Influence of the Self-Heating Temperature on the Cyclic Durability of Composite Materials

Постановка задачи. Для определения выносливости полимерных композиционных материалов используют различные методы ускоренных испытаний. Одним из таких методов является температурный, который имеет свои ограничения применения. Это подразумевает необходимость установления возможности его применения для эпоксидных полимерных материалов. Результаты. Предложена формула для определения величины усталостной долговечности эпоксидного композиционного материала, опытным путем установлена достоверность величин, рассчитываемых по данной формуле. Доказано, что интенсивность роста температуры зависит от скорости загружения. Выводы. Достоверность расчетов по предложенной формуле для расчета показателей усталостной долговечности подтверждена сравнением результатов с опытными данными, значения достаточно близко коррелируют, что позволяет применять эту формулу при расчете выносливости для образцов из эпоксидного композита. Statement of the problem. Various methods of accelerated testing are used to determine the endurance of polymer composite materials. One of these methods is the temperature method which has its own limitations of application. Thus the possibility of its application for epoxy polymer materials should be established. Results. The article proposes a formula for identifying the value of the fatigue life of an epoxy composite material. The reliability of the values calculated using this formula is experimentally established. It is proved that the intensity of the temperature increase depends on the loading speed. Conclusions. The reliability of the calculations according to the proposed formula for calculating the fatigue life indicators is confirmed by comparing the results with experimental data, the values are quite closely correlated, which allows us to use this formula when calculating the endurance for samples made of epoxy composite.

Physicomechanical and design characteristics of surface high-entropy alloys

We investigated the phase composition of high-entropy shape memory alloys CoCuTiZrHf, NiCoTiZrHf, NiCuTiZrHf, ZrCuNiCoTi, TiNiZrHfCoCu after HVOF, thermomechanical treatment and thermal cycling. We have also developed criteria for calculating the energy capacity, enthalpy, entropy, theoretical strength of high-entropy alloys, taking into account the chemical composition and structural-phase state according to the results of X-ray phase analysis. We proposed a criterion for assessing the damageability of high-entropy alloys. The article describes calculations of energy consumption, entropy, enthalpy, theoretical strength of high-entropy alloys CoCuTiZrHf, NiCoTiZrHf, NiCuTiZrHf, ZrCuNiCoTi, TiNiZrHfCoCu both after HVOF and after thermomechanical treatment. After full-scale mechanical tests of surface-modified layers of high-entropy materials for bending with rotation, we obtained experimental values of cyclic durability and plotted fatigue curves. The calculated assessment of the cyclic durability was carried out according to the developed mathematical criteria. We calculated the damageability of high-entropy alloys and constructed the graphical curves of the dependence of the damageability on the cyclic life.

ENDURANCE OF CARCASS TYPE POLYMER COMPOSITE MATERIALS AT DEFORMATION JOINTS OF BRIDGE STRUCTURE’S ELEMENTS

Numerous studies of road surfaces in the areas of deformation joints of bridges and overpasses have shown that the use of polymer composite materials can significantly reduce cracks and destruction. The cyclic durability of such materials prevents rutting in the zone of deformation seams, due to their damping properties. Effective building materials based on furfural acetone monomers (FAM) are used for the manufacture of tides that experience cyclic impacts of vehicle wheels. Therefore, tests were conducted on the endurance of FAM polymer concrete under the influence of cyclic application of load. Today cyclic and static durability of traditional FAM polymer concretes has been studied in detail. However, the carcass technology can improve the characteristics of polymer concrete, in particular, reduce shrinkage. These polymer concretes are produced in two stages. First, a carcass is created from the filler grains glued together, and then the voids are filled with a matrix composition. This article presents the results of endurance tests of polymer concrete made using carcass and traditional technologies, with the same set of raw materials. To determine the limit of endurance, we used the method of planning an experiment with the construction of an orthogonal-composite plan of the second order. The cycle asymmetry coefficient and loading level (as a percentage of the destruction load) were selected as variable factors affecting the cyclic durability. Lines of fatigue strength of traditional polymer concrete FAM and obtained by carcass manufacturing technology at different values of the cycle asymmetry coefficient are also constructed. The results of endurance tests under the influence of repeated application of load showed that the polymer composite material based on furfural acetone monomer, obtained by carcass technology, has an increased cyclic durability compared to traditional polymer concrete.

Modeling of Residual Stresses After Shot Peening and the Effect of Accounting Their Influence on the Stress State of Turbine Blade Fir Tree Roots

Numerical modeling approaches have been developed for simulating shot peening processes and consideration of compressive residual stresses when performing strength calculations of turbine wheel joints. A three-stage method is presented to combine strength analyses of turbine blade with the output of LS-DYNA simulations (RS diagrams) of multiple impacts. Predictions of RS distributions obtained using the suggested approach are compared with experimental data and good correlation was achieved. The effect of the RS diagrams obtained using various SP parameters on the stress-strain state of the turbine blade root and the values of its cyclic durability are estimated.

Nitinol, Stainless Steel, and Titanium Kirschner Wire Durability

Kirschner wires (K wires) are a common fixation device in foot and ankle surgery, particularly in lesser-toe fixation. Fatigue failure is a known complication of this fixation. The material properties of the K wire are a factor in the strength and durability of the wire. The purpose of this study is to compare the durability of K wires made of stainless steel, titanium, and Nitinol. Ten samples each of stainless steel, titanium. and Nitinol underwent cyclic durability testing using a rotating beam approach, and S-N curves (applied stress vs the number of cycles to failure) were generated. The results demonstrate that, generally, Nitinol K wires have a shorter life for the same applied stress than the stainless steel or titanium wires. Titanium had a longer life at low stresses compared with stainless steel, and stainless steel had a longer life at higher stresses. This study provides comparative durability data for K wires made of different metals, which have not been previously reported. Although there was a statistically significant difference in durability for wires used in K wire fixation, all 3 metal types are reasonable choices for temporary K wire fixation. Levels of Evidence: Level 5: Mechanical study

WEAR APPRAISAL OF MOVEMENT JOINTS’ STRUCTURES AND WAYS TO IMPROVE THEIR DURABILITY

Movement joints are one of the most important structural elements of bridge structure and represent gaps between end face of span structure and cabinet wall of support or head part of support. The durability of the structure as a whole depends largely on the correct choice and, then, the installation of the movement joints. The results of numerous technical surveys of bridges and overpasses show that the main defects and damages of movement joints structural elements are: weld structure disorder due to incorrect selection and installation; Formation of cracks in the zone of seams on the coating of different length and with different opening width. In addition to the above-mentioned defects, the formation of gauge due to differences in the marks of the bridge web at the joint of the road clothes and the movement joints plays a major role in the process of breaking the coating in the zone of movement joints. Destruction of coating in zones of movement joints in many cases is due to intensive gauge formation, at the same time, formation of wheels is due to difference of marks of road clothes and movement joints. To prevent colour formation in the zone of movement joints the following technical solutions are used: arrangement of pedestrian zones; Application of concrete tides (boundaries). In these zones it is recommended to arrange tides on the basis of polymer composite materials (PCM), having high damping properties and cyclic durability. Endurance tests and the study of damping properties were carried out according to conventional methods for polymer betons FAM and FAZIS-30. The values of the vibration decree for the above-mentioned materials and their cyclic durability are obtained.