Speakers
Description
The lecture focuses on understanding and describing within the multiscale modelling frameworks the void growth and coalescence leading to the ductile damage of polycrystalline metals and alloys deforming by slip and twinning. Our motivation stems from solids with a high plastic anisotropy, like magnesium with hexagonal close packed (HCP) lattice, which are known to suffer from reduced ductility and fracture toughness. Those drawbacks result from insufficient number of easy slip systems and activity of twinning. Void growth failure mechanism under the condition of locally constrained plastic deformation and the strongly heterogeneous stress field in a polycrystalline volume is not yet well understood and incorporated into the validated constitutive models.
The large strain elastic-viscoplastic model of the single crystal with twinning is a basis for the performed analyses [1]. This local model accounts for mutual interactions between different slip modes and twinning, which modify hardening laws for material parameters such as critical shear stresses, as well as for an abrupt lattice reorientation in part of the considered grain by a probabilistic twin-volume consistent reorientation scheme. Two approaches are proposed to analyse overall behaviour of voided crystalline material:
i. the full-field finite element analyses of unit cells of FCC and HCP crystals containing voids, performed to understand local mechanisms affecting porosity evolution and cavities coalescence [2], especially in the presence of twinning,
ii. the multiscale micromechanical framework formulated at small strain format, including mean-field model of two-phase medium: anisotropic elastic-(visco)plastic matrix, governed by the crystal plasticity constitutive rule, with embedded void inclusion, and the self-consistent framework to describe porous polycrystal of prescribed texture. The outcomes of mean-field approach are compared to the results of full-field analyses.
The study of multiple factors influencing material ductility will be presented, including overall loading scheme, local variations of crystal orientation and initial porosity. Moreover, the effect of void growth and coalescences on the microstructure evolution in the matrix material will be discussed.
Acknowledgements.
The research was partially supported by project No.2021/41/B/ST8/03345 of the National Science Centre, Poland.
[1] Frydrych, K., Maj, M., Urbański, L., \& Kowalczyk-Gajewska, K. (2020). Twinning-induced anisotropy of mechanical response of AZ31B extruded rods. Materials Science and Engineering: A, 771, 138610. https: //doi.org/10.1016/j.msea.2019.138610
[2] Virupakshi S., Kowalczyk-Gajewska K., Cylindrical void growth vs. grain fragmentation in FCC single crystals: CPFEM study for two types of loading conditions, International Journal of Solids and Structures, 280, 2023, 112397, https://doi.org/10.1016/j.ijsolstr.2023.112397.
