FEATURES OF QUANTITATIVE MEASUREMENTS OF THE DYNAMIC MODULE OF ELASTICITY OF BINDERS IN OPTIMIZATION OF PRODUCTION TECHNOLOGY SEROGYPSUM COMPOSITE

The paper considers the issues of studying the structure formation of binders during hardening to determine the optimal moments of mechanical action on gypsum concrete specimens, which makes it possible to optimize the technology of their impregnation with sulfur melt. The time dependence of the elastic modulus of a hardening, binder is its important physicochemical characteristic, since it is used to objectively identify the stages of structure formation, to simulate the processes occurring at each of the stages. It is noted that the method of acoustic resonance of bending vibrations, in the case of hardening binders, needs correction with respect to the measurement technique and interpretation of the results obtained. The kinetics of the resonance frequency of a sample consisting of a rigid cell and a dispersion poured into it is a function of the elastic properties of the cell, the dispersion itself, the contact zone of the dispersion with cell and therefore cannot be used for either qualitative or quantitative analysis of the kinetics of hardening. Taking into account the elasticity of cuvette is necessary to obtain reliable information. It has been established that in the presence of shrinkage or significant expansion of the binder, the study of structure formation by the resonance method should be carried out in plastic cuvettes. Regardless of shrinkage, the use of a cuvette requires compulsory consideration of its elastic properties. It is advisable to objectively distinguish the stages of structure formation on the basis of the kinetics of not the dynamic modulus of elasticity itself, but the rate of its change. The time dependence of the logarithmic damping decrement is also an important characteristic of the concrete structure. The studies carried out make it possible to obtain serogypsum composites with the necessary performance characteristics and to manufacture elements of architectural décor, wall fencing products of increased aesthetics, durability and reliability from them.

EXPERIMENTAL AND COMPUTATIONAL STUDY OF LIQUID OSCILLATION DAMPING IN A FREE SURFACE VESSEL

Studying the issues related to solving the problems of the movement of fluid in partially filled structures of various shapes has always been relevant.This is due, in particular, to the need to ensure the longitudinal and lateral stability of the movement of objects in which the liquid is transported. Contemporarymethods and research tools that allow describing the movement of liquid in a container are overly complex and require in-depth knowledgefrom a scientist. Therefore, development of a mathematical algorithm that would be simple and at the same time ensure sufficient accuracy in determiningthe oscillatory motion in a container is advisable. Each development of a new mathematical algorithm requires experimental research to verifyits adequacy. The purpose of this work is to confirm the feasibility of using the created mathematical apparatus for determining the main parameters offree vibrations depending on the level of liquid in a rectangular prismatic container. The experimental research methodology provides for checking theadequacy of the mathematical algorithms in determining the frequencies of free oscillations of liquid in a container by comparing the theoretical andexperimental values of the oscillation periods, as well as determining the damping decrement of oscillations for liquids of different viscosity. As a result,the adequacy of the formulas for determining the frequencies of free oscillations of liquid in a container is proved; the maximum error does notexceed 4.35%. The decrements of vibration damping are determined experimentally, as well as using theoretical models of the motion of viscous liquidin the so-called partial surface layers, for three liquids of different viscosity, namely, for water, for 20% sugar and water solution, and for vegetable oil.On the basis of experimental studies, the amplitudes and frequencies of forced vibrations of various types of liquids are determined by constructing anamplitude-frequency characteristic. It is shown by calculation how the damping decrement of the liquid affects the value of the horizontal displacementof the surface layer of the liquid in the tank during its transportation by a wheeled tractor.

DEDETERMINATION OF THE LOGARITHMIC DECREMENT OF NATURAL VIBRATIONS OF BUILDINGS AND STRUCTURESTERMINATION OF THE LOGARITHMIC DECREMENT OF NATURAL VIBRATIONS OF BUILDINGS AND STRUCTURES

For the passport of buildings and structures, it is required to determine the logarithmic damping decrement. The proposed expressions [1, 2] to determine the decrement use the value of the Q-factor, however, an expression is known in which the damping decrement is determined through the logarithm of the ratio of the amplitudes of the damped signal. Comparison of the formulas for calculating the logarithmic decrement of vibrations was carried out using the example of data obtained when testing a beam with reinforcement.

Relevant issues of periodic vibration monitoring of buildings and structures

Introduction. The author proposes a new universal optimization approach to mechanical safety monitoring of buildings and structures in the process of their operation. The new approach involves periodic monitoring of mechanic vibrations. Materials and methods. The methodology of periodic monitoring performable within the framework of general monitoring is based on the analysis of changes in the first natural frequency of a building or a structure and the logarithmic decrement of its damping along three mutually perpendicular axes. The shape and position of resonance peaks of the amplitude spectrum are employed to analyze resonant frequencies and logarithmic decrements of damping. The analysis of those electronically archived parameters is performed, whose values change over time proportionately with vibrations of a monitored facility. The time dependence of the first resonant frequency of a structure is considered as a generalized characteristic of its mechanical safety. Results. The author has shown that findings of the spectral analysis performed in respect of the vibration process are irrespective of a measurement method, provided that the uniformity of external influences is ensured. The frequency dependence of the structure’s first mode of vibrations on time (per year) has two non-linear sections within the entire term of operation. Following the analysis of measurements taken at construction facilities exposed to wind loads, it’s been found that advanced monitoring instruments can identify changes in the value of the first resonant frequency and the damping decrement with a reasonable degree of accuracy. The author believes that this finding has great practical importance. Conclusions. Identification of a trend towards a change in frequency and damping decrement values for the first mode of natural vibrations can help to schedule actions for the improvement of the mechanical safety of an engineering structure, and in some cases it can prevent an upcoming accident.

Graphic method for assessing the margins of resistance to acoustic vibrations in the chambers of rocket engines by combustion noise

An experimental method is proposed for estimating the damping decrements of pressure fluctuations in the combustion chambers of forced rocket engines. The method is based on the statistical processing of noise pressure pulsations in the vicinity of natural resonance frequencies for normal modes of acoustic vibrations of the reaction volume and the subsequent prediction of the instability of the combustion process relative to acoustic vibrations. Based on the theory of statistical regression for multidimensional experimental data, the problem of predicting unknown parameters of sample distributions is solved by asymptotic determination of the correlation coefficient of the damping decrement of pressure vibrations through optimal linear predictors and the Kolmogorov distribution. Keywords rocket engine, combustion chamber, acoustic vibrations, combustion noise, spectral characteristics, Kolmogorov criterion, damping decrement. [email protected]

Diagnostic benchmarks on dynamic characteristics of thin-walled marine damaged structures

Among structural health monitoring (SHM) methods of thin-walled structures, a vibrodiagnostic method is one of the most promising. The accelerometer recorded responses provide diagnostic information that requires mathematical processing to extract the essential dynamic characteristics. The authors have been looking for new parameters - diagnostic benchmarks which can be applied to non-destructive, automatic testing of thin-walled marine structures (especially their welded joints) like ship hulls. All characteristics have been based on recorded data generated during the vibration tests of welded joints with and without failures. For this purpose, the authors proposed method based on: FFT windowing analysis, benchmark with using 2D or 3D time – frequency dynamic characteristics and the determination of damping decrement in function of time. The work presents the algorithm and exemplary results obtained from the application of proposed method to several selected sample plates with different type of welds.

Evaluation of the Influence of the Location Solid-State Inclusions on the Amplitude-Frequency Characteristics under Pulsed Acoustic Excitation in the Process of Uniaxial Compression

Most dielectric materials and heterogeneous dielectric structures are operated under mechanical loads. Therefore, the usage of acoustic monitoring of the presence of defects and the destruction of such materials is difficult because of the high ultrasound damping decrement in these materials. This article presents assess the influence of the location of steel inclusions relative to the loading axis.

ЕКСПЕРИМЕНТАЛЬНЕ ВИЗНАЧЕННЯ ЕНЕРГЕТИЧНИХ УТОМНИХ ХАРАКТЕРИСТИК СПЛАВУ Д16Т (2024) МЕТОДОМ ВІЛЬНИХ КОЛИВАНЬ

In the process of studying fatigue characteristics of materials, components, assemblies and entire structures, as well as the prediction of durability, it is necessary to know the energy fatigue characteristics of various materials. These parameters include α – a fatigue failure parameter and W-1– irreversibly dissipated energy per loading cycle at stresses equal to the fatigue limit based on N = 107 cycles. The logarithmic damping decrement shows the fraction of irreversibly scattered energy when the oscillations decay from the total elastic energy of the oscillations. It has been proven that for metals fatigue failure is a constant "dangerous" energy. This paper describes the experimental determination of these energy characteristics for one of the most common materials in aviation, D16T (2024). By measuring the logarithmic damping factor in the fatigue test process, the dissipated energy is found over the loading cycle. Tests are conducted at two different loading levels. This allows to obtain a system of two equations to determine the two energy characteristics α and W-1.

MODELLING OF A GLASS GATHERER ROBOT'S ARM WITH A FRICTIONAL DAMPER

A numerical model of a friction damper used for damping vibration in glass gatherer robots was described. The damper with a lance was modelled using finite elements. Primary natural frequency of the system was determined. Numerical calculations were performed to determine the best operating parameters of the damper for excitations using a impulse of a force. Results of the damping decrement calculations for the friction damper model with a constant coefficient of friction and for the model, in which the coefficient of friction varied depending on the sliding velocity and the normal pressure occurring at the contact surfaces of the damper’s friction rings, were presented. Based on numerical simulations, the values of relative displacements between the damper’s friction rings were also determined.