MICROMECHANICAL MODELLING OF METALS AND ALLOYS OF HIGH SPECIFIC STRENGTH

The thesis reports the research effort aimed at the micromechanical description of various phenomena characteristic for elastic-viscoplastic deformations of polycrystalline materials. The attention has been focused on metals and alloys of high specific strength, in which the inelastic deformation at the local level is constrained by an insufficient number of easy deformation modes and the presence of lamellar substructure. The monograph consists of seven chapters. The first chapter has an introductory character. It outlines the motivation and scope of the thesis and indicates fields of applicability of the results obtained. In Chapter 2 a model of a single crystal deforming by slip and twinning is proposed, together with a new reorientation scheme formulated in order to account for appearance of twin-related orientations in polycrystalline aggregates. In the second part of the chapter an implementation of this model within known scale transition schemes is discussed. The validation of the proposed framework, when modelling the overall response and texture evolution for polycrystalline materials of high specific strength, is presented. In Chapter 3 a theoretical analysis of bounds and self-consistent estimates of overall properties of polycrystals of low symmetry, particularly those characterized by the constrained deformation at the local level, is performed. In the study two invariant decompositions of Hooke‘s tensors are employed. In Chapter 4 predictions of different extensions of the self-consistent method applicable to non-linear viscoplastic crystals of strong anisotropy are analysed. In Chapter 5 a micromechanical three-scale model of polycrystals of lamellar substructure is discussed, together with its extension to the large strain framework. An influence of the confinement effects induced by lamellar substructure on the overall response of polycrystals is evaluated. In Chapter 6 a new method of sequential linearisation of elastic-viscous response is presented. The procedure developed is applied to extend the self-consistent averaging scheme to elastic-viscoplastic heterogeneous materials. The last chapter recapitulates the most important conclusions and includes an outlook for future research employing the developed modelling tools.