The paper studies physical and mechanical properties of an epoxy and the silica sand polydisperse mixture. As a dispersion medium we used the epoxy L with hardener EPH 161, and as a disperse material we used the silica sand mixtures of two varieties, here named fine and coarse ones (two characteristic particle sizes). The particles microphotographs are given. The particle size distribution histograms are constructed. Student's t-test was calculated to determine the difference between the mean values of two independent samples. The statistical difference between the two samples was shown to be statistically distinguishable. The mixture porosity and permeability depending on the fine sand proportion were measured. It is shown that each component’s porosity has almost the same values, and the porosity has its minimum if the fine sand content is 40 %. The dependence of permeability on the fine sand proportion is plotted. It is calculated how the effective pore radius affects the proportion of the fine particles. Mechanical tests of the polymerized samples were performed using the universal testing machine ZWIC Z-250. Non-monotonic dependence of ultimate tensile and compressive strength of the polymerized samples depending on the fine particle proportion was revealed. Pairwise linear correlation coefficients of mechanical characteristics with the medium porosity have been calculated. It is shown that there is an inverse relationship between tensile and compressive strains

An electromechanical mathematical model is developed to locate a single force effect of pressing a rigid ball particle into the sensor surface of an indicator piezoelectric MDS coating with an integrated double spiral of electrodes. We consider formation of informative voltage pulses on arcs of electrodes of a double spiral in a circular perturbation zone of an indicator coating due to piezoelectric deformation between the electrodes when pressing a rigid ball particle. Shape and duration of informative voltage pulses as functions of time are found by solving the corresponding differential equation taking into account piezoelectric and geometric characteristics, value, nonuniformity, duration and distance from the epicentre of the electrode/piezoelectric/electrode disturbance arcs acting on each of the piezocells within the circular disturbance zone of the indicator coating. The number of pulses generated and recorded is proportional to the ratio of the perturbation zone radius and the sensor spiral pitch of the indicator coating. Here the perturbation zone radius is proportional to the diagnosed force. A simple, convenient and applicable solution of location is obtained, i.e. finding polar coordinates of the epicentre of the force effect, while the accuracy of the location improves when the number of the spiral turns increases, i.e. the pitch of the sensor spiral decreases, relative to the radius of the perturbation zone.

Active development of mechanical metamaterials has currently led to the widespread application of auxetic structures in various applications with differing loading conditions. This research explores thermomechanical behaviour of novel in-plane cylindrical auxetic lattice structures by studying the correlation between their deformational characteristics and the coefficient of thermal expansion (CTE) of the material. Unlike traditional auxetic cylinders, the plane of auxeticity in the developed models is oriented perpendicular to the cylinder axis, which defines their specific behavior. To understand the behavior of auxetic lattices under combined thermal and mechanical loads, computational experiments were conducted based on the finite element method (FEM). Deformations of both rectangular and cylindrical lattice structures were investigated. The relationships between transverse deformation and CTE were obtained and compared. The influence of CTE on the structural Poisson's ratio of rectangular auxetic lattices was assessed, which is a key parameter characterizing the auxetic behavior of the structure under thermomechanical loading. The feasibility of modeling the mechanical behavior of auxetic cylinders using an orthotropic mechanical model with effective material properties was verified. The constants for defining such a material model were obtained by simulating a numerical experiment on tensile and shear testing of the rectangular auxetic lattices along coordinate axes. Using an example with artificial material properties, it was demonstrated that the predominant deformation mechanism, caused by the opposing effects of mechanical and thermal loads, can be controlled by selecting a material with an appropriate CTE. This allows for regulating the structural response to changes in temperature and mechanical load. Such results can be utilized for creating cylindrical auxetic lattice structures subjected to mechanical and thermal deformations in applications requiring controlled thermomechanical responses.

A two-dimensional diffusion-kinetic model is proposed to research the effect of oxygen diffusion along grain boundaries on the oxidation dynamics of the intermetallic alloy Ti3Al. The contribution of grain boundaries is evaluated by comparing the dynamics of processes in a structure with clearly defined grains and boundaries and in a material with effective properties, where the diffusion coefficient was calculated depending on the fraction of the boundary phase. Oxygen diffusion occurs in a mixed kinetic mode typical of additively fabricated nanoscale structures. The structure with an explicit consideration of grains and boundaries in the model has its symmetry. Rectangular grains are located relative to each other similar to "brickwork" so that they form triple junctions. The material with effective properties is a continuous rectangular region, in which the fraction of the boundary phase is taken into account through the diffusion coefficient. A constant oxygen source is specified on the surface. The problem is solved numerically in dimensionless variables. An implicit difference scheme of splitting by coordinates is used to solve the diffusion equation. To solve the kinetic equations, a method similar to the explicit Euler method is used with the organization of the iterative process. The results are compared for the isothermal mode and for the conditions of linear heating with subsequent cooling. The study is carried out for the initial stage of oxidation of the nanosized intermetallic alloy Ti3Al. The contribution of grain boundaries to the oxidation dynamics is estimated in the range of the fraction of the boundary phase from 0.1 to 0.5, which changes due to the variation of the grain sizes relative to the boundary width. The results obtained are in a qualitative agreement with the literature data.

When using thermosensitive sensors and servos, based on shape memory alloys (SMA), it is necessary to take into account the influence of shifting factors capable the temperatures of martensitic transformations (MP). One of these factors is the martensite stabilization effect (MSE), which manifests itself as an increase in reverse MP temperatures after preliminary deformation. Previous MSE studies allowed, based on experimental data, to hypothesize that this effect is due to damage to the boundaries orientation of the martensite domains. This suggests that minimizing or eliminating MSE is possible while minimizing damage to these boundaries. One of the ways to achieve this is to cool the SMA from the austenitic state under constant load in an incomplete temperature range of transformation. Numerical experiments performed within the framework of a microstructural model that takes into account MSE made it possible to determine the dependence of the temperature shift of the reverse transformation on the value of the fraction of direct transformation achieved during cooling. The results showed that the temperature shift remains zero or negligible until a certain critical fraction of the transformation is reached.