Damage Evaluation for Ti Alloys in Creep based on Incompatibility Field Measurement via EBSD Technique and Micro-Pillar Experiments Toward Identification of Roles of Dislocation Substructures on Fatigue Crack Initiation

摘要

A definite limit of all the continuum models would be the inability of taking into account microscopic degrees of freedom in the constitutive framework. For crystalline metallic materials, microstructural degree of freedom in terms of dislocations is one of those sorts, which is currently recognized to be critically important to model and simulate multiscale aspects of deforming metals especially in plasticity. One and only sophisticated solution to this problem has been recently provided by the Field Theory of Multiscale Plasticity (FTMP) advocated by Hasebe (PI). In this new theoretical framework, such additional degrees of freedom are implemented via FTMP-based incompatibility tensor model, derived based on the differential geometrical curvature tensor for describing the metric defects of the crystalline space to be incorporated in a crystalline plasticity-based constitutive framework. This study aims at developing a new non-destructive damage evaluation technique based on field theory of multiscale plasticity (FTMP). Construction of an EBSD- based direct measurement technique of incompatibility tensor field is attempted by utilizing a data obtained under wedge indentation against a single crystal sample. Corresponding crystalline plasticity-based FE simulations are conducted with and without taking account of the FTMP-based incompatibility model. Major results obtained are presented in the report.