Problemy mašinostroeniâ i nadežnosti mašin

Статья посвящена разработке динамического гасителя колебаний, представляющего собой систему, в которой пневмопружина перемещается между направляющими заданной формы перпендикулярно их оси симметрии. Форма направляющих определяется из условия, что характеристика динамического гасителя – линейная, что эквивалентно пружине с заданной жесткостью. Основным недостатком большинства современных динамических гасителей является то, что они эффективны при работе только на определенной частоте вынуждающей силы, действующей на защищаемый объект. При небольшом изменении этой частоты, амплитуда защищаемого объекта может многократно возрасти. В статье доказано, что, изменяя расчетным образом давление в пневмопружине предлагаемого гасителя, можно получить заданную жесткость динамического гасителя, при которой он эффективен при различных частотах вынуждающей силы.

In this article, a new fracture criterion for a mixed-type crack (type I + type II) is proposed. It is based on the assumption that the maximum tangential stresses in the prefracture region are equal to the local strength of the material. In this case, the size of the prefracture area and the local strength are determined taking into account nonsingular Тхx and Тzz stresses included in the expansion of the Williams stress function. The use of Тхx and Тzz stresses in the calculations allows one to describe the two-dimensional local constraint of the deformation along the crack front in three-dimensional bodies. In addition to KI and KII, the expression for the effective stress intensity factor (SIF) includes the ratios of the Тхx and Тzz stresses to the yield strength. This makes it possible to take into account the constraint of deformations in the transverse and longitudinal directions of the crack front, respectively. An example of the implementation of the developed criterion in relation to the determination of the fracture load of a tensile-stressed plate with a through inclined crack is given. Dependences of the Тxx and Тzz stresses on the plate thickness are presented for various crack slopes and plate thicknesses. It is shown that an increase in the plate thickness and a decrease in the crack slope lead to a decrease in the fracture load.

The protective properties and temperature resistance of sulfonate greases based on petroleum oil KS-19 have been assessed. Highly alkaline calcium sulfonates of Russian and foreign production are used as thickeners for such greases. Sulfonate greases have been shown to have good protective properties. It has been established that the ability of sulfonate greases to prevent corrosion depends on the protective properties of calcium sulfonate used as a thickener. Based on the totality of the indicators obtained, the grease based on the Russian-made K-314 thickener has the best properties; in temperature resistance, it is superior to the sample on the foreign thickener Lubrizol 86 GR, and in terms of protective properties, it is on the same level with it.

The influence of resonance wave effects on the sedimentation stability of potato and corn starch nanoparticle dispersions obtained by coprecipitation was studied. It has been established that the proportion of the dispersed phase of potato starch nanoparticle dispersions formed using traditional mixing remains unchanged for two days. For corn starch nanoparticle dispersions, this indicator remains at the initial level only for the first five minutes. The use of wave action at the stage of coprecipitation leads to an increase in the values of the ξ-potential of the obtained nanoparticles by 4.5 and 3.5 times for corn and potato starches, respectively. Due to this, the dispersion stability of corn starch nanoparticles increases up to two days and dispersions of potato starch nanoparticles increase up to forty days. The results presented in this article are the basis for the development of a resource-saving technology for obtaining highly stable dispersions of biopolymer nanoparticles for food, medical, pharmaceutical, and other industries.

A mechanism with a remote center of rotation, intended for use in medicine, and in particular, minimally invasive operations, is discussed. The basic mechanism consists of two parallelograms with common links, which allows the surgical instrument to duplicate the movement of the drive link of the mechanism. To ensure greater rigidity of the mechanism, it is proposed to introduce drive redundancy through the use of an additional RRR dyad with a drive pair. The position problem has been solved for the resulting mechanism. A 3D model and a prototype of the mechanism have been also presented.

This paper is devoted to model tribological experiments and analysis of the research results obtained for new materials and coatings, such as SiSiC, with the aim to rank them and to make recommendations for use in thrust hydrodynamic friction units operating at high speeds and loads.

Test results on fretting wear of metalopolymer materials in a friction couple with structural materials—cast iron 20 and stainless steel 12Kh18N10T—performed over the direct and reverse test schemes are presented. As the metalopolymer material, we took the BELZONA 1111 two-component paste-like material based on a mixture of a metal–ceramic alloy with high-molecular polymers and oligomers.

В статье приведены основные зависимости, позволяющие определять и оценивать динамические составляющие напряжений и перемещений в магистральных газопроводах под действием движущейся сосредоточенной силы. Решения задачи приводятся для однопролетных, двухпролетных и трехпролетных балочных переходов. Согласно требованиям отраслевых документов принимались решения о дальнейшей эксплуатации переходов или необходимости их реконструкции.