases: (1) Due to the ductile properties of constituent phases for stainless-steel/bronze IPCs, a widely used porous plasticity constitutive model, Gurson-Tvergaard-Needleman (GTN) model, is adopted to investigate elastoplastic-damage behavior of stainless-steel/bronze IPCs. (2) For porous Ti₂AlC, a continuum damage mechanics (CDM) based plastic-damage coupled constitutive model is used to study damage evolution in porous Ti₂AlC, which can take distinct tensile and compressive inelastic behaviors of Ti_(2)AlC into consideration. From the simulation results of FE models of 3D RVEs, it is found that: Porosity and interfacial layer with low effective thermal conductivity lowers the overall heat flux flowing through NiTi/Ti₃SiC₂ IPC. The existence of thermal residual stress within stainless-steel/bronze IPCs leads to plastic deformation, especially in bronze phase, which further results in reduction of apparent moduli subjected to uniaxial tension. Nucleation of the new voids, which occurs at the second-phase particles by decohesion of the particle-matrix interface, has the main contribution to the overall damage. For porous Ti₂AlC with aligned ellipsoid-like pores, tensile stress plays a very important role in local damage of porous Ti₂AlC due to the relatively low tensile strength and brittle-like tensile behavior of dense Ti₂AlC. Different than typical porous ceramic, porous Ti₂AlC fails in a quasi-brittle manner even with 30-40 vol.% porosity. The transversely isotropic material system has higher compressive strength in transverse direction than that in longitudinal direction. The electronic version of this dissertation is accessible from http://hdl.handle.net/1969.1/151769 |
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