Appearance Of Cracks Research Articles

Investigation of the Influence of NiBSi/NiCrBSi Coatings Applied by Flame Spraying with Simultaneous Fusing on the Substrate Material

The aim of this research is to investigate the influence of nickel alloy type from the same group, the parameters of flame spraying, as well as the preparation of the substrate and the heat treatments of the substrate on the microstructure of the coating/substrate system. Due to the possibility of applying nickel alloys in corrective maintenance of tools used on elevated working temperatures, hot work tool steel X38CrMoV5-1 was selected as a substrate material. The investigation of the microstructure of the coating/substrate system was carried out according to the factorial design of experiment, where the input factors were varied on two levels. The factors that were varied are: Ni based self-fluxing alloys - NiCrBSi and NiBSi; distance of the burner from the workpiece - small (6 mm) and large (20 mm); preparation of the substrate - roughened and non roughened and the heat treatments of the substrate - soft annealed and tempered condition. Ni-based self-fluxing alloys were applied on samples (12,5 × 25 × 25 mm) by flame spraying with simultaneous fusing process. Analysis of the microstructures of the coating/substrate system was carried out on the Leica DM 2500M light microscope. After the conducted analysis the paper concluded that by spraying the selected coatings onto the X38CrMoV5-1 tool steel base, poor quality coatings are obtained, due to the appearance of cracks (NiCrBSi) or separation of the coating from the substrate (NiBSi). This is attributed to the formation of martensitic structure of the substrate after spraying and the presence of residual stresses.

Selenium loaded sodium alginate/polyvinyl alcohol nanocomposite film as wound dressing: structural, optical, mechanical, antimicrobial properties and biocompatibility

In the current research, synthesized Se-NPs were loaded into sodium alginate/polyvinyl alcohol SA/PVA blend, 1:2 (w:w), with different proportions to form nanocomposite films by using the solution casting method. The main goal is to enhance the physical and antibacterial properties of the polymer blend; therefore, it can be utilized for wound dressing applications. The physical aspects of the prepared films were characterized by X-ray diffraction (XRD), Fourier transform infrared (FTIR), atomic force microscope (AFM), scanning electron microscope (SEM), Energy dispersive X-ray (EDX), UV–Vis spectroscopic technique, and mechanical analysis to show the effect of increasing the concentration of Se-NPs from zero to 0.5 wt% on their properties. Regarding the XRD analysis, the calculated values of lattice strain (ε\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\varepsilon$$\\end{document}) increased from 0.005 to 0.013. The FTIR absorption spectrum recorded an intensity reduction and position shift in the main characteristic peaks of SA/PVA. The morphology of Se-NPs revealed a spherical shape with a mean diameter of 131.76 nm, as revealed by transmission electron microscopy (TEM). The surface morphological images showed the appearance of a few cracks; besides, the average roughness increased from 1.59 to 2.08 nm. According to the UV–Vis spectroscopic analysis, the optical band gap reduces (from 5.425 to 5.216 eV) for the direct transition and from (5.07–4.78 eV) for the indirect transition, which is an indication of the interaction between Se-NPs and SA/PVA blend. Young’s modulus, tensile strength, and yield strength of the films increased with the addition of selenium nanoparticles. On the other hand, the amount of selenium release significantly increased with enhancing the concentration of Se-NPs in SA/PVA blend film from 0.1 to 0.5 wt%. Additionally, the inclusion of Se-NPs supplied the polymer blend with excellent antimicrobial activity, which would remove the possibility of microbial infection at the wound site. Moreover, the prepared SA/PVA/Se nanocomposite films have good biocompatibility with Human Skin Fibroblast (HSF). The results suggest the potential of this nanocomposite to be used in wound dressing applications.

Fracture propagation characteristics of pre-cracked red clay in roadbed filling under three-point bending

Red clay was a special roadbed filling soil that was easy to expand and shrink because of the characteristics of high liquid limit and high porosity, leading to the appearance of a large number of cracks. In order to understand the cracking mechanism and nonlinear fracture failure process of red clay, the fracture toughness and crack sensitivity of red clay with different saturation, compaction and gravel content were analyzed by three-point bending cracking experiment and Image processing technology, and then the cohesive crack model was established to describe the fracture toughness. The results showed that the cracking process of red clay could be divided into three stages: crack incubation period, crack initiation and propagation period and visible cracks appearance stage. There was a conic function relationship between fracture toughness and saturation and a positive correlation between fracture toughness and compactness. The influence of gravel content on the final fracture path of red clay was the most significant, while the effects of saturation and compaction could be ignored. In addition, the fracture toughness converted from the cohesive crack model was basically as the same as the measured. This work provided a basis for theoretical analysis and numerical calculation for the fracture toughness of red clay under three-point bending.

DEVELOPMENT OF MODELS COMPLEX OSCILLATIONS FOR AUTOMATION SYSTEMS OF VIBROACOUSTIC OPERATIONAL SAFETY CONTROL OF BUILDINGS AND STRUCTURES

Problem statement. Long-term safe operation of buildings and structures is impossible without determining the stability of their load-bearing elements, especially after shocks and dynamic loads under the influence of explosions and fires. In such conditions, reliable and productive monitoring of the reliability of buildings and structures is a critical element in increasing human safety. Vibroacoustic is an effective and informative method that allows for non-destructive assessment of the condition of concrete, reinforced concrete, brick, multi-layer walls and other types of structures. However, to increase the speed and quality of determining the state of objects, maximum automation of the vibroacoustic method is required. Purpose of the study. Increasing the productivity and reliability of vibroacoustic monitoring of buildings and structures by automating the impact action with specified parameters based on the development of dynamic models of complex oscillations. Methods. Analytical studies of dynamic and kinematic models of the exciter of mechanical vibrations, computer modeling, laboratory tests of the vibration generator control system. Research results. Models of complex oscillations have been developed to improve reliability and implement new control laws that are impossible for classical vibration systems and are necessary for automated vibroacoustic control of buildings and structures and ensure the safety of their operation. The use of reduced bit depth coefficients in the calculation scheme using the Jack W. Crenshaw algorithm is justified in a wider range of argument values than with initial coefficient values for controlling vibration systems with limited computational performance. This is necessary when creating executive bodies of modern systems for automated vibroacoustic monitoring of the cracks and violations of the homogeneity of load-bearing structures of buildings and structures. The oscillation exciter has been tested in laboratory conditions. Scientific novelty. New methods and algorithms for automatic control of vibration exciters have been developed to obtain polyfrequency oscillations, linear waves and wave fields with specified amplitude and frequency characteristics. Practical significance. An oscillation exciter has been developed for a system of automated vibroacoustic control of the buildings and structures operation safety. This provides a necessary and sufficient basis for improving methods for assessing changes in the environment as a result of the appearance of cracks and loss of homogeneity.

Effect of patterns on Polyacrylamide hydrogel surface towards enhancement of water retention

Polyacrylamide hydrogel was investigated to improve its water retention capacity. Among the several hydrogel samples prepared, a sample with ∼0.55 % cross-linker was found sufficiently rigid with high water content. The drying and rehydration cycles induced the appearance and disappearance of cracks respectively within the hydrogel and were confirmed by FESEM analysis. The effect of mili-patterns on hydrogel surface was studied and was found that the patterns enhanced the duration of water retention by ∼60 %. Even after 100 h of drying of a swelled hydrogel, the one with the pattern retained sufficient water so that its length remained ∼35 % longer compared to a non-patterned flat hydrogel. These findings were discussed in light of the Kelvin equation and were supported by the time-resolved Raman spectra that ensured the presence of the bound water for a longer duration. Based on the intensity of O–H stretching, it was inferred that patterned hydrogel exhibited water retention efficiency (RE) of ∼97 %, whereas, a flat non-patterned hydrogel had RE merely of ∼70 % after 3 cycles of drying and rehydration.

EFEKTIVITAS PENAMBAHAN SERAT POLYPROPYLENE TERHADAP KUAT LENTUR BETON GEOPOLIMER dengan SUPERPLASTICIZER

Geopolymer concrete is concrete composed of a mixture of coarse and fine aggregate without Portland cement binder. Fly ash is used as a substitute, because it contains a lot of silica and alumina. Geopolymer concrete has good strength and durability, but concrete also has disadvantages, namely brittleness, workability and often cracking due to tensile loads. Superplasticizer (SP) is used at 2% of fly ash weight to improve workability. The SP used is Sika viscocrete 1003. The addition of polypropylene fiber is one way to overcome brittle properties and the appearance of fine cracks in concrete. In this paper using Sika fiberforce 48mm polypropylene fiber which has a tensile strength of 465N/mm2(MPa) at a dose of 0%, 0.5%, 1%, 1.5% and 2%. The alkaline activator used is a mixture of NaOH and Na2SiO3 solutions. The molarity of the NaOH solution used is 8M with a ratio of NaOH/Na2SiO3 2: 3. From the test results, it is known that the influence of polypropylene fiber is effective for increasing the bending strength of geopolymer concrete. The bending strength value of geopolymer concrete with the addition of polypropylene fibers increased by 60.19%. The polypropylene fiber content will be maximum at a percentage of 0.5% of the total volume of the mixture.Keywords: Fiber, Flexural Strength, Fly Ash Geopolymer Concrete, Polypropylene, Superplasticizer

Justification of parameters of impact-spreading finger shaft for grinder-mixer-dryer using the example of eggshells

The object of the study is to determine the critical impact speed during shell destruction, study crack formation in the shell, and grind the shell. When operating a grinder-mixer-dryer, problems arise such as determining the speed of impact on the shell depending on the height of its fall, the lack of ability to determine the speed of shell fall from certain heights, which complicates planning the operation of the finger shaft. As a result of research, it was found that an auger with knives crushes and moves feed raw materials, and the impact-spreading shaft ensures partial grinding of fragile raw materials and intensive processes of mixing and drying wet feed with uniform filling of the installation hopper. The appearance of cracks on the shell when it falls from a height of 0.15 m has been experimentally recorded. Therefore, this speed of impact of the shell on a metal surface is the critical peripheral speed of the impact-spreading shaft, which ensures partial crushing of the shell. As a result of theoretical studies, an analytical expression was obtained that provides the determination of the shell impact speed depending on the height of its fall. The value of the critical peripheral speed of the fingers of the impact-spreading shaft is determined to be 1.66 m/s. The experimental results showed the effective occurrence of grinding, mixing and drying processes. Moreover, within 15 minutes of operation of the installation, the wet shell was crushed in accordance with the requirements. The uniformity reached up to 90 % within 4 to 6 minutes of its operation, and drying proceeded at a rate of 26.54 % per hour. All this proves the effectiveness of the processes of grinding, mixing and drying wet food, and also confirms the reliability of theoretical research

Pixel-level concrete bridge crack detection using Convolutional Neural Networks, gabor filters, and attention mechanisms

Cracks are prominent defects that significantly impact concrete bridges' structural safety and serviceability assessments. The conventional manual bridge inspection is often limited by multiple challenges related to the heavy workload of data processing and the subjective judgment of inspectors. Several vision-based methods, from traditional image processing techniques to segmentation deep learning models, have been employed for pixel-level crack detection to detect cracks in various scenes and surfaces automatically. The present paper proposes an end-to-end framework for crack segmentation combining UNet, Gabor filters, and Convolutional Block Attention Modules leveraging the complementary strengths of both spatial and frequency domains to enhance crack feature extraction and mitigate the impact of image disturbances. The designed network is trained and evaluated on a multi-source annotated crack dataset established by the authors to expose the model to multiple instances of crack appearance and background complexity and enhance its generalization ability. The proposed model achieves an Intersection over Union (IoU) of 60.62 % and an F1-score of 74.49 %, outperforming benchmark segmentation networks. Experimental results demonstrate the effectiveness of cross-domain feature fusion and multi-source data utilization in segmenting cracks with diverse patterns and background interference scenarios.

Aging and Small-sized Particles Release Characteristics of Tire Microplastics in Various Environmental Media

In recent years, research on microplastics has mostly focused on thermoplastic materials, and there is a lack of research on the pollution status and environmental behavior of tire microplastics, a type of rubber elastomers. In order to investigate the aging and small-sized particles release characteristics of tire microplastics in various environmental media, the aging process of two different tire microplastics, one for cars and the other for electric bicycles, was simulated in dry and aquatic environments under laboratory conditions. The results showed that the tire microplastics would be aged after 30 d of UV illumination, which was manifested by the roughness of the surface and the appearance of cracks and flaking. The Fourier infrared spectra showed that the carbonyl index of the surface also increased. In addition, tire microplastics released a large number of small sub-micron particles under the influence of UV illumination and hydrodynamic action, and the number of particles released from car tire microplastics in aquatic environments reached 694.8 million particles per milliliter of solution at 30 d of the UV light condition, among which 694.6 million particles with a particle size of less than 1 μm were released, which was approximately 100 times of that in the dark condition. The study showed that tire microplastics in aquatic environments were more susceptible to aging and released more small particles under light conditions and that car tire microplastics released more small particles than electric bicycle tire microplastics, posing ecological and environmental risks.

Wafer Scale Insulation of High Aspect Ratio Through-Silicon Vias by iCVD.

In microelectronics, one of the main 3D integration strategies consists of vertically stacking and electrically connecting various functional chips using through-silicon vias (TSVs). For the fabrication of the TSVs, one of the challenges is to conformally deposit a low dielectric constant insulator thin film at the surface of the silicon. To date, there is no universal technique that can address all types of TSV integration schemes, especially in the case requiring a low deposition temperature. In this work, an organosilicate polymer deposited by initiated chemical vapor deposition (iCVD) was developed and integrated as an insulating layer for TSVs. Process studies have shown that poly(1,3,5-trivinyl-1,3,5-trimethyl cyclotrisiloxane) (P(V3D3)) can present good conformality on high aspect ratio features by increasing the substrate temperature up to 100 °C. The trade-off is a moderate deposition rate. The thermal stability of the polymer has been investigated, and we show that a thermal annealing at 400 °C (with or without ultraviolet exposure) allows the stabilization of the dielectric films by removing residual oligomers. Then, P(V3D3) was integrated in high aspect ratio TSV (10 × 100 μm) on 300 mm silicon wafers using a standard integration flow for TSV metallization. Functional devices were successfully fabricated (including daisy chains of 754 TSVs) and electrically characterized. Our work shows that the metallization barrier should be carefully selected to eliminate the appearance of voids at the top corner of the TSV after the Cu annealing step. Moreover, an appropriate integration process should be used to avoid the appearance of cohesive cracks in the liner. This work constitutes a first proof of concept of the use of an iCVD polymer in a quasi-industrial microelectronic environment. It also highlights the benefit of iCVD as a promising technique to deposit conformal dielectric thin films in a microelectronic pilot line environment.

Amelioration of Flexural Performance for Reinforced Concrete Beams by Soffit Bonded High Performance Self Compacting Concrete Prisms

Abstract This paper presents a strengthening technique using a high-performance fibre-reinforced cement-based composite (HPFRCC) mixture. To evaluate the performance of this approach, two types of concrete mixtures were used one high performance and other high strength in strengthening process and compared to strengthening using CFRP laminate. The results showed that the strengthening was in the proportions (42 %, 58.03 %, 74.32 %) for (Mhs, Mcfrp, Mhp), respectively, Where the strengthening improved the bending capacity for beam (Mhp) to a greater extent of the other types and it reduced the appearance of cracks in the beam when loading until occur failure. As appeared failure modes in all elements were due to rupture in the flexure region and crush in the compression region. In addition, ductility index of the strengthened beams was acceptable and energy absorption of the strengthened samples high if compared to the reference beam Therefore, it can be said that this technology may provide a safer alternative for flexural strengthening of RC beams.

Interfacial delamination mechanism of thermal barrier coatings with real microstructure considering gradient thermal and growth strains based on the fracture phase field

The interface of atmospheric plasma spray (APS) thermal barrier coatings (TBCs) is highly irregular and rough, while their microstructure is porous and extremely uneven. This complexity leads to intricate patterns during the growth of thermally grown oxide (TGO), the distribution and evolution of the generated stress, as well as the initiation and expansion of cracks. Along these lines, in this work, a phase-field theory considering both the thermal gradient strain and TGO growth was established to thoroughly investigate the interface oxidation cracking in TBCs. More specifically, a two-dimensional geometric model of APS TBCs was established, incorporating real interface morphology and microstructure. Numerical simulations and experiments were also conducted to study the temperature and stress distribution, as well as the underlying mechanism of interface cracking during the service of TBCs. The results indicated that at high temperatures, the bottom temperature of the top coating (TC) layer with a porosity of 3.1% and a thickness of 200 μm was approximately 5 °C lower than that of the TC layer without porosity. Compared to the ideal model without pores, the model considering the real microstructure, with the presence of microcracks in the TC, makes it easier for the normal stress in the TGO at the peak region to be released. The inter-lamella cracks (Type A) in the TC near the peaks initiated earliest, followed by the creation of inter-lamella cracks at other locations, accompanied by the appearance of lamella-fracture cracks (Type B), inter-lamella to interfacial cracks (Type C), inter-lamella to TGO cracks (Type D), and internal TGO cracks (Type E). The coalescence of all these types of cracks will ultimately lead to coating failure.

Study and Optimization of the Punching Process of Steel Using the Johnson–Cook Damage Model

Sheet metal forming processes are widely used in applications such as those in the automotive or aerospace industries. Among them, punching is of great interest due to its high productivity and low operating cost. However, it is necessary to optimize these processes and adjust their parameters, such as clearance, shear force or tool geometry, to obtain the best finishes and minimize crack generation. Thus, the main objective of this research work is to optimize the punching process to achieve parts that do not require subsequent processes, such as deburring, by controlling the properties of the starting materials and with the help of tools such as design of experiments and simulations. In the present study, tensile tests were performed on three steels with different compositions and three sample geometries. The information obtained from these tests has allowed us to determine the parameters of the Johnson–Cook damage criteria. Moreover, punching was performed on real parts and compared with simulations to analyze the percentage of burnish surface. The results obtained show that the methodology used was correct and that it can be extrapolated to other types of die-cutting processes by reducing the percentage of surface fractures and predicting the appearance of cracks. Furthermore, it was observed that clearance has a greater influence than processing speed, while the minimum percentage of the burnish area was observed for the minimum values of clearance.

Analysis of the effect of hydration heat resulting in the formation of cracks on the experimental block of the spillway at Orlik reservoir

This article concentrates on the numerical analysis of hydration heat resulting in formation of cracks on the experimental block of the spillway at Orlik Reservoir and its verification with the experimental measurement. In order to eliminate the maximum of critical factors which could lead to appearance of early age cracking and faulty execution of the spillway, an experimental block was concreted. It served as a trial block for all steps of the execution process as well as a validating temperature measurement during cement hydration to confirm with the preliminary numerical analysis.

Evaluation of Correlation Between Development of Multiple Cracks in Nonendodontically Treated Tooth and Placement of Dental Implants with Prosthesis.

The result of increased occlusal stresses might be fractures in the teeth. It is still unclear how possible risk factors may affect the occurrence of tooth cracks after dental implants with prostheses in nonendodontically restored teeth. To evaluate the correlation of dental implants with prostheses as a risk factor for the development of cracks in teeth restored nonendodontically. Records of 414 patients with 570 teeth who underwent tooth restoration nonendodontically were obtained. The data was obtained regarding the number of implants with prostheses placed before the diagnosis of cracks in nonendodontically treated teeth, the time interval between placement of dental implants, and appearance of cracks in teeth, location of dental implants with respect to cracked tooth. Cracks in tooth was observed in 160 teeth out of 570 teeth evaluated (28.07%) and 144 patients out of 414 patients (34.78%). It was observed that out of 160 teeth with cracks, 66 teeth (41.25%) had cracks after placement of dental implants with prosthesis. Placement of a dental implant with a prosthesis can be a risk factor for appearing cracks in teeth treated nonendodontically.

TRM strengthening as effective prevention against premature failure of masonry walls

Masonry structures are very prone to cracking and premature failure in the presence of shear loading. Therefore, effective prevention of their premature damage is needed. This paper presents laboratory tests of small models made of autoclaved aerated concrete (AAC) blocks, which were externally reinforced using two different strengthening sets consisting of mortar and mesh, and subjected to diagonal compression. The experiments used a commercialised system designed for the strengthening of typical masonry substrates (brick, stone) and a low-cost and lowstrength mesh and mortar set used as part of a system for insulating buildings. The analyses presented are of a comparative nature and describe changes in the behaviour of the models depending on the strengthening set used. The application of full-surface strengthening clearly changed the behaviour of AAC walls from brittle one to the ‘pseudo-ductile’ one observed after the appearance of the first cracks. In all strengthened models, a significant increase in the load capacity (from 3% to 62%) and a post-peak phase were reported. An interesting finding was the high efficiency of nonstructural materials (plastering system), comparable to the effects of the use of commercialised system solutions. This strengthening can be successfully considered as an effective preventive action. Finally, a simplified method is provided to calculate the contribution of the strengthening to the load bearing capacity of the strengthened models. The method defines the effect of the mesh and the mortar independently, based only on the basic material properties of these two components.

RECYCLING METHODS FOR STEEL FIBER REINFORCED CONCRETE

The favorable impact of steel fibers in concrete is well known. Steel fibers can affect various fresh and hardened properties of concrete, for instance the appearance and propagation of cracks in the concrete matrix. Thus far, extensive research has been conducted to describe and to analyze those phenomena. Furthermore, Steel Fiber Reinforced Concrete (SFRC) is state of the art and is used extensively in industrial floors, walls, and ceiling constructions. But, beside the beneficial impact, the recycling of SFRC and, in particular, the separation of crushed concrete and steel fibers should be focused too. Only a few research programs are described in literature and comprehensive suggestions or guidelines are missing completely. So, a first test program was carried out to evaluate the usual procedure to break the concrete with a jaw crusher and to separate the contained steel via magnet. In tests, the amount and the type of the fibers used were varied as well as the concrete strength. The tests suggest that a certain amount of fibers can be separated, but the majority of fibers is still bound to the crushed concrete. Via sieving, it is possible to further separate concrete still containing fibers from aggregates without fibers. Conglomerates of broken concrete and fibers may be crushed again afterwards, but, allegedly, the success of the described procedure strongly depends on the fiber amount and the concrete properties. Furthermore, the available test data is too small to sufficiently describe the entire recycling path, making further research inevitable.

RECYCLING METHODS FOR STEEL FIBER REINFORCED CONCRETE

The favorable impact of steel fibers in concrete is well known. Steel fibers can affect various fresh and hardened properties of concrete, for instance the appearance and propagation of cracks in the concrete matrix. Thus far, extensive research has been conducted to describe and to analyze those phenomena. Furthermore, Steel Fiber Reinforced Concrete (SFRC) is state of the art and is used extensively in industrial floors, walls, and ceiling constructions. But, beside the beneficial impact, the recycling of SFRC and, in particular, the separation of crushed concrete and steel fibers should be focused too. Only a few research programs are described in literature and comprehensive suggestions or guidelines are missing completely. So, a first test program was carried out to evaluate the usual procedure to break the concrete with a jaw crusher and to separate the contained steel via magnet. In tests, the amount and the type of the fibers used were varied as well as the concrete strength. The tests suggest that a certain amount of fibers can be separated, but the majority of fibers is still bound to the crushed concrete. Via sieving, it is possible to further separate concrete still containing fibers from aggregates without fibers. Conglomerates of broken concrete and fibers may be crushed again afterwards, but, allegedly, the success of the described procedure strongly depends on the fiber amount and the concrete properties. Furthermore, the available test data is too small to sufficiently describe the entire recycling path, making further research inevitable.

Self-Healing Transparent Poly(dimethyl)siloxane with Tunable Mechanical Properties: Toward Enhanced Aging Materials for Space Applications.

When exposed to the geostationary orbit, polymeric materials tend to degrade on their surface due to the appearance of cracks. Implementing the self-healing concept in polymers going to space is a new approach to enhancing the lifespan of materials that cannot be replaced once launched. In this study, the elaboration of autonomous self-healing transparent poly(dimethylsiloxane) (PDMS) materials resistant to proton particles is presented. The PDMS materials are functionalized with various compositions of urea and imine moieties, forming dynamic covalent and/or supramolecular networks. The hydrogen bonds induced by the urea ensure the formation of a supramolecular network, while the dynamic covalent imine bonds are capable of undergoing exchange reactions. Materials with a broad range of mechanical properties were obtained depending on the composition and structure of the PDMS networks. As coating applications in a spatial environment were mainly targeted, the surface properties of the polymer are essential. Thus, percentages of scratch recovery were determined by AFM. From these data, self-healing kinetics were extracted and rationalized based on the polymer structures. The obtained data were in good agreement with the relaxation times determined by rheology in stress relaxation experiments. Moreover, the accelerated aging of materials under proton irradiation, simulating a major part of the geostationary environment, revealed a strong limitation or disappearance of cracks while keeping the transparency of the PDMS. These promising results open routes to prepare new flexible autonomous polymeric materials for space applications.

Lnvestigation of the Effect of a Mechanical Stress Concentrator on the Processes of Occurrence and Development of Cracks in Structural Elements of Aviation Equipment

The purpose of the research is investigation of the patterns of crack development in structural elements of aviation equipment from a stress concentrator under the influence of a force stretching along the main axis, symmetrical alternating loads (vibrations) and combined effects in order to determine the criticality of operation of aircraft products with crack-type defects, substantiation or refutation of the need for research and operation of the processes of development of stress-strain states preceding the occurrence of a crack, in systems and complexes of periodic, preflight and operational control of the technical condition of aircraft products.Methods. Еxperimental study of the patterns of crack development from a stress concentrator in structural elements of two form factors: a cylindrical sample (GOSТ 25347-82) simulating a stringer or a load-bearing structural beam, and a plate sample (GOSТ 1497-84), simulating an aircraft skin element. Cylindrical samples were subjected to deformation caused by the kinetics of rotation, plate samples were subjected to uniaxial tensile stress and the effects of alternating loads (vibrations) individually and in combination.Results. Тhe patterns of near-surface and deep crack development, their relationship with the frequency of application of symmetric alternating loads, have been studied. Еxpressions are established for the approximate engineering calculation of the material endurance limit, fracture surface area and constant endurance with an approximation accuracy Proceedings of the Southwest State University. Series: Control, Computer Engineering, of about 0.8. For samples in the form of flat plates, a stress-strain diagram is constructed, clearly illustrating the decrease in the endurance of the material to the effects of combined loads in relation to the effects of static tensile stresses only. Тhe approximate number of residual cycles before the structural element is destroyed is estimated, taking into account the amplitude-frequency parameters of the acting vibration in the presence of a crack in the sample. Тhe estimation method using the load intensity coefficient and mathematical expressions for its calculation is given.Conclusion. /t is concluded that it is necessary to analyze the dynamics of the development of stress-strain states (fatigue) of the material as states preceding the appearance of cracks in order to carry out sufficient control of the technical condition of structural elements of aircraft products.