An acoustic emission method for assessing the degree of degradation of mechanical properties under conditions of complex dynamic deformation stresses is proposed. It has been shown that changing the operating conditions of metal structures, peak loads, external collisions, and thermally changing loads, which cannot be taken into account, leads to uncertainty and unpredictable structural changes in the material. This in turn makes it difficult to identify the state of the structure material to ensure trouble-free operation of the equipment. Changes in the mechanical properties under difficult loading conditions are identified by polynomial approximation of the results of AE measurements and the construction of boundary curves separating the operability region from the fracture region. This is achieved by approximating the experimental dependences of the acoustic parameters for various types of loading. This approach significantly expands the capabilities of the technical means of identification systems of metal structures, and in particular, allows the current state of the equipment and its suitability for further operation to be assessed without stopping the equipment in real time. It is of interest not only to fix the damage, but also to diagnose the processes of reducing the mechanical properties during the operation of the equipment.

A simulation mathematical model of the state of operability of metal structures under difficult operating conditions without stopping the equipment was developed in the form of similarity criteria found on the basis of the laws of conservation of data obtained experimentally during tensile and four-point bending tests. Criteria are proposed for the similarity of the state of the material of the samples and the products in service, in which the kinetics of destruction are determined through the rate of damage accumulation and the movement of the structural components of the material. The residual life of the equipment under conditions of complex deformation effects was determined based on the theory of similarity and the analysis of the dimensions of the parameters of acoustic emission in real time. The use of concepts and models of fracture mechanics when creating methods and criteria for assessing the results of diagnostics and monitoring allows important information about the technical state of objects to be obtained.

Theoretical study of excitons spectra is offered in this report as for Zn₃P₂ crystals. Spectra are got in the\ud zero approach of the theory of perturbations with consideration of both the anisotropy of the dispersion law\ud and the selection rules. The existence of two exciton series was found, which corresponds to two valence\ud bands (hh, lh) and the conductivity band (c). It is noteworthy that anisotropy of the dispersion law plus the\ud existence of crystalline packets (layers) normal to the main optical axis, both will permit the consideration of\ud two-dimensional excitons too. The high temperature displaying of these 2D-exciton effects is not eliminated\ud even into bulk crystals. The calculated values of the binding energies as well as the oscillator's strength for the\ud optical transitions are given for a volume (3D) and for two-dimensional (2D) excitons. The model of energy\ud exciton transitions and four-level scheme of stimulated exciton radiation for receiving laser effect are offered.Представлено теоретичне дослiдження екситонних спектрiв для кристалiв Zn₃P₂. Енергетичний спектр екситонiв отримано у нульовому наближеннi теорiї збурень з урахуванням анiзотропiї закону дисперсiї та правил вiдбору. Зафiксовано прояв двох серiй екситонних станiв, якi вiдповiдають двом валентним зонам (hh, lh) i зонi провiдностi (c). Гранична анiзотропiя закону дисперсiї та шарувата кристалiчна структура дозволяють очiкувати на квазiдвовимiрний характер екситонiв. Наслiдком цього може стати високотемпературний прояв екситонних ефектiв, навiть в об’ємних кристалах. Розраховано значення енергiї зв’язку та сили осцилятора оптичного переходу для об’ємних (3D) i двовимiрних (2D) екситонiв. Запропоновано модель екситонних переходiв i чотирирiвневу схему стимульованого екситонного випромiнювання для отримання лазерного ефекту

This study examines the impact of calcium-rich fly ash as an additive on metakaolin-based geopolymers. Six types of fly ash (FA1-FA7) from different thermal power plants in the Czech Republic were collected and characterized based on their physical and chemical properties. The addition of fly ash into the geopolymers was evaluated through a multicriteria assessment that focused on density and mechanical properties. By using a multi-criteria approach, the assessment provides a comprehensive and holistic evaluation of the material, allowing for a more informed decision about the optimal addition of additives. This approach helps to minimize any negative impact on the material’s properties while maximizing the utilization of the by-product. The result is an optimized geopolymer mixture with improved properties and increased sustainability, as the by-product is used beneficially. Furthermore, calcium content is the key factor that affects the physical properties of geopolymers by accelerating the curing time. This rapid process can result in reduced strength with increasing fly ash content. The multicriteria assessment revealed that the optimal condition is achieved using fly ash (FA2) from the Loucovice thermal power plant (5.2 wt.% Ca) that was treated at a temperature of 615 °C. The flexural strength of FA2-based geopolymers increased by 13% compared to concrete (standard). However, the addition of fly ash significantly reduced the compressive strength of geopolymers throughout the range of specimens. The Charpy impact strength of FA2 was higher than the standard due to the presence of unburned biomass solids in the ash structure that can absorb energy easily.

Propagation of acoustic emission signals in continuous conjugated media under real-time loading was explored. The results of explored plastic deformation polymer coatings on a metal base using the acoustic emission method with synchronization of deformations and the moments of occurrence of acoustic emission signals are presented. Using the principal component method, the acoustic emission spectra, which make it possible to trace the evolution of deformation transformation processes, were analyzed. Presented the results of theoretical and experimental studies on the separate propagation of acoustic emission vibrations in a polymer coating, a metal base, and their joint combination in the form of multilayer structures. Boundary problems of propagation of acoustic emission signals in the conjugation of continuous media are considered from the standpoint of an elastic continuum and wave representations. The main variables are the force that initiates the appearance of acoustic emission signals and the displacement that determines the propagation of elastic waves. Based on the local rearrangement of the internal structure of conjugated media under conditions of development of deformation processes in the material, the verification of the main theoretical models of energy spectrum acoustic signals in continuous media at the micro-, meso-, and macro-levels was carried out. In this work, we present experimental data on a set of basic acoustic emission characteristics for four-point bending. It is shown that the principal components method reduces the dimension of data while maintaining the least amount of new information. Using the method of principal components to determine the stages of plastic deformation of polymer coatings on a metal base using the acoustic emission method. With the digitalization of acoustic emission signals and noise filtering, new possibilities for isolating a weak signal at the noise level appear even when its amplitude is significantly lower than the noise level. The study results can be used to predict the degree of destruction of two-layer materials under loading.

The results of theoretical and experimental research of the energy spectrum of acoustic emission signals of the model of forerunners of deformation processes in media with a microstructure are presented. The laws governing changes in the oscillatory properties of acoustic emission signals during the destruction of the structure of materials under load are established. The existence of a relationship between changes in the spectral characteristics and the moments of occurrence of acoustic emission signals with the parameters of the force field at various stages of deformation is proved. An explanation of the causal relationships of the occurrence of acoustic emission signals with defects in the microstructure is given. The results obtained make it possible to watch the dynamics of the development of defects and to provide prediction of the state of materials.