Physical Mesomechanics最新文献

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.

This work discusses the predictable control of plasma-assisted physical vapor deposition (PVD) of coatings. The multiple process parameters and the instability of the nonequilibrium ion plasma system create substantial obstacles to the wide industrial application of promising multicomponent functional coatings. Here we propose a solution to this problem, which includes: creation of a database of diamond-like carbon (DLC) coatings to identify a limited set of adjustable process control parameters, determination of how these parameters affect the coating properties, analysis of the revealed effects using statistical methods and neural network algorithms, and use of the results for the predictable tuning of specified coating properties. The object of research is original DLC coatings whose structure is stabilized with nitrogen instead of conventionally used hydrogen. The experimental database of DLC coatings is created based on our previous studies and includes structural, morphological and architectural characteristics of coatings, various types of substrates, sublayers, physical, mechanical and tribological properties, and various combinations of coating deposition parameters. A specific problem is solved to determine the influence of deposition parameters such as chamber pressure P, stabilizer content (% nitrogen), ion flux rate (coil current λ) and deposition time t on hardness H and elastic modulus E of coatings. Based on the results obtained, the deposition parameters are optimized so as to obtain predictable strength values of the formed carbon coating. The optimization procedure is developed using both classical statistical methods and modern algorithms of ridge regression, randomized trees (ExtraTrees), and a fully connected neural network (multilayer perceptron MLP).

An experimental study is presented on the wear and failure of initial coarse-grained and modified ultrafine-grained Ti-6Al-4V alloy with a TiN protective coating, subjected to high-speed dynamic erosion by solid corundum particles with an average size of 109 μm in an air flow at a speed of 150 m/s and an erosion time of 30, 60, 180, 300 and 600 s. The experimental results are used to determine the erosive wear rate and the shear area percentage, as well as to measure the worn layer depth and erosion-induced changes in microhardness and structure of the alloy near the coated and uncoated surface. It is shown that all alloy samples are prone to wear and failure under the given high-speed erosion conditions, but their behavior is closely related to the erosion time and the structure of the substrate. The protective coating deposited onto the surface of ultrafine-grained Ti-6Al-4V titanium alloy significantly reduces the erosive wear rate compared to a similar coating on as-received coarse-grained alloy.

Friction stir welding is a relatively new way to join solid materials without melting using a nonconsumable tool, which has many applications in different industries including automotive, shipbuilding, and aerospace. Destructive testing is an integral part of engineering science, which costs a lot. Reducing the number of destructive tests via numerical calculations to determine the quality of welded parts is valuable. On the other hand, advances in computer technology and embedded sensing systems in different domains have made it possible to collect a variety of data in huge volume at an unbelievable velocity, which provides an opportunity and at the same time a challenge to engineers and practitioners to utilize this rich source of information efficiently. Functional data as a rich form of structured data allows for high dimensionality modeling and analysis of the data. In this paper, we develop a fully functional linear regression model to quantify and predict the quality of the process outputs by reducing the number of destructive tests and presenting a change-point detection model to avoid using the model when a change has occurred in one of the components of the process. Important issues such as autocorrelation and correlation are taken into account in the presented model. The functional variables of the model are solved by polynomial basis function expansions. The results of the experimental tests indicate that the proposed method performs well in detecting out-of-control conditions as well as estimating the change-point location. The obtained value of the multiple correlation coefficient 0.98 and the corresponding F-value equal to 652.95 support these results.

This study presents the flexural analysis of Ti-6A1-4V/ZrO₂ functionally graded (FG) sandwich plates under combined thermal and mechanical loading via exponential-cubic-sinusoidal integral shear deformation theory. The current formulation used in the modeling provides a parabolic distribution of transverse shear stresses without requiring additional factors in the formulation. Various sandwich plate models with different layer thicknesses and material types are considered. The FG layers vary continuously and smoothly according to exponential and power-law functions. The governing differential equations of the system are derived and solved analytically using the virtual work principle and Navier’s approach. Benchmark comparisons are performed to validate and show the accuracy of the proposed model. Various parametric examples are presented to illustrate the effect of the geometry, dimensions, FG sandwich type and material gradient on the static flexural response of the studied structure.

This paper is a part of the study on the rupture propagation and seismic wave emission during the movement along the fault, whose fracture surface in different regions is made of geomaterials with different frictional properties. The slip surface of the fault is frictionally heterogeneous. It contains weakening zones (asperities), strengthening zones (barriers), and “background” zones that are almost neutral with respect to velocity and displacement. The scenario of a seismogenic rupture is determined precisely by the presence, number, and size of such zones with different dynamics of frictional characteristics. The study deals with the mechanics of supershear earthquakes, in which the rupture propagates with an unusually high velocity exceeding the shear wave velocity of the medium. Numerical simulation results confirm the existence of two different mechanisms governing the transition of an earthquake to the supershear regime. A model of the so-called “weak” fault is considered, for which the rupture velocity continuously increases from the sub-Rayleigh velocity C_R to the shear wave velocity C_s and quickly exceeds it without any jump. This scenario is typical for faults with the measure of strength S under 0.8. The solved problem is not only of fundamental importance for understanding the earthquake mechanics, but also can find application in engineering seismology and the study of earthquake-induced rupture processes, because unlike an ordinary earthquake, supershear or fast ruptures cause strong shaking at a much greater distance from the source of the event (from the fault). This is confirmed by direct data on near-field ground motion obtained in recent years by research groups from different countries.

Statistical distributions of the elastic strain and stress tensor components in the grains of polycrystalline materials are necessary to calculate the probabilities of various local critical events, such as damage and others, which are of random origin due to the stochastic grain structure. Many experimental and computational studies suggest that these distributions can be approximated by a normal distribution. The normal distribution parameters are determined from histogram-like plots obtained experimentally or by computer simulation. Most published histogram distributions are highly skewed, in contrast to the normal distribution. Here we present a new direct calculation method for the probability densities of the elastic strain tensor components. The method uses an integral equation for strains in heterogeneous solids, which reduces the solution of the boundary value problem of polycrystal deformation to the sum of solutions of some problems for neighboring grains. The focus is on the influence of random grain interactions on the strain distribution. Calculations are carried out for polycrystals with different elastic symmetries and degrees of grain anisotropy. All probability densities are finite, asymmetric, and noticeably different from Gaussian ones. It is shown that very few particularly located neighboring grains (of dozens) have a much greater effect on the distribution pattern and limiting values of the strain tensor components than all the others.

The present study explores dispersion characteristics of thermal, viscoelastic and mechanical waves in graphene sheets subjected to uniform thermal loading and supported by the visco-Pasternak foundation. Kinematic relations for graphene sheets are deduced within two-variable refined higher-order plate theory. Damping effects of the viscoelastic medium are modeled using the Kelvin–Voigt model. The research extensively investigates the size-dependent behavior of graphene sheets by incorporating nonlocal strain gradient theory. Nonlocal governing equations are formulated under Hamilton’s principle and solved analytically to determine wave frequency values. To validate the results, a comparative analysis is conducted, and the outcomes are tabulated to confirm the effectiveness of the approach. Finally, graphical representations are employed to depict the influence of each parameter on the wave propagation responses of graphene sheets.

This paper explores the vibrational properties of double-walled carbon nanotubes embedded in a polymer matrix within different gradient elasticity theories. The study considers how the mechanical behavior of double-walled carbon nanotubes and the polymer matrix changes with temperature. The research highlights the significance of scale effects on wave propagation in double-walled carbon nanotubes and shows that certain characteristics of transverse vibrations in double-walled carbon nanotubes are affected by temperature variations. In addition, the paper derives consistent governing equations for modeling free transverse vibrations of double-walled carbon nanotubes using the nonlocal Euler–Bernoulli beam model, considering the effects of temperature and Van der Waals forces between the inner and outer nanotubes.

Deformation mechanisms of the Al₃(TiTaZrNbHf) high entropy intermetallic compound under tensile loading were studied using molecular dynamic simulations. To this end, the site occupancy of the five constituent atoms that form the high entropy sublattice of Al₃(TiTaZrNbHf) was first determined by simulating the near-equilibrium melting/crystallization process. It is shown that nuclei of intrinsic stacking faults are formed under early plastic deformation due to dislocation nucleation and glide, which further contribute to the formation and growth of twin boundaries. Twinning and 1/6<112> Shockley partial dislocations are key components in the plastic deformation of Al₃(TiTaZrNbHf) at room and elevated temperatures, which is in good agreement with the experimental observations for D0₂₂-structured materials. The tensile strength of Al₃(TiTaZrNbHf) is 4.6 GPa at 300 K and slightly decreases to 4.34 GPa at 1000 K, highlighting the unique properties of high entropy intermetallic compounds in retaining their mechanical properties at elevated temperatures. The derived results provide grounds for understanding the atomic-scale origin of deformation mechanisms in high entropy intermetallic compounds. They also show potentials for tailoring the chemical composition of intermetallic compounds to overcome the problem of low ductility, paving the way to their industrial applications.