Journal of Dynamics and Vibroacoustics

The paper presents the results of using some domestic materials in the manufacture of photoelastic coatings to study the stress-strain state in the process of strength testing of parts and assemblies of complex geometric shapes. Based on the analysis of the market for domestic materials for the production of photoelastic coatings, several materials were tested, their mechanical and optical characteristics were determined, and the technology for the production of photoelastic coatings was developed. This paper presents comparative results of a study of the stress-strain state (SSS) of a number of samples and products of aviation and space technology of different levels of complexity, prepared with domestic and foreign photoelastic coatings.

A study was conducted of the influence of some geometric factors on such parameters as the position of dangerous points determining the cyclic durability of a part, and the values of cyclic durability at these points. Based on the results of the validation carried out using the results of non-destructive testing and fractographic studies of opened cracks in the main part with operational defects, the adequacy - the degree of compliance with the research results - of the calculation models used to determine the cyclic durability was established. The work was carried out as part of the task of determining the resource indicators of the main part, taking into account the presence of an initial defect.

This article presents the results of a study of the bearing capacity and dissipative properties of an aerostatic linear bearing developed at JSC RESHETNEV for modal testing of complex structures. When selecting equipment for modal testing, the main condition is the requirement to minimize the distortions introduced into the determined dynamic characteristics: frequencies of natural vibration modes, the vibration modes themselves, as well as modal masses and damping coefficients. In other words, all equipment used for ground-based modal testing should ideally have zero added mass, stiffness and friction. The main systems containing elements that create dissipative forces that affect the determination of damping coefficients are systems for weight compensation and vibration excitation on natural modes. The weight compensation system usually contains either elastic elements or a system of guides with rolling or sliding bearings. If the former bring additional rigidity and mass to the test object, the latter bring mass and friction (dry or viscous), which increases the error in determining the dynamic characteristics. The excitation of vibrations on natural modes, in most cases, is carried out by electrodynamic vibrators consisting of a magnetization coil (or permanent magnet) and a movable coil moving in a magnetic gap. The movable coil is oriented in the magnetic gap using a special system containing either elastic elements or a linear guide bearing. Vibrators with elastic coil suspension elements cannot be used for modal tests of extended structures with low rigidity. The problem of creating an ideal bearing to replace classic linear (sliding or roller) ones arose during preparation for modal tests of the wing of a solar battery of a spacecraft (SC). Aerostatic bearings (supports) have virtually zero friction and sufficient load-bearing capacity, in which compressed air acts as a lubricant, eliminating physical contacts of the interacting surfaces. To confirm the possibility of using aerostatic bearings in equipment for conducting modal tests of extended structures with low frequencies of natural oscillations, comparative tests of a roller and aerostatic bearing were carried out. During the tests, optimal air flow parameters (nozzle diameter, operating pressure and gap) were selected, which ensure the required load-bearing capacity for radial forces and torques (bending and torsion). A comparative assessment of dissipative properties was carried out when measuring the attenuation parameters of single-mass harmonic oscillators, which include aerostatic and roller linear bearings. With a nozzle diameter of 0.6 mm, a working gap of 40 μm and a bearing input pressure of 1.0 bar, the logarithmic decrement of oscillations of the harmonic oscillator with an aerostatic bearing was 0.084, which is more than 28 times lower than the logarithmic decrement of oscillations of an oscillator with a roller bearing. The conducted studies confirmed the possibility of using the developed aerostatic bearing in test systems used in modal tests of large-sized transformable spacecraft structures.

The article considers various types of leg prosthesises with active damping based on pneumatic, hydraulic and electric drives. For each type of drive used, its advantages and disadvantages, features of design solutions were described with the aim of further selecting a prototype from existing knee modules of leading manufacturers to develop a domestic solution with characteristics and functionality not inferior to the best world samples. The article considers not only various design and circuit solutions, but also pays attention to the analysis of the applied control algorithms of leg prosthesises, allowing to implement various convenient options, for example, protection against tripping, ascent and descent on uneven surfaces, energy saving and energy recovery systems.