PSI - Issue 40

Sergey Smirnov et al. / Procedia Structural Integrity 40 (2022) 378–384 Sergey Smirnov, Marina Myasnikova / Structural Integrity Procedia 00 (2022) 000 – 000

379

2

Experimental investigations and numerical simulation of the plastic deformation of structurally inhomogeneous materials are successfully pursued within this research area (Smirnov et al. (2016), Pyo and Lee (2009), Pavan et al. (2009)). The application of a hierarchical approach to the deformation and fracture of materials allows one to solve two important problems for industrial applications: firstly, to develop and optimize forming technological processes for a specific material; 2) to develop and optimize the composition of the material so that the technological processes can result in the required strength of produced parts. This study uses the concept of multilevel material description and damage mechanics failure criteria to simulate plastic deformation and fracture in the structural constituents of a heterophase material. Randomly chosen microscopic volumes of a metal matrix composite (MMC) and complexly alloyed brass have been chosen as models. The model materials are chosen to demonstrate two different fracture mechanisms: in the case of the composite, fracture develops in the malleable matrix, but the reinforcement particles have high strength and hardly experience any strain at all; on the contrary, in complexly alloyed brass fracture starts in brittle inclusions enclosed in the malleable base. The models explicitly account for the internal material structure and constituent rheology 2. Material and Investigation Procedures A specific metal matrix composite was chosen to be the first model material. The constituents of the composite are 99.8% commercially pure aluminum and silicon carbide reinforcement particles. The dominant particle shape is considered to be irregularly prismatic; the particle sizes range between 1- 5 µm and 15 - 20 µm. The composite microstructure is depicted in Fig. 1a. As tensile tests show, MMC damage is initiated and then governed by the emergence and development of cracks in the matrix, while the SiC inclusions demonstrate high strength and they do not suffer any substantial strain (Pugacheva et al. (2016)). In view of this failure behavior, the stress-strain response evolution and damage accumulation in the matrix under uniaxial loading conditions was studied. Complexly alloyed brass was chosen as the second model material. It has the following chemical composition, wt%: 71.13 Cu, 1.82 Fe, 5.27 Al, 2.06 Si, 7.04 Mn, 0.04 Ni, 0.94 Pb, the rest Zn. The brass contains three main structural constituents, namely a ductile base consisting of an α -phase, solid solution of zinc and alloying elements in copper with low values of microhardness; a strengthening β -phase, which is present in the form of an ( α + β ) mechanical mixture and characterized by higher hardness and lower plasticity; Mn 5 Si 3 and (Fe;Mn) 5 Si 3 silicide inclusions having high hardness and playing a reinforcing role in the material. A typical alloy structure is depicted in Fig. 1b. The silicide particles in the alloy are columnar and globular (Smirnov et al. (2016)). Investigations show that, under upsetting, brass deformation takes place mainly in malleable matrix, i.e. the solid α -phase and the colonies of the ( α + β ) phases. The brittle silicide inclusions are fractured first. This distinctly differentiates the brass from the metal matrix composite, in which fracture is initiated in the ductile matrix by microscopic crack emergence. Experimental investigations of microcrack initiation and development in the brass as dependent on the amount of strain were made by a series of upsetting tests on prismatic specimens. The experimental apparatus featured polished heads and lubrication. The experimental procedure allowed us to reproduce sufficiently accurately the plane strain loading conditions. The fractured inclusions were counted after each stage of loading. Microcrack emergence was chosen as the failure criterion. Since it does not seem possible to evaluate the equivalent plastic strain of silicides sil  directly from experiments, finite element simulation results were used. The computational models of the composite and the brass are based on the two-level structural-phenomenological approach for coupling the micro- and macroscale material behavior (Haritos et al. (1988)). According to this approach, the material is considered to be a homogeneous isotropic medium with isotropic hardening at the macroscale. At the microscale, the material is considered to be an inhomogeneous medium partitioned into connected non-intersecting domains, which represent the corresponding constituents.