Numerical investigation of strengthening mechanisms in metallic heterostructured materials

Zhu, Shuai 2024. Numerical investigation of strengthening mechanisms in metallic heterostructured materials. PhD Thesis, Cardiff University. Item availability restricted.

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Abstract

Metallic heterostructured materials (HSMs) are composed of multiple heterogeneous zones. These zones can be made of various phases of the same constituent metallic element with different grain sizes or can consist of different metals. Through the suitable design and synergistic integration of various phases/metallic compositions, HSM components can be developed to exhibit beneficial and tailored structural and functional properties at predetermined locations, such as an enhanced balance of strength and ductility, higher wear and corrosion resistance, higher thermal conductivity and reduced coefficient of friction. While such advanced structural configurations have been shown to be beneficial in numerous scientific reports and heterogeneous deformation has been widely proven to provide extra strengthening in heterostructured metallic materials, the explicit modelling of underlying plasticity mechanisms for HSMs at both grain and sample levels remains a challenge for the scientific community. In this context, the focus of this Thesis is on developing numerical frameworks to investigate the strengthening mechanisms and underlying damage evolution of HSMs. To start with, the research presented in Chapter 3 proposes a methodology to compute explicitly the plastic strain gradient value in real time at every simulation iteration within a three-dimension strain gradient modified Johnson-Cook (JC) computational framework to capture size effect. The advantages of this method are that 1) no calibration from experimental data is required, 2) it is intrinsically physically based, as not restricted to any material deformation scenarios, and 3) it provides practitioners with the means to extend existing continuum-based models for the simulation of material behaviour on the microscale when both size and strain rate effects are present. The proposed iii approach was shown to agree well with experimental data reported in the literature on the deformation of microscale copper wires in both tension and torsion. In Chapter 4, a novel 3D numerical framework for heterostructured laminates (HSLs) is proposed by considering the evolution of various types of dislocations and back stress while being coupled with the JC damage criterion. Overall, a good correlation between numerical and experimental results was achieved under indentation and uniaxial tensile loading scenarios. Through the evaluation of the damage accumulation factor, the simulations results yielded quantitative information which aligned with the following known experimental observations: 1) the smaller the layer thickness, then the smaller the internal damage and 2) the internal damage increases with the increase in volume content of the nanograined (NG) layer. For a set simulated strain of 10%, it was also shown that the damage accumulation factor in the NG layer was 10 times lower than that in its counterpart, i.e., a stand-alone NG layer not sandwiched between two coarse grained (CG) layers. The research presented in Chapter 5 reports on the development and testing of a novel non-local crystal plasticity finite element model (CPFEM) to simulate the deformation of HSMs. This model explicitly includes geometrically necessary dislocations (GNDs), back stress hardening and damage criterion and does not rely on a homogenisation scheme. This approach enables the numerical investigation of dislocation-mediated plasticity simultaneously at both grain and sample levels. The model was validated against experimental data when simulating the deformation of a bi-layered high entropy alloy (HEA). The obtained results aligned well with experimental findings. In particular, the simulations confirmed that shear bands (SBs) preferably propagate along grains sharing similar orientation while causing severe damage and grain rotation. In the last part of the thesis, presented in Chapter 6, the research investigated the strengthening mechanisms and fracture modes in HSLs through a full-field non-local CPFEM framework and incorporated progressive continuum damage iv mechanics (CDM) model for crack initiation and propagation. The constitutive model was validated with simulated homogenous Twinning-Induced Plasticity (TWIP) steel and Maraging steel specimens before being applied to the TWIP/Maraging steel laminates. It was observed that the non-local CPFEM-CDM model based on maximum slip accurately captured the typical brittle and ductile damage of stand-alone Maraging and TWIP steels, respectively. It was further found that, when contained in a HSL configuration, the hard Maraging layer exhibited a fracture process of void nucleation, coalescence and propagation, hence displayed a brittle to ductile fracture trend, which is in stark contrast to the stand-alone Maraging layer where a typical brittle fracture was observed. In summary, the modelling frameworks developed in this Thesis provide a solid theoretical framework for the future design of HSMs to achieve optimal strength-ductility balance and to predict potential crack nucleation sites and SBs evolution in such materials.

Item Type:	Thesis (PhD)
Date Type:	Completion
Status:	Unpublished
Schools:	Schools > Engineering
Uncontrolled Keywords:	Heterostructured material; Strengthening mechanisms; Strain gradient plasticity; Crystal Plasticity; Continuum damage mechanics; Shear bands
Date of First Compliant Deposit:	9 May 2025
Last Modified:	09 May 2025 15:43
URI:	https://orca.cardiff.ac.uk/id/eprint/178189

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