Friction Elements Research Articles

Thermal Behavior of Conical Friction Element Under Different Contact Pressure Boundaries

Abstract The high temperature generated on the contact interfaces of the conical friction element in clutches due to the sliding frictional heat should be responsible for the synchronization failure. In this study, an analytic model taking account of the capsizing moment and stress singularity at the end of the contact interface is established to solve the contact pressure distribution. Then, a three-dimensional finite element model has been developed to analyze the transient thermal behavior of the conical friction element. The contact pressure and temperature distribution generated along the contact interfaces are investigated and compared between the proposed new model, the combined wear assumption, and the uniform pressure assumption. Furthermore, the variations in temperature obtained from the new model and the other two assumptions are compared to the experimental results. The results show that the temperature simulated by the new model has a good agreement with reality. The maximum temperatures obtained by the new model are 95.53 °C and 71.67 °C, and the measured values are respectively 84.98 °C and 65.46 °C at the measuring position under the given two working conditions.

Analysis of powertrain’s workload during the turning process of a high-speed tracked vehicle

In order to analyze the efficiency of a high-speed tracked vehicle powertrain, it is necessary to understand the powertrain workloads in specific working regimes. Experimental tests are conducted on a specific high-speed tracked vehicle, in various terrain conditions, in order to obtain accurate workload data and isolate the maximum workload regimes. From the power balance point of view, the most demanding working regime is the vehicle turning process, so corresponding test results are analyzed with special attention. The obtained results indicate that the slip of the turning mechanism friction elements greatly influences the character of the power balance change.

The braking performance of pads for high-speed train with rigid and flexible structure on a full-scale flywheel brake dynamometer

The performance of two brake pads with rigid structure (Rigid pad) and flexible structure (Flex pad) were systematically compared and analyzed by braking test on a full-scale flywheel brake dynamometer. 109 brakes were conducted according to test program in China Railway Production Certification (CRCC) standard, including dry condition, recovering brake, static brake, wet condition, and continuous brake, as well as various clamping force to simulate the service of pad on the high-speed train from 50 km/h to 275 km/h of initial brake speed (IBS). Two pads displayed similar tendency of coefficient of friction (COF) when braking at IBS below 200 km/h under dry condition. However, the obvious fading and fluctuation of COF was detected on Rigid pad when the IBS was higher than 200 km/h, stability of COF was just 77%, lower than 91% of Flex pad. More severely, the total wear rate of Rigid pad was 0.13 cm3/MJ, which was 3 times more than 0.04 cm3/MJ of Flex pad. Nevertheless, Rigid pad presented more stable and higher COF under wet condition, and the minimum COF for Rigid pad was 0.262 when braking with 25 L/h of water flow, 2 times higher than 0.12 of Flex pad. All these differences attributed to the adjusting function of pad structure, which gave different contact status on rubbing surface. Flex pad contributed to an intimate contact status with brake disc during braking by adjusting friction elements, resulting in a uniform temperature distribution and stable COF. On the other hand, the intimate contact benefited to the formation of water film during wet braking, decreasing COF observably. This study provides useful information for the structural design of brake pad and braking control strategy for high-speed train.

PHYSICOCHEMICAL ASPECTS OF THE WORK OF PASSENGER CAR BRAKE LININGS. PART II THE EFFECT OF LUBRICATING ADDITIVES

The paper presents the influence of various systems of lubricating additives which determine the performance of the friction materials of brake linings. The base hybrid friction material formulation was modified with various types of lubricating additives. These additives are divided into groups containing commonly used lubricating materials: carbons and sulphides, compounded in various proportions, influencing the formation and structure of the so-called third body layer (TBL) on the surface of the brake disc because of braking. Raman Spectroscopy (RS), time of flight Secondary Ion Mass Spectroscopy (ToF-SIMS) and high-resolution scanning electron microscopy with an X-ray analyser (SEM-EDS) equipped with a focus ion beam (FIB) were used for chemical and morphological analysis of the surface layer of brake disc after breaking tests. The results of the physicochemical analysis of TBL were correlated with the results of tribological tests (according to the SAE-J2522 procedure, commonly known as AK-Master) on a brake dynamometer adapted to the measurements of acoustic signals (NVH – noise, vibration, and harshness). The obtained results confirm the important role played by the so-called third body layer, formed on the surface of the brake disc for safety (COF), durability (wear of friction elements) and the acoustic spectrum accompanying braking.

COMPOSITE MATERIAL WITH CAST IRON MATRIX DESIGNED FOR BRAKE SYSTEMS OF TECHNICAL MEANS OF TRANSPORT

The paper presents the basics of manufacturing and the tribological properties of the developed cast ironceramic composite designed for brake discs or drums. The matrix of the composite consists of GJL-150 grey cast iron used for the production of brake discs. The reinforcing phase is a SiC foam with an activated surface. The use of ceramic foam simplifies the production process because it does not require expensive mixing of the matrix and the reinforcing phase to ensure the homogeneity of the composite. An addition of 10% SiC (λSiC=100-350 Wm-1K-1) improves the thermal conductivity of cast iron (λCI=50-60 Wm-1K-1). The presence of foam elements homogenously distributed throughout the whole matrix volume reduces the wear of both the composite and the counter-sample. The results of comparative studies of contacts between the cast iron and the composite brake disc showed almost a threefold lower wear of the pad and disc and about a 10°C lower temperature in the pad near the friction zone under the pressure of 1 MPa and at a sliding velocity of 0.5 m/s. The significantly lower wear of the friction elements of the brake system will contribute to a reduction in environmental pollution by wear debris, which is required by European Union directives.

Interfacial wear damage mechanism between Ti-alloy and Al-alloy in interference-fit joint and influence of surface coatings: Experimental and numerical study

Interfacial wear in Ti-alloy/Al-alloy interference-fit joint resulting from micro-displacement is considered one of the primary causes of structure failure. This paper described an experimental and numerical study on the interfacial wear damage mechanism between Ti-alloy and Al-alloy in interference-fit joints and revealed the influence of surface coatings. The evolution of friction coefficients (COFs), wear topography and element transfer were adopted as the characterization methods. Ploughing effect (Ti-Al) and adhering effect (Al-Ti) are two main wear mechanisms for uncoated samples. Hard-anodized film has more stable COFs and the film integrity is well maintained. Wear layer has lower COFs but is easier to be peeled off due to better lubrication and poor adhesion characteristics. A wear model considering variable COFs is established by combining energy consumption and adaptive grid technique to simulate the wear scar and predict the wear depth and volume, the predication results are in good agreement with experimental results.

Time fractional calculus for liquid-path dynamic modelling of an isolator with a rubber element and high-viscosity silicone oil at low frequency

Time fractional calculus for liquid-path dynamic modelling of an isolator with a rubber element and high-viscosity silicone oil at low frequency

Mechanical Properties and Constitutive Model of the Cement-Improved Loess under Freeze-Thaw Conditions.

Cement-improved loess (CIL) is used as a common filler for subgrade construction projects in loess areas. The freeze-thaw (F-T) conditions have a significant effect on the stability of cement-improved loess subgrades in seasonally frozen regions. In this paper, the CIL samples, experiencing different numbers of F-T cycles at varying freezing temperatures, were used in consolidated undrained triaxial compression tests to investigate the effect of F-T conditions on the mechanical properties of CIL. The results show the stress-strain curves of CIL are of a strain-softening type with strong elastic brittleness. The initial tangent modulus of CIL increases with the growing confining pressure and gradually decreases with the increase in the F-T cycle number and the decreasing freezing temperature. It loses 46.4% of its original value after the twelfth F-T cycle with the confining pressure of 150 kPa and at the freezing temperature of −15 °C. The strength of CIL decreases with the increasing F-T cycle number, but it gradually tends to keep stable after the sixth F-T cycle. The strength also decreases with the reduction in the freezing temperature. It loses 37.7% of its original value after the twelfth F-T cycle with the confining pressure of 150 kPa and the freezing temperature of −15 °C. To express the nonlinearity correlation between the strength and confining pressure under F-T conditions, the Weibull function was applied and a nonlinear Mohr-Coulomb strength criterion was proposed. Through introducing a breakage rate function and a local strain coefficient, a binary-medium constitutive model consisting of bonded elements (soil-particle cohesion) and frictional elements (soil particles or soil aggregations) was established to describe the stress-strain relationships of CIL under F-T conditions. The test results indicated that the model can well describe the strain-softening phenomenon of the stress-strain curve of CIL and reflect the breakage mechanism of CIL.

Complex Heat Exchange in Friction Steam of Brakes

In this article the structural features of friction pairs of brakes are analyzed. Heat transfer processes with new boundary conditions are described analytically with the addition of flow conditions and the appearance of a boundary thermal layer to convective heat transfer. The joint action of heat conduction and convection fields is presented. The release of heat during friction is due to the destruction of adhesive bonds in the actual contact zones, and the stress–strain state of micro-roughnesses. It should be said that due to the presence of accompanying transfer processes, complex heat transfer is much more complex compared to purely conductive, convective, and radiative heat transfer, which significantly complicates its analytical and experimental study. In this regard, the processes of complex heat transfer are currently studied little. From the point of view of non-equilibrium thermodynamics, the main task of describing the transfer process is to establish a relationship between the magnitude of the specific flux and the surface-volume temperatures that it causes in the metallic friction elements of the brakes. Additionally, as a result, an assessment of conductive and convective heat transfer in friction pairs of brake devices was made.

Effect of ferrite grain shape in friction element welds on cross tension strength

High-strength steels (HSSs) have been increasingly used in car bodies in order to simultaneously achieve the weight reduction and high collision safety of vehicles. In resistance spot welding, which is widely used for joining car bodies, low cross tension strength (CTS) of joints using HSSs is a problem. In our previous study, we focused on friction element welding (FEW) of HSSs to improve CTS and reported that the poor local ductility of the area quenched from two-phase temperature region (inter-critically annealed and quenched area) due to the presence of soft ferrite (α) and hard martensite (M) causes a decrease in CTS of FEW. The local ductility of steels with dual phase structure is known to be affected by the microstructural morphology. Therefore, in this study, we prepared joints of FEW with both the equiaxial α (C30) and the acicular α (C30L) in dual phase structure by controlling parent structures prior to the inter-critical annealing and quenching during FEW. C30L exhibited the higher CTS than C30. C30L fractured along the thickness direction of the lower sheet from the inter-critically annealed and quenched area near the edge of the joint to the softened area of heat affected zone, while C30 fractured along the inter-critically annealed and quenched area; however, the dimples were observed on the fracture surfaces irrespective of materials. Taking into account the fact that C30 and C30L showed no difference in the hardness distribution of the joints and the hardness difference between α and M hardness, it was suggested that morphology of α plays an important role in determining CTS. It is inferred that the local strain concentration in the inter-critically annealed and quenched area is relaxed by the presence of fine acicular α, which leads to the improvement of the local ductility, i.e. CTS.

Numerical study of chipping during friction element welding

Chipping phenomena during the friction element welding (FEW) process is investigated using finite element modeling. Intensive chipping is observed in a cast aluminum alloy when it is welded to a steel alloy. A Coupled Eulerian-Lagrangian scheme is used to investigate the underlying mechanisms enabling chipping. It is found that chipping is severe when the friction element initially contacts the workpiece and tends to reduce as the former progresses into the latter. Chipping decreases with the increase of rotational speed and the decrease of linear feed rate. Chipping can be minimized by using high rotational speeds coupled with low feed rates.

Mechanical Properties and Binary-Medium-Based Constitutive Model for Coral-Reef Limestone Samples Subjected to Uniaxial Loading

The mechanical and deformation mechanism of coral-reef limestone is vital for the stability and safety of infrastructures built on the ground composed of those materials. Upon loading, strain softening behavior of the coral-reef limestone occurs, usually due to the nonuniform cementation distribution, and the cementation within the samples may break up gradually and reduce the bearing capacity. In order to study their mechanical features, uniaxial compression tests were carried out in this study, and, based on the test results, a binary-medium-based constitutive model was formulated, in which, the sample was idealized, respectively, as the bonded and frictional elements. The bonded elements are composed of strong cementation and may gradually break up to transform into the frictional elements, both of which bear the external loading conjointly. In the new model, the parameters determination method was adopted based on uniaxial compression testing, and comparisons were made between the tested and computed results, which demonstrate that the model can reflect the salient features of coral-reef limestone samples, such as the strain softening and bonding breakage during the loading process. The study can provide a basis for the basic design of coral-reef limestone.

Investigating the Effects of SiC Abrasive Particles on Friction Element Welding

The use of dissimilar materials is increasing exponentially in the automotive industry due to the possibility of achieving weight reduction from the multi-material design. Friction Element Welding (FEW) is an advanced solid-state joining technique employed for joining dissimilar materials using a friction element. The processing time of FEW is relatively higher than a few of its competitive joining techniques, with the cleaning step contributing to the majority of the processing time. The current research investigates the effect of SiC abrasive particles on the processing time of FEW and its joint strength. The experimental results show a decrease in the processing time and an increase in the joint strength by reducing the abrasive particle size and the volume fraction of the abrasive particles used. When subjected to tensile loading, one of the samples showed interfacial failure, whereas others exhibited button pull-out failure. The best case from the experiments was chosen for comparison with the standard FEW test, which did not involve abrasives. The comparison shows a 14.3% reduction in processing time with a 10.8% increase in joint strength using abrasives. Inspection of the microscopic images revealed the presence of the SiC phase at the periphery of the friction element around the weld zone and the formation of a defect-free joint. The microhardness test detected a higher hardness along the weld zone for the case involving abrasives compared to the standard FEW test. The hardness data support the higher joint strength results obtained for the FEW joints formed with the abrasives.

Numerical Study of Temperature Evolution During Friction Element Welding

Abstract Welding of dissimilar materials is critical in industries where mixed materials with high strength-to-weight ratios are urgently needed. Friction element welding (FEW) is a promising solution, with the ability to join high strength materials for a wide range of thicknesses with low input energy and a short processing time. However, the temperature evolution and the influence of different processing parameters remain unclear. To bridge this knowledge gap, this work develops a coupled thermal–mechanical finite element model to study the FEW process. The simulation results agree well with the experimental measurements of material deformation and transient temperature evolution. It is found that the friction element’s rotational speed has the greatest impact on friction heat generation, followed by the processing times for different steps. The aluminum layer is heated during the penetration and cleaning steps, thus a lower rotational speed during the penetration step can help prevent the aluminum layer from undesired overheating. The steel layer and the friction element are mainly heated during the cleaning and welding steps. The strong heating, potentially melting, will be beneficial to the friction element’s plastic deformation and bond formation. To enhance the heating of the steel layer and the friction element, faster rotational speeds or longer processing periods could be employed during the cleaning and welding steps. The results by this study establish the relationship between processing conditions and the temperature evolution of different parts, which will guide the design and optimization of the FEW technique for various applications.

Hysteresis Behavior Modeling of Hard Rock Based on the Mechanism and Relevant Characteristics

The modeling of cyclic behavior in rock remains a challenge due to complex deformation characteristics. This paper studied the mechanical behaviors of granite samples under uniaxial cyclic loading and unloading through cyclic compression tests and acoustic emission (AE) monitoring. Then, a comprehensive body that consisted of an elastic element, plastic element, and friction element was proposed to describe the stress–strain relationship with respect to cyclic behavior, in which the friction element was connected in parallel with the serial combination of the elastic element and plastic element. Finally, the parameters of the proposed model were calibrated based on the mechanism analysis and backpropagation (BP) neural network. Results show that the behavior during unloading is primarily elastic and is accompanied by the obstruction of friction. During reloading, the behavior changes from elastic to elastic–plastic before and after the Kaiser point. The tangential modulus of the elastic element is dynamic in a linear positive correlation with elastic strain and a linear negative correlation with plastic strain; specifically, the elastic strain controls the variation process of the elastic modulus while the plastic strain determines the lower limit. The constitutive law of the plastic element is expressed by a logistic function, which means that the plastic strain increases in a trend of acceleration–deceleration. The friction element plays a major role in processing the massing effect, and the plastic element is prompted before the historical maximum stress, which reflects the ratcheting effect and Felicity effect. The reliability of the proposed constitutive model is confirmed by the comparison of the simulated stress–strain curves with the experimental curves.

A Binary Medium Model for Frozen Silty Sand Simplified by Breakage Parameter

In order to investigate the strength-deformation characteristics of frozen silty sand, the triaxial compressive strength tests of saturated frozen silty sand under different fine particle contents were carried out, and the binary medium theory was introduced to interpret the stress-strain relationship. Due to the characteristics of the existing binary medium model with many parameters and complicated determination method, a simplified binary medium model based on breakage parameter is proposed. The derived model was verified by the triaxial tests of frozen silty sand. The results show that the stress-strain relationship can be divided into three stages with the increase of axial strain, namely, linear elastic deformation stage, plastic deformation stage, and strain softening stage. All three stages can be well explained by the transformation theory of bonded element and frictional element with the binary medium model. In the linear elastic deformation stage, the external stress is mainly borne by the bonded element. In the plastic deformation stage, the stress sharing ratio of the bonded element decreases and that of the frictional element increases. In the strain softening stage, the stress sharing ratio of the bonded element decreases rapidly, while that of the frictional element increases rapidly. Under the same confining pressure, both deviator stress and the maximum values of bulk expansion decrease, while the shear strength decreases linearly with the increase of fine particle content. By comparing the measured deviator stress in triaxial test with the calculated values of binary medium constitutive model simplified by breakage parameter, the proposed model can better simulate the stress-strain relationship of frozen silty sand. The results of the study can provide some theoretical reference for the constitutive model of seasonal frozen soil.

Research on the Material Compatibility of Elastomer Sealing O-Rings

Significant attention has been paid to combustion engines for the utilization of new liquid fuels and their testing at the present. Research activities in ensuring the optimum function of the engine by watching sealing and distribution rubber elements, which are part of fuel systems, should be an integral part of fuels research. When evaluating fuels utilization in combustion engines, the issue has to be judged in a complex. However, when using biofuels in combustion engines, it is not always simple owing to the different degradation properties of these products. Elastomer material is not entirely resistant to various types of fuels. More or less, it is possible to expect changes in its mechanical properties. For the evaluation of the functionality of elastomer sealing elements based on ACM, HNBR and FVMQ type O-rings with pure and blended fuels, the evaluation of changes in mass, hardness Shore A, permanent deformation CS, tensile strength TS and deformation Eb after immersion with the tested fuel is mainly used. Permanent changes were found by the tests. The degradation of elastomer O-rings was more pronounced for the tested fuels containing ethanol, iso-butanol, n-butanol, methanol and dodecanol. HVO 100 fuel containing hydrotreated vegetable oil did not show significant degradation of elastomer O-ring seals. Of the O-rings tested, the FVMQ type O-rings showed the best performance in terms of material compatibility for all fuels tested.

The role of recycled rubber inclusions on increased confinement in track substructure

Large cyclic and impact loads exerted by heavy haul trains can cause significant deformation and degradation of ballast, leading to poor track geometry and track instability. The application of recycled rubber elements in track substructure to increase confinement of both sub-ballast and shoulder ballast is an innovative solution. In Australia, there is a lack of adequate recycling that leads to large stockpiles of waste tyres. In addition, the reusability of giant off-the-road tyres discarded from mining industry is seriously limited due to their size and weight (over 3.0 m in diameter weighing about 3 tonnes). This study presents a real-size prototype test using the Australia’s first and only National Facility for Cyclic Testing of High-speed Rail to investigate the performance of a hybrid track where tyre-infilled granular waste materials were placed below the ballast layer to replace the traditional capping layer, and arc segments cut from the giant off-the-road tyres were used to confine shoulder ballast. The performance of this hybrid track is compared with an unreinforced track conducted earlier at the same loading conditions. Test results demonstrate that the use of this hybrid system with recycled rubber elements significantly decreases vertical and lateral displacements of ballast and effectively controls the distribution of vertical stress with depth, while reducing vibration and ballast breakage. The outcomes of this study provide a unique solution in a circular economy perspective to strengthen railways to cater for heavier and faster freight trains.

Effective use of motor oil resources of the tractor of the company “Claas” in the conditions of Uzbekistan

AnnotationThe article describes in detail the reliable operation of modern high-performance and complex “CLAAS” techniques, the correct selection of lubricants and compliance with the optimal operating procedure, as well as the results of the analysis of friction elements of motor oils. It is necessary to compare the quality indicators determined on the basis of research and the concentration of friction elements in the oil with standard values. In order to determine the recommended engine oil change intervals in the engines of CLAAS tractors, it is necessary to determine their quality indicators and the concentration of friction elements in the oil. In order to maintain the performance of the oil, it is recommended to add additives during operation. Study of wear conditions of oils used in internal combustion engines. Determination and justification of the limit working life of oils used in internal combustion engines. Study and justification of properties of interchangeable oils used in internal combustion engines. It is necessary to develop scientific justification and recommendations for increasing the service life of the oils used in internal combustion engines.

PHYSICOCHEMICAL ASPECTS OF THE WORK OF PASSENGER CAR BRAKE LININGS. Part I: THE EFFECT OF FRICTIONAL ADDITIVES

The paper presents the influence of various systems of abrasive additives which determine the performance of the friction materials of brake pads. A friction material was used for the tests, in which the base recipe was modified with various types of abrasive additives: 1. “low steel” – of low steel content, containing aluminium and chromium oxides; 2. “hybrid” – containing in addition to abrasive components from the low steel family, abrasive components such as zirconium silicate, magnesium oxide or iron oxides, which are characteristic of the family of asbestos-free organic materials (NAO); and 3. “mild hybrid” – containing abrasive components found in the friction materials of the NAO family, on the formation and structure of the so-called third body on the surface of the brake disc as a result of braking. High-resolution scanning electron microscopy with an X-ray analyser (SEM-EDS) equipped with a focus ion beam (FIB) was used to study film thickness, morphology, and chemical composition. The results of the physicochemical analysis of the third body were correlated with the results of tribological tests on a brake dynamometer adapted to the measurements of acoustic signals (NVH – noise, vibration and harshness). The tests were carried out in accordance with the SAE-J2522 procedure, commonly known as AK-Master. The obtained results confirm the important role played by the so-called third body, formed on the surface of the brake disc for safety (COF), durability (wear of friction elements) and the acoustic spectrum accompanying braking.