Physical Mesomechanics最新文献

This review summarizes the effects of mechanical impact on crystal lattices of some inorganic substances (Si, S, NaCl, KCl, CaO₂, BaO₂, YBa₂Cu₃O_7–x, hematite α-Fe₂O₃, ordinary glass Na₂O ∙ CaO ∙ 6SiO₂) in a centrifugal mill. It was found that powder particles subjected to short-term impact-shear loading are deformed and reduced in size, and have structural damage after grinding in the mill. Examination of disordered compound particles showed that the resulting activated states have a certain amount of energy. Intensive mechanical activation in a centrifugal mill leads to an excess enthalpy and a change in the properties for all studied compounds. The results obtained can be used in exploratory studies of substances and materials using various mechanochemical reactors.

In this work, the relationship was considered between the structure and cyclic loading resistance of a layered composite consisting of PEI (PEEK) plate/PEI (PEEK) film/PEI-impregnated carbon-fiber fabric prepreg/PEI (PEEK) film/PEI (PEEK) plate by analyzing the time variation in the parameters of mechanical hysteresis loops calculated using digital image correlation. It was shown that the polyetherimide-based layered composite has low fatigue life under cyclic loading (0.8 of the yield strength), resulting from incompatible deformation between the PEI plates and the prepreg due to a layer interface formed by low-melting TecaPEI film. In the PEEK layered composite, the layer interface was formed by neat PEEK energy director and therefore had a little amount of defects, due to which the load was well transferred from the PEEK plates to the middle reinforcement layer. As a result, the fatigue life at a load level of 0.8 of the yield strength corresponded to high-cycle fatigue (more than 86000 cycles).

The structural features and phase composition are examined in near-surface layers of specimens of Al-Mg, Al-Cu-Mg alloys and commercially pure titanium obtained by plasma cutting using direct current straight polarity (DCSP) and direct current reverse polarity (DCRP). It is found that the flows of molten metal ejected by the gas stream from the cut cavity during cutting form the fusion and heat-affected zones, whose structural morphology, phase composition, and thickness depend on both the selected material and the cutting mode. The fusion zone is thicker in specimens cut using DCRP than in those cut with DCSP. The thickness of the adjacent heat-affected zone is also the largest in the mode that provides a thicker fused layer. Aluminum alloy specimens cut in ambient air are characterized by the presence of oxygen in the near-surface layers. The lowest degree of oxidation is observed in Al-Mg alloy. Oxygen penetrates into the fused layer to a depth of 350–500 μm in Al-Cu-Mg and up to 200–250 μm in Al-Mg alloy. In titanium alloy, the thickness of oxide layers does not exceed 100–150 μm during straight polarity cutting and 200–250 μm during reverse polarity cutting. A thin brittle layer of TiO and TiO₂ oxides is formed on the titanium alloy surface. It is shown that the generation of “water mist” around the plasma jet when cutting materials of all types with DCRP leads to a more intensive oxidation of metal, less thermal effect on the material, and reduced roughness of the cut face.

TEM studies were performed to examine the effect of holding of dispersion-strengthened heat-resistant reduced activation 12% chromium ferritic-martensitic steel EK-181 in static liquid lead for 3000 h at 600°C on the steel microstructure in comparison with the steel after conventional heat treatment by quenching and tempering at 720°C. It was found that the steel microstructure has good thermal stability under the specified experimental conditions. Microstructural deformation of EK-181 steel was studied in the neck region of tensile specimens tested at the temperatures 20, 680, 700, and 720°C with and without holding in liquid lead, and their fracture mechanisms were investigated. As a result of plastic deformation during tensile testing at room temperature, martensite plates and laths near the fracture surface are distorted and fragmented with the formation of new low-angle boundaries, and the dislocation density increases. At the deformation temperatures 680–720°C, nearly equiaxed ferrite grains are formed, the density and size of second-phase particles (M₂₃C₆ and MX) increases due to dynamic strain aging, and the dislocation density decreases locally. As the test temperature rises, the degree of martensite tempering increases. At T ≥ 700°C, some dynamic polygonization and dynamic recrystallization are observed. At elevated tension temperatures, ferrite coarsening is more significant in the specimens held in lead as compared to the conventionally treated material. The plastic deformation and fracture behavior of the steel are largely determined by the test temperature, rather than by the treatment mode.

Bone tissue engineers are paying close attention to titanium and titanium oxide for use in orthopedic implants due to their good mechanical properties, corrosion resistance, and low toxicity. A drawback of these materials is that there is an insufficient fit between the elastic moduli of titanium compounds and cortical bone, which leads to early bone degradation and implant failure as a result of improper load distribution. Here we report for the first time on TiO₂/Al₂O₃ composites with 20–50% porosity synthesized using bicomponent Ti/Al nanoparticles with an average size of 98 nm. The developed double sintering procedure allows the formation of transport pores through which the porogen and binder can be uniformly removed, and the use of Ti/Al nanoparticles allows the production of specimens with an optimal elastic modulus for cortical bone replacement (2.33 GPa) and low toxicity in in vitro experiments (more than 90% 3T3 cell viability, no more than 3.85% cell apoptosis). The concentration of ions released into the SBF solution depends on the specific surface area of the specimens, but in all cases it is significantly lower than the maximum permissible values. The obtained specimens have great potential for use as biomaterials for the manufacture of scaffolds and screws.

Adequate mathematical models of the mechanical properties of particle-reinforced polymer composites (PRPCs) require verification, which is difficult to do for at least the following reasons: lack of information on the mechanical characteristics of the transition layer formed at the modified particle–polymer interface, and lack of information about the mechanical characteristics of agglomerates that inevitably form during PRPC fabrication. This paper proposes a mathematical model for calculating the effective mechanical properties (bulk modulus, shear modulus, Young’s modulus, and Poisson’s ratio) of PRPCs with encapsulated filler particles. The model is verified on PRPC specimens with inclusions in the form of air bubbles. Simplified equations are derived for calculating the effective mechanical properties of PRPCs with low-modulus inclusions in the form of air bubbles. It is shown that the proposed model provides reliable estimates of the bulk modulus, shear modulus, Young’s modulus, and Poisson’s ratio of PRPCs at a small relative volume of submicron-sized filler particles in the matrix.

The paper briefly reviews the achievements of ISPMS SB RAS in the development of numerical computation methods and models for modeling the mechanical behavior of materials with hierarchical structure in the range of scales from nano to macro. The main stages in the development of several key areas are considered: atomistic modeling at the nanoscale level, continuum numerical methods, and particle method for studying the effect of structure on the behavior and properties of materials at larger spatial and temporal scales. The application of the multiscale approach to the structural modeling and design of metallic and ceramic materials is discussed. Prospects are outlined for transitioning to complete digital twins that link the structure formation process of the material with its final structure, mechanical properties, and mechanical behavior.

Aluminum matrix composites reinforced with ceramic particles are widely used in parts and components operating under severe abrasive friction and wear conditions. This work investigates the effect of the particle size and the amount of B₄C and SiC reinforcements ranging from 0 to 25 wt % in the initial powder mixture on the microstructure, micromechanical properties, and abrasive wear resistance of aluminum matrix composites. It is shown that B₄C and SiC reinforcement particles contribute to the refinement of the aluminum matrix. Micromechanical properties determined by instrumented microindentation indicate that the hardness of the composites exceeds the hardness of sintered aluminum, and Al–25% SiC composite has the highest mechanical load resistance compared to other composites studied. Pin-on-plate wear tests of samples sliding against fixed electrocorundum grains revealed the greatest abrasive wear resistance of Al–25% SiC and Al–12.5% В₄С–12.5% SiC composites. The minimum resistance was observed for Al–25% B₄C. These materials demonstrate adhesive and abrasive wear behavior with the formation of characteristic wear grooves and tear pits.

An important goal of industrial development is to improve the forming and thermomechanical processing technologies, both in order to get the best characteristics of finished products and to reduce energy costs and material consumption. The key step in solving such problems is the correct formulation of a material constitutive model. The temperature and strain rate attained in particular metal forming processes can vary significantly and have a strong influence on the structural evolution of the material and, consequently, on the resulting physical and mechanical properties. However, there are almost no processes in which the temperature and strain rate are constant and equal at all points of the processed product. In this regard, it is relevant to build constitutive models that correctly account for the influence of changing temperature and strain rate on the material response. Based on our previous review, we propose here a modified two-level statistical model that correctly accounts for the temperature and strain rate effects on intragranular dislocation slip and the associated material response. The model parameters are determined for an fcc polycrystal of Al 2024-T351 alloy using literature data on the compression behavior of this alloy at different temperatures and strain rates. A detailed description is given for an algorithm developed to identify the model parameters using data from constant temperature and constant strain rate experiments. The proposed model showed adequate results for loading conditions with changing temperature and strain rate.

This study reveals the impact of the formation mechanism of a two-phase (β + γ) structure during heat treatment on thermoelastic L2₁(B2)-10M/14M-L1₀ martensitic transformations and elastocaloric parameters of polycrystalline Ni₅₄Fe₁₉Ga₂₇ alloy. It is experimentally shown that annealing of the as-cast Ni₅₄Fe₁₉Ga₂₇ alloy in the temperature range 1173–1463 K for 0.5 h followed by water quenching leads to the precipitation of the γ phase at grain boundaries and inside grains. As the annealing temperature increases from 1173 to 1463 K, the thickness of the γ-phase layer at the grain boundaries doubles, particles inside the grains coarsen, and their volume distribution becomes nonuniform. Simultaneously, the martensitic transformation temperatures increase by 31–69 K. The nonuniform distribution of the γ-phase particles and the morphological features of martensite (refinement of its twinned structure) lead to a 5–6-fold widening of the martensitic transformation intervals in crystals annealed at 1448 K compared to the as-cast alloy. After cyclic superelastic tests with 20 to 100 loading/unloading cycles, two-phase (β + γ) polycrystals demonstrate the stable adiabatic cooling temperature ∆T_ad (2.7–3.0 K) and do not crack along grain boundaries, unlike those in the as-cast state. Significant fatigue strength and a high coefficient of performance (up to 18.3) make (β + γ) Ni₅₄Fe₁₉Ga₂₇ polycrystals promising for practical use in solid-state cooling.