Multi-cycle Loading Research Articles

Numerical Simulation Study on the Mechanics and Pore Characteristics of Tectonically Deformed Coal under Multi-Level and Multi-Cycle Loading and Unloading Conditions

Horizontal well cavern completion and stress release is considered a potential technique for efficient development of coalbed methane in tectonically deformed coal (TDC). Pulsating loading and unloading is a key technique for the controlled expansion of caverns and broader stress release within the reservoir. However, current understanding of the mechanical characteristics and pore network structure evolution of TDC under cyclic loading and unloading conditions is still limited. This paper employs numerical simulation methods to study the mechanical behavior and damage characteristics of TDC under cyclic loading and unloading. After obtaining a set of micromechanical parameters reflecting the behavior of TDC samples under triaxial compression in high-stress states, the effects of different stress gradients and cyclic amplitudes on the stress–strain curve, porosity changes, and crack propagation in TDC samples were analyzed. The study results indicate that under various cyclic loading and unloading conditions, the mechanical response characteristics of TDC samples are broadly similar, primarily divided into compression, slow expansion, and accelerated expansion phases. Under low unloading level conditions, the volume expansion of TDC samples is minimal. Also, at the same unloading level, the strain increment decreases with an increasing number of cycles. Correspondingly, under these conditions, the porosity and microcrack expansion in TDC are less than in high-stress gradient scenarios. Under the same unloading level but different amplitudes, the volume expansion rate at 50% unloading amplitude is higher than at 1 MPa unloading amplitude for TDC, with an increased number of crack expansions. Therefore, under cyclic loading conditions, the sensitivity of crack propagation within TDC samples to amplitude is greater than that to unloading level. Under actual pulsating excitation conditions, a low-amplitude, low-stress gradient pulsation method should be used to maintain the stability of horizontal well caverns, and gradually increase the cyclic amplitude to achieve the efficient extraction of coalbed methane in TDC reservoirs. The findings of this study can serve as an important reference for optimizing process parameters in cyclic pulsating stress release engineering for TDC.

Behaviour of nickel coatings made by brush plating technology in conditions of cavitation erosion and corrosion

The basic hypothesis of the research was that the structure of the coating, i.e. the type of defects, affects the mechanical and electrochemical properties, as well as the resistance to cavitation erosion and corrosion. For this purpose, nickel coatings produced by brush-plating technology using two different electrolytes and deposited on X20Cr13 steel were tested. The electrolytes affected the structure and properties of the coatings: one coating had a network of cracks, and the second one had a “cauliflower-like” structure. The hardness and Young's modulus of both coatings were investigated under multi-cycle loading modes. Cavitation erosion resistance was tested in a cavitation tunnel equipped with a barricade system at an inlet pressure of 600 kPa and outlet pressure of 120 kPa. Both nickel coatings protected the substrate against cavitation erosion. The lowest rate of cavitation erosion had a coating with a network of cracks and high hardness. Microscopic examinations showed no influence of the net of cracks on the degradation process. Electrochemical tests confirmed the better corrosion resistance of the compact coating. The compact coating had about an order of magnitude lower corrosion potential and about 100 mV higher corrosion current density than that of the agglomerate coating. The agglomerate coating had electrochemical parameters comparable to the substrate.

EFFICIENCY OF THE USE OF POLYMERIC MATERIALS IN THE SUPPORT-GUIDING UNITS OF HYDRAULIC CYLINDERS

The reliability of hydraulic cylinder sealing units is largely determined by the physical, mechanical and tribological properties of polymer materials of the support and guide rings. They provide optimal loading conditions for sealing assemblies and reduce wear of hydraulic cylinder parts. Analysis of loading conditions and failures of hydraulic cylinder support and guide assemblies shows that when modeling loading, it is necessary to synchronously take into account the processes of friction, wear and accumulation of residual deformations in polymer rings. The concept of accelerated loading of nodes, developed on the basis of the finite element method, allows you to simultaneously describe all the processes occurring during the period of trouble-free operation of the support and guide units of hydraulic cylinders. (Research purpose) The research purpose is evaluating the effectiveness of the use of polytetrafluoroethylene, polyamide 6 and composites based on them in the support and guide units of hydraulic cylinders on the basis of numerical approaches for determining the reliability of assemblies with polymer parts. (Materials and methods) Developed and implemented in ANSYS a finite element model of multi-cycle loading of hydraulic cylinder support and guide units. We performed a series of calculations for polytetrafluoroethylene, polyamide 6 and composites based on them. (Results and discussion) It was shown that the run-in period of polymer rings does not exceed two years. The service life of polymer rings is mainly determined by the processes of wear, and not due to the accumulation of residual deformations. It was revealed that the operating time for failure of support and guide assemblies with polymer rings is: polytetrafluoroethylene - 2.08 years, composite (polytetrafluoroethylene + 20 percent carbon) - 3.91 years, polyamide 6 - 3.11 years, composite (polyamide 6 + 0.5 percent graphite + 2 percent shungite) - 7.08 years. (Conclusions) The developed composite provides an increase in the service life of the rings of the support and guide units of hydraulic cylinders by more than 1.8 times compared with polytetrafluoroethylene and a composite based on it.

Eddy Current Measurement of Chemiresistive Sensing Transients in Graphene-hBN Heterostructures.

The development of graphene-based electronic and gas sensing devices has motivated considerable research interest in the properties of graphene-hBN heterostructures. Eddy current measurements of the sheet conductance of graphene-hBN heterostructures show a relatively low conductance, as compared to results previously reported in the literature, all of which were obtained using contact-based measurement methods. Chemiresistive measurements of the graphene-hBN heterostructure response to oxygen adsorption, including hysteric effects under transient multicycle loading, show that the incremental sheet conductance responses of graphene and graphene-hBN sensors differ in sign. A transient, nonlinear, history dependent constitutive model of graphene-hBN response to oxygen adsorption distinguishes stochastic variations in material properties from deterministic variations in sensor performance. The deterministic variations are due to sensing process hysteresis, a phenomenon of central interest in the development of graphene-based sensor systems.

Temperature-Shift-Induced Mechanical Property Evolution of Lithium-Ion Battery Separator Using Cyclic Nanoindentation.

The evolution of mechanical properties of separators affected by temperature shifts is imperative for the performance of the lithium-ion battery. The flexible film characteristics hinder the evaluation of the micromechanical properties of separators. In the present study, considering the susceptibility of separators to temperature fluctuations, the temperature distribution of the battery during the discharging process at subzero temperature is obtained. Three sets of separator samples subjected to various temperature shifts are prepared. Through multicycle depth-sensitive nanoindentation, the temperature-dependent weakening of elastic modulus and hardness of separators is experimentally verified. Moreover, the variation trends of elastic modulus, hardness, and hysteresis response of the separator specimens in terms of temperature are investigated via extracting from the multicycle loading-unloading nanoindentation responses. The temperature-dependent variations in the elastic modulus of the separator were investigated by following heating, cooling, and thermostatic processes. Meanwhile, the indentation tests also verify that the effect of temperature shifts on the hardness exhibits an attenuation trend when heating or cooling is followed by a thermostatic process. The variation analysis of nanoindentation hardness as a function of temperature shifts shows typical size effects dependent on the nanoindentation depth. The temperature-induced residual stress and elemental distribution are also analyzed through characterization using X-ray diffraction and energy-dispersive X-ray spectroscopy, respectively. The obtained evolution law of temperature shift-induced mechanical properties of a separator could facilitate the optimal design of the separators and provide the supporting data to enhance the safety performance of lithium-ion batteries.

The Effects of Magnesium Borate Whiskers on the Mechanical Performance of Oil Well Cement

Quasi-brittle behaviors of cement-based material can be reinforced through diverse methods due to its unique multiscale features. Among them, reinforcing agents are the most direct and effective means, such as slag, metakaolin, and fly ash. These materials can improve the performance of cement stone to a certain extent, but their chemical composition is still mainly silica, which does not in essence change the defects of cement. Therefore, in this experiment, magnesium borate whisker (Mg2B2O5) was used as reinforcer of 90°C class G oil well cement and magnesium borate whisker reinforced cement-based material (MBWRC) was prepared. On the one hand, the performance of mechanical strength was controlled, and the resistance to compression, traction, and bending was included. Furthermore, static stress-strain behaviors analysis and toughness behaviors analysis (dynamic multicycle loading test) were further conducted. Second, mercury intrusion porosimetry (MIP) and scanning electron microscope (SEM) were used to test the characteristics of pores and interfaces of cement-based materials. Through multiscale microstructure analysis, MBWRC was found to have excellent 90°C mechanical performances when compared to control sample’s, for which tensile strength increased to 235% of controlled sample’s, and flexural strength increased to 130%, plus a healthy developed compressive performance, and MBWRC showed much denser pore structure, in which harmless micropore increased from 13.3% to 14.40%, porosity decreased from 17.01% to 16.20%, and permeability decreased from 0.2533% to 0.0205%. Furthermore, MBWRC showed resistance capability to mechanical loading, which can be attributed to the formation of denser pore structure and more excellent mechanical performance.

АВТОРСЬКА МЕТОДИКА ВИЗНАЧЕННЯ НЕСУЧОЇ ЗДАТНОСТІ ПОХИЛИХ ПЕРЕРІЗІВ БАЛКОВИХ КОНСТРУКЦІЙ ЗА ДІЇ ПОВТОРНИХ НАВАНТАЖЕНЬ

Analysis of the results of both our own tests and studies of other scientists shows that the destruction of structures under the action of repeated loading occurs at lower stresses than the destruction of structures under the action of short-term static loads. Namely, the bearing capacity of beams under the action of cyclic loads is on average 10% lower compared to the bearing capacity of their "twins" under static forces, that must be taken into account when calculating and designing structures. In this regard, the author's method for calculating inclined sections of reinforced concrete beam structures under low-cycle and multi-cycle loads is presented in the paper. Repeated loads are proposed to be taken into account by calculating the fatigue strengths of the beam’s materials, namely the compressed zone of concrete above the critical inclined crack, the longitudinal reinforcement at the intersection with the inclined crack, as well as the anchoring of the longitudinal reinforcement. In particular, the design lines of endurance of concrete and reinforcement are considered. In practical calculations, the change in stresses that occurs due to the development of vibrocreep deformations of compressed concrete at complex stress state is taken into account by the functions of stress accumulation in concrete, longitudinal and transverse reinforcement. These functions of deformations of concrete vibrocreep are calculated according to the theory of vibrocreep. According to the results of the research, the corresponding author's expressions and dependencies are derived and presented, which allow determining the limit forces of structural element with a given shear span. In addition, it is proposed to introduce the coefficient kcyc into the calculation, which takes into account the more destructive effect of a multi-cycle load compared to a low-cycle repeated one. Thus, kcyc is the ratio of the breaking shear force to the minimum design ultimate endurance force of the near support sections of the specimens-beams, calculated using the characteristic values of the strength of concrete and reinforcement, that is, the prismatic strength of concrete and the yield strength of reinforcement.

Computational modelling of the effect of microstructure on the abrasive wear resistance of tungsten-carbide nickel composite coatings under sub-critical cyclic impact loading

Abrasive wear was simulated for tungsten carbide-nickel (WC–Ni) composite coatings with different volume fractions of reinforcing particles under abrasive cyclic loading. Using parallelized computing approaches, for the first time in the literature, the effects of reinforcing particle and normal load on material removal mechanisms and wear rates were numerically analyzed for multi-cycle loading. The results demonstrated how various material removal mechanisms compete with each other for varying load, cycles, and particle concentrations. This both confirmed previous experimental observations, as well as motivates future areas towards materials tailoring and optimization. Finally, a statistical predictive model was developed to define the relationship between the wear rate, reinforcing particle volume fraction, and load in order to inform future efforts in materials design.

Failure Mechanisms and Parameters of Elastoplastic Deformations of Anchorage in a Damaged Concrete Base under Seismic Loading

The article addresses mechanisms of anchorage failure in a concrete base studied within the framework of physical experiments. The authors investigated the most frequently used types of anchors, such as the cast-in-place and post-installed ones. The anchorages were studied under static and dynamic loading, similar to the seismic type. During the experiments, the post-earthquake condition of a concrete base was simulated. Within the framework of the study, the authors modified the values of such parameters, such as the anchor embedment depth, anchor steel strength, base concrete class, and base crack width. As a result of the experimental studies, the authors identified all possible failure mechanisms for versatile types of anchorages, including steel and concrete cone failures, anchor slippage at the interface with the base concrete (two types of failure mechanisms were identified), as well as the failure involving the slippage of the adhesive composition at the interface with the concrete of the anchor embedment area. The data obtained by the authors encompasses total displacements in the elastic and plastic phases of deformation, values of the bearing capacity for each type of anchorage, values of the bearing capacity reduction, and displacements following multi-cyclic loading compared to static loading. As a result of the research, the authors identified two types of patterns that anchorages follow approaching the limit state: elastic-brittle and elastoplastic mechanisms. The findings of the experimental research allowed the authors to determine the plasticity coefficients for the studied types of anchors and different failure mechanisms. The research findings can be used to justify seismic load reduction factors to be further used in the seismic design of anchorages.

СТАТИЧЕСКАЯ И ДИНАМИЧЕСКАЯ НАГРУЖЕННОСТЬ ПРУЖИН БУКСОВОГО ПОДВЕШИВАНИЯ ТЕЛЕЖКИ ЭЛЕКТРОПОЕЗДА ЭС2Г

It is possible to determine a service life of an electric-multiple unit and its assemblies by actual time of proper operation or theoretically according to results of comprehensive test of components and parts. According to standards of car calculation on strength, for parts that work in conditions of long and intense influence of dynamic loads it is necessary to determine fatigue strength at multi-cycle loading. Calculation is carried out with the consideration for probabilistic dispersion of fatigue strength characteristics and stochasticity of dynamic loading of a part, on the basis of which a life cycle is determined. Oscillograms of dynamic processes gained at tests on the line in theoretical calculations are substituted by a number of simple cycles. Study results presented in the paper allow determining static and dynamic parameters of springs of the primary spring suspension for electric-multiple unit bogie and a type of a simple cycle and its parameters.

Steel fatigue under non-stationary cyclic loading with low cycle overloads

The regularities and mechanisms of the elastoplastic strain of structural steels of two different types under two-stage cyclic loading regime conditions combining multicycle fatigue loading and hard elastoplastic strain under repeated overloading are considered. Based on experimental results and metallographic studies, repeated elastoplastic overloads on changes in the structural state of the material, mechanisms of fatigue damage accumulation, and lifetime indicators compared to the stationary process of cyclic loading are evaluated. It is shown that the combination of multicycle loading modes and low-cycle overloading leads to a change in fatigue resistance mechanisms of steels and changes in fatigue life depending on the loading history. Predict the effect of pre-elastoplastic loading of different types of metals, a change ratio in lifetime depending on the parameters of the two-step cyclic loading regime is proposed.

Ferrofluid-lubricated thrust bearing with an air cushion

This study develops a ferrofluid-lubricated thrust bearing with an air cushion. The bearing comprises a rotor, a stator, and a ferrofluid ring formed between them due to absorption by an annular magnet under the stator. The design makes it possible for the air cushion (air sealed inside the ferrofluid ring) as well as the magnetized ferrofluid to supply supporting forces. A model of the bearing for a static supporting force is proposed and validated by experiments. As the gap between the rotor and stator was 0.25 mm, the maximum static supporting force of the bearing was 3.2 N, much higher than the support provided by the pure ferrofluid ring (without the air cushion, 1.7 N). The operating space of the bearing was detected by multicycle load–retract tests with remarkably high and repeatable accuracy. The results of dynamic experiments show that the speed of rotation of the rotor has a minor effect on the supporting force. Such a ferrofluid-lubricated bearing offers promise for use in precise positioning or low-friction systems.

Modification of the Stamp Topological Optimization Taking into Account Cyclic Fatigue based on the Finite Element Approach

The study is devoted to optimizing the volume of stamping tools used in pressure processing processes. The relevance of the research is due to the active development of additive technologies and the possibility of producing stamping tools from plastic of optimal shape, which has an important practical significance in the manufacture of thin-walled products in the aviation and automotive industries. The purpose of the study was to carry out a mathematical formulation of the problem of topological optimization of a forming die made of a polymer material with restrictions on fatigue durability and minimum volume. The task of topological optimization was to maximize the stiffness of the die under multicyclic loading. The vector description of topological optimization was based on the finite element approach. The optimization model was built on the basis of the solid isotropic material penalization method with the introduction of additional restrictions in the model of searching for pseudo-densities of the material, taking into account the duration of the force action on the stamp under multicyclic loading. In view of the nonlinearity of the resulting system of equations, the solution of the conditional optimization problem is proposed to be carried out by constructing the Lagrange objective function and using the Lagrange multiplier method. The result of the study is the proposed approach to the topological optimization of the stamp, taking into account the multicyclic loading and restrictions on the desired volume.

Multicyclic indentation on brittle glasses

Instrumented indentation testing is widely used to determine the mechanical properties of materials. In particular, this technique allows to study brittle materials for which cracks can be generated around the impression during the indentation test. Cracking can result in the formation of pop-ins on the curve load-segment which can be used to characterize the cracking resistance of the material.In this work, the mechanical properties of the studied materials were determined by applying multicyclic indentation tests. The pop-in phenomenon is mainly observed under constant multicyclic loading on Zerodur® glass whereas under progressive multicyclic loading, this phenomenon appears for all glasses after several indentation cycles. The indentation fracture toughness, (KIc), was calculated from the developed cracks’ length by using different established relationships.Finally, the values of (KIc) and brittleness factor are compared with each other, allowing a classification of the tested glasses according to their resistance to cracking.

Change of Acoustic and Magnetic Properties of Metals of Main Pipelines under the Influence of Cyclic Loads

Today, the assessment of the technical condition of objects taking into account the effects of variable loads is gaining popularity in the world. As a rule, such loads do not lead to simultaneous destruction of structures. Such facilities include trunk pipelines. The variable loads arising in them are determined by the technological mode of operation. For main pipelines, a low-cycle load is characteristic, for gas pipelines, a multi-cycle load. During cyclic impact on the metal, its slight damage occurs at the micro level, which is almost impossible to detect without special diagnostic methods. Microdamage in the metal accumulates in the form of microcracks and, with an increase in the number of loading cycles, the number of microcracks increases several times, which can ultimately cause macrocracks and lead to design failure. When analyzing accidents that occurred on pipelines, the fact that failure occurred without the presence of characteristic crack-like defects in the pipe wall is often noted. Thus, fatigue damage to the metal is a dangerous factor that can lead to the destruction of pipelines. Given the new trends in diagnostics, one of the key issues is the assessment of damage to prevent accidents on main pipelines. The article considers the study of the dependence of the acoustic and magnetic properties of specimens from 09G2S steel loaded in the equivalent mode of the main gas pipeline, depending on the level of accumulated damage.

Theoretical foundations of design optimization ship's control, decision-making systems and information processing

Problem setting. The problems of optimizing the protection parameters of REA structures operating under complex mechanical influences, their diagnostics of quality, reliability and strength, as well as structural and parametric synthesis in the last decade are devoted to the work [1 9]. However, these works do not consider the issues of optimisation of vibration prote ction parameters and strength of structures on the basis of determination of functional dependencies of forces against deformation and damping against deformation rate for vibration insulation systems and structural elements included in the instrument. The main results given in these works relate to the determination, at best, of resonant frequencies, which is insufficient to optimize vibration protection parameters and diagnose the reliability of devices. The aim. Develop a methodological basis for the use of quality and durability control and diagnostics methods to improve the reliability of the operation of ship information and control systems in extreme operating conditions by optimizing their vibration protection. Results. The basics of modeling the designs of radio-electronic equipment devices for various mechanical influencing factors are described. Description of models and mathematical peculiarities of organization of initial data for modeling is given. When comparing design stresses and allowable stresses, the strength of the product is determined. Allowable stresses are obtained using endurance curves for each material of the device design. Simulation of the panel instrument design under vibration impact is considered and processing of its results is presented. When creating a typical product operation model, the main operating modes and levels of external influencing factors and loads of each mode are determined. The example of the console instrument shows the procedure for modeling strength and determining the value of failure-free operation. It has been found that for a given console device the most complex effect is vibration, since it creates a multi-cycle loading of the structure, which affects the strength of the product as a whole. Practical significance. The proposed approach to determination of structural strength makes it possible to find the number of loading cycles under vibration impact for each element and time operating time, as well as the calculated value of failure-free operation of the console device. This simulation can be performed at any stage of the instrument design.

Structural response and wall thickness design of pulse detonation combustor

This paper deals with the structural response and wall thickness design of pulse detonation combustor. The pulse detonation combustor is a chamber with cylindrical shell structure, which is loaded with internal moving detonation pressure and thermal load. Much higher strain and stress can be excited under moving pressure load than static load. How to choose the attenuation coefficient during detonation pressure were discussed. The results of structural response simulation based on finite element method were compared with analytical result in the literature. The multi-cycle detonation pressure load and thermal load were measured on a pulse detonation engine principle prototype initialed through deflagration-to-detonation transition for the first time. The structural response characteristics of the detonation chamber were studied based on the measured load under different working frequencies. A series of comparison between numerical simulation and experimental measurement were carried out. The wall thickness of the chamber was designed based on the fatigue load spectrum under real detonation load and the chamber’s target fatigue life. Special attention was paid to the mutual influence between the dynamic amplification factor and the wall thickness.

Relationship of deformation meso- and macrostructures types with the staging of damage accumulation in welded joints of stainless steel under high-cycle fatigue

ABSTRACT The fatigue fracture mechanism of spot-welded joints of stainless constructional steel at multi-cycle loading condition is studied using the method of digital images correlation. Analysis of deformation meso- and macrostructures was carried out within the framework of the four-stage scheme of deformation and fracture of welded joints identified in the work. Characteristic fields of displacement vectors are presented and quantitative indicators and duration of damage accumulation stages are determined. On the basis of inverse pseudo-images, new types of deformation structures (trickle and cellular hexagonal) have been discovered.

ДЕФОРМИРОВАНИЕ И РАЗРУШЕНИЕ ЛИПЫ И СОСНЫ ПРИ ИНТЕНСИВНЫХ ДИНАМИЧЕСКИХ ВОЗДЕЙСТВИЯХ

The paper presents the results of dynamic tests under compression of two wood species: linden and pine under loading along and across the fibers. Dynamic tests were carried out using the modified Kolsky method with the realization of multi-cycle loading of the sample during one test. As a result, strain diagrams were obtained for uniaxial stress state taking into account additional loading cycles The use of the multi-cycle loading mode made it possible to obtain a significantly greater degree of the sample deformation than with traditional single-cycle loading. To create a pulse load, a gas gun was used. According to the experimental results, dynamic deformation diagrams were obtained, as well as ultimate strength and deformation characteristics, fracture energy for linden and pine were determined depending on the cutting angle of the samples and the strain rate. A strong anisotropy of the properties of the tested materials is observed: the samples have the greatest strength when a load is applied along the fibers, and the least - across the fibers. A positive effect of the strain rate is noted. The module of the load branch is non-linear and, as a rule, is smaller than the module of the unload branch (while maintaining the integrity of the sample). The nature of the deformation and fracture of the samples strongly depends on the angle of cutting-out. At cutting angle across the fibers, the deformation diagram after reaching a certain threshold value is close to an ideally plastic diagram. At cutting angle along the fibers, the initial portion of the diagrams is close to linear, i.e. elastic deformation takes place. However, after reaching a certain value (“yield strength”), the diagram becomes nonlinear. This kind of behavior takes place in those experiments in which the destruction of the samples occurs. For both wood species, there is a significant excess of energy absorption by samples cut and tested along the fibers, compared with samples cut and tested across the fibers.

Growth of high-density horizontal SWNT arrays using multi-cycle in-situ loading catalysts

Density of horizontal single-walled carbon nanotube (SWNT) array is considered as one of most important index in SWNT-based integrated circuits. However, it is still a challenge to directly obtain horizontal SWNT arrays with ultra-high density on quartz. Herein, we developed multi-cycle in-situ loading catalysts method to directly grow horizontal SWNT arrays with high density on quartz substrate. In this method, Cu catalysts showed much higher efficiency to grow SWNT, which were in-situ loaded through depositing Cu vapor produced by hot copper mesh. Density and size of catalysts could be directly controlled by depositing temperature and time. Moreover, the high efficiency of in-situ loaded Cu catalysts can be maintained after multi-cycle loading, which leads to the linear increase of SWNTs density with loading times. Finally, further optimizing depositing temperature and time, horizontal SWNT arrays with the average density higher than 60 SWNTs/μm and area larger than 8 × 12 mm on quartz have been obtained. This method opens up an opportunity for obtaining SWNT arrays with any density, which shows great potential in the nanoelectronics application in the future.