Accumulation Of Residual Deformations Research Articles

Переходные участки бесстыкового пути, примыкающие к стрелочным переводам

Purpose: consider the problem of interaction between turnouts and adjacent sections of a seamless railway track. Methods: statistical data analysis. Results: an analysis of the results of domestic and foreign studies has been carried out, which show that in such areas there is a jump with subsequent extrusion of material of less rigidity and an increase in the slope of the elastic unevenness, i. e., an undesirable phenomenon occurs — a shock wave. The impact force depends on the mass of the rolling stock and the speed of movement, the geometric evenness of the rail track and the chosen approaches to designing the transition zone as a whole. Jump and mainly occurs due to compression and pushing out of structural layers and materials of lower rigidity in the under-rail area. The impact force depends on the mass of the rolling stock and the speed of movement, the geometric evenness of the rail track and the chosen approaches to designing the transition zone as a whole. Jump and mainly occurs due to compression and pushing out of structural layers and materials of lower rigidity in the under-rail area. Shock waves caused by uneven rigidity of sections have negative consequences (the appearance of deviations in level, subsidence, distortions, increased intensity of rail wear, the appearance of rail defects), which increase the cost of maintenance of the railway track. An analysis of the accumulation of residual deformations has been carried out, which shows the systematic formation of geometric irregularities in adjacent areas in the turnout area. Practical importance: from the point of view of the design of the transition zone, the expected advantage will be the differentiation of structural materials and elements and their influence on achieving the optimal gradation of railway track rigidity in the vertical and horizontal (transverse, longitudinal directions), selection of the optimal ratio of the mechanical properties of individual elements of the superstructure structure. It should also be noted that it is necessary to conduct an additional feasibility study of the feasibility of constructing transition sections in the area where the track and switches meet, taking into account the operational features of individual railway lines.

Собственные напряжения в рельсах, возникающие вследствие эксплуатации железнодорожного пути с отступлениями по его содержанию

Purpose: approaches to the maintenance of the railway track play a significant role in the interaction between the track and the rolling stock. The analysis [1–10] shows that existing methods for assessing the impact of rolling stock on the track have not completely resolved the issues of taking into account the residual deformation of the track, which does not allow us to have the most complete understanding of the ongoing interactions and processes between the railway track and the rolling stock in real operating conditions. In developing the issue of the need to take into account the residual deformation of the track, deviations in the geometry of the rail track in the profile, the article considers the “intrinsic” stresses in the track that are not under the influence of any load, arising as a result of the operation of a railway track with deviations in its contents. Methods: statistical analysis of the accumulation of residual deformations of a section of the railway track, review of existing methods for assessing the impact of rolling stock on the track, simulation modeling of the stress-strain state of the rail. Results: an analysis of the accumulation of residual deformations of a section of the railway track, a review of existing methods for assessing the impact of rolling stock on the track, modeling of the stress-strain state of a rail under load in two states (straight beam, curved beam) were carried out. Practical significance: the results can be applied when solving the problem of interaction between rolling stock and the railway track.

Оценка интенсивности накопления остаточных деформаций основной площадки земляного полотна на участках обращения тяжеловесных и длинносоставных поездов

Objective: the article presents an assessment of the intensity of accumulation of residual deformations of the main platform of the roadbed in the areas of circulation of heavy and long-composite trains formed from wagons with an axial load of up to 25 tons. Methods: measurements of residual deformations of the main site of the roadbed were carried out by geodetic methods by laying a closed leveling course. To do this, each experimental site was equipped with soil stamps installed on the main site of the roadbed and reference points. The measurements were carried out from 30.05.2022 to 08.11.2023. Results: as a result, the dependences of the accumulation of residual deformations of the roadbed on the missed tonnage have been established for various railway track structures, operating conditions and engineering and geological conditions. Practical importance: measures are proposed to reduce the intensity of accumulation of residual deformations of the main site of the roadbed.

Experimental study on the freezing-thawing behavior of compacted earth

Most of compacted earthen constructions are located at temporary and seasonal frozen areas, consequently exposed to repeated freezing-thawing (F-T) environment induced by significant temperature fluctuations. The F-T cycles can cause severe damage to the compacted earthen materials and reduce the structure’s durability. In this paper, a series F-T tests were performed in order to study the damage mechanism of the compacted earthen materials subjected to F-T cycles. The experiments were carried out under two confining pressures (σc= 0 kPa and 50 kPa) and three freezing temperatures (TF=−5℃, −8℃ and −13℃), with a thawing temperature of TT= 9℃. Evolution of elastic moduli and accumulation of irreversible strain at the end of each F-T processes were analyzed through cyclic loading–unloading tests under undrained condition. Results indicate that each F-T cycle could be characterized by main six stages, whose physical meaning has been explained through a thermodynamic approach. With increasing number of F-T cycles, a growth of the Young’s modulus was observed when the material was in a frozen state, and the opposite was found for the thawed state. This may be explained by an increase in macro-porosity as F-T cycles progress, which would be in line with the accumulation of residual deformation and the increase of freezing and thawing temperatures. The applied confining pressure was eventually found to provide a positive resistance against permanent deformation. This discovery can provide experimental support to the safety design of earthen wall situated in cold regions.

Study on distress of airport pavement foundation and solution applied to Noi Bai international airport

The service quality and life of the runway, taxiway and apron pavement system heavily depends on the condition of its foundation, including base and/or subbase layers and subgrade. In the state of water-saturated condition, the strength of foundation would decline significantly, then inducing the downgrade of overall strength of the pavement. In the long term, the impacts from adverse environmental conditions and aircraft wheel loading will mix-up the materials of foundation layers, leading to the degradation of the original physical and mechanical properties of the original designed material. Furthermore, the accumulation of residual deformation and appearance of voids in the granular material can formulate the large holes beneath cement concrete slab. That, in turn, changes the load bearing model of the slab compared to the original design and causes the structural damage of the slab and threatens flight safety. Due to the complication of pavement foundation, the traditional treatment countermeasures usually need a long time for completion, while the airfield system often requires short and high-quality repair time. Therefore, there should be special solutions to satisfy the practical application. The article analyzes the cause, proposes the solutions for pavement foundation treatment and presents an initial application to Noi Bai International Airport. The findings of this study could be critical and significance basis for both academic and practical applications to maintain the service quality of airport construction infrastructure in Vietnam.

Elastic-plastic deformations of single-turn solenoid under cyclic effects of a strong pulsed magnetic field

The processes of destruction of a monolithic single-turn solenoid with multiple generation of pulses of a strong magnetic field with an amplitude of 15- 40 T are considered. Based on models of the electromagnetic field and elastic-plastic deformation in a continuous medium, two modes of destruction during the cyclic process of generating pulses of a strong magnetic field are investigated: accumulation of residual deformation and low-cycle fatigue in the surface layer of the conductor. It is shown that both mechanisms of destruction act simultaneously. At the same time, the first of them limits the resource of the inductor at the level of hundreds of pulses. The destruction by the mechanism of low-cycle fatigue becomes the main factor limiting the inductor's life in the case of oscillatory magnetic field pulses with relatively small attenuation at induction amplitudes below 20 T. The resource of the product in this case is estimated within 103-104 pulses.

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.

Energy-based assessment of cyclic liquefaction behavior of clean and silty sand under sustained initial stress conditions

In practical engineering, sand deposits containing some finer particles usually sustain an initial static shear stress. This study investigates the sustained initial stress effect on liquefaction response of saturated sand through conducting cyclic undrained triaxial tests. The obtained response of sand samples containing a small amount of silty fines is compared to that of clean sand under similar relative densities. The results exhibit that various stress conditions result in two response patterns named as cyclic mobility and residual deformation accumulation. It is shown that the addition of silty fines can either enhance or reduce the cyclic liquefaction resistance of sand, depending on the fines content, while the sustained initial stress plays a beneficial role in resisting cyclic failure for samples with or without the addition of fines under otherwise identical testing conditions. It is also found that the dissipated energy accumulated in both the silty and clean sand follows a power-law relationship to the generated residual pore pressure during cyclic loading. A unified relationship is further established between the liquefaction resistance and dissipated energy, which may be useful for developing an energy-based assessment of in-situ soils using strength data from laboratory experiments.

Undrained Cyclic Response and Resistance of Saturated Calcareous Sand considering Initial Static Shear Effect

Sand elements in the natural or manmade field have often undergone initial static shear stresses before suffering cyclic loading. To explore the effect of static shear stress, a series of undrained cyclic triaxial tests were performed on dense and loose calcareous sand under different initial and cyclic shear stresses. The triaxial test results are used to describe the effect of static shear stress on the cyclic response of the calcareous sand with different relative density. Cyclic mobility, flow deformation, and residual deformation accumulation are the three main failure modes under varying static and cyclic shear stress levels. The cyclic resistance of dense sand is greater than that of loose sand, but the initial static stress has different effects on the cyclic resistance of the two kinds of sand. The dense sand owns a higher cyclic resistance with SSR increasing, while for the loose sand, 0.12 is the critical SSR corresponding to the lowest value of the cyclic resistance. The dense sand has more fast accumulation of dissipated energy, compared with loose sand. Additionally, an exponential relationship is established between static shear stress, relative density, and normalized energy density.

Метод оценки коэффициента формы зерен щебня, применяемого в балластном слое железнодорожного пути

A decrease in the strength properties of crushed stone in combination with an increase in its contamination during tonnage operation reduces the load-bearing capacity of the ballast layer and intensification of the accumulation of residual deformations of the track. The strength properties of crushed stone ballast depend on the shape (rolling edges) of crushed stone grains. The paper discusses the theoretical and practical foundations for determining the shape of crushed stone ballast grains. As an indicator characterizing the shape of crushed stone grains, it is proposed to use the grain shape coefficient indicator. The grain shape coefficient refers to the ratio of the actual specific surface of the grain to the specific surface of a perfectly round particle of the same volume. The paper proposes a method for determining the specific surface based on the Kozeni-Karman theory of the flow of a liquid or gas through a granular layer and the equation relating the water permeability of a porous medium to its specific surface. The basic design of the device for the specific surface area of crushed stone ballast grains is presented. The article describes and presents the results of the experiment on calibration of the device, establishes recommended and boundary conditions for its use, as well as the results of the experiment to determine the specific surface in experiments with crushed stone of category II according to GOST 7392-2014 in comparison with an alternative method of measuring the specific surface of crushed stone grains.

Failure mechanisms of sand under asymmetrical cyclic loading conditions: experimental observation and constitutive modelling

In practical engineering, natural soil deposits often sustain an initial driving force prior to cyclic shear, owing to earthquakes, traffic and waves; such asymmetrical loading conditions may significantly affect the liquefaction susceptibility and failure mechanism of sand. To understand the typical cyclic liquefaction responses, comprehensive asymmetrical cyclic loading tests were conducted on sand samples subjected to either compressional or extensional static stress. The results indicated that different stress conditions can result in three distinct failure mechanisms: flow liquefaction, cyclic mobility and residual deformation accumulation. According to the experimental observations, an anisotropic sand model was developed within the framework of the anisotropic critical state theory. The model employed a fabric-dependent dilatancy, and accounted for the effects of the fabric evolution and accumulated loading index on the plastic hardening, in order to better reflect the cyclic degradation of the plastic modulus. The predictive capacity of the model was confirmed through undrained monotonic test results for samples with different densities. Comparisons between the model responses and experimental results indicated the excellent capabilities of the developed model in terms of capturing the typical deformation, strength and fabric characteristics of different cyclic failure mechanisms of sand under either symmetrical or asymmetrical loading conditions.

Интенсивность накопления остаточных деформаций железнодорожного пути, эксплуатируемого в сложных природно-климатических условиях

Objective: To analyze the results of observations conducted to assess the intensity of the accumulation of residual deformations in the railway track structure operated in severe natural and climatic conditions (the observation site is located above the Arctic Circle). The following were also taken into account: the railway track design (type of intermediate fasteners, track slab, condition of the ballast bed), the railway line scheme, the tonnage handled, the train speed and the axle load. Methods: Mathematical statistics, data processing. Results: The dependences of the railway track deformation and strength properties, including the tonnage handled, have been obtained. Practical importance: The presented observation results of the assessment of the intensity of deformation accumulation in the railway track structure operated in the severe natural and climatic conditions of the North of the Arctic Circle indicate that the use of increased axle load wagons will entail a significant reduction in overhaul life and an increase in the track maintenance operating expenditures

Comparison of cyclic liquefaction behavior of clean and silty sands considering static shear effect

In practical engineering, liquefiable sand deposits in natural or manmade slopes, dams, and embankments may contain a certain amount of silty fines and often sustain a static shear prior to subsequent cyclic loading. To understand the effect of static shear stress on the cyclic liquefaction behavior of silty sand, a small amount of crushed fines was added to clean sand, and a series of triaxial tests considering a wide range of static and cyclic shear stress levels were performed. The results indicate that different stress conditions result in two liquefaction failure patterns for silty sand: cyclic mobility and residual deformation accumulation. A comparison of the liquefaction responses of silty and clean sands with the same relative density confirms that the former typically has a moderately higher cyclic resistance than the latter, which can be explained by the reinforced effect of fines on the soil skeleton. It is also demonstrated that the flow deformation type behavior accompanied by rapid development of pore pressure and severely degraded stiffness is more prominent in clean sand, which is responsible for the continuous decrease in its liquefaction resistance when the extensional static stress increases. Furthermore, a unique correlation of equivalent modulus versus cyclic strain amplitude is observed, which depends significantly on the static shear stress level but relatively insensitive to the addition of fines at least up to the considered fines content.

Functional and Structural Fatigue of Pseudoelastic NiTi: Global Vs Local Thermo-Mechanical Response

Functional and structural fatigue properties of a pseudoelastic NiTi alloy were analyzed at the light of local non-homogenous thermo-mechanical response, resulting from Luder’s-like transformation bands. To this aim, in-situ full-field strain and temperature measurements were made during fatigue tests. Structural and functional fatigue damage phenomena were studied by analyzing the evolutions of strains and temperature at the sample scale as well as within the transformation bands. Marked losses in the pseudoelastic recovery capabilities were recorded, mainly occurring in the first loading cycles, leading to material stabilization after about 200 cycles. Very large differences between the two scales were observed, that is, reduction of pseudoelastic recovery at the global scale is attributed to the accumulation of residual deformation in the transformation bands. These local effects tend to vanish for strains beyond the stress-induced transformation regime, due to the saturation of martensitic bands. The effects of local deformations on the structural fatigue properties, in terms of strain-life curves, were also analyzed. It was demonstrated that localized strains play a very important role on the evolution of structural damage, especially within the pseudoelastic regime of the alloy, and they represent the key to understand unusual strain-life curves at the global scale.

Experimental Research on Inhibition of temperature to inverse martensitic phase transformation of NiTi Shape Memory Alloy

The effects of temperature changes, load cycles, and amplitude changes on the mechanical properties of NiTi shape memory alloys such as the attenuation of energy dissipation capacity, equivalent damping ratio, and residual strain were studied experimentally. Experimental results show that: under different temperature and amplitude, the shape memory alloy achieves stable performance after 10 cycles, and the attenuation of energy dissipation capacity mainly occurs in the first 6 cycles; as the temperature decreases or the number of cycles increases, equivalent damping ratio tends to decrease; When the temperature decreases near the completion temperature of austenite transformation, the residual strain is significantly affected. Even if the strain amplitude is small, residual deformation accumulation will occur, inhibiting the occurrence of reverse martensite transformation, and it is not good for the super-elasticity of SMA.

Liquefaction of sand under monotonic and cyclic shear conditions: Impact of drained preloading history

In-situ sand deposits inevitably undergo a preloading history caused by factors such as overlying structures, adjacent construction work, or repeated sedimentation and erosion; this will in turn affect their mechanical behavior and liquefaction susceptibility during subsequent loading. An experimental program was developed to explore the potential influence of the drained preloading history on the undrained response of sand subjected to both monotonic and cyclic loadings. The results indicate that the shear strength, dilatancy, and stiffness characteristics in monotonic tests depend on the relative directions of the drained preloading and subsequent undrained shearing. Two typical types of behavior are observed and identified in the cyclic tests, i.e., cyclic mobility and residual deformation accumulation failure, depending on the stress state prior to the undrained cycling. The cyclic resistance is quantified based on a failure criterion defined in terms of the triggering of flow behavior, and it is compared to that determined using a criterion of specified strain threshold. In particular, the direction–wise (compressional or extensional) influence of the preloading history on the liquefaction resistance and pore pressure generated in sand during cyclic loading agrees well with that observed during monotonic loading. Furthermore, a correspondence between the cyclic and monotonic tests can be derived, and a unified approach is proposed to evaluate both the monotonic and cyclic responses, irrespective of the drained preloading history.

Size Effect of the Post-Peak Cyclic Behavior of Plain Concrete in Uniaxial Tension with Acoustic Emission Technique

Abstract At present, studies about the size effect of concrete mainly focus on macroscopic mechanical behaviors like strength and fracture energy, while research on the size effect of the cyclic nonlinear properties of concrete is very rare. To further analyze the ambiguous concept of specimen size, three types of precut cylindrical concrete specimens with the same diameter but different heights, the same height but different crack depths, and the same aspect ratio but different volumes are used for the uniaxial post-peak cyclic tensile test. At the same time, the acoustic emission (AE) device is used to monitor and collect the AE signals in the loading process. According to the test results, no size effect exists in the accumulation of residual deformation, but the degradation of the unloading modulus is related to the specimen diameter. Meanwhile, the Kaiser effect is found in the analysis of AE signals. After the data analysis, a post-peak cyclic tensile model of concrete is proposed based on the size effect and damage evolution. The quantitative relationship among the model parameter, specimen aspect ratio, and damage is calculated. Finally, a good comparison is found between the predicted model and experimental result.

Studying the railroad track geometry deterioration as a result of an uneven subsidence of the ballast layer

A method for calculating impairment of the track geometry under influence of dynamic loads in the course of passing the track unevenness by the rolling stock was developed. The method takes into consideration interrelated short-term processes of dynamic interaction and long-term processes of subsidence of the ballast layer in a mutual influence on each other. Mathematical model of dynamic interaction of the track in the form of a planar three-layer continual beam system with a two-mass discrete system corresponding to the rolling stock is the basis of the first part of the method. This model makes it possible to simulate dynamic loads from individual sleepers to the ballast when the rolling stock passes geometric unevennesses and the track elasticity unevennesses.The second part of the method is based on the phenomenological mathematical model of accumulation of residual deformations formed using the results of laboratory studies of subsidence of individual sleepers in the ballast layer. Peculiarity of this model consists in taking into consideration not only uniform accumulation of residual subsidence from the passed tonnage but also presence of a plastic component of subsidence which depends on the maximum stresses in the history of ballast loading by each sleeper.A new theoretical mechanism of development of the track unevenness was proposed. It takes into consideration not only residual subsidences of the ballast layer but also appearance of gaps under sleepers resulting in a local change of the track elasticity. This mechanism enables taking into consideration the ambiguous influence of subsidences with occurrence of gaps under the sleepers. Subsidence causes an increase in dynamic loads on the track and the ballast layer on the one hand and onset of the gap causes a decrease in the track rigidity and corresponding reduction of dynamic loads on the other hand.Practical application of the developed method was demonstrated on an example of quantitative estimation of long-term uneven subsidences of the ballast layer when changing the sleeper diagram

Mullins Effect and its Reversibility for Zinc Dimethacrylate-Reinforced Thermoplastic Vulcanizates Based on a Ethylene-Vinyl Acetate Copolymer/Nitrile-Butadiene Rubber Blend

The Mullins effect during uniaxial compression tests, together with its reversibility, of ethylene-vinyl acetate copolymer (EVA)/nitrile-butadiene rubber (NBR)/zinc dimethacrylate (ZDMA) thermoplastic vulcanizates (TPVs) were investigated systematically. The experimental results indicated that the Mullins effect could be observed during the cyclic uniaxial compression tests and was accompanied with stress softening, residual deformation accumulation and hysteresis. The reversibility of the Mullins effect showed a temperature-dependent feature and was enhanced with increasing temperature.

The complex phenomenological model for prediction of inhomogeneous deformations of railway ballast layer after tamping works

The given article considers the method of calculating the track geometry deformation with respect to uneven accumulation of residual deformations along the track. The technique proposes two significant changes in existing approaches to calculating the efficiency of the ballast layer. The transition from the approach of allowable stresses design in the ballast layer to the deformative approach of accumulations of track geometry deformations allows us to draw conclusions regarding the intervals of track tamping and the duration of ballast layer life cycle. The transition from the determinative to probabilistic approaches makes it possible to draw conclusions not only from the average unevenness, but also with regard to all possible facts of unevenness. The method is based on the mechanism of sudden and gradual deformations occurrence, which depends on a number of key factors: dynamic stresses on the ballast, non-uniformity of track elasticity, performance of current maintenance work. Based on the experimental studies results, the dependencies of sudden deformations and the intensity of gradual deformations on the level of stress on the ballast layer were established. The experimental results of the influence of the sub-ballast base elasticity on the intensity of accumulation of residual deformations are shown. On the basis of the developed method, the prediction of track geometry deterioration for a given structure of the track, the rolling stock and the permissible level of geometric deviations for track maintenance is presented.