Effects of the Temperature–Time Regime of Curing of Composite Patch on Repair Process Efficiency

Repair procedures with the use of composite patches are considered to be the most effective among the current technologies of repair of the structures of various applications. In the process of moulding-on of a patch made of polymeric composite material by means of curing, technological stresses arise in the patch. Determination of residual technological stresses is a priority task for the modelling of the repair process. Reduction of residual stresses can be achieved by optimization of the mode of repair patch curing. For meeting this objective, the method for determination of technological stresses, which arise in the structure under repair in the process of curing of a composite patch, has been developed. The method takes into account the shrinkage, change in physico-mechanical characteristics, rheological processes occurring in the binder during moulding process, and determination of stresses in the structure under repair at any time. Therefore, premature failure of the repair joint at the stage of repair can be avoided. It is shown that the method adequately describes the level of deformations and stresses in the structure being repaired at the stage of heating and holding of the composite patch. Increase in the moulding temperature leads to a reduction in residual stresses in the structure under repair. However, current stresses at the stages of heating and temperature holding are increased significantly. Reliability of assumptions and developed method is confirmed by the comparison with the experimental data. The obtained experimental graph of total deformation of the composite patch allowed us to clearly determine the moment of residual stress occurrence in the structure under repair. This moment matches quite exactly (with the discrepancy not exceeding 5 min) the gel point determined analytically based on dependence of the degree of curing on the moulding mode. Consequently, the research together with the results previously obtained allows making an integrated choice of geometric parameters of the repair composite patch and temperature–time regime of its curing in order to ensure the specified level of strength and stiffness of the structure under repair.

Accounting method for residual technological stresses in modeling the stress-deformed state of a railway wheel disk. Report 2

The actual problem of increasing the service life of stamped-rolled railway wheels is a complex problem. Residual technological stresses, which cannot be completely eliminated, have a significant effect on the stress-strain state of the wheel as a whole and its disk in particular. At different stages of roughing wheels machining, the residual stress field is continuously changing. This makes it difficult to take into account the residual stresses in the wheels strength calculations. In Report 1 of this work, an accounting method for residual technological stresses was proposed, the essence of which is to set the value of interference between hub and axle when modeling is greater than the actual one. This approach made it possible to obtain additional stresses in the wheel, which adequately reflect the effect of residual technological stresses. In this part of the work, the authors have carried out practical implementation of the developed method and assessment of the degree of residual technological stresses influence on stress-strain state of the wheel disk under the action of operational loads. With regard to the design of a 957 mm diameter wheel with a flat-conical disk (GOST 10791 – 2011), calculations of stress-strain state of the disk under the action of mechanical types of load have been performed. The 60 % increase in the interference between hub and axle realized in the calculations made it possible to establish that the presence of residual technological stresses in the wheel causes an increase of 5 – 38 % in maximum equivalent stresses in the disk zones most loaded during operation. Thus, the proposed method for residual technological stresses accounting allows obtaining an upper estimate of the wheels strength characteristics, and, therefore, more adequately predicting their service life.

Accounting method for residual technological stresses in modeling the stress-deformed state of a railway wheel disk. Report 1

The work is devoted to development of a method for accounting residual technological stresses in wheel disks, which will provide both the versatility of the approach and the accuracy of calculations. The analysis of stresses in the wheel disk from the action of assembly (interference between the hub and the axle) and operational loads is carried out on basis of the results of finite element modeling. Verification of adequacy of the used model was made by comparing the calculated information with the experimental data of JSC “VNIIZHT”. The analysis of calculated and experimental values of radial stresses was carried out for the most loaded (critical) zones of the disk during operation – the zones of its interface with the rim and the hub. It was found that by setting the interference fit value to be greater than the actual one, it is possible to obtain the formation of additional stresses in the wheel, which, with a sufficient degree of accuracy, reflect the effect of residual technological stresses on its stress-strain state. On the example of calculating a wheel with a flat-conical disk (GOST 10791 – 2011), it is shown that an increase in the interference fit value by 60 % (from 0.25 mm to 0.4 mm per diameter) makes it possible to adequately predict the magnitude of stresses in the most critical disk elements. The maximum relative deviations of the calculated values of radial stresses from the experimental ones, both along the outer and inner sides of the wheel, do not exceed 14 %. Despite the simplicity of implementation, the proposed method provides an increase in the accuracy of predicting the strength characteristics of wheels, as well as the possibility of using it for various standard wheel sizes.

The influence of technological stresses and their correction in mink during cage keeping

During cage keeping of minks, one of the important problems is the high level of stress of animals caused by a number of factors: microclimate, feeding, low locomotion, etc. High stress levels have a negative effect on the physiological status of animals and can lead to serious pathological changes. Stress reactions activate neuroendocrine mechanisms, while at the same time mobilizing the body’s protective functions and inhibiting the processes of growth, development and reproductive function. The level of cortisol in the body clearly shows the degree of its stress, since the adrenal glands are responsible for the regulation of the stress response and are a source of catecholamines and corticosteroids. The experiment was carried out on the young mink males. Under observation were 60 animal analogues. Blood was taken from 6 animals from each group at the beginning and at the end of the experiment. An autopsy of 6 male minks from each group was performed to assess the condition of the internal organs. The level of cortisol in male minks at the beginning of the experiment was increased (more than 700 nmol/l). It is shown that with the introduction of the Emidonol 20%, the stress of animals decreases, in comparison with the control. The adrenal mass in the control group was 29% higher than in the group where the additive was used. The cortisol level at the end of the experiment in minks that were the additive was input (541 nmol / L (p≤0,05) significantly decreased in comparison with the control (815 nmol / L). Also, a decrease in the level of stress may indirectly be indicated by a decrease in heart and liver (p≤0,05) and kidney mass, compared with the control group.

Algorithms and software for UAV flight planning for monitoring the stress conditions of plantations

Remote monitoring technology is a mandatory component of the crop management concept. The available solutions allow determining the presence of plant stress but not identifying its causes. A particular danger is presented by stresses of a technological nature, and chemical poisoning of plants due to the aftereffect of herbicides, compaction of the subsoil, and the like. Plant stresses of a technological nature lead to a decrease in plant immunity and, accordingly, special measures are needed to restore their productivity. Laboratory methods for analyzing stress, in particular, chemical poisoning of plants, are technologically complex and expensive, which prevents their widespread use. Remote sensing technologies are capable of identifying areas with manifestations of technological stresses since such stresses have characteristic features. As our studies have shown, a promising method for identifying plant areas with signs of technological stress is the method of leaf diagnostics. For such areas, it is necessary to carry out monitoring with the highest image resolution, it is assumed in the UAV flight program. Taking into account the above, the aim of the work was to develop an algorithm and software for its implementation of UAV flight planning for the identification of plant stresses of a technological nature. The software was developed in the cross-platform programming language Python, and it allowed processing maps of the distribution of vegetation indices (for experimental studies, maps were used that were created using the Slantrange spectral sensor system). The use of the algorithm, implemented in the cross-platform programming language Python, made it possible to identify the paths of movement of technological equipment, the contours of areas with close values of the vegetation index, and the main features of areas with plant stress of a technological nature. The accuracy of identifying areas with technological stresses has been confirmed by ground surveys in production fields.

Substantiation of the choice of the optimal UAV flight altitude for monitoring technological stresses for crops of winter rape

Crop monitoring using UAVs is becoming standard practice in scientific research due to the possibility of an operational examination of large fields with high data quality due to high-resolution images. The need for operational inspection of crops on an industrial scale requires a certain balance between the permissible image quality and the acceptable monitoring time due primarily to the number of UAVs and their energy. The newest and most relevant stress factor for Ukraine is technological stresses. The aim of the study is the optimal flight altitude for monitoring stresses of a technological nature. Field studies were carried out from September to November 2019 in the Boryspil region on industrial crops of winter rape. Monitoring was carried out using the Slantrange 3p complex. Stresses were recorded according to 2 parameters — the area of the dome and the abnormal coloration of the 2 lower leaves of red, yellow, and a mixture of these colors. The maximum quality of identification is achieved at the maximum resolution of the images, that is, the minimum height, however, the issues of UAV energy determine the maximum height and, accordingly, the flight speed for the UAV. Thus, the optimal compromise is between the determination accuracy and the production-appropriate flight parameters, that is, a lot of metric optimization is needed. As a generalized criterion, the criterion of consistent products was chosen, where the number of local optimization criteria is s = 3, and the weighting coefficients of the criteria are selected subjectively by experts. The proposed algorithm for choosing the optimal UAV flight altitude to identify the technological nature of the stress of winter rape crops will allow planning monitoring activities and justifying the choice of UAV parameters relative to the duration of its flight. The type of objective function used will allow specialists without specialized education in programming to solve the problem of multi-criteria optimization by its own weight coefficients. The proposed approach has no restrictions on the number of optimization parameters and the number of local optimality criteria and can be used when the user chooses his own indication indicators.

Technology development for automobile glass assembly

The analysis of glass assembly technology and impact of different factors upon strength and accuracy of glass positioning is presented. The modeling of residual stresses after manufacturing as a result of technological impact has shown the presence of residual stresses of stretching along the edges. To the stresses there are summed up assembly stresses caused by shrinkage processes in the glue joint. It is defined that at the minimum width of the glue roll during dry-out a discontinuity of the glue joint along the contour is possible and at the maximum layer width the additional technological stresses in glass arise.

COMPRESSED FLANGES OF ARCHED STEEL THIN-WALLED COLD-ROLLED PROFILED SHEETS: DETERMINATION OF RESIDUAL STRESSES

Introduction. The construction sphere widely uses steel thin-walled cold-formed profiles. In arched steel coldformed trapezoidal section profiles, residual normal stresses oriented along the profile occur at the stage of manufacturing arched blanks from flat profiled sheets and are caused by the cold bending process involving the extreme zones of the profile in the plastic stage with unloading without subsequent heat treatment. According to preliminary estimates, the residual stresses are up to one third of the calculated resistance of sheet steel at small radii of the arch profile. At present, the researchers do not take into account the residual technological stresses of the longitudinal bending when designing structures from thin-walled longitudinally bent rolled trapezoidal sections. The purpose of the paper is to develop a method for determining residual stresses in compressed flanges of arched steel thin-walled cold-rolled profiled sheets, which provides simplicity of the measurement and calculation methods, reliability and high accuracy of the obtained stress values.Materials and methods. The authors made the analysis of previously published materials and identified the advantages and disadvantages of previous studies. Moreover, the authors showed the advantages of the proposed method for determining the residual technological normal stresses in compressed flanges of arched steel thin-rolled profiled steel.Results. The researches formed a new method for making sections of a compressed shelf and measuring residual normal stresses in the compressed flanges of an arched steel sheet of cold-rolled profiled steel. The proposed method greatly simplified the existing method of determining residual technological normal stresses in compressed profile flanges, improved the accuracy of measuring normal stresses in compressed profile flanges.Discussion and conclusions. The method of measuring residual process stresses allows improving existing methods for determining residual stresses, simplifying calculations, as well as improving the accuracy of stresses. In the future, the authors will make a numerical simulation of the bending arch profiles, as well as an experimental assessment of the adequacy of the proposed method.The authors have read and approved the final manuscript. Financial transparency: the authors have no financial interest in the presented materials or methods. There is no conflict of interest.