Action Of External Forces Research Articles

Mesoscopic shear evolution characteristics of frozen soil-concrete interface

The mechanical properties of frozen-concrete interfaces affect the stability and durability of engineering structures in cold regions. To investigate these properties, laboratory tests and numerical simulations were conducted to study the mesoscopic evolution of the shear stress-displacement relationship and the shearing process at the interface. The direct shear tests were performed at different environmental temperatures (−2 °C, −5 °C, and −10 °C) and normal stresses (100 kPa, 200 kPa, and 300 kPa) on the frozen soil-concrete interface, and Particle Flow Code (PFC) model of direct shear was developed. The mesoscopic parameters (particle displacement, rotation, force chain, stress, coordination number, porosity, fabric, etc.) of the interface during shearing were simulated using the PFC model. Moreover, the relationship among the interface temperature, cohesion, and friction coefficient was determined based on experimental data, and the accuracy of the PFC model was verified using previous experimental data. The results of the PFC shear model aligned well with those of the laboratory test, and the formation of shear bands was simulated well. The displacement of the soil particles on the upper layer outside the shear zone was uniform, and the direction was the same, whereas the particles inside the shear zone showed significant differences in the dislocation and rotation of the soil particles. The force chain, stress field, coordination number, and porosity were similar in the shear process and showed a concentrated distribution in the opposite direction of the shear motion, which reflected the consistency of the microcosmic response of the particles under the action of macroscopic external forces. The regression equations for the temperature, cohesion, and friction coefficient in this study can be used to simulate the shear behavior of frozen soil-concrete interfaces under different temperatures and normal stresses.

Stress Analysis of Radial Compression Disk Based on MATLAB

Elastic mechanics is an important branch of solid mechanics, mainly studies the deformation and internal force of elastic objects under the action of external forces and other external factors, also known as elastic theory. The study object of elasticity is elastomer. The detailed theoretical structure helps us solve more practical engineering problems. We used Matlab software in the data simulation for visualization processing. On the basis of the study of elasticity, this paper explores the stress distribution of the uniform ideal elastic body to the radial compression disk model, and observes the change of the stress of the radial compression disk when the external pressure changes gradually. The expressions of the corresponding stress components , and are obtained by using the theory of normal concentrated force on the boundary of a half plane body. The stress solutions considering the thickness t of the disk are derived. Finally, the drawing software in Matlab software is used to visualize the theoretical derivation results in order to intuitively feel the change of stress. After the data simulation, the data simulation results are compared with the stress analysis results derived from the theoretical deduction, and the conclusion is drawn.

Dynamic analysis of six-bar tensegrity-based robot

Abstract The tensegrity-based robot is a hot research topic in the research field of robotics. The dynamics of the robot, describing the specific motion patterns under the influence of forces and torques, play an important role in the application of robotics. In addition, the dynamics should be considered when revealing the internal mechanisms of robots and predicting their dynamic behaviors. In this work, a dynamic model for a rolling six-bar tensegrity-based robot is established. In terms of kinematic representation, quaternions are chosen as the tool for attitude description, simplifying the derivation process of the complex three-dimensional rotational kinematics calculations. Quaternions play a crucial role in mathematical processing for robot attitude control and path planning due to their effective representation of three-dimensional space rotations. The classic Newton-Euler dynamic framework was adopted to conduct in-depth and detailed studies on the dynamic characteristics of the robot under various force conditions and motion states, with a particular focus on rolling dynamic analysis. Special attention was paid to the dynamic response mechanisms of each component of the robot under the combined action of internal and external forces and torques.

СТІЙКІСТЬ ЗАЛІЗОБЕТОННИХ СТІЙОК ПРИ КОРОТКОЧАСНІЙ ТА ТРИВАЛІЙ ДІЇ НАВАНТАЖЕННЯ

The behavior of hinged support at the ends of the rack with initial bending under the action of load is considered. Spring rods are arranged symmetrically. The rack has an initial bend, compressed by forces constant in time. All real elements have one or another imperfections in the form of technological bends, therefore, they begin to bend from the very beginning of the load. The load, when it is exceeded even by an infinitesimally small amount, there is a loss of stability of this type of deformation, is called critical. In the calculation of stability under the long-term action of external forces, it is necessary to determine the load, at which the rate of movement in time monotonically decays. Solving the problem in such a setting is acceptable for systems, the development of movements of which in time leads to a change in the stress state. This condition for a compressed rack is fulfilled only in the presence of initial imperfections (initial bending, off-center application of compressive force, etc.). When solving the problems of the theory of stability, taking into account the creep of the material plays an important role. Creep can be limited in time or unlimited. When solving the problem of the stability of racks with initial imperfections, made of a material that has creep and reinforced with elastic rods, the following assumptions are made: 1) the hypothesis of flat sections is considered valid; 2) the deformations of the creeping material and the elastic rods at the points of contact are the same; 3) the modulus of deformations during stretching and compression are equal; 4) the creep material works in the stretched zone without the appearance of cracks. The relationship between deformations and elasticities in the material of the rack is established by a formula based on the linear relationship between deformations and elasticities. The creep rate of concrete is based on the hereditary theory of aging. In the work, an integro-differential equation was obtained - the equation of slow motion of the rod, expressions were obtained for the study of bends in any at what point in time, the formula for determining the critical force with long-term load action is derived.

Form-Finding of Tensegrity Basic Unit with Equal Cable Length

Tensegrity is a lightweight, self-stressing, and self-stabilizing structure made up of cables and bars, with each member bearing either tension or compression but not affected by shear stress. This design allows for optimal utilization of the material properties of the members. In a tensegrity basic unit, the bar members are of equal length, while the cable members come in three lengths: lower-end surface horizontal cable, upper-end surface horizontal cable, and stayed cable. The tensegrity basic unit with equal cable length simplifies this further by ensuring that all cables are the same length, resulting in a structure with only two member lengths, i.e., bar length and cable length, enhancing interchangeability. In order to find the form without the action of external forces, the force density coefficient ratio is introduced. By performing a force balance analysis on any node of the unit, the equilibrium equation of the structure is determined, incorporating the additional constraint of equal cable length. Two methods are employed to ascertain the force density coefficient ratio of each member in the unit: the theoretical derivation method based on the stable configuration condition of the tensegrity basic unit with equal cable length, and the method of solving the characteristic equations of the force density matrix. A program is developed to validate the form-finding method using basic units with three, four, five, and six bars as examples. The results show that the model accurately represents the physical structure, confirming the reliability of the form-finding methods.

DEFORMATION MECHANISMS IN CASE OF DESTRUCTION OF THE TUBING NOZZLE MADE OF FERRITE-PEARLITE STEEL

In the work by methods of experimental studies and computer modeling, deformation mechanisms were analyzed during the destruction of the steel suspended branch pipe of the tubing. Tubing rupture occurred during production well operation for 306 days as a result of hydrogen sulfide stress corrosion cracking (SSCC), which was preceded by hydrogen embrittlement of the metal and cyclic action of external forces. Scanning electron microscopy (SEM) shows that the suspended branch pipe is characterized by a ferrite-pearlite structure, and in the area of its fracture, which occurred in the threaded part, there is an increased content of degenerated pearlite grains and traces of hydrogen blisters. Analysis of the crystallographic texture of the original nozzle showed the presence of Br {110} < 112 >, G {110} < 001 >, TG1 {111} < 110 >, TG2 {111} < 011 >, RG {110} < 110 > and RC {001} < 110 > grain texture components. It was found that after operation of the nozzle in well conditions, in the area far from the fracture, the grain orientations related to Cube {001} < 100 >, TG1 {111} < 110 >, TG2 {111} < 011 >, TB3 {331} < 136 > texture components increase. It was found that in the fracture area, in addition to the grain orientations characteristic of the nozzle body, there are also Br {110} < 112 >, G {110} < 001 >, RC {001} < 110 >, RG {110} < 110 >, TC {112} < 110 >, TB1 {111} < 112 > and TB2 {554} < 225 > texture components It is shown that Cube and grain orientation TB3 in the branch pipe after operation accelerate the process of hydrogen embrittlement of metal, and the presence of TB1 orientation indicates the process of return and/or recrystallization in the product. It was found that the process of hydrogen embrittlement led to a decrease in the strength properties and ductility of the steel of the branch pipe. Within the framework of viscoplastic self-consistent (VPCC) model, textures and deformation behavior of samples cut from different sections of the nozzle (before and after operation) were simulated. It was found that at the initial stages of tension the samples of the new branch pipe, the most active is the operation of {110} < 111 > slip systems. In samples of the nozzle after operation, the activity of {110} < 111 > slip systems decreases. At the same time, the activity of {123} < 111 > slip systems increases, and the nature of the operation < 112 > {111} of the slip system does not change. It was found that in all studied states before destruction the activity of {123} < 111 > systems increases ~ 1.4 times. It was concluded that the growth of TG2 {111} < 011 >, {332} < 110 > and {557} < 110 > texture components, as well as the activity of < 123 > {111} slip systems are associated with the effect of shear deformations that generate microcracks in pearlitic grains, and the applied forces contribute to the development of cracks and subsequent destruction of the product. It has been shown that by controlling the crystallographic texture and, accordingly, deformation mechanisms, it is possible to produce new pipeline steels that are more resistant to SSCC.

Optimal Solutions for a Class of Impulsive Differential Problems with Feedback Controls and Volterra-Type Distributed Delay: A Topological Approach

In this paper, the existence of optimal solutions for problems governed by differential equations involving feedback controls is established for when the problem must account for a Volterra-type distributed delay and is subject to the action of impulsive external forces. The problem is reformulated within the class of impulsive semilinear integro-differential inclusions in Banach spaces and is studied by using topological methods and multivalued analysis. The paper concludes with an application to a population dynamics model.

COMPUTATIONAL AND EXPERIMENTAL STUDY OF THE STRESS-STRAIN STATE OF A PIPE UNDER EXTERNAL RADIAL LOAD, INTERNAL PRESSURE AND TEMPERATURE DIFFERENCE

Oil and gas pipelines are subjected to complex of loads and impacts during operation. The purpose of this article is an experimental assessment of the stress-strain state of a pipe under the action of external radial force on a laboratory bench by the strain gauge method, as well as a computational and experimental assessment of the stress-strain state under the combined action of radial force, internal pressure and temperature difference. Accounting for internal pressure and temperature difference (other factors affecting the pipeline) is carried out using well-known theoretical formulas which are confirmed by practice. The total stresses from the effects of several factors of influence are determined due to the principle of superposition.Experimental and computational studies of the stress-strain state of the pipe cross section under the influence of external radial force corresponding to the pipe deflection from 0 to 8 mm; internal pressure from 0 to 14 MPa; temperature difference from minus 60 C to 60 C have been carried out. Graphs of the dependence of maximum stresses on the factors of influence are constructed. Empirical formulas have been obtained for calculating the maximum equivalent von Mises stress of the cross-section of the pipe with a diameter of 325 mm under various loading options, they are necessary to assess the strength of the pipeline structure.

RESISTANCE OF FERRITE-PERLITE STEEL TUBING BRANCH PIPE METAL TO DESTRUCTION IN HYDROGEN SULFIDE MEDIUM

This paper discusses the problems of resistance of the metal of the tubing branch pipe (tubing) to the process of its destruction in a medium containing hydrogen sulfide and when exposed to external forces. A 73х73 tubing nozzle made of 38G2SFA steel was selected as the material for research. The tubing fragment was destroyed during production well operation. To establish the reasons for the failure of the tubing nozzle, a visual inspection was carried out, tests were performed to assess the hardness and mechanical properties, the microstructure and microtexture of the metal were analyzed using scanning electron microscopy (SEM) methods. To analyze the nature of the distribution of introduced defects, the mutual orientation of structural components and crystallographic texture, studies were carried out by the method electron backscatter diffraction (EBSD). Studies of the suspended branch pipe, which does not have chemical protection, showed that the cause of its destruction was hydrogen sulfide stress corrosion cracking (SSCC) as a result of hydrogen embrittlement and the action of external tensile forces exceeding the yield strength of the metal. It was established that as a result of the interaction of hydrogen sulfide of the distilled product with the metal of the branch pipe, hydrogen embrittlement of the material of the branch pipe occurred. The process of hydrogen embrittlement of the fragment was proved by detecting hydrogen blisters in the metal microstructure and establishing the process of coalescence of neighboring inclusions. In addition, the results of the test to measure the hardness of the metal along the wall thickness further supported the hypothesis of hydrogen embrittlement of the tubing. EBSD analysis showed that the threaded part of the branch pipe is characterized by a small size of structural elements and an increased density of introduced defects (geometrically necessary dislocations), which are a promising site for the deposition of molecular hydrogen. It is concluded that reaching the limit concentration of molecular hydrogen reduces the binding energy of metal atoms and this process initiates the formation of pores. It has been established that the development of cracks along large-angle grain boundaries is facilitated, and small-angle and coincidence site lattice (Σ3, Σ5, Σ11 and Σ13b) grain boundaries are active barriers to crack propagation. It has been shown that by optimizing the elemental composition of steel, controlling the microstructure, crystallographic texture, as well as the type and state of grain boundaries, new pipeline steels can be produced that are more resistant to SSCC.

Research on foldable two-matrix 3D braided composites: Manufacturing and bending progressive damage

Research on foldable two-matrix 3D braided composites: Manufacturing and bending progressive damage

Research on axial nonlinear vibration characteristics of ball screw feed system considering segmented restoring force

Taking the ball screw feed system as the research object, the two degree of freedom axial dynamic model of the system is constructed firstly. Based on Hertz contact theory, when the ball screw pair adopts variable lead self-preloading to eliminate the assembly clearance between the ball and raceway, considering the nonlinear segmented axial elastic recovery force generated by the uneven contact deformation between the ball and raceway under the action of external excitation force, further derive the nonlinear dynamic equation group of the system. Next, the fourth-order Runge-Kutta method was used to numerically solve the equation system, obtaining the system’s two and three-dimensional phase diagrams, Poincaré sections, time-domain waveform diagrams, frequency spectra, and bifurcation diagrams. Then, the effects of damping constant, initial contact angle between ball and raceway in ball screw pairs, and number of balls on the system’s response characteristics were analyzed, and the influence of external excitation forces on system stability was further studied. Finally, it was verified through experiments that the axial vibration of the system is indeed nonlinear vibration, providing a theoretical basis for the study of the dynamic characteristics of the ball screw feed system.

Features of the contact angle hysteresis at the nanoscale: A molecular dynamics insight

Understanding the physics of a three-phase contact line between gas, liquid, and solid is important for numerous applications. At the macroscale, the response of a three-phase contact line to an external force action is often characterized by a contact angle hysteresis, and several models are presented in the literature for its description. Yet, there is still a need for more information about such model applications at the nanoscale. In this study, a molecular dynamics approach was used to investigate the shape of a liquid droplet under an external force for different wetting regimes. In addition, an analytic model for describing the droplet shape was developed. It gives us the possibility to evaluate the receding and advancing wetting angle accurately. With our modeling, we found that the interplay between capillary forces and viscous forces is crucial to characterize the droplet shape at the nanoscale. In this frame, the importance of the rolling movement of the interface between liquid and vapor was pointed out. We also demonstrate that in the range of the external forces when capillary forces are most significant compared to others, hysteresis is well described by the macroscale Cox–Voinov model.

Modeling the fracture process of wheat straw using a discrete element approach

The cracking and breaking of wheat straw under the action of external force are rarely studied, they affect the precision of its simulation using the discrete element method. The process of straw change due to cracking and breaking consists of two stages: ring collapsing and breaking. In order to restore the real process of straw change, this study develops a discrete element model based on the Hertz-Mindlin bonding V2 contact model. The bond parameters were calibrated using the test of compression, shear, and three-point bending. An orthogonal experiment was conducted to determine the optimal parameter combination. The obtained results showed that the proposed straw model accurately simulated the cracking, breaking, and flow characteristic. The relative errors of compression strength, shear strength, and deflection were 9.48, 8.74, and 11.51%, respectively. The relative error of the angle of repose (AOR) was only 1.67%, which indicates that the mechanical properties and flow characteristic of the model are consistent with those of real straw. This study holds significant importance in accurately replicating the authentic straw treatment process in the field.

Fluidic undulation effects on carangiform swimmers propelled by internal active bending moments

With different shapes and material properties, fish all achieve undulatory swimming gait under the action of internal active muscle stimulation and external fluid forces. Such locomotion can be decomposed into deformation affected by internal and external forces in the body frame and overall translation and rotation solely determined by fluid forces. In order to revisit the undulatory swimming gait, we investigate the hydrodynamic performance of two-dimensional flexible carangiform swimmers with varying stiffnesses and thicknesses, which are driven by the active internal bending moments, and employ the complex orthogonal decomposition and Fourier decomposition methods to quantitatively measure and analyze the proportion of undulation. It is found that standing wave deformation characteristics are prominently observed along fish-like bodies with high stiffness, whereas traveling wave characteristics are more evident in bodies with lower stiffness. The self-propelled fish body demonstrates lateral oscillation and rotation around its center of mass, namely, the heaving and pitching movement, particularly in specimens with high stiffness. The present analysis shows that the heaving and pitching locomotion induced by the fluid significantly increase the traveling wave proportion by modulating the amplitude and phase of the left and right traveling waves viewed in forward frame. We called it fluidic undulation effects (FUE), which is different from the undulation of body deformation. This effect is more pronounced for large stiffnesses and thin airfoils. The standing wave deformation observed with a large stiffness transforms into a traveling wave propulsion pattern, with its traveling wave index even slightly surpassing that of a small-stiffness pattern. Although the efficiency of the standing wave deformation is low, it facilitates a faster forward speed (body lengths per stroke). The positive impact of the FUE on the swimming performance is also confirmed by restricting the recoil motions of the lateral translation and rotation of the body. Furthermore, we observe that there is no undulatory swimming gait that has both the highest energy efficiency and the highest speed.

Stretchable, stable, and structural color reversible enabled by mesoscopic regulation and design for flexible photonic crystal mechanical sensors

This paper reports a flexible mechanical sensor developed by combining an opal photonic crystal and a flexible medium through UV curing technology. Under the action of external force, the deformation of the flexible medium causes the change of the photonic crystal lattice constant, which leads to the displacement of the reflection peaks, thus realizing the detection of the deformation of the film. The flexible medium is mixed by photoinitiators and polymer monomers, and its mechanical properties are directly related to the mass fraction of photoinitiators and polymer monomers. The results show that the film can reach a maximum strain of about 180% when the mass fraction of photoinitiator is 3% and the volume ratio of the polymer functional monomers is 8:2. In addition, for the responsiveness test of the sensor under tensile, the results show that at 0%, 26%, and 78% of tensile strain, its structural color is blue-shifted sequentially, and its spectral peaks are 668 nm, 535 nm, and 488 nm, respectively. Finally, the sensor is applied to the detection of acoustic waves in air, and it is found that its spectral response peaks can be obtained for acoustic waves of different frequencies (250–650 Hz), and a spectral peak at 500 Hz. This flexible photon sensor has the potential to match the acoustic resistance of water. It will greatly expand the response research of ocean exploration in the low frequency range.

Reorientation of grain crystal lattices in metals/alloys during electrocrystallisation under the action of force

The purpose of the study was experimental verification of the proposed concept of phase formation in electrocrystallised metals/alloys via the stage of supercooled liquid state. In accordance with the purpose, the task was to reveal the features of formation of the crystallographic texture in metals/alloys during their electrocrystallisation under the action of small force. The effect of the emergence of a new crystallographic texture with lower surface energy in metals/alloys during electrocrystallisation under the action of small external force exerted in the direction opposite to the initial axis of the texture was experimentally established. The obtained result is one more proof of the validity of the concept of phase formation in electrocrystallised metals/alloys via the stage of supercooled liquid state.

Forced oscillation of planetary mechanism synchronizer for spindle drive

The article is devoted to the results of a theoretical and experimental study of forced oscillation of the epi-hypocyclic planetary mechanism synchronizer used to drive the spindles of the cotton machine apparatus. Spectrum of natural oscillation frequency of synchronizer is determined and mass moment of their inertia is set for stability in operating mode when satellite comes in and out of gear engagement of planetary mechanism. Periodic nature of system oscillations under action of external forces of satellite is considered. The graph of oscillations of actual excitation of the synchronizer in the form of a pulse semi-sinusoidal curve is obtained. The beam diagram is built that allows you to make delaminations from the resonant modes of operation of the synchronizer.

Mathematical modeling of small soil channel laboratory stand drive and evaluation of its energy state

The article presents data on improving the design of the Small Soil Channel research laboratory stand. The possibilities of experimental works on study of kinematic parameters and structural parameters, spatial dynamometering of working elements of tillage and sowing machines are described. The article considers the method for assessing the energy state of the laboratory stand small soil channel and studying the power distribution in its moving mechanisms. Based on the parameters obtained as a result of solving the equations of motion and energy state, using the full differential of the Hamelton function, the power distribution in the mechanisms under the action of external forces and the total mechanical energy of the stand are determined. The traction resistance of stand working body was determined using the Goryachkin formula. Based on the developed kinematic scheme, a mathematical model has been developed that imitates the movement of the belt transmission mechanism of the stand. Based on the developed mathematical model, calculation experiments were carried out using the Runge-Kutt numerical method, the results made it possible to find the motion parameters of the belt transmission mechanism of the stand. The results obtained when solving the mathematical model of the belt transmission mechanism of the stand made it possible to determine the parameters of movement of the stand engine and the drum. This article presents the results of determining the stiffness and elasticity coefficients of the belt, the moment of resistance of the drum, the driving moment of the driving pulley, angular speed, angular rooting, the moment of inertia of the driving and driven pulleys by compiling a mathematical model of the Laboratory Stand Small Soil Channel that imitates the working process of tillage and sowing machines.

Bolt looseness identification using a knocking acoustic signal

As a common failure form of the bolted joint, bolt looseness can lead to relative slip between the connected surfaces. Under the action of shear external forces, the bolt experiences fatigue failure and fracture, which can affect the service performance and connection strength of the equipment, and even cause major safety accidents. At present, good results have been achieved in detecting the tightness of bolt connections through Structural Health Monitoring (SHM) technology. However, most of them are still carried out under laboratory conditions and cannot be applied in engineering. Therefore, this article proposes looseness recognition of bolts by knocking acoustic signals. This method converts the acoustic time series signal into a Mel-Frequency Cepstral Coefficient (MFCC) frequency spectrum and then it recognizes the bolt looseness status through the Mobilenetv3 deep neural network. The results show this method can identify loose bolts. Meanwhile, it has a strong engineering application background.

STUDYING THE MECHANISM OF CREATING WORK AT THE LESSON BY THE METHOD OF INTEGRATED APPROACH

The main aim of the article is to explore the study of mechanisms of creating work in the lesson by the interactive method. The article explains the essence of the concept of work, which is one of the important quantities in physics, and analyzes the mechanism of the phenomenon of its various forms. Here they distinguish between ordered and irregular forms of work, explain the imbalance within the system as a result of the action of external forces, and the relationship between the processes within the system and the work performed against this background. Importance of the application: material can be used in organizing interactive classes in lecturers and seminars in Higher Education Institutions. Keywords: regular work, irregular work, dissipative process, system, substituting force.