Instytut Podstawowych Problemów Techniki

UMO-2021/41/B/ST8/03345

2022-01-18 / 2025-01-17

Jedyny wykonawca

NCN

OPUS

21

The aim of the project is to understand and describe within the micromechanical modelling framework the void growth and coalescence leading to the ductile damage of polycrystalline metals and alloys of low lattice symmetry. Contrary to the well-grounded studies available for phenomenological material description or more recent crystal plasticity frameworks for high symmetry metals, the respective proposals and analyses addressing the ductile failure phenomenon for low symmetry metallic materials are in its infancy. Such highly anisotropic solids, like magnesium alloys with hexagonal close packed (hcp) lattice, are known to suffer from low ductility and fracture toughness. Those drawbacks result from insufficient number of easy slip systems and activity of twinning. Better understanding of void growth failure mechanism under the condition of locally constraint plastic deformation within the crystallite and the strongly heterogeneous stress field in a polycrystalline element may reduce limitations hindering use of hcp alloys as structural elements. In the frame of proposed research the large strain elastic-(visco)plastic model of the porous single crystal deforming by slip and twinning will be developed. In particular, the proposed constitutive description will contain the yield potential, the flow rule, the strain and kinematic hardening description and evolution laws for void growth and coalescence. Next, the analyses of multiple factors influencing material ductility will be performed, including overall loading scheme (triaxiality, Lode parameter and orientation of principal axes), local crystal orientation, initial porosity and space distribution of voids and their location with respect to grain boundaries. The model will be implemented in the finite element (FE) method and validated in terms of its computational efficiency and applicability in the analysis of large-scale problems. The main tools to be used within the project are: i) the multiscale framework including mean-field (MF) model of two-phase medium with anisotropic elastic-viscoplastic matrix and void inclusion and the self-consistent scheme to describe porous polycrystal of prescribed texture, ii) the full-field FE analyses of representative volume elements of low symmetry crystals containing voids, performed to understand local mechanisms affecting porosity evolution as well as to verify the proposed MF model of effective properties, iii) experimental validation, combining assessment of mechanical response and microstructure analysis, performed on samples made of single crystals with pre-existing voids as well as porous polycrystalline samples. MF modelling will be focused on accounting for the presence of voids of prescribed geometry and space distribution in the non-linear medium being either the strongly anisotropic single crystal or textured polycrystal. In terms of the mechanical properties the sequential linearization method, used up-to-now only for the two-component Maxwel-type elasto-viscoplasticity, will be extended to account for an arbitrary multi-component material model. This extension will deliver a refined description of the macroscopic effect of kinematic hardening at the local level. Most of the FE analyses will be performed within the paradigm of numerical homogenization. Accordingly, representative volume elements of voided single crystal or polycrystalline material will be generated and subjected to the periodic boundary conditions with an additional multi-point constraint imposed to control constant triaxiality and Lode parameter for the macroscopic stress. Additionally, FE implementations of the proposed MF model will serve to prove computational efficiency of the developed framework in the simulations of large scale problems. Understanding of the relationship between the microstructure features and failure of low-lattice-symmetry metallic materials is essential from the point of view of commercial use of novel materials such as advanced magnesium or titanium alloys of high specific strength. They are increasingly used in transport and aerospace industry searching for fuel-consumption-reduction solutions. Nevertheless, these applications are often hindered because of material insufficient ductility. An access to the reliable physically-based description of the mechanical behaviour leads to the reduction of risk connected with an unexpected failure of the designs employing new material solutions.