Physical Mesomechanics最新文献

One of the most critical degradation modes in polymeric composites is fiber–matrix debonding. Therefore, utilizing nanoparticles in the fiber sizing instead of dispersing nanoparticles in the matrix as a traditional method could postpone the separation of fibers from the matrix. Covering of fibers during the production process is called sizing. The present study simulates two three-dimensional representative volume elements (RVEs) to predict the transverse elastic modulus of the glass/epoxy composite. The sizing region in the RVEs, provided in Abaqus software, is simulated with both homogeneous and heterogeneous mechanical properties. Then the numerical models are validated using the available numerical and experimental data. Furthermore, the Mori–Tanaka, Halpin–Tsai, and random distribution methods are employed to calculate equivalent properties for the nanoparticle-reinforced sizing, which are used for the sizing region of the RVEs to predict the transverse elastic modulus of the four-phase glass/epoxy composite. Compared to the available experimental data, the random distribution method is a more accurate procedure to predict the transverse Young’s modulus. Finally, with the assistance of the random distribution method, nanoparticles with different dimensions or even types are dispersed in the sizing region. In fact, carbon nanofibers (CNFs) and silica (SiO₂) nanoparticles are simultaneously distributed in the sizing with various dimensions to predict the overall transverse elastic modulus of the composite. Once again, these nanoparticles are modeled in the sizing region with specific measurements. Besides, the results for all of the states are compared.

This paper discusses the use of multicomponent composites as advanced nanostructured coatings. Their composition and synthesis conditions allow a simultaneous nucleation of islands of different mutually insoluble phases, which limit the island growth. Components for the coatings are chosen so that, firstly, to form nitrides, carbides, oxides, and more complex compounds with a high enthalpy of formation. Secondly, to form insoluble copper and nickel in order to reduce differences in the elastic moduli of the substrate and coating, eliminate stress concentrators, and increase the fracture toughness of the surface layers. The phase-structural state and the elastic stress distribution in the coatings are investigated to assess the torsional lattice curvature and local internal stresses as one of the most important factors in increasing the coating microhardness to HV = 40 GPa. Two types of substructures were distinguished in the nanocoatings depending on the composition: a nanocomposite one with less than 20-nm crystals in the amorphous matrix, and a two-level substructure with grains of hundreds of nanometers fragmented into 10- to 20-nm crystals. High elastic and elastoplastic bending-torsion was observed in coatings of various types. Using Ti-Al-Si-Ni-Cr-Cu-C-O-N coatings as an example, we confirm the effectiveness of the proposed multicomponent coating design principles that provide high hardness, fracture toughness, and thermal stability.

The description of cyclic plasticity requires experimental determination of the constants entered into respective resulting equations. In this paper, a method is proposed for determining the parameters and constants of a Lemaitre-type damage accumulation model on the example of P2M rotary steel. The model is based on the Voce isotropic and the Armstrong–Frederick kinematic hardening law. The method of experimental determination involves standard uniaxial tension tests as applied to the parameters of isotropic hardening, and low-cycle fatigue tests, to the constants of damage accumulation and parameters of kinematic hardening. The method is applicable to any alloy that fits the model representations. Using the constants and parameters found, the behavior of cylindrical P2M steel specimens under cyclic loading is modeled by finite element simulation and their fatigue curve is plotted. The predicted fatigue life of P2M steel correlates well with experimental data.

In this study, highly porous biocompatible and biodegradable zinc, iron and magnesium alloy foams were fabricated for temporary implant and scaffold applications. Specimens with open porous structure were fabricated by powder metallurgy based space holder method. Mg, Fe and Zn are the main bioabsorable metals. Mg alloys biodegrade too fast with H₂ evolution. Biodegradation rate of Fe alloys is too slow, and by-products remain inside the body. Zn alloys show biodegradation rates in the middle of Mg and Fe alloys, and their biodegradation by-products are bioresorbable. Here several Fe, Zn, and Mg alloys were manufactured, and comparatively characterized. Effects of alloying elements on biodegradation, corrosion and mechanical properties were investigated separately. As the mechanical properties of temporary implants must decrease slowly, the variation of mechanical properties with time in the foams was investigated. Corrosion performance was tested in simulated body fluid. Biodegradation rate was investigated by using weight loss and metal ion release measurements. The corrosion and biodegradation rates of Zn specimens were lower than in Mg specimens and higher than in Fe specimens. Fe²⁺, Zn²⁺ and Mg²⁺ ion release amounts were lower than the upper limit for humans.

This study discusses CrAlSiN coatings obtained by vacuum arc plasma deposition. The structural and compositional parameters that are responsible for the most essential coating properties are identified. The structural morphology, elemental distribution, and phase composition of the coatings are investigated. The physicomechanical, adhesive and tribological characteristics are determined. Coatings were deposited on substrates of nitrided and carburized structural steels widely used in mechanical engineering. The coating properties are determined and compared with the corresponding surface properties of the standard uncoated specimen. The coating thickness for the experimental specimens was 0.82–1.18 µm. A comparative analysis of the coating phase composition is carried out using X-ray photoelectron spectroscopy (XPS) and thermodynamic calculations with Termo-Calc software. It is shown and proved experimentally that ion plasma coatings are nonequilibrium. In addition, CrAlSiN coatings significantly increase the mechanical characteristics of the material, such as hardness and resistance to elastic and plastic deformation, and adhere well to the substrate surface. In tribological tests, CrAlSiN coatings reduce the wear rate by a factor of 2–4 compared to nitrided steel and by an order of magnitude compared to carburized steel. These high properties are also attributed to the nonequilibrium structural-phase state of the coating. The obtained results indicate that vacuum arc plasma CrAlSiN coatings can be used as wear resistant protective coatings, including under friction conditions.

The influence of Ca on the microstructure characterization, mechanical performance, corrosion behavior, and cytocompatibility of Mg-Zn-Al magnesium alloy was studied. Mg-Zn-Al and Mg-Zn-Al-xCa alloys were evaluated as cast. Scanning electron microscopy demonstrated that the microstructure of the Ca-containing alloys was substantially finer and more uniform than the standard Mg-Zn-Al alloy. Hardness and compressive strength tests revealed that the addition of Ca boosted hardness and compressive strength while decreasing ductility. The corrosion resistance of the investigated alloys was enhanced initially but dropped as the Ca concentration increased. The corrosion resistance performance of Mg-Zn-Al-0.5Ca alloy was the best, with a corrosion rate of 3.7 mm/y due to the specific microstructure and dense products related to the corrosion on the sample surface. Cytotoxicity experiments showed that Mg-based alloys with a low Ca content have higher cell viability than Mg-Zn-Al and Mg-based alloys with a high Ca concentration, indicating improved biocompatibility. As a result, Mg-Zn-Al-0.5Ca alloys can be termed alloys with superior corrosion resistance and great mechanical properties that display high corrosion resistance as well as good biocompatibility.

In the current paper, a generalized thermoelastic model with two-temperature characteristics, including a heat transfer equation with fractional derivatives and phase lags, is proposed. The Caputo–Fabrizio fractional differential operator is used to derive a new model and to solve the singular kernel problem of conventional fractional models. The suggested model is then exploited to investigate responses of an isotropic cylinder with variable properties and boundaries constantly exposed to thermal or mechanical loads. The elastic cylinder is also assumed to be permeated with a constant magnetic field and a continuous heat source. The governing partial differential equations are formulated in dimensionless forms and then solved by the Laplace transform technique together with its numerical inversions. The effects of the heat source intensity and fractional order parameter on the thermal and mechanical responses are addressed in detail. To verify the integrity of the obtained results, some comparative studies are conducted by considering different thermoelastic models.

Understanding the mechanical response of polymer components fabricated by fused deposition modeling (FDM) is an important issue. Therefore, the present study deals with the effects of raster angle and layer orientation on the tensile properties and fracture toughness of acrylonitrile butadiene styrene (ABS) specimens produced by the FDM method. Two groups of specimens are considered. The first group includes specimens with the same layer orientation and the four different raster angles 0°/90°, 15°/–75°, 30°/–60°, and 45°/–45°. Specimens in the second group have the fixed raster angle 45°/–45° and three different layer orientations. Tensile tests are performed using dumbbell specimens, and semicircular bending (SCB) specimens were used for fracture mechanics tests. The critical value of J-integral obtained from finite element simulations is used as a parameter to characterize fracture properties. In the first group of specimens, the critical value of J-integral for the 45°/–45° specimen is 4389 J/m² while it is about 1880 J/m² for the 0°/90° specimen. In the second group, the vertically printed specimens have the least fracture resistance 1004 J/m², while this value reaches 5934 J/m² for the specimens in which the precrack is perpendicular to the printed layers. In addition, the fracture surface of tensile specimens is analyzed using scanning electron microscopy for the mesomechanical study of failure in the printed specimens. Lastly, the crack path in SCB specimens is explored experimentally to understand how the raster angle and layer orientation affect the fracture trajectory and to justify different values of fracture loads.

Strength measurement results are reported for hot-rolled cast cold-resistant structural alloy steel 09CrNi2MoCu subjected to shock compression up to 15.5 GPa within the strain rate range of 10⁵–10⁶ s^–1. Specimens fabricated by direct laser deposition were used to study the effect of the deposition direction and shock compression amplitude on the Hugoniot elastic limit and critical stresses during spall fracture. The strength characteristics were determined by analyzing the full waveform data recorded during loading by a VISAR laser Doppler velocity interferometer. It was found that the spall strength of the cast steel specimens is almost independent of the shock compression pressure, but strongly depends on the strain rate before spalling. The spall strength of the additively manufactured specimens is slightly lower than that of the hot-rolled cast steel specimens and does not depend on the deposition direction. The α ↔ ε phase transformation expected at 13 GPa was not observed in experiments on cast steel 09CrNi2MoCu with the maximum shock compression pressure.

Polycarbonate (PC) has diverse applications in different industries such as transportation, electronics, biomedical and solar energy sectors. Polycarbonate is used as a material for structural components that are usually complex in shape and subjected to severe mechanical loading. The presence of notches such as holes, grooves, or cuts reduces the load-carrying capacity of structural components because of the stress concentration. Therefore, it is essential to understand the mechanical behavior of polycarbonate in the presence of different notch geometries. Machining of inclined notches at different angles to the applied load is simple, but this can produce complex mixed-mode I/II states that exist in real-life applications. The present study is performed on PC specimens with U-notches of different geometry. They differed in depths, radii, and angles. These specimens were tested under quasi-static loading, and selected specimens were analyzed using digital image correlation. Two linear elastic methods were used to analyze the fracture of U-notched PC specimens: the theory of critical distance with the point method (TCD-PM) and the strain energy density with the equivalent material concept (SED-EMC). Satisfactory estimates with the error between –4% and 2.5% were achieved using the TCD-PM method. Estimates derived by the SED-EMC method were mostly within the error of about ±13%.