A. S. Smirnov

Modelling and Simulation of Strain Resistance of Alloys Taking into Account Barrier Effects

The paper proposes a model of strain resistance of alloy under high-temperature deformation. The model describes hardening of alloy due to the increase of dislocation density, as well as the barrier effect of blocking free dislocations, boundaries of grains and subgrains by dispersoids. The model also takes into account the softening processes associated with the recovery and dynamic recrystallization. The model has been tested on the rheological behavior of an Al-Mg alloy named AMg6 at temperatures of 400 and 500 oC in the range of strain rates from 5 to 25 s. It was found in this temperature – strain rate range that the curve of strain resistance of the AMg6 alloy consists of several portions. First there is hardening of the material, then there is material softening, which is again replaced by hardening of the material. With the use of the electron backscatter diffraction technique and transmission electron microscopy, it was found that the main process of softening at investigated temperatures is dynamic recrystallization. The appearance of the second portion of hardening on the strain resistance curve is the inhibition of dynamic recrystallization, as well as manifestation of the barrier effect of blocking free dislocations, grain and subgrain boundaries by dispersoids.

A hierarchial modeling of stress-strain state of multiphase material subjected to uniaxial loading

On the example of an Al/SiC metal matrix composite, we propose a numerical study of multiphase material stress-strain response evolution using the structural-phenomenological approach. The study covers micro- and macrolevel analyses of uniaxial tension and compression and takes material rheology and internal structure into consideration. We describe features of the emergence of stress concentration regions leading to local plastic deformation causing a heterogeneous stress-strain state on the microlevel. We depict a strain dependence of the stress stiffness coefficient and the Lode-Nadai coefficient fields.

Peculiarities of the rheological behavior and structure formation of aluminum under deformation at near-solidus temperatures

This paper deals with a peculiar rheological behavior of aluminum at near-solidus temperatures. It has been experimentally established that there is an inverse strain rate dependence of strain resistance at temperatures ranging between 560 and 640°С and strain rates ranging from 0.06 to 1.2 s−1. Electron backscatter diffraction analysis has shown that at temperatures ranging between 540 and 640°С and strain rates ranging from 0.06 to 0.1 s−1, the main process of softening is dynamic polygonization, resulting in in situ recrystallization. At higher strain rates, ranging between 0.8 and 1.2 s−1, and temperatures ranging between 560 and 640°С, the recovery is dynamic. This unusual behavior of the mechanism of softening and the presence of the inverse strain rate dependence of strain resistance can be explained by blocking the motion of free dislocations by foreign atoms, which occurs at strain rates ranging between 0.06 and 0.1 s−1. This process results in dislocation pile-up, thereby causing in situ recrystallization. At strain rates exceeding 0.16 s−1, there is no intensive blocking of dislocations, leading to a direct strain rate dependence of strain resistance.

Effect of silicon carbide particles on the mechanical and plastic properties of the AlMg6/10% SiC metal matrix composite:

This work deals with studying the effect of reinforcing SiC particles on the mechanical and plastic properties of a metal matrix composite with a matrix of aluminum alloy AlMg6 (the 1560 aluminum alloy according to the Russian State Standard GOST 4784−97). We assess this effect using the results of mechanical tests at the microscale and macroscale levels. The paper analyzes the fracture mechanism at the microlevel under tensile and compressive stress conditions, as well as the type of contact between the composite constituents. The experimental results obtained for the metal matrix composite are compared with analogous experimental data for the AlMg6 alloy and a compacted material made from the AlMg6 alloy (a compacted powder without addition of SiC reinforcing particles). The studied compacted materials were not previously subjected to extrusion. The tests show a decisive influence of the reinforcing particles on the plastic and mechanical properties of the AlMg6/10% SiC metal matrix composite under compression and tension. For example, the addition of silicon carbide increased the initial yield stress of the compacted material by 26% under tensile tests, and the percentage elongation after fracture was increased up to 1.1%, while it amounted to 0.02% for the compacted material without addition of silicon carbide. Under compression, on the contrary, the addition of silicon carbide degraded plastic properties. As a result, the percentage compression before cracking was 28.4% and 57.9% for the compacted materials with and without addition of silicon carbide, respectively.

Modeling the stress-strain state of the V95/SiC aluminum alloy matrix composite under uniaxial loading

In the paper we develop a computational model of plastic deformation of an aluminum matrix composite. The composite is produced by sintering, and it has a cellular microstructure. SiC reinforcement particles form a stratum along the pellet boundaries of the V95 (analogous to 7075) aluminum alloy. The effective properties of the plastic flow of the stratum material are obtained by the rule of mixtures, depending on the volume fractions of the aluminum alloy and the reinforcement particles in the composite material. The feasibility of the model is demonstrated on the example of numerical simulation of the micro- and macroscopic stress-strain state of the composite under uniaxial tensile and compressive loading conditions.

A Computational Model of V95/sicp (7075/ Sicp) Aluminum Matrix Composite Applied to Stress-Strain State Simulation under Tensile, Compressive and Shear Loading Conditions

Adhering to the structural-phenomenological approach, we develop a computational model of aluminum matrix composite deformation. The model allows us to simulate the stress-strain state parameters of the composite at the microscopic and macroscopic scales and in different loading scenarios. The composite is produced by sintering, and it has a cellular internal structure. The SiC reinforcing particles are grouped around sintered aluminum alloy pellets, forming a stratum. It has been experimentally established that, during the hot deformation process, the stratum undergoes structural changes. The changes influence the effective mechanical properties of the stratum. In order to account for these changes, we use the rule of mixtures, assuming the plastic flow properties of the stratum to be distributed proportionally to the volume fraction of its constituents. The model is used to simulate stress-strain state evolution at the microscopic and macroscopic scales in three loading scenarios – tension, compression and shear. We construct equivalent (von Mises) strain and average normal stress distribution fields in the finite-element nodes of the finite element mesh of a randomly selected micro volume and show that the local plastic deformation regions emerge in the composite structure. The presence of tensile stresses is also noted, which are the most adverse in terms of internal fracture probability.

Study of the Resistance of Steels 18KhMFB And 18Kh3MFB to Hot Deformation

Experimental data are presented on the resistance of new steels 18KhMFB and 18Kh3MFB to deformation at temperatures of 1000 and 1150°C and strain rates of 0.05, 0.5, and 5 sec−1. A method of conducting experiments and analyzing the resulting data is described. The curves of deformation resistance that are obtained can be used for theoretical studies and modeling of hot-working processes in order to design technologies and equipment for the production of pump-compressor tubing.

Simulation of the rheological behavior of the 01570C alloy under high-temperature deformation

The paper investigates the possibility of using a previously developed mathematical model of strain resistance to describe the rheological behavior of the 01570C alloy (Russian Standard) of an Al-Mg-Sc-Zr system at 300 °C in the range of strain rates between 0.1 and 5 s−1. The model takes into account hardening due to an increase in dislocation density, as well as the barrier effect of blocking the motion of free dislocations, and softening due to dynamic recovery and dynamic recrystallization. The identification and verification of the model is made by the experimental data of cylindrical specimen compression obtained on a plastometric apparatus built at Institute of Engineering Science, Ural Branch of the Russian Academy of Sciences. According to the verification results, we can conclude that the considered model, with the calculation accuracy acceptable for engineering, describes the rheological behavior of the 01570C alloy at 300 °C for strain rates ranging from 0.1 to 5 s−1.

Rheological behavior and the formation of the microstructure of a composite based on an Al-Zn-Mg-Cu alloy with a 10% SiC content

The paper deals with the rheological behavior and microstructure formation of a metal matrix composite (MMC) based on a matrix made of the V95 alloy (analogue of the 7075 alloy) with reinforcing SiC particles. The rheological behavior has been investigated from plastometric testing results on cylindrical specimen compression at temperatures ranging from 400 to 570 °C and strain rates ranging between 0.1 and 0.25 s−1. It has been established that the flow stress curve for a V95/10%SiC MMC consists of a few pieces at 400 and 570 °C. First there is material hardening, then there is softening followed by another portion of hardening. At a temperature of 500 °C, instead of a descending branch, on the flow stress curve there is a steady horizontal portion followed by hardening. Electron backscatter diffraction has shown that dynamic recovery and dynamic recrystallization occur in a V95/10%SiC MMC under deformation. Dynamic recovery is more active at 500 °C and 570 °C than at 400 °C due to the annihilation of di...