Friction Properties Of Materials Research Articles

Impact of Sacrificial Hydrogen Bonds on the Structure and Properties of Rubber Materials: Insights from All-Atom Molecular Dynamics Simulations.

The inclusion of sacrificial hydrogen bonds is crucial for advancing high-performance rubber materials. However, the molecular mechanisms governing the impact of these bonds on material properties remain unclear, hindering progress in advanced rubber material research. This study employed all-atom molecular dynamics simulations to thoroughly investigate how hydrogen bonds affect the structure, dynamics, mechanics, and linear viscoelasticity of rubber materials. As the modified repeating unit ratio (β) increased, both interchain and intrachain hydrogen bond content rose, with interchain bonds playing a predominant role. This physical cross-linking network formed through interchain hydrogen bonds restricts molecular chain movement and relaxation and raises the glass transition temperature of rubber. Within a certain content of hydrogen bonds, the mechanical strength increases with increasing β. However, further increasing β leads to a subsequent decrease in the mechanical performance. Optimal mechanical properties were observed at β = 6%. On the other hand, a higher β value yields an elevated stress relaxation modulus and an extended stress relaxation plateau, signifying a more complex hydrogen-bond cross-linking network. Additionally, higher β increases the storage modulus, loss modulus, and complex viscosity while reducing the loss factor. In summary, this study successfully established the relationship between the structure and properties of natural rubber containing hydrogen bonds, providing a scientific foundation for the design of high-performance rubber materials.

The effect of sand-crumb rubber mixture treatment on the seismic response of a low-rise building located on liquefiable soil

One of the most effective measures to reduce earthquake risks in high-seismic areas is to reduce the input forces caused by earthquakes to the structure. The properties of rubber materials in geotechnical projects are energy absorption, dynamic deformation change as well as damping of latent energy in loads, high shear modulus and damping ratio, easy access and their economic nature. In this research, with finite difference modeling, the effect of using sand- crumb rubber layer on the seismic behavior of the model has been obtained. In the following, by changing the thickness and depth of the sand-crumb rubber layer, the seismic behavior such as floor displacement and internal forces have been investigated. This research numerically models liquefaction (UBCsand with FLAC) and predicts the effects of the sand-crumb rubber layer of different thicknesses (as % weight of the mixture) under the foundation and evaluates the structure's damage and settlement interacting with the soil by validating the numerical model with the laboratory model and calibrating it with different ratios. The results show that liquefaction, pore water pressure excess ratio and soil settlement will be significantly reduced with the presence of sand-crumb rubber layer, and also the base shear has shown an increase, but the structural damage is reduced.Graphical

Fatigue characteristics of rubber isolation layers used in high speed railway ballastless tracks: A theoretical and experimental study

In order to enhance operational conditions for high-speed trains on long-span bridges, the utilization of rubber under-ballast mats were taken as a novel isolation layer in ballastless tracks. Due to the increased train axle load, it is imperative to conduct investigation into the fatigue properties of the rubber isolation layer, so as to ensure the smoothness of the railways. In this work, a series of fatigue tests were performed on the rubber isolation layer to obtain the influence of stress amplitude and loading cycles on its fatigue performance. The results demonstrate a pronounced non-linear load–displacement relationship of the rubber isolation layer with increasing load, while the fatigue endurance significantly decreases with escalating the stress amplitude. Moreover, considering the hyperelastic properties of rubber material, the Mooney-Rivlin constitutive model was employed in finite element simulations. Subsequently, the stress distributions of the rubber isolation layer were analyzed, and the fatigue life was evaluated based on Luo stress method. The rubber isolation layer exhibits localized damage that does not affect the overall performance after 32 years of normal service condition. Therefore, the fatigue performance of the rubber isolation layer remains reliability, providing assurance for the application in ballastless tracks on high-speed railway long-span bridges.

Simultaneously achieving excellent heat aging resistance and grip performance in carbon black/glass flake/EPDM rubber composite for overhead line spacers

The preparation of wire clamp rubber with semiconductivity, low compression set (C-Set), high mechanical strength, heat aging resistance, and high grip strength is vital for overhead line spacers. This study delves into the formulation design of high-performance ethylene-propylene-diene monomer (EPDM) composite materials for wire clamp rubber. The effects of the vulcanization system, carbon black type, and loading on the essential material properties of EPDM rubber were investigated. The results showed that a hybrid vulcanization system containing peroxide and sulfur simultaneously endowed EPDM rubber with high elasticity and tear strength. N330 carbon black-filled EPDM rubber had the advantages of semiconductivity and high tensile strength, and N774 carbon black-filled EPDM rubber exhibited low C-Set and high heat aging resistance. When EPDM rubber was reinforced with the mixture of 50 phr N330 and 20 phr N774 carbon black, the rubber synchronously exhibited semiconductivity (2.64×106 Ω·cm), high tensile strength (20.2 MPa), low C-Set (32.5%, 150°C×3d), and high heat aging resistance (maintaining 98% of its initial tensile strength after aging at 150°C for 3d). In addition, introducing a 10-phr glass flake into EPDM wire clamp rubber improved the grip force by 83%. The improvement mechanism may be attributed to the increased compression stress of wire clamp rubber on cable and the restricted slippage of rubber molecular chains.

Prediction and comparative analysis of friction material properties using a GA-SVM optimization model

PurposeWith the rapid advancement in the automotive industry, the friction coefficient (FC), wear rate (WR) and weight loss (WL) have emerged as crucial parameters to measure the performance of automotive braking systems, so the FC, WR and WL of friction material are predicted and analyzed in this work, with an aim of achieving accurate prediction of friction material properties.Design/methodology/approachGenetic algorithm support vector machine (GA-SVM) model is obtained by applying GA to optimize the SVM in this work, thus establishing a prediction model for friction material properties and achieving the predictive and comparative analysis of friction material properties. The process parameters are analyzed by using response surface methodology (RSM) and GA-RSM to determine them for optimal friction performance.FindingsThe results indicate that the GA-SVM prediction model has the smallest error for FC, WR and WL, showing that it owns excellent prediction accuracy. The predicted values obtained by response surface analysis are closed to those of GA-SVM model, providing further evidence of the validity and the rationality of the established prediction model.Originality/valueThe relevant results can serve as a valuable theoretical foundation for the preparation of friction material in engineering practice.

PEMFC sealing modeling relating to fractal characteristics of gasket-BPP interface based on micro-contact

The interface leaking of the gasket-BPP sealing structure affects the efficiency, safety, and reliability of PEMFCs. Aiming to reveal the basic cause of interface leaking and predict the leakage rate, the contact behavior at the micro-scale had been researched by FEM with the fractal multi-scale method, which could eliminate the negative influence of a single observation scale on the gasket-BPP rough interface modeling. Furthermore, in order to relate the contacting behavior at the micro-scale to the leakage rate at the macro-scale of PEMFCs, the mapping model had been established to analyze the sealing performance of the entire interface through the self-affine and self-similar characteristics of the fractal multi-scale contacting model of the gasket-BPP. Not only macroscopic properties of gasket rubber materials are considered in this model, but also microscopic morphologies are taken in to investigate the interface leakage rate, which had not been studied in traditional macroscopic research. By comparing the compression curves and interface leakage rates of the flange sealing device in testing and calculating approaches, the accuracy and reliability of the mapping model had been verified, leading to the analysis and the prediction of the PEMFC interface leakage rate rapidly.

Experimental Comparison of Manufacturing Parameters in Automotive Friction Materials

In this study, a fixed automotive friction material content was determined and the mechani-cal and tribological effects of manufacturing parameters on friction materials were investigat-ed. Parameters; pre-forming time (1-3-5 min) and pre-forming pressure (8-10-12 MPa), hot pressing time (5-10-15 min) hot pressing pressure (8-10-12 MPa) and hot pressing temperature (125-150-175 °C), curing time (4-8-12 h) and curing temperature (120-150-180 °C) were de-termined. The friction test of the produced samples was carried out under 0.551 MPa pressure and 7 m/s rotation speed for 90 min. In addition, the average COF, friction stability, specific wear rate, density and hardness values of the samples were calculated. According to the results obtained, the average COF value increased as the pre-forming time and pressure increased. With the increase in hot pressing time, the tribological properties of friction materials improved. Although there was an increase in the average COF value with increasing hot pressing pressure and temperature, the specific wear rates increased in these parameters. The specific wear rate increased with the increase in curing time and temperature. The highest specific wear rate among all samples was obtained in the sample cured at 180 °C. Finally, it has been suggested that 3 min for pre-forming time, 12 MPa for pre-forming pressure; 15 min for hot pressing time, 12 MPa for hot pressing pressure, and 150°C for hot pressing temperature; and a curing time of 8 h and curing temperature of 150 °C may be sufficient.

Self-heating and fatigue crack growth behavior of reinforced NR/BR nanocomposites with different blending ratio

Fatigue crack growth and dissipative self-heating due to viscoelasticity are crucial properties of rubber materials under dynamic service conditions. Systematic evaluation of the thermo-mechanical coupled fatigue properties with suitable lab testing methods could contribute to the development of long-lasting and robust elastomer materials. In this work, on the one hand, the hysteresis energy density, thermal conductivity, and surface temperature rise, which are closely related to the self-heating generation rate, heat transfer rate and heat build-up of the carbon black reinforced seven different natural rubber (NR) and polybutadiene rubber (BR) blends were measured. A thermo-mechanical coupling simulation method was used to reproduce the experimental observation. On the other hand, the fatigue threshold (T0), critical tearing energy (Tc), and fatigue crack growth rate (FCGR) under different tearing energy were investigated by using the advanced rubber fatigue instruments. The Lake-Lindley model was utilized to describe the rubber fatigue responses from the intrinsic strength to the ultimate strength. The results show that the dissipative self-heating of NR/BR:30/70 blend is the most obvious one, which could be well explained by the simulation results. The T0 shows an upward trend while Tc shows a downward trend with the increasing blend ratio of BR. The existence of carbon black fillers showed tiny effect on T0 of NR, but significantly enhanced the T0 of BR. The FCGR of reinforced NR/BR nanocomposites have Lake-Lindley law responses that cross over each other. Therefore, which rubber material is superior to others in resisting crack propagation depends on the magnitude of the input tearing energy.

A new method for selecting and evaluating the hyperelastic model of tread rubber material under rolling contact condition

The selection and evaluation of the hyperelastic model of tread rubber material were of great value and significance to the clarification and application of the mechanical properties of tread rubber material. In this article, a non-contact tread rubber material rolling test bench was established. The improved digital image correlation method was used to calculate the strain rate distribution of the marked point under different test conditions. Combined with the stress distribution of the marked point, the rolling dynamic stress-strain characteristics of tread rubber material were obtained. Based on rubber material models under different tensile test modes, the parameter inversion identification of the hyperelastic model was completed, and the influence of the tensile test mode on the parameter inversion of the tread rubber hyperelastic model was revealed. A new method for selecting and evaluating the hyperelastic model of tread rubber material under rolling contact conditions was proposed. The selection criterion for the hyperelastic model of tread rubber material was developed under different rolling conditions. The experimental and analytical results show that the nonlinear degree of the constitutive relation of the hyperelastic model decreased with the increase in rolling speed. Compared with hyperelastic models under different tensile modes, the fitting error of the Yeoh model was less than 3%, and the overall fitting error of the Yeoh model was less than 2%. Therefore, the Yeoh model had better stability and accuracy and was more suitable for describing the rolling mechanical properties of tread rubber under rolling contact conditions.

Effect of Nano-sea shells Reinforcement on Friction and Wear Properties of Aramid Fiber Friction Materials

Effect of Nano-sea shells Reinforcement on Friction and Wear Properties of Aramid Fiber Friction Materials

Enhancing mechanical properties and stabilising the structure of epoxide natural rubber using non-covalent interactions: Metal–ligand coordination and hydrogen bonding

Non-covalent interactions can enhance the mechanical properties of rubber materials diversifying potential applications. Epoxidized natural rubber (ENR), derived by modifying natural rubber (NR), can establish metal–ligand (M-L) coordination and H-bonding. In this research, ENR samples with non-covalent interactions were prepared by adding (i) sodium alginate (Alg) with FeCl3 and (ii) dopamine (D) with FeCl3. Both H-bonding and M-L coordination were detected by FTIR and Raman spectroscopy. The overall mechanical properties were increased due to non-covalent interactions, especially self-healing performance, which reached 60 %. From the mechanical stability data, storage hardening phenomenon of ENR was explained for the first time. These samples exhibited constant Mooney viscosity as a function of time. Furthermore, the effect of M-L coordination in dopamine modified samples were the strongest due to dopamine was grafted on ENR molecules. Therefore, this research provides a possible new way to stabilise the structure and enhance the mechanical properties of ENRs.

Full-field contact dynamic mechanical properties of tread rubber material under rolling and slippery conditions based on digital image correlation

The dynamic mechanical properties of rolling tire on special road surface were closely related to the vehicle’s handling stability, driving safety and braking effectiveness. The tire tread rubber material was the only contact part of the vehicle with the road surface, so the strain distribution characteristics of tread rubber material within the contact patch of rolling tire on thin water film pavement played a crucial role in the mechanical characteristics of vehicle. In this paper, a non-contact tire tread rubber rolling mechanical test system was developed. The improved digital image correlation (DIC) method was used to obtain the full-field strain distribution of tread rubber blocks. The effects of load and velocity on the strain rate of the marked points, the full-field strain distribution in the region of interest and rolling resistance were investigated under thin water film pavement. The experimental results were compared with dry condition to analyze the effect of water film on the rolling dynamic characteristics. The results showed that the strain rate increased first and then fluctuated under the action of thin water film. With the increase of speed and load, the full-field strain distribution of tread rubber contact patch was gradually occupied by low strain zone. The change rate of rolling resistance firstly increased and then decreased with the increase of rotational speed.

Predicting Natural Rubber Crystallinity by a Novel Machine Learning Algorithm Based on Molecular Dynamics Simulation Data.

Natural rubber (NR) with excellent mechanical properties, mainly attributed to its strain-induced crystallization (SIC), has garnered significant scientific and technological interest. With the aid of molecular dynamics (MD) simulations, we can investigate the impacts of crucial structural elements on SIC on the molecular scale. Nonetheless, the computational complexity and time-consuming nature of this high-precision method constrain its widespread application. The integration of machine learning with MD represents a promising avenue for enhancing the speed of simulations while maintaining accuracy. Herein, we developed a crystallinity algorithm tailored to the SIC properties of natural rubber materials. With the data enhancement algorithm, the high evaluation value of the prediction model ensures the accuracy of the computational simulation results. In contrast to the direct utilization of small sample prediction algorithms, we propose a novel concept grounded in feature engineering. The proposed machine learning (ML) methodology consists of (1) An eXtreme Gradient Boosting (XGB) model to predict the crystallinity of NR; (2) a generative adversarial network (GAN) data augmentation algorithm to optimize the utilization of the limited training data, which is utilized to construct the XGB prediction model; (3) an elaboration of the effects induced by phospholipid and protein percentage (ω), hydrogen bond strength (εH), and non-hydrogen bond strength (εNH) of natural rubber materials with crystallinity prediction under dynamic conditions are analyzed by employing weight integration with feature importance analysis. Eventually, we succeeded in concluding that εH has the most significant effect on the strain-induced crystallinity, followed by ω and finally εNH.

Harnessing local flow in buckling pores for low-frequency attenuation

While attenuation at low frequencies remains highly desirable for industrial applications such as multistory buildings or spacecraft propellant tanks, fluid-filled rocks can achieve this goal naturally by so-called local flow in their heterogeneous pore structure. The present work aims at combining this natural phenomenon with controlled instabilities in light-weight structures. Buckling of their pores is harnessed to break local geometric symmetry and maximize the local-flow effect. A prototype structure with elliptical pores is analyzed numerically. It does not show local flow or attenuation for the starting geometry, but reversibly switches into an attenuating structure by imposing a critical buckling strain. The simulations reach inverse quality factors larger than 0.3 around 5Hz for material properties of air-filled silicone rubber. A key to high attenuation is a tradeoff between the unstable structure and the pore fluid. If the solid is too soft, the fluid-filled pores are not compressed and buckling is not triggered. If the solid is too stiff, most energy is stored elastically and not dissipated by fluid flow. The proposed, fluid-filled structure allows for a scalable, light-weight material exhibiting significant low-frequency attenuation.

Effect of Iron Powder Type on Friction and Wear Properties of Copper-Based Friction Powder Metallurgy Material

The sintered copper-based friction materials for high-speed train brake pads have a complex composition that should possess good physical, mechanical, and tribological properties in practical applications. For this article, four kinds of friction materials were prepared by powder metallurgy technology and the effects of iron powders on the microstructural and tribological properties of copper-based friction materials were characterized using a scanning electron microscope (SEM) and x-ray diffraction (XRD). The results showed that iron powder as an enhancing component could effectively change the friction and wear properties of the experimental materials. The copper-based friction materials containing hydroxy iron (1–5 μm) have a relatively higher coefficient of friction: The friction coefficient was significantly improved by 16.8% compared with reduced iron under a rotation speed of 4000 r/min. The friction coefficient of friction material containing water-atomized iron powder is relatively reliable with 3000–7000 r/min speed range. In a high-speed environment, the friction surface of material containing reduced iron or hydroxy iron (1–5 μm) mainly has cracks and brittle fractures, and the material containing hydroxy iron (10 μm) or water-atomized iron has an obvious layered structure and shows fatigue wear.

Experimental investigation of three-body wear for rubber seals in abrasive slurry environment

Three-body wear is a complex phenomenon occurring when abrasive particles present between two material surfaces. By developing a new experimental setup, we systematically study wear at the contact between stainless steel and three different rubbers (TPU, NBR and LSR) in a slurry environment, i.e. water containing sand particles. Results showed that wear on both metal and rubber pads increases exponentially with the sliding speed, while a weak correlation was observed with the applied normal load for the given range of load. Wear analysis showed that the stainless steel experienced the most wear when in contact with NBR and the least when in contact with LSR. The TPU rubber pads experienced the most wear, whereas the LSR pads barely exhibit any wear when in contact with the stainless steel. Furthermore, frictional measurements indicated an inverse relationship between the system coefficient of friction and the amount of wear observed on the rubber elements. These observations are discussed in terms of the probability of the sand particles being clung to the rubber pads, after which they abrade the steel surface. This probability is justified as a function of the rubber material properties and the system friction coefficient. The findings in this study suggest new directions for minimizing three-body wear at the contact between metals and rubbers.

Temperature dependent tensile fracture strength model of rubber materials based on Mooney-Rivlin model

With the increasingly widespread application of rubber in many fields, the demand for quantitative characterization of temperature dependent mechanical properties in service environments over a wide temperature range is increasing. Tensile fracture strength is one of the most important mechanical properties of rubber materials, but its temperature dependent model without fitting parameters is still rarely reported. In this work, based on Mooney-Rivlin hyperelastic constitutive model, a strain energy expression that explicitly includes tensile fracture strength is derived, and a temperature dependent tensile fracture strength model for rubber materials without fitting parameters is further developed in combination with the Force-Heat Equivalence Energy Density Principle. The prediction results of the model in a wide temperature range are in good agreement with the experimental results. Furthermore, a quantitative analysis of the effect of elastic modulus on tensile fracture strength at different temperatures is conducted. Finally, based on the above conclusions, some useful suggestions on the selection of rubber materials for service in a wide temperature range are proposed.

Comparison of the theoretical and experimental coefficient of friction for the brake disc-brake pad system

Contact between the automotive brake pad and the disc is mathematically modelled to estimate the coefficient of friction (COF). The mathematical model is proposed for the prognosis of the COF of brake pad material, by considering the contact mechanics between the interfacing surface and their material properties. The Greenwood-Williamson contact model is applied for rough contact surfaces for the estimation of the real contact radius. A MATLAB program has been formulated for generating the surface of brake pad material by considering its material properties which aid in the analytical evaluation of the COF. The proposed model is further validated with experimentation on pin-on-disc apparatus, as it is considered suitable for friction pad product testing according to previous research. The 25 pins were fabricated as per the ASTM G99 test for testing under varying loads and speeds. The obtained results showed that the range of COF has been between 0.2 and 0.4. The investigation presents an analytical approach for estimating COF and contact radius for brake disc and brake pad, which can be used to design an efficient automotive brake disc-brake pad system under the given load and rotational speed. The artificial neural network (ANN) is modelled for predicting the values of the COF for brake disc-brake pad systems, which can be further used for determining the tribological properties of new friction materials and their compatibility for efficient brake systems.

Железнодорожный дисковый тормоз с термоизолированными узлами трения, содержащими материалы с различными фрикционными свойствами

Purpose: Description of the design of the disc brake with thermally insulated friction units and the peculiarities of its manufacture. Methods: Analysis of the properties of friction materials for friction units of the railway disc brake. Results: The design of disc brake with thermally insulated friction units is proposed, a characteristic feature of which is thermal insulation of friction units A and B from each other. In addition, different friction materials are used in friction units – brake discs and brake linings. The basic principle of the disc brake is to compensate for the friction force of the friction assembly A in low temperature conditions where the carbonbased friction material is placed. Features of brake manufacturing are given. It is noted that the recommended material for thermally insulated working parts of the disc brake is chrysotile-asbestos. This material has a low thermal conductivity and an acceptable cost. It is recommended to use adhesive joints based on ABRO TM-185 glue by thermal insulation of brake discs. Practical significance: The design and features of the manufacture of a disc brake with thermally insulated friction units are described, as well as the best friction materials for it are determined. The results of the study can be used in specialized and locomotive manufacturing enterprises in order to eliminate the existing drawbacks regarding the friction characteristics of the friction materials used, as well as to reduce the cost of manufacturing a carbon-based disc brake.

Effects of Pre-Curing on the Structure and Properties of Paper-Based Materials.

Paper-based friction material is a typical paper-based composite that is usually cured via hot-pressing. This curing method does not account for the effect of pressure on the matrix resin, resulting in uneven distribution of resin in the material and reducing the mechanical properties of friction materials. To overcome the above shortcomings, a pre-curing method was introduced before hot-pressing, and the effects of different pre-curing degrees on the surface morphology and mechanical properties of paper-based friction materials were studied. The pre-curing degree significantly affected the resin distribution and interfacial bonding strength of the paper-based friction material. When the material was cured at 160 °C for 10 min, the pre-curing degree reached 60%. At this point, most of the resin was in a gel state, which could retain abundant pore structures on the material surface without causing mechanical damage to the fiber and resin matrix during hot-pressing. Ultimately, the paper-based friction material exhibited improved static mechanical properties, decreased permanent deformation, and reasonable dynamic mechanical properties.