Friction Properties Of Materials Research Articles

Evaluation of mechanical and tribological properties of Cu-based friction materials reinforced by 3D mesh structure

Cu-based friction materials (CBFMs) are widely used in brake system such as High-Speed Trains and Wind Power Generation, its mechanical and tribological properties are of vital importance for the stable and safe operation. In this study, CBFMs holding 3D mesh structure were designed and fabricated by wet granulation and particle coating technology. Stress and temperature fields were obtained by finite element simulation. After that, the mechanical and tribological properties were investigated. The results showed that 3D mesh structure can enhance the compressive strength of CBFMs to 34.56 % and reduce wear rate to a large extent. This study was expected to open up a new direction in enhancing comprehensive performances of CBFMs without changing its composition.

Visco-Hyperelastic Constitutive Modeling for High-Damping Rubber Materials During Combined Quasi-Static Compression–Cyclic Shear Deformation Process

High-damping rubber materials utilized in high-damping rubber isolation bearings are frequently subjected to multiple deformations during the occurrence of earthquakes. Typically, large combined compression–shear deformations of the material could potentially cause compressive shear damage to rubber bearings. During this process, visco-hyperelastic properties of rubber materials will greatly change, which would significantly impact the seismic performance of rubber bearings. Thus, to give out a deep insight into their variations, it is necessary and urgent to develop a high-performance numerical method to investigate this process. This paper proposed a visco-hyperelastic constitutive modeling approach for high-damping rubber materials based on the experimental assessment of combined quasi-static compression–cyclic shear deformation process. Within the thermodynamic framework, the Clausius–Duhem inequality associated with the intrinsic dissipation of the material was firstly derived in accordance with the Lagrangian formulism. Then, stress–strain relations were obtained upon considering the occurrence of entropy production due to viscous dissipation. In the model, Stumpf–Marczak strain energy density function, which satisfies the Baker–Ericksen (B–E) inequality, was harnessed to describe the hyperelasticity of the material. By introducing higher orders of strain and strain rates and taking their couplings into account, a generalized viscous dissipation potential was proposed to capture nonlinear strain and strain rate-sensitivity effects of the material. To identify constitutive parameters, the deformation gradient was particularized for the combined quasi-static compression–cyclic shear deformation process. And, an inverse identification procedure was carried out at different levels of compression stress. The prediction results revealed that the proposed model exhibits remarkable prediction ability and adaptivity for different rubber materials during this process. Several new insights were highlighted on the variations of visco-hyperelastic characteristics of high-damping rubber materials with respect to the compression stress. The accuracy of the model was further validated by design parameters including initial shear modulus, secant shear modulus and equivalent viscous damping factor. This work could provide a fundamental guideline for the optimization and reliability analysis of high-damping rubber isolation bearings used in the field of seismic engineering.

Experimental Comparison of Manufacturing Parameters in Automotive Friction Materials

In this study, a fixed automotive friction material content was determined and the mechanical and tribological effects of manufacturing parameters on friction materials were investigated. 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 determined. 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. The lowest specific wear rate among all specimens was calculated as 7.622x10-6 cm3/Nm in PFP-12 specimen. With the increase in hot pressing time, the tribological properties of friction materials improved. The highest friction stability among all samples was calculated as 79.42% in the HPT-15 sample. 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 highest average COF value among all samples was obtained in the CT-12 sample with a value of 0.553. The specific wear rate increased with the increase in curing time and temperature. The highest specific wear rate among all samples was calculated 10,743x10-6 cm3/Nm in the CTe-180 sample. 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.

Synergistic Effect of Aluminum Nitride and Carbon Nanotube-Reinforced Silicon Rubber Nanocomposites.

Constructing a synergistic effect with different structural fillers is an important strategy for improving the comprehensive properties of polymeric composites. To improve the comprehensive properties of two-component additive liquid silicon rubber (SR) materials used in electronics packaging, the synergistic effect of granular aluminum nitride (AlN) and tubular carbon nanotube (CNT)-reinforced SR nanocomposites was investigated. AlN/CNT/SR composites with different AlN/CNT ratios were fabricated with two-component additive liquid SR via the thermal curing technique, and the influence of AlN/CNT hybrid fillers on the hardness, strength, elongation at break, surface resistivity, thermal conductivity, and thermal decomposition was investigated in detail. With the incorporation of AlN/CNT hybrid fillers, the comprehensive properties of the obtained AlN/CNT/SR composites are better than those of the AlN/SR and CNT/SR composites. The synergistic thermal conductive mechanism of AlN/CNT hybrid fillers was proposed and demonstrated with the fractural surface morphology of the obtained composites. The obtained AlN/CNT/SR composites show promising applications in electronic packaging, where necessary mechanical strength, electrical insulating, thermal conductivity, and thermal stable materials are needed.

Insights into the fracture properties of recycled ceramic and rubber composite cement-based materials: Fracture mechanics, acoustic emission, and digital image correlation

Recycling plays a pivotal role in construction waste management, offering a path toward sustainability for the industry. Although waste ceramics can compensate for the mechanical properties of rubberized cement-based materials, the smooth glaze surface of waste ceramics increases the risk of brittle failure. This study investigated the effect of ceramic waste aggregate (CWA) on the fracture properties of rubberized mortar through the three-point bending experiment. The fracture parameters were calculated using the Double-K fracture criterion. Simultaneously, acoustic emission (AE) and digital image correlation (DIC) technologies were used to explore the fracture damage mechanism and the crack evolution process. The results indicate that the integration of 15 % and 45 % CWA significantly enhances both initiation (KICini) and unstable (KICun) fracture toughness, whereas incorporating 90 % CWA leads to a 16.8 % and 8.2 % decrease in (KICini)and (KICun), respectively. The fracture energy (GF) of rubberized mortar exhibits a continuous decline as a function of increasing CWA substitution rates. Furthermore, GMM-based RA-AF analysis elucidates a positive correlation between CWA content and tensile crack proportion in specimens. When the CWA content reaches 90 %, the proportion of tensile cracks is quantified at 29.83 %, surpassing that in standard mortar. Crack tip opening displacement (CTOD) at 0.5post-Pmax for specimens with 15 %, 45 %, and 90 % CWA substitution reveal improvements of 49.1 % and 17.2 %, and a decrease of 23.3 %, respectively, compared to standard mortar, indicating that 15 % and 45 % CWA effectively preserve the ductility of rubberized mortar. Elevated CWA substitution leads to an amplified strain localization phenomenon around the crack tip, heightening the propensity for brittle failure.

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.

Research on dynamic sealing performance of sealer structure under the influence of temperature

Affected by the extreme environment of high temperature and high pressure downhole, the mechanical behavior of the sealer rubber sleeve undergoes significant changes during service, leading to a sharp decline in the mechanical properties of the rubber material within the high-temperature environment. To address the issue of seal failure in the sealer rubber barrel under high-temperature loads, experimental investigations were conducted to analyze the compression properties of rubber materials at various temperatures. The constitutive parameters of the rubber were then fitted using the Reduce-Polynomial model. Subsequently, a finite element model was employed to study the sealing performance and mechanical response of the three-compartment rubber-tube structure sealer at different temperatures. The findings demonstrate that temperature fluctuations have a substantial impact on the sealing performance and bearing strength of the sealer. Consequently, this research holds crucial guiding significance for the structural design of the sealer rubber cylinder under high-temperature conditions.

Effect of mo content on the microstructure and properties of powder metallurgy iron based friction materials

This article uses powder pressing and sintering methods to prepare iron-based friction materials. The influence of molybdenum on the microstructure and comprehensive properties of powder metallurgy friction materials was studied from the aspects of density, hardness, and wear resistance. The results show that with the increase of Mo mass fraction, the sintering density of iron-based friction materials gradually increases, and the hardness of sintered materials first shows an increasing trend. As the Mo content increases by more than 12%, the hardness of sintered friction materials decreases. With the addition of Mo, the wear amount of the friction material first decreases and then increases. When the mass fraction of Mo added to the sintered friction material is 12%, the wear rate of the material is lower than that of other samples, and it has good wear resistance. Adding Mo element to iron copper based friction materials improves the wear resistance of sintered friction materials due to the strengthening effect of Mo.

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.

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.