No 3 (2026)

Problem. Ensuring the technosphere safety of industrial facilities in the oil and gas sector is complicated by
processes of hidden microstructural degradation of metal, which initiates more than 31 % of emergency situations. Traditional
nondestructive testing methods are significantly limited by the need for thorough surface preparation and ensuring stable liquid acoustic contact, which hinders the operational monitoring of pipelines and pressure vessels through insulation layers.
Aim. The aim of this study is to establish quantitative relationships between the spectral parameters of the electromagneticacoustic (EMA) signal and the stages of stress-strain state and damage of structural steels. Methods. A series of experiments
was performed on St3sp, 09G2S, and 12Kh18N10T steels under static tension on a servohydraulic system. Signal registration
was carried out using an EMA thickness gauge. The analysis is based on dynamic approach: the control zone was identified as
a linear system, the mathematical reference of which is a second-order transfer function W(p) reconstructed by the method of
moments. To automate state recognition, a transition to frequency models in the form of hodographs of amplitude-phasefrequency characteristics (APFC) was implemented. An artificial neural network based on the ML.NET library was trained
on 3 samples of 720 measurements, using the amplitudes and phases of the first 15 signal harmonics as input features.
Results. It was experimentally proved that the accumulation of structural damage causes a regular migration of the roots of
the characteristic polynomial on the complex plane and a qualitative transformation of the shape of the APFC hodographs.
The developed intelligent classifier provided an identification accuracy of the stress-strain state (SSS) stages at the level of
92.16 %, while the error in determining the numerical stress values did not exceed 3.5 %. Conclusions. The spectral parameters of the EMA signal in combination with machine learning technologies make it possible to identify reliably pre-defect
states of metal. The proposed method minimises the influence of the human factor and ensures the detection of zones of critical stress concentration before the initiation of macroscopic cracks.

Problem. The relevance of this work is caused by the absence of a generally accepted method for the quantitative assessment of cavitation activity, as well as the limitations of traditional erosion tests associated with long experiment durations, low reproducibility, and distortion of the cavitation field structure by massive test specimens. Aim. To
develop a highly sensitive and reproducible erosion test method that allows assessing the spatial distribution of erosion
activity in an ultrasonic field. Methods. To study the dynamics of cavitation erosion, it is proposed to use video recording
of the destruction process of aluminum foil followed by automated image processing. The developed software implements
computer vision algorithms using the OpenCV library and neural network segmentation based on a modified Segment
Anything Model (SAM) with a U-Net type output layer and a ResNet34 encoder. This allows delineating automatically
the erosion damage zone and calculating quantitative damage characteristics. The method was tested in the ultrasonic field
of a 22 kHz immersion transducer, varying the ultrasound intensity, distance to the transducer, and gas content of the liquid. Results. High reproducibility of the method was established. It is shown that the use of 15 μm thick foil (GOST 745-
2014) provides high sensitivity to non-stationary cavitation processes. It was found that the active cavitation zone in
the field of an immersion transducer is localised near the radiating surface (up to 5 mm), with the erosion rate rapidly
decreasing with increasing distance from the transducer. Conclusions. The developed method for recording and analysing
the dynamics of cavitation destruction of test specimens allows reducing the experiment duration by at least an order of
magnitude compared to the ASTM G32-16 method. The method also makes it possible to obtain the distribution of cavitation erosion activity in the investigated volume in a single pass, i.e., using a single specimen. The possibility of correlating
erosion damage characteristics with the parameters of the cavitation noise spectrum is demonstrated.

Problem. Chromium-nickel austenitic steels of the AISI 300 series are important structural materials for industrial applications over a wide range of operating temperatures. The most effective way to increase the strength, wear
resistance, and durability of products made from such steels is the creation of diffusion or cladding layers, which both
harden the steel and perform a protective function. Aim. To identify the influence of the chemical composition of AISI
310S and AISI 321 chromium-nickel austenitic steels on the features of structure formation during liquid carburizing.
Methods. The studies were carried out using optical and scanning electron microscopy, X-ray diffraction, and durometric
analysis. Results. It was found that after liquid carburizing at a temperature of 780 °C, the total content of carbide phase in
AISI 310S steel is almost four times higher than in AISI 321 steel, amounting to 39.3 and 9.3 wt.%, respectively. Differences in the type of chromium carbides precipitated during carburizing of the investigated steels were revealed (Cr23C6 in
AISI 321 steel and Cr7C3 in AISI 310S steel). It was identified that in both investigated steels, cementite Fe3C is also
formed; however, discrepancies in the position of the characteristic peaks of cementite are observed. It was shown that
the intensity of carbide formation processes during liquid carburizing of austenitic steels directly affects the depth of
the hardened layer, which amounted to about 500 μm for AISI 321 steel and about 200 μm for AISI 310S steel. It was established that carburized AISI 321 steel has a significantly higher surface hardness (890 HV0.025) compared to the surface
hardness of carburized AISI 310S steel (590 HV0.025), which is due to the presence of α-martensite in the structure of
AISI 321 steel. Conclusions. The chemical composition of austenitic AISI 310S and AISI 321 steels has a significant impact on the processes of structure formation during liquid carburizing, which is caused by different diffusion conditions.

Problem. Two-dimensional transition metal dichalcogenides (TMDs) are promising candidates for
applications in next-generation optoelectronic and plasmonic devices due to their outstanding electronic and optical
properties. However, monolayer CrS2 remains understudied, and its strain-dependent optical response has not been
systematically investigated. Aim. To conduct a comprehensive first‑principles investigation of the effects of biaxial strain
on the optoelectronic properties of monolayer CrS2, in order to elucidate the microscopic mechanisms governing
strain‑induced optical responses and to provide a theoretical basis for the design of tunable optoelectronic and plasmonic
devices based on 2D materials. Methods. The study used density function theory (DFT) to analyze the electronic band
structure, dielectric function, and optical constant under different strain levels. Results. The results show that CrS2
possesses a direct bandgap of ~0.96 eV at the K-point, and the complex dielectric function ε(ω) exhibits distinct anisotropy
between in-plane and out-of-plane orientations. Furthermore, optical constants, including refractive index (n), extinction
coefficient (k), absorption coefficient (α), reflectivity (R), and energy loss function (L), are comprehensively analyzed.
Under biaxial strain ranging from −6 % to +6 %, a pronounced variation in the absorption and attenuation coefficients was
observed, with intensity increasing under tensile strain and decreasing under compressive strain, while reflectivity
remained low in the infrared–visible region, confirming optical behavior dominated by absorption. The energy loss
function revealed that plasmon resonances can be tuned by strain in the ultraviolet region. Conclusions. These findings
demonstrate that biaxial strain is an effective strategy for tuning the optical response of monolayer CrS2, highlighting its
potential in tunable optoelectronic and plasmonic applications.