Nanosurgical Manipulation of Titin and Its M-Complex

Titin is a multifunctional filamentous protein anchored in the M-band, a hexagonally organized supramolecular lattice in the middle of the muscle sarcomere. Functionally, the M-band is a framework that cross-links myosin thick filaments, organizes associated proteins, and maintains sarcomeric symmetry via its structural and putative mechanical properties. Part of the M-band appears at the C-terminal end of isolated titin molecules in the form of a globular head, named here the “M-complex”, which also serves as the point of head-to-head attachment of titin. We used high-resolution atomic force microscopy and nanosurgical manipulation to investigate the topographical and internal structure and local mechanical properties of the M-complex and its associated titin molecules. We find that the M-complex is a stable structure that corresponds to the transverse unit of the M-band organized around the myosin thick filament. M-complexes may be interlinked into an M-complex array that reflects the local structural and mechanical status of the transversal M-band lattice. Local segments of titin and the M-complex could be nanosurgically manipulated to achieve extension and domain unfolding. Long threads could be pulled out of the M-complex, suggesting that it is a compact supramolecular reservoir of extensible filaments. Nanosurgery evoked an unexpected volume increment in the M-complex, which may be related to its function as a mechanical spacer. The M-complex thus displays both elastic and plastic properties which support the idea that the M-band may be involved in mechanical functions within the muscle sarcomere.

Kinetics of Damage of Materials under Various Regimes of Re-Changeable Loads

Kinetics of accumulation of damages in engineering objects, which work at repeated-alternating soft and hard modes of loading of details and elements of constructions of vehicles (cars, cars, railway transport, etc.). When changing the direction of the load force to the opposite in the structural material there is a phenomenon of changing the kinetics of accumulation of damage, ie the damage factor at separation and shear changes, which affects the effective stresses and service life of equipment. This effect of the factor of the influence of repeated variables on the redistribution of the kinetics of damage accumulation is considered experimentally for materials with different plastic properties

DEVELOPMENT OF RESOURCE-SAVING TECHNOLOGY OF POROUS-HOLLOW CERAMIC STONES

A resource-saving technology of porous ceramic materials using low-quality non-sintering sandy loam as a basic raw material has been developed. Based on the analysis of the plastic properties of two- and three-component ceramic masses, including sandy loam, expanded clay and fuel slag in various ratios, it was found that the required level of their plasticity provides the content of the main raw material in the following range (wt%): fuel slag – 15 – 20; sandy loam – 50 – 65; expanded clay – 20 – 30. By the method of planning the experiment, the rational composition of the three-component ceramic mass was substantiated. This which contains: 62.5 wt. % sandy loam, 20 wt. % medium-sintering plastic clay as a plasticizer and 17.5 wt. % fuel slag of TPP as a porous agent. For the developed mass, the main technological properties were investigated, which made it possible to recommend the drying mode of the raw material – 60 hours, the optimal firing temperature – 950 °С. Such conditions ensure that samples are obtained without drying cracks and signs of deformation. Оn the results of dilatometric analysis of mass the rational mode of firing high-hollow semifinished products was designed. The firing mode provides for a 44-hour firing and a decrease in the heating rates in the areas of dehydration of clay minerals, direct quartz transition and intensive sintering of the mass, as well as a decrease in the cooling rate in the area of the reverse quartz transition. The proposed firing mode provides the degree of sintering and their properties necessary for ceramic materials. Based on the developed mass under the recommended drying and firing modes, porous ceramic materials with an apparent density of 1.48 g/cm3, a compressive strength of 18.2 MPa and frost resistance of 30 cycles were obtained. The developed materials belong to the group of conditionally effective, and if 50% of the voids are organized, they can be classified as effective.

Energy power parameter effect of hot rolling on the formation of the structure and properties of low-alloy steels

The temperature and degree of hot deformation for steel 10HFTBch have been determined. This made it possible to ensure an increase in the mechanical properties of this steel, namely, the ultimate strength up to 540–560 MPa, as well as the relative elongation up to 25–29 %. As a result, it became possible to increase the service life of wheels with increased carrying capacity. This, in turn, will make it possible to increase the load of the transported cargo by motor vehicles several times. The mechanism of the influence of the energy-power parameters of rolling on the formation of the macro- and microstructure of a two-phase steel in the process of hot deformation is disclosed. The applied scheme provided an increase in the homogeneity of the structure of the developed steel, which saved the central part of the rolled section from overheating. It has been established that a decrease in the temperature of the end of deformation leads to a decrease in the size of the recrystallized austenite grain, and, consequently, to a refinement of the ferrite grain. Also an important factor in preventing the growth of ferrite grains in the upper part of the ferritic region is the abolition of cooling of the steel in coils. The recommended mode for multicomponent alloy steel 10HFTBch is as follows: the temperature of the end of rolling is 850 °C, the beginning of accelerated cooling is 750 °C, and the temperature of strip coiling into a coil is 600 °C. The basis for ensuring the increased strength of two-phase steels is the ratio and distribution of structural fractions – ferrite (initial and precipitated from austenite), as well as martensite. When hardened by such traditional "martensite formations" as manganese, the ability to control properties is limited. This is reflected in a narrow range of variation in the strength and ductility of the developed steel. The optimal combination of strength characteristics of plastic properties reduces the metal consumption of the product by 15–25 %.

Numerical analysis of the elastic-plastic behavior of a tubular structure in FGM under pressure and defect presence

Given the field of application and the many advantages, the use of FGM (Functionally Graded Materials) materials has recently been extended in several components and more particularly in cylindrical structures, which have been the subject of several recent studies. Our work aims to use the finite element method to analyze a cylindrical structure in FGM with properties gradated in the direction of the radius (Thickness) solicited purely in internal pressure by the implementation of a UMAT subroutine in the calculation code ABAQUS. The elasto-plastic behavior of the FGM is described by the flow theory represented by the equivalent stress of Von Mises and an incremental hardening variable. The TTO model (Tamura-Tomota-Ozawa) was used only to determine the elastic-plastic properties of the FGM material. The radial, tangential and axial stresses according to the thickness were evaluated in the first part of our work. In the second part, these stresses are evaluated under the same conditions but with the presence of a micro-cavity. The results obtained show clearly that these stresses are in direct relation not only with the thickness and properties of the FGM tube but also with the presence of the cavity.

Computational Analysis of the Forces Distribution in a Metal Frame Structure Taking into Account Plastic Deformations of the Material

Постановка задачи. С целью снижения материалоемкости строительных конструкций нормативные документы рекомендуют учитывать пластические свойства стали в прочностных расчетах. Это требует развития соответствующих методов расчета с применением современного программного обеспечения. Результаты. Усовершенствована методика расчета плоского стального рамного каркаса на статическую нагрузку на основе принципа предельного равновесия с применением программно-вычислительного комплекса «ЛИРА». Исследован поэтапный характер разрушения конструкции при воздействии сверхнормативных нагрузок. Выводы. Показано, что применение пошагового метода нагружения позволяет моделировать поведение конструкции в ходе увеличения нагрузки. Проведенные исследования позволяют давать верхнюю оценку максимально возможной нагрузки, возникающей в исключительных условиях эксплуатации. Statement of the problem. In order to reduce the material consumption of building structures, in regulatory documents it is recommend that the plastic properties of steel in strength calculations are taken into account. This requires the development of appropriate calculation methods by means of modern software. Results. The method of calculating a flat steel frame structure for static load based on the principle of limiting equilibrium using the design-computational complex LIRA has been improved. The gradual nature of structural failure under the influence of excessive loads is studied. Conclusions. It is shown that the application of the step-by-step loading method makes it possible to model the behavior of the structure during an increase in load. The studies allow us to provide an upper estimation of the maximum possible load that occurs under exceptional operating conditions.

Analysis of the reasons for the formation of under-collar cracks in the bushing of medium-speed combustion engines

Вибрация цилиндровой втулки, вызванная перекладкой поршня, развивает колебания вдоль по длине втулки от бурта до основания и акустические колебания внутри втулки, которые приводят к возникновению растягивающих напряжений и деформаций в поверхностных слоях металла; при взаимодействии с водой создаются условия для диффузии водорода во втулку. Диффузия водорода повышает внутреннее давление, что вызывает растрескивание структуры металла под действием напряжений. Происходит деградация металла – снижение прочностных и пластических свойств. Причиной появления подбуртовых трещин и кавитационные разрушения цилиндровой втулки является усталость деградированного металла от «водородного растрескивания под напряжением» и действия циклических растягивающих напряжений. Для повышения долговечности втулок по подбуртовым трещинам необходимо: 1. Увеличение износостойкости скользящей поверхности втулки для стабилизации величины теплового зазора; 2. Повышение жесткости втулки за счет увеличения толщины втулки в подбуртовой зоне; 3. Применение метала втулки с малой чувствительностью к «водородному растрескиванию под напряжением» (замена чугуна с пластинчатой формой графита на сферическую). The vibration of the cylinder bushing caused by the piston displacement develops the vibrations along the length of the bushing from the collar to the base and acoustic vibrations inside the collar, which lead to tensile stresses and deformation in the surface layers of the metal; when interacting with water, conditions for the diffusion of hydrogen into the bushing are created. The diffusion of hydrogen increases internal pressure, which causes the cracking of the metal structure under stress. The degradation of the metal that is the decrease in strength and plastic properties occurs. The reason for the formation of under – collar cracks and cavitation destruction of the cylinder bushing is the fatigue of the degraded metal from "hydrogen stress cracking" and the action of cyclic tensile stresses. To increase the durability of the bushings along the under – collar cracks, it is necessary to: 1. Increase the wear resistance of the sliding surface of the bushing to stabilize the value of the thermal gap; 2. Increase the stiffening effect of the bushing by increasing the thickness of the bushing in the under – collar zone; 3. Apply the metal of the bushings with low sensitivity to "hydrogen stress cracking" (replace the cast iron with lamellar graphite for the spherical one).