Friction Properties Of Materials Research Articles

Significant enhancement on the mechanical and tribological performances of paper‐based friction materials by designing silicone@SiO2 core‐shell structure

AbstractUnder the heavy‐loading harsh condition, achieving prominent mechanical and tribological performances of paper‐based friction materials are an extreme demand for meeting their application in the braking of vehicles. In this study, modifying carbon fiber with epoxy groups and designing silicone@SiO2 core‐shell structure as efficient and feasible strategies, were employed to boost the mechanical and tribological properties of friction materials. The above core‐shell hybrid, acted as an effective interfacial linker, contributed to forming strong mechanical interlocks and increasing chemical cross‐linking density at the interphase. The tensile and interlaminar shear strength of silicone@SiO2‐modified sample were improved by 28.6% and 12.9%, respectively. Meanwhile, the toughness of silicone@SiO2‐modified sample showed a 102.82% increase. Moreover, compared with pristine sample, the dynamic friction coefficient of silicone@SiO2‐modified sample increased from 0.1020 to 0.1202, while the wear rate decreased from 0.617 × 10−8 cm3 J−1 to 0.432 × 10−8 cm3 J−1.

Tribological modification of hydrogenated nitrile rubber nanocomposites for water-lubricated bearing of ship stern shaft

A water-lubricated rubber bearing (WLRB) of ship stern shaft often operates under harsh conditions, which requires a higher tribological performance for bearing materials. Uniformly dispersed nano-fillers can significantly improve the various properties of rubber materials, but nano-fillers are prone to agglomerate in the process of operation, which affects the modification effect. In this paper, a solution blending masterbatch method was used to prepare hydrogenated nitrile rubber (HNBR) nanocomposites and the modification effects of ultra-high molecular weight polyethylene (UHMWPE), nano graphite (NG) powder, nano molybdenum disulfide (NM) and graphite fluoride (GF) on HNBR basic formulation were studied. The results show that the tribological modification of HNBR by UHMWPE is better under low-speed conditions, while the tribological modification of HNBR by GF is better under high-speed conditions. Therefore, in practical engineering application, the reasonable nano fillers are selected for tribological modification according to the operating conditions of water lubricated rubber bearings. It should be pointed out that in order to cover all working conditions, multi nano filler synergistic tribological modification technology is an important technical way to obtain the best comprehensive performance results.

Friction and wear characteristics of brake friction materials obtained from fiber and huntite blends

PurposeThe purpose of this paper, brake friction material samples with six different contents were produced using three different fiber types consisting of variable proportions of huntite mineral and basalt, glass and steel fibers. The friction properties and formation of the transfer film in these friction materials were investigated.Design/methodology/approachFriction materials were produced using a hot molding method from materials containing 10%–15% huntite in varying proportions, consisting of basalt, glass and steel fibers. The densities and hardness values of the samples were measured. Friction tests were performed using a brake pad friction material tester to determine tribological properties. After the friction tests, microscopic examination of the sample surfaces was performed using scanning electron microscope (SEM) and three-dimensional (3D) surface profilometer devices.FindingsHuntite mineral content and fiber type affected the friction coefficient. With an increase in the amount of huntite, the friction coefficient increased in the friction material samples formed with glass and steel fibers. The fiber type and amount of huntite also affected the transfer film formation. The surface roughness values of all the friction materials decreased with an increase in the amount of huntite. The surface roughness values of the samples with glass fibers were higher than those of other samples.Originality/valueThe importance of using huntite minerals and different fiber types in automotive brake friction materials is emphasized. This will help industrial companies and academics study the tribological properties of friction materials.

Research and Development of High-Performance High-Damping Rubber Materials for High-Damping Rubber Isolation Bearings: A Review.

At present, high-damping rubber materials, widely used in the field of engineering seismic isolation, generally have the problems such as narrow effective damping temperature range, low damping loss factor and strong temperature dependence, which lead to prominent dependence of temperature and load conditions of the isolation performance of high-damping rubber isolation bearings. Research and development of high-performance high-damping rubber materials with broad effective damping temperature range, high damping loss factor and weak temperature dependence are very urgent and necessary to ensure the safety of the seismic isolation of engineering structures. This paper mainly reviews the recent progress in the research and development of high-damping rubber materials using nitrile butadiene rubber (NBR), epoxidized natural rubber (ENR), ethylene propylene diene rubber (EPDM), butyl rubber (IIR), chlorinated butyl rubber (CIIR), and bromine butyl rubber (BIIR). This is followed by a review of vulcanization and filler reinforcement systems for the improvement of damping and mechanical properties of high-damping rubber materials. Finally, it further reviews the constitutive models describing the hyperelasticity and viscoelasticity of rubber materials. In view of this focus, four key issues are highlighted for the development of high-performance high-damping rubber materials used for high-damping rubber isolation bearings.

Effect of the Coke/Flake Graphite Ratio on the Microstructure and Properties of Cu-Based Powder Metallurgy Friction Materials

Effect of the Coke/Flake Graphite Ratio on the Microstructure and Properties of Cu-Based Powder Metallurgy Friction Materials

Hyperelastic modelling of rubber with multi-walled carbon nanotubes subjected to tensile loading

This study thoroughly examined the application of inverse FE modelling and indentation tensile tests to identify nanotubes' rubber material properties. Carbon nanotubes with various percentages of multi-walled carbon nanotubes exposed to high tensile stress were used to enhance the mechanical qualities of natural rubber (NR). In this work, carbon nanotubes have been added to natural rubber. By using a solvent casting technique, toluene was used to make nanocomposites. 0.2%, 0.4%, 0.6%, 0.8%, and 1%. In this article, rubber and multi-walled carbon nanotubes interact in practical ways. Mechanical features of carbon nanotubes in NR have been researched. The results will lead to rubber products with improved mechanical qualities compared to present nanocomposite rubber containing various percentages of multi-walled carbon nanotubes exposed to large tensile test loading. The relative fitness error for significant stresses is reasonable with a second or third-order deformation model in numerical results. Non-linear finite element analysis is widely used to optimise complicated elastomeric components' design and reliability studies. However, accurate numerical results cannot be achieved without using rubber or rubber nanocomposite materials with reliable strain energy functions. The indentation tensile tests of rubber samples have been simulated and confirmed using a parametric FE model. An inverse materials parameter identification algorithm was used to calculate the hyperelastic material properties of rubber samples evaluated in uniaxial tensile. Using ABAQUS FE software, material parameters and force-displacement data may be automatically updated and extracted. The numerical data for the inverse method of material property prediction has been successfully established by developing simulation spaces for various material characteristics. The force-displacement curve can be represented using technical methods. The results demonstrate that the inverse FE modelling process might be simplified by using these curve fitting parameters and plot equations to build a mathematical link between curve coefficients and material properties. The first, second, and third-order deformation models were tested using FE simulations for the tensile test.

Influence of ecological Juniperus Drupacea cone powder on mechanical and physical properties of fiber-reinforced composite friction materials

This work is aimed to study the mechanical and physical properties of composite friction materials (CFMs) produced by using various fiber types (glass, carbon, and basalt) filled and unfilled Organic Juniperus Drupacea Cone Powder (JDCP). The CFMs were tested by using a pin-on-disc tribo-test-rig under dry contact conditions. The JDCP gradually reduced the density of CFMs. The surface hardness of the CFMs exhibited a decreasing trend with the addition of JDCP filler. The presence of JDCP within the CFMs considerably increased the water and oil absorption. The results showed that the JDCP filled and unfilled basalt fiber reinforced CFMs had higher friction coefficients than JDCP filled and unfilled glass and carbon fiber reinforced CFMs. In addition, the friction coefficient of filled and unfilled carbon fiber reinforced CFMs was found to be the lowest. The tensile strengths obtained from the indirect tensile (Brazilian) test of basalt, glass, and carbon fiber reinforced test CFMs increased with JDCP filler. In addition, the tensile strength of JDCP filled and unfilled carbon fiber reinforced FCMs proved to have better wear resistance than other all CFMs. The wear resistance of basalt, glass, and carbon fiber reinforced CFCMs decreased with the increase of JDCP wt. % filler. Among JDCP filled and unfilled all CFMs, the highest wear resistance was detected in carbon fiber reinforced CFM. The minor wear resistance was seen in glass fiber reinforced CFMs than carbon and basalt reinforced samples.

Study of the influence of ultra disperse powder additives of the NiAl/Al<sub>2</sub>O<sub>3</sub> system on the tribotechnical properties of the frictional material based on copper

The results on the impact of additives on the ultra-fine composite powder system, obtained by MASVS on the tribotechnical properties of friction material based on tin bronze with 12 % of tin are presented. It is shown that the powder additive in the range of 0.5–2.5 % increased the dynamic friction coefficient from 0.040 to 0.051. The introduction of a 1.5 % composite powder reduced the surface roughness of the counter body from 2.9 to 0.9 μm. The change in the tribotechnical properties is due to the structural changes in tin bronze, the additive particles, the surface layer of the friction material and the counter body.

Effect of Rubber Strain Rate on Performance of Aircraft Tire

An aircraft tire is a kind of rubber product with a complex structure. When subjected to impact load, the mechanical properties of rubber material on strain history and strain rate cannot be ignored. According to the previous impact compression experiment data of rubber materials, this paper built a dynamic constitutive model by modifying Mooney-Rivlin constitutive model to describe the rate-dependent material behavior. The calculated stress–strain values were in good agreement with the experimental ones. The proposed constitutive equation was implemented in ABAQUS via a user-defined subroutine (VUMAT) and used to predict the dynamic response of aircraft tire landing impact in the experiments for the first time. The model’s numerical results considering the strain rate effect are closer to the test results than the traditional model. It shows that considering the strain rate effect of rubber material in the case of tire impact can make the results more accurate.

Compressive stress-hydrothermal aging behavior and constitutive model of shield tunnel EPDM rubber material

The damage and aging of the ethylene-propylene-diene monomer (EPDM) rubber material significantly impact the attenuation of the shield tunnel's waterproof performance. Furthermore, the compressive stress acting on the rubber material will further exacerbate this consequence. Therefore, it is necessary to explore the time-dependent properties of rubber under compressive stress. In this study, the EPDM rubber was subjected to compressive stress-hydrothermal aging (CS-HA) test at different pre-compression strains, temperatures, and time according to the application environment of the shield tunnel. The rule of compression set (CS) and the variation rule of mechanical properties of rubber materials after aging were investigated, and the reasons for these rules were analyzed. According to the rule of rubber material performance degradation, a constitutive model of EPDM rubber for shield tunnel segment squeezing environment was proposed. Using compression set as the index of material performance deterioration degree, the time and temperature conversion relationship between laboratory aging and service environment aging of the EPDM rubber segment joint was obtained. Furthermore, based on the constitutive model and related parameter expressions proposed in this paper, the attenuation rule of rubber mechanical properties and residual properties was obtained. It was proposed that the service performance of EPDM rubber under compressive stress should be considered when setting the pre-tightening force during the construction of the shield tunnel, and a reasonable pre-compression force should be adopted. This work provides an effective test method and constitutive model for predicting the time-dependent characteristics of the mechanical properties of rubber materials under compressive stress.

Molecule Dynamics Simulation of the Effect of Oxidative Aging on Properties of Nitrile Rubber.

The effects of oxidative aging on the static and dynamic properties of nitrile rubber at the molecular scale were investigated by molecular dynamics simulation. The aged nitrile rubber models were constructed by introducing hydroxyl groups and carbonyl groups into rubber molecular chains to mimic oxidative aging. The static and dynamic properties of the unaged and aged nitrile rubber under different conditions were evaluated by mean square displacement, self-diffusion coefficients, hydrogen bond, fractional free volume, radial distribution function, cohesive energy density and solubility parameter. The results show that the elevated temperature intensified significantly the mobility of rubber molecular chains and fractional free volume, while the compressive strain displayed the opposite effect resulting in packing and rearrangement of rubber chains. The introduction of hydroxyl groups and carbonyl groups enhanced the polarity, intermolecular interactions, the volume and rigidity of molecular chains, implying weaker mobility of molecular chains as compared to unaged models. The compressive strain and oxidative aging both decreased the fractional free volume, which inhibited gaseous and liquid diffusion into the rubber materials, and slowed down the oxidative aging rate. This study provides insights to better understand the effect of molecular changes due to oxidative aging on the structural and dynamic properties of rubber materials at the molecular level.

Effect of Alternation of Aging and Seawater Erosion on Properties of Rubber Material Used in Lead Rubber Bearing

An artificially accelerated alternation of aging and seawater erosion test of rubber materials used in lead rubber bearing (LRB) was performed, mainly to study the time-varying laws of rubber materials mechanical properties. Time-varying laws of the Mooney–Rivlin and Neo-Hookean constitutive parameters of rubber materials under the alternation of aging and seawater erosion were also analyzed. Results indicate that the rubber material mechanical properties were significantly affected by alternation of aging and seawater erosion. Hardness and elongation stress increased exponentially with test time. And 120 days after the test, the hardness increased by 14%, the maximum percentage increase in stress of 124.76% occurred at 100% constant elongation and the minimum percentage increase in stress of 68.32% occurred at 300% constant elongation; Tensile strength and elongation at break decreased by 44.96% and 53.09%. Besides, constitutive parameters of Mooney–Rivlin and Neo-Hookean all changed greatly with test duration. Finally, time-varying laws of constitutive parameters were verified by comparing the simulated and experimental results of the lead rubber bearing’s stiffness. Research results are of great significance to the seismic performance research and life-cycle performance analysis of offshore traffic engineering such as cross-sea bridges and bridges in the marine environment.

Simulation, analysis and comparison of cutting parameter during turning of Ti-6Al-4V alloy with assorted industrial coated carbide

This work focuses on studying the special effects of processing conditions on the J-C (Johnson-Cook) material model factors for orthogonal turning of Ti-6Al-4V. It is highly corrosive resistant materials. Two sets of factors of the Johnson-Cook material model describing material behavior of both alloy were investigated by comparing cutting forces, chip study, and chip tool interfaces temperature. A 2-D finite element model was made and validated with the results of published literature. Cutting tests were conducted at low, medium, and high-speed cutting speeds with three different cutting tools. Chip formation and cutting forces were compared for both numerical models. It was observed that cutting forces decrease as cutting speed increases. Three different types of cutting tools are used here with the same geometry so that the result can be compared attractively. The results are then compared with experimental references and more standard models: an ALE model developed with ABACUS (FEA software). It was observed that the Polycrystalline Diamond tool produces less force as compared to other tools. The results obtained through simulation analysis after including changes in the coefficient of friction and other material properties showed a good agreement with the experimental results.

Insights on the Formation Mechanism of Ultra-Low Friction of Phenolic Resin Graphite at High Temperature

In the present paper, the influences of high temperature on the tribological properties of phenolic resin graphite (PRG) sliding against tungsten carbide-nickel (WC-Ni) alloy in ambient air were investigated systematically. Results demonstrated that the antifriction behaviors of PRG was sensitive to high temperature and PRG exhibits ultra-low coefficient of friction (CoF) of about 0.01–0.015. The low CoF is attributed to the formation of graphite tribofilms, which shows different formation processes on the contact interface at different temperatures (room temperature, 200, 300 and 400 °C). These findings provide insight into the formation mechanism of graphite tribofilms, and provide an important basis for improving the tribological properties of graphite-based friction materials and manufacturing new graphite for seal applications.

Experimental studying the effect of water temperature on friction properties of marine propeller sliding bearing

This paper presents the effect of water’s temperature on the friction properties of materials used in marine propeller sliding bearing. Copper-Rubber and Copper-Capron, two common pairs of material in the shaft water-lubricated polymer bearing were chosen to conduct experiments with the pin-on-disc model. Various conditions including water temperature, stress, and sliding velocity were examined, their results showed that in the range 30 °C to 100 °C of water temperature, the frictional coefficient of both friction pairs were unchanged under the small stress and low sliding velocity (0.3 MPa and 0.9 m/s). While in the case of stress and sliding velocity were both high (0.6 MPa and 1.5 m/s), it increased significantly in a certain transition temperature range. This temperature range of the pair Copper-Rubber and Copper-Capron is 50 °C to 60 °C and 80 °C to 90 °C, respectively. The experiment’s results also pointed out that in these transition temperature ranges, the friction coefficient of two pairs was slightly influenced by the change in sliding velocity, whereas the stress change has an important impact on its values. Nonetheless, when the water temperature was below the transition range, the effect of the stress change on the friction coefficient was not significant. Thus, high water temperature is the main reason for the friction coefficient’s increase rather than the increase of the stress. This work is expected to broaden the understanding of the friction behavior of the water-lubricated polymer bearing.

Walter Krenkel – CMC‐pioneer and dedicated expert on ceramics

Professor Walter Krenkel is a worldwide known specialist for Ceramic Matrix Composites (CMC), the Liquid Silicon Infiltration (LSI) process and the invention of the C/C-SiC ceramic brake disc. He was born in 1955 in Bad Cannstatt, a famous part of the well-known city of Stuttgart in Germany. After school, he decided to study aerospace engineering in 1976 at the University of Stuttgart where he got his diploma in 1984. Immediately after finishing his diploma, he started his career as a research assistant in the Institute of Structures and Design at the German Aerospace Centre (DLR) in Stuttgart. Since 1990 he worked on the commercial application of C/C-SiC materials that was used for the space application so far. In 1992, within a research project he and his colleagues from DLR created as a spin-off from thermal protection materials for re-entry space vehicles, a ceramic brake disc, based on C/C-SiC for railway vehicles. After gaining valuable experiences in research and development projects, in 1996, he started to work as a leader of the Ceramic Composites and Structures Group in the same department. His continuous work on ceramic brakes led to the invention of the ceramic brake discs for passengers’ cars, together with several industrial partners between 1997 and 2001. His increasing know-how about ceramic matrix composites in general and about ceramic brakes in particular make him the perfect choice as the head of the Centre of Excellence about Ceramic Lightweight Structures and High Temperature Applications in 1999. One year later, he finished his PhD on the subject of cost-efficient manufacturing of CMC, based on the LSI-process in the Faculty of Aerospace Engineering of the University of Stuttgart. Due to his initiative, the LSI-process was successfully transferred to the industry and was developed to the most established high temperature-process to manufacture CMC at reasonable costs. On the basis of his professional performance, it was offered to him to work as a Professor at the University of Bayreuth at the Chair of Ceramic Materials Engineering (CME) in 2004. He continued his engagement in several ceramic societies, as the Dean of the Faculty of Engineering Science in the University of Bayreuth during 2015–2017 and as a Guest Professor in the Southeast University in Nanjing and the Central South University of Changsha (China). During his career, he wrote more than 200 articles and 35 patents. In Bayreuth he led the Chair of Ceramic Material Engineering to the top in the university, regarding the funding from third parties. His engagement constantly influenced the whole ceramic community. He was responsible for organizing numerous national and international conferences. In 2010, he brought the HT-CMC 7 conference to Bayreuth and managed this scientific premium event in very remarkable fashion. Due to his constant work as a scientist and a professor in Bayreuth, he gained a huge knowledge in almost all fields of ceramics, with focus in CMC, polymer derived ceramics (PDC), the evaluation of structural and functional ceramics and the tribological properties of high-performance ceramic friction materials. His worldwide reputation is unique and his experiences in the field of ceramics influence the research and development activities in the whole ceramic community. After winning prizes from all significant ceramic societies worldwide (German, American and European), for example, the Bridge Building Award from the ACERS and the Seger Medal of the DKG, he is enjoying the well-deserved retirement since April 2021. His contributions to the field of CMC and ceramics in general are fundamental and lead the way to the future of this material class. The ideas of Professor Krenkel will give his former chair and the ceramic community the best chances to enhance the impact of ceramics and to find new applications within the megatrends and challenges in the 21th century.

The Use of Copper Oxides as Cross-Linking Substances for Chloroprene Rubber and Study of the Vulcanizates Properties. Part II. The Effect of Filler Type on the Properties of CR Products.

The properties of rubber materials are dependent on the characteristics of the elastomer matrix, the filler type, the cross-linking agent, the number of ingredients, and their interactions. In the previous article, we showed that chloroprene rubber can be efficiently cross-linked with copper(I) oxide or copper(II) oxide. During the processing of rubber compounds, the incorporation of a filler and a curing substance are two substantial parameters, such as the homogeneity of mixing and cross-linking that significantly affect the properties of the vulcanizates. Therefore, this work aimed to evaluate the curing characteristics, mechanical and dynamical properties, morphology, and flammability of the composites containing chloroprene rubber cross-linked with Cu2O or CuO and filled with different fillers (silica, carbon black, montmorillonite, kaolin, chalk). It was found that the type of filler and curing agent had a significant impact on the degree of cross-linking of the chloroprene rubber and the properties of its vulcanizates. The degree and speed of the cross-linking of filled CR were higher when the CR was cured with copper(II) oxide. Among the fillers used, the presence of carbon black or silica ensured the highest degree of CR cross-linking and the most useful properties. The flammability tests indicated that all produced vulcanizates were characterized by a high oxygen index, which allows them to be classified as non-flammable materials.

Optimization of pore structure and wet tribological properties of paper-based friction materials using chemical foaming technology

Paper-based friction materials are porous materials that exhibit anisotropy; they exhibit random pore sizes and quantities during their preparation, thereby rendering the control of their pore structure difficult. Composites with different pore structures are obtained by introducing chemical foaming technology during their preparation to regulate their pore structure and investigate the effect of pore structure on the properties of paper-based friction materials. The results indicate that the skeleton density, total pore area, average pore diameter, and porosity of the materials increase after chemical foaming treatment, showing a more open pore structure. The addition of an organic chemical foaming agent improves the curing degree of the matrix significantly. Consequently, the thermal stability of the materials improves significantly, and the hardness and elastic modulus of the matrix increase by 73.7% and 49.4%, respectively. The dynamic friction coefficient increases and the wear rate is reduced considerably after optimizing the pore structure. The wear rate, in particular, decreases by 47.7% from 2.83 × 10−8 to 1.48 × 10−8 cm3/J as the foaming agent content increases. Most importantly, this study provides an effective method to regulate the pore structure of wet friction materials, which is conducive to achieving the desired tribological properties.

Effect of radiation on mechanical properties and molecular structure of rubbers for nuclear robots

As polymers, rubber materials are easily affected by radiation; therefore, their radiation resistance must be considered for their use in robots and automation equipment in high-radiation environments. In this study, the properties of several common rubber materials, ethylene propylene diene monomer (EPDM), nitrile rubber (NBR), hydrogenated nitrile rubber (HNBR), fluororubber (FKM), and acrylate rubber (ACM), were investigated under high-dose gamma-ray irradiation. The dose rate of gamma rays was 66.76 Gy/min, and the cumulative dose was 1214965.24 Gy. Oxidative decomposition of the double bond of EPDM occurred, leading to slight decreases in the strength and elongation. NBR and HNBR were mainly subjected to crosslinking of the molecular structure, resulting in small increases in strength and significant decreases in elongation. The cyano decomposition reaction occurred in ACM, and its crystallinity increased, leading to embrittlement and decreases in the strength and elongation. Oxidative decomposition and cross-linking simultaneously occurred in FKM, resulting in an increase in strength and decreases in elongation and the elastic modulus.

Optimization of Process Parameters for Friction Materials Using Multi-Criteria Decision Making: A Comparative Analysis

Friction materials, mainly made of reinforced composites, should possess excellent physical and tribological properties, such as a higher coefficient of friction, minimum wear, adequate surface hardness, and higher porosity for various automotive brake applications. Attainment of those properties greatly depends on the settings of different input parameters, such as molding pressure, temperature and time, temperature and time of heat treatment/sintering, etc., during the processing of friction materials. In this article, four multi-criteria decision-making (MCDM) tools, i.e., technique for order of preference by similarity to ideal solution (TOPSIS), evaluation based on distance from average solution (EDAS), VlseKriterijumska Optimizacija I Kompromisno Resenje (VIKOR), and multi-objective optimization on the basis of ratio analysis (MOORA) are applied to identify the optimal parametric combinations for two different friction materials. A comparative analysis of the derived results suggests the same optimal parametric mixes for all the MCDM techniques for both case studies. Thus, for the considered case studies, the optimal parametric combinations as molding time = 8 min, molding temperature = 175 °C, molding pressure = 27 MPa, sintering time = 10 h and sintering temperature = 225 °C, and molding pressure = 27.90 MPa, molding temperature = 170 °C, curing time = 8 min, and heat treatment time = 1 h, respectively, would help in attaining the most desired properties of friction materials. Improvements in the predicted response values prove the efficacy of the adopted MCDM techniques in determining the optimal combinations of various process parameters for friction materials.