Characteristics of statistical properties of deformation defects of structural metallic materials within elastic deformations

At this paper was established result of the correlations characteristics of structural parameters of low-carbon steels during periodic loading under elastic deformations. According to the results of the research, the kinetic characteristics of the influence of the load parameter on the distribution of deformation defects of the surface layer of structural materials under elastic deformations are obtained. The regularities of the influence of elastic deformations on the distribution of discrete surface properties are revealed. Linear dependences of the parameter of distribution of discrete relief properties of the deformed surface on loading are revealed. The regularities of the influence of elastic deformations on the distribution of discrete surface properties are revealed. It is established that regardless of the type of load, the surface density of deformation defects of scattered fracture accumulates in the mother to a certain state of damage, which is characterized by the current state of density of elements of deformation defects.

Attenuation and Prediction of the Ground Vibrations Induced by High-Speed Trains Running Over Bridge

This paper aims to study the transfer laws of vibration signals in the free field near a high-speed train line by conducting a field test. The characteristics of ground vibration acceleration were analyzed in the time and frequency domains, and a prediction method in the frequency domain was proposed. The results show: (1) there is a vibration amplification area away from the bottom of the pier under the influence of high-speed trains running over the bridge due to the fluctuation attenuation of the vibration waves; (2) the dominant peak frequency points in the frequency spectrum of the acceleration can be regarded as the resonance frequency induced by periodic loading; and (3) the soil vibration can be effectively predicted by the proposed method with a strong capability to defend the interference of environmental vibrations according to the comparison between the predicted value and the experimental data.

Increasing the Yield of Biogas and Electricity during Manure Fermentation Cattle by Optimally Adding Lime to Extruded Straw

The aim of the work is to increase the yield of biogas and the generation of electricity in biogas plants through the combined fermentation of cattle manure with extruded wheat straw and slaked lime. To achieve this goal, the following tasks were solved: the biogas yield from cattle manure with pellets of extruded wheat straw was determined without the use of slaked lime; when fermenting manure and pellets of extruded straw with different amounts of lime before extrusion, during extrusion and after extrusion with periodic loading of the bioreactor. The biogas volume was measured using the Krivoruchko method. To carry out the experiment, we used plastic bags (fermenters), a device for sealing the bags, a pH meter, and a calibrated cylinder. A seed was added to the calculated amount of biomass at the rate of 1 part of the sample to 4 parts of the seed, air was displaced from the fermenter and the hole was hermetically sealed. After that, the bag was placed in a thermostat at 37.5°C for 35 days. The volume of the bags was measured every seven days. On the basis of the experimental studies, the dependence of the biogas yield depending on the concentration, as well as the method of adding a solution of slaked lime in straw (before, during, after extrusion) was determined. The most significant research result is that the optimal ratio of straw extruded together with lime as a cosubstrate will increase the output of biogas and electricity by more than 60%.

Creep damage and fracture of notched specimens under static and fast periodic loading

Creep-damage processes in notched specimens subjected to static and periodic loading are studied experimentally. Subsequent simulations were carried out using Rabotnov evolution equation. In case of dynamic creep (fast periodic loading) the constitutive equations derived by use of asymptotic and averaging methods were used. Numerical results were obtained by the combination of FEM and predictor-corrector time integration scheme. Fracture process was studied using designed numerical procedure based on the elimination of the finite elements with critical values of damage parameter. The fracture times and directions of the crack propagation were determined. The qualitative difference between processes of crack propagation in cases of static and periodic loading were observed.

INCREASING THE EFFICIENCY OF ELECTRIC DRIVES WITH PERIODICAL LOADING BY USING COMPREHENSIVE MATHEMATICAL MODELING MEANS

The mode of operation of induction motors (IMs) affects their performance. In most cases, motors are optimally designed for steady state operation. When operating in other modes, additional attention is required to the problems of energy efficiency. Induction motors are the most common type of electromechanical energy converters, and a significant part of them operate under conditions of periodic changes in the load torque. The work is devoted to solving the problem of increasing the energy efficiency of asynchronous motors of electromechanical systems with a periodic load, including pumping and compressor equipment. The traditional solution to this problem for compressor equipment is the optimal design of an IM under static conditions, as well as the use of flywheels, the use of an IM with an increased slip value and controlled IM with a squirrel-cage rotor and with frequency converters. In this work, the modes of operation of asynchronous motors with periodic loading are investigated. For this, complex mathematical models are developed in the simulation system. Such models are effective in modeling taking into account periodic load changes: repetitive transient processes, their possible asymmetry and non-sinusoidality, increased influence of nonlinearity of electromagnetic parameters. In complex mathematical modeling, the mutual influence of the constituent parts of the electromechanical system is taken into account. Simulation allowed quantifying the deterioration in energy efficiency under intermittent loading, in comparison with static modes. Criteria for evaluating quasi-static modes have been developed and areas of critical decrease in efficiency have been determined. The paper proposes and demonstrates a methodology for solving this problem. For this purpose, tools have been created for the optimal design of asynchronous motors as part of electromechanical systems with periodic loading. These tools include: complex mathematical models of electromechanical systems with asynchronous motors with periodic load, mathematical tools for determining the parameters of quasi-steady-state modes, the methodology of optimal design based on the criterion of the maximum efficiency of processes under quasi-steady-state modes of operation. The possibilities, advantages and prospects of using the developed mathemati-cal apparatus for solving a number of problems to improve the efficiency of electric drives of compressor and pumping equipment are demonstrated. It is shown that by taking into account quasi-static processes, the use of complex mathematical models for the optimal design of asynchronous motors with a periodic load provides an in-crease in efficiency up to 8 ... 10%, relative to the indicators of motors that are de-signed without taking into account the quasi-static modes. The areas of intense quasi-steady-state modes are determined using the devel-oped criterion. In these areas, there is a critical decrease in efficiency compared to continuous load operation. A decrease in efficiency is associated with a decrease in the amount of kinetic energy of the rotating parts compared to the amount of electromagnetic energy. In connection with the development of a frequency-controlled asynchronous drive of mechanisms with a periodic load, the relevance of design taking into account the peculiarities of quasi-static has increased significantly. For example, a variable frequency drive of a refrigerator compressor or a heat pump can increase energy efficiency up to 40%, but at low speeds, due to a decrease in kinetic energy, the efficiency can decrease to 10 ... 15%, unless a special design methodology is applied. This problem can be solved by using the complex mathematical modeling tools developed in the article.

Deformation of a spherical, viscoelastic, and incompressible Earth for a point load with periodic time change

SUMMARY Planetary-scale mass redistributions occur on Earth for certain spatiotemporal periods, and these surface mass changes excite the global periodic loading deformations of a viscoelastic Earth. However, the characteristics of periodic viscoelastic deformations have not been well investigated even in a simple earth model. In this study, we derive the semi-analytical Green's functions (fully analytical Love numbers) for long-standing point sources with given periods using a modified asymptotic scheme in a homogeneous Maxwell spherical earth model. Here, the asymptotic scheme is needed in order to obtain accurate semi-analytical time-dependent Green's functions. The amplitudes and phases of the Green's functions may be biased if only the series summations of the Love numbers are used because the influence of viscoelasticity is degree-dependent. We compare the viscoelastic and elastic periodic Green's functions with different material viscosities and loading periods and investigate the amplitude increase percentage and phase delay of the periodic displacement and geoid change. For example, our analysis revealed that the viscosity increases the amplitude by 40–120 per cent and delays the phase approximately −100° to 60° for the displacement and geoid change when bearing a 10-yr loading period, assuming a viscosity of 1018 Pa s and a shear modulus 4 × 1010 Pa.

Debonding Performance of CFRP-Strengthened Nanomaterial Concrete Beam Using Wavelet Packet Analysis

The carbon fiber reinforced polymer- (CFRP-) strengthened nanomaterial concrete beam (SNCB) has been increasingly attracting a widespread attention because of the advantages of using the excellent properties of nanomaterials to improve structural properties. An active sensing approach based on a piezoceramic transducer is developed to detect the interfacial debonding performance of CFRP-SNCB. A CFRP-SNCB specimen was fabricated and subjected to periodic loading test to initiate the debonding damage. Three piezoceramic smart aggregates (SAs) and three piezoceramic smart nanomaterial aggregates (SNAs) are embedded in the specimen and used as an actuator and sensor. Experiments show that the nanomaterial concrete becomes a good conduit for wave propagation due to the nucleation and filling effect of nanomaterial. The stress wave signal caused by the embedded SNAs is more sensitive to the debonding performance between CFRP and concrete than SA. The attenuation of stress wave caused by the increase of the severity of debonding damage can be clearly observed from the signals received from SAs and SNAs in the frequency domain analysis. The debonding cracking of the tension end region is earlier than the bond end region, which proves the starting point of structural debonding damage. Furthermore, the debonding state can be evaluated by wavelet packet analysis. The research results demonstrate that the proposed method has potentials to detect the interfacial debonding performance of CFRP-SNCB.