Polytetrafluoroethylene (PTFE) is a self-lubricating material but has poor wear resistance. The wear resistance of the composites was enhanced by the incorporation of polyetheretherketone (PEEK), whereas the friction-reducing performance was compromised, thus resulting in an inherent trade-off between wear resistance and lubricity. Graphene nanosheets (GNSs) with high strength and lubricity were introduced as a reinforcement for PEEK/PTFE composites. Composite specimens with varying GNS contents were fabricated and characterized for their mechanical and tribological properties and wear morphologies. Combined with molecular dynamics (MD) simulations, the micro-mechanisms were further elucidated. The optimal GNS content was determined to be 2 wt%, which improved the tensile strength by 10.58% and reduced the wear rate by 17.88% compared to PEEK/PTFE. It achieved the synchronous enhancement of mechanical strength and wear resistance while maintaining desirable friction-reducing performance. MD simulation results demonstrated that the strong interfacial interactions between GNSx and the polymer enabled GNSs to adsorb polymer chains and form a dense rigid network with reduced free volume (FV). The mechanical properties were enhanced by efficient load transfer and the suppression of interfacial delamination enabled by this unique structure; meanwhile, wear resistance was improved due to the mitigation of friction-induced molecular chain scission.

In this study, the excellent rolling contact fatigue (RCF) property and failure mechanism of 8Cr4Mo4V steel with ultrafine primary carbides were investigated. The maximum equivalent diameter of the primary carbides was refined to less than 10 μm and an excellent RCF L10 life (10% failure probability) of 1.91×10⁸ cycles under contact pressure of 6 GPa was achieved. To the best of our knowledge, this represents the best RCF performance of 8Cr4Mo4V steel reported in the literature. Fatigue defects such as white etching area (WEA) were not found in the test specimen and the fatigue cracks primarily initiated from the micro-pitting on the specimen surface. The refinement of carbides suppresses the formation micro-pitting, thereby improving rolling contact fatigue life and life stability. Besides, the high contact stress induces plastic deformation in the subsurface of test specimen, forming oriented martensitic domains (OMD) and light etched region (LER). It was first found in this investigation that the mismatch in stress and strain distribution between LER and the martensite matrix results in the formation of long-fatigue cracks with lengths of several millimeters. The formation mechanism of sub-surface long-crack and OMD were also discussed emphatically.

To improve the oil swelling resistance and service life of nitrile butadiene rubber (NBR) under oil conditions, the reinforcing effects of glass fiber (GF), basalt fiber (BF), and polyethylene fiber (PE) at varying contents were investigated under normal and swelling conditions. The NBR/GF composites (10 phr) exhibited superior mechanical and tribological properties compared to NBR/BF and NBR/PE composites. The tensile strength and elongation at break of NBR/GF increased to 31.63 MPa and 251%, respectively, while the coefficient of friction (COF) decreased by 13.5% compared to pure NBR. After swelling, the NBR/GF composites maintained a tensile strength of 20.27 MPa, with a 33.7% reduction in elongation at break, and only a 5.93% increase in COF. Microscopic analysis of the wear surface and molecular dynamics simulations revealed the interfacial bonding mechanisms between NBR and fibers, explaining the contribution of fibers to improved mechanical and tribological properties. These findings offer valuable insights for developing NBR composites with enhanced swelling resistance and performance under oil conditions.

ABSTRACT This study combines molecular dynamics (MD) simulations and experimental characterization to investigate the regulatory patterns and underlying mechanisms of the effect of carbon nanotube (CNT) content on the tribological properties of poly(chlorotrifluoroethylene) (PCTFE)‐based composites at room temperature (25°C) and low temperature (−100°C). MD simulation results indicate that the incorporation of CNTs significantly enhances the structural stability and interfacial load‐bearing capacity of the composites. Experimental characterization shows that, at 25°C, 3% CNT/PCTFE exhibits the lowest wear rate (AR), reduced by 27.3% compared with pure PCTFE. Dispersed CNTs form a robust self‐lubricating transfer film on the friction surface, protecting the PCTFE matrix. At −100°C, the PCTFE matrix becomes more brittle, and 1% CNT/PCTFE demonstrates the best performance, with coefficient of friction (COF) and AR reduced by 29.1% and 66.7%, respectively, compared with pure PCTFE. The transfer film formed at low temperature shows higher compactness and stronger bonding with the matrix than that formed at room temperature. This study clarifies the reinforcing effects of CNTs on PCTFE at both temperatures, reveals the regulatory mechanisms of transfer film evolution and interfacial interactions governing the tribological properties, and provides quantitative theoretical support for the precise design of PCTFE‐based tribological materials for extreme environments.

Reversible ionic associations endowed carboxylated nitrile butadiene rubber (XNBR) with mechanical reinforcement and self-healing. However, further strengthening such associations often restricts chain rearrangement during self-healing, leaving a trade-off between tensile strength and self-healing efficiency. Herein, a small amount of sodium alginate (ALG) was proposed and introduced as an intermediate component into ionic XNBR. The effects of ALG and zinc oxide (ZnO) loading, and healing protocol on mechanical and self-healing properties were systematically evaluated. Results showed that at 0.25 phr ALG and 8 phr ZnO, a tensile strength of 28.3 MPa was achieved, together with recovery ratios of 97.46 % in tensile strength and 98.25 % in elongation at break after self-healing at 160 degrees C for 60 min. In this formulation, ALG was indicated to facilitate chain rearrangement at the fracture interface during self-healing. However, excessive ALG or ZnO reduced both properties. Additionally, a self-healing efficiency of 67.17 % was retained over three self-healing cycles. The loss factor, glass transition temperature, and storage modulus were analyzed together with fracture surface morphology to elucidate the underlying mechanisms governing mechanical and self-healing properties of ionic XNBR. Molecular dynamics simulations were further used to probe chain migration and the self-healing process, providing a molecular-scale insight for formulation design.

To enhance the sealing efficacy of nitrile butadiene rubber (NBR) in oil conditions, the synergistic reinforcing effects of glass fiber (GF) and polyethylene fiber (PE) ratios on the mechanical and tribological properties of NBR composites were explored under normal, aging, and swelling conditions. The mechanical properties of NBR composites were first investigated under three different conditions. The results indicated that the composite with a GF/PE ratio of 7:3 shows the optimal effect, achieving a tensile strength of 22 MPa. After aging and swelling, the tensile strength of composites with this ratio was 21.2 and 20 MPa, respectively, showing a decrease of only 3.6% (aging) and 9.3% (swelling) compared to normal conditions. Then, the tribological properties of NBR composites under different conditions reveal that the composite with a GF/PE ratio of 7:3 also behaved the best tribological performance. Its coefficient of friction further decreased by 3.6% after aging and increased by 10.3% following swelling, compared to the normal condition. The wear surface of composites was experimentally examined to reveal the wear morphology and fiber debonding behavior. Overall, a GF/PE ratio of 7:3 in NBR composites provided optimal mechanical and tribological performance under three conditions. In addition, the synergistic enhancement mechanism of different GF/PE ratios in NBR composites was examined at an atomic level using molecular dynamics simulations. The findings of this work are expected to support the development of high-performance and durable rubber sealing materials for the oil sealing industry.

This study explores the influence of functionalized graphene nanosheets (GNSs) on the tribological behavior of polyetheretherketone (PEEK)/polytetrafluoroethylene (PTFE) composites. To this end, pure GNS (PGNS) and GNS grafted with hydroxyl, carboxyl (COOH-GNS), and amino functional groups are prepared to fabricate PEEK/PTFE composite samples for friction experiments. The microstructure of the worn surface and energy dispersive spectroscopic distribution of the dual-surface transfer film are analyzed. The experimental results demonstrate that the COOH-GNS-reinforced PEEK/PTFE composite samples exhibit outstanding tribological properties. Specifically, the wear rate decreases by 20.9% compared to that of the PGNS-reinforced PEEK/PTFE composite samples, and a denser transfer film is formed on the dual surface. Additionally, molecular dynamics simulations are used to simulate the friction process and investigate the mechanism by which functionalized GNS enhances the tribological properties of the PEEK/PTFE composites. The simulation results reveal that the functional groups remarkably enhance the interaction between the GNS and the PEEK/PTFE composites, reduce the temperature and atomic concentration at the friction interface, and weakene the interaction between the PEEK/PTFE molecular chains and the friction pair, thereby improving the wear resistance of the PEEK/PTFE composites. Thus, this study provides a theoretical basis for the development of PTFE-based composites.

To enhance the wear resistance of polyether ether ketone (PEEK)/polytetrafluoroethylene (PTFE) composites, a friction model of PEEK and PTFE with a 1:9 mass ratio was first constructed using molecular dynamics (MD) simulations. Different mass fractions of nano-zirconium dioxide (ZrO2) were introduced as fillers to improve the wear resistance of the composites. The simulation results demonstrated the superior performance of the PEEK/PTFE composites with 6

Hydrogen peroxide, graphene oxide (GO), and hydroxylated carbon nanotubes (OHCNTs) were used to chemically modify ground tire rubber (GTR) of 40 mesh (40GTR) and 80 mesh (80GTR), which were then blended with styrene-butadiene rubber (SBR) to prepare recycled rubber and study its mechanical, friction, and damping properties. Compared to SBR/40GTR, the elastic modulus and tensile strength of SBR/80GTR rose by 19.5% and 25.2%, respectively. Compared to SBR/80GTR, the elastic modulus of acid-oxidized SBR/80GTR (SBR/80GTR-AO) increased by 2.49%. The mechanical properties of SBR/GTR composites indicated an initial increase followed by a decrease with increasing content of GO or OHCNTs. Among these, the performance enhancement of SBR/GTR-AO-GO was most significant. At 1 phr GO, the elastic modulus of SBR/GTR-AO-GO composites increased by 9.53%, and the coefficient of friction decreased by 1.74% compared to SBR/GTR. The wear surface morphology and dynamic mechanical properties of the composites were analyzed using scanning electron microscopy and a dynamic mechanical analyzer. Additionally, molecular dynamics simulations elucidated that the mechanical and tribological properties of the modified SBR/GTR composites are enhanced, thereby validating the effectiveness of the modified GTR in reinforcing these properties.Highlights Chemical modification of ground tire rubber (GTR) with diverse particle sizes. Grafting of nanomaterials onto the surface of GTR. Modified GTR improves mechanical properties of recycled rubber. Molecular dynamics simulations of the tensile and tribological properties of recycled rubber.

This study introduced a molecular dynamic (MD)-based numerical model to evaluate the mechanical and piezoelectric behavior of boron nitride nanotubes (BNNTs) and their composites, alongside a strategy to modulate mechanical and piezoelectric properties of their composite by controlling BNNTs defects. First, effects of BNNTs diameter and vacancy defects on their mechanical and piezoelectric properties were investigated, revealing the relationship between the defect orientation, symmetry, and electromechanical response. Subsequently, a Monte Carlo random number algorithm was applied to construct the coupling model of BNNTs/polydimethylsiloxane (PDMS) nanocomposites, enabling theoretical predictions of composite's mechanical and piezoelectric properties. Specifically, both the Young's modulus and piezoelectric coefficient (e33) of BNNTs decreased as their diameter increased. The vacancy defects had a complex effect on electromechanical properties of BNNTs. An increase in the number of defect atoms, dispersed vacancy defects, and circumferential defects significantly reduced the strength of BNNTs, whereas B atomic vacancies, symmetrical defects, and circumferential defects enhanced their piezoelectric performance. For BNNTs/PDMS composites, a larger BNNTs diameter and a moderate number of vacancy defects improved the interfacial bonding, which enhanced the Young's modulus and e33 values of composites. The BNNTs composites with circumferential defects exhibited higher mechanical strength than those with axial defects. These findings provided valuable insights into optimizing BNNTs diameter, defect management, and interfacial characteristics for designing high-performance piezoelectric nanocomposites for next-generation flexible devices.

This study constructs four functionalized graphene/nitrile-butadiene rubber (FGNS/NBR) molecular dynamics (MD) models under the COMPASS force field to evaluate mechanical properties and abrasion rates. For each composite, 50 independent shear simulations (200 samples) were run; averages of force-field energy components over the post-steady-state segment built a bonded/non-bonded energy-fingerprint library. Feature screening relied on the consensus across multiple importance measures, yielding 17 descriptors. A Random Forest regressor (RFR) was trained, and mechanistic interpretation combined SHapley Additive explanations with mutual information. The MD analyses indicate that functionalization generally enhances mechanical properties and improves wear resistance. Subsequently, the RFR explanatory model further revealed three principal determinants of wear performance-Fe layer van der Waals energy, total bond length after shearing, and the torsion-stretch energy of FGNS-and indicated that the interplay between chain extension and interfacial adsorption constitutes the dominant anti-wear pathway. Overall, the study introduces an interpretable comparative method focused on relative trends across functionalizations, offering a useful analytic perspective for small-difference systems and for considering functional group and grafting choices.

The recycling of the rubber powder was demonstrated to be an effective method for reducing waste rubber pollution and promoting resource circularity. This study prepared recycled rubber composites by incorporating waterjet-modified rubber powder (WMRP) and mechanically crushed rubber powder (MCRP) into a natural rubber matrix. The effects of the rubber powder type, mesh size, and loading of the rubber powder on the mechanical and tribological properties of the recycled rubber were investigated through comparative experiments. Significant enhancements in tensile strength (12.23 %) and elongation at break (29.41 %) were achieved by incorporating 30 phr of 120-mesh WMRP into the matrix, compared to an equivalent formulation utilizing 120-mesh MCRP. Furthermore, the incorporation of WMRP effectively reduced the coefficient of friction in the recycled rubber. The underlying mechanisms were elucidated through Fourier transform infrared spectroscopy and scanning electron microscopy. Molecular dynamics simulations at an atomic scale were conducted to study the friction mechanism of recycled rubber composites. In addition, machine learning was also employed to predict the coefficient of friction and tensile strength based on important features. The scientific findings in this work are expected to promote the value-added recycling of waste rubber and support the development of recycled rubber products.

Straightness is one of the important indices to measure the quality of bars; multi-roll straightening is an essential process in bar production. Materials undergo multiple cycles of alternating tensile and compressive loading during multi-roll straightening, subject to the influence of the Bauschinger effect. However, most existing studies have failed to adequately account for the Bauschinger effect, leading to insufficient prediction accuracy of the process. This study establishes an eleven-roll straightening finite element model (FEM) for bars based on the nonlinear combined hardening model. The orthogonal experimental design method is employed to optimize the process parameters. Straightening experiments of 20CrMnTi bars using an eleven-roll straightener were conducted. Based on the FEM, the influence patterns of different process parameters on the straightening results were investigated. The results indicate excellent agreement between the eleven-roll straightening finite element simulation results and the experimental results. Using the optimized parameters, both the simulated and experimental straightness after straightening were within 1‰, with a relative error between them below 8%. The findings of this study can improve the prediction accuracy of the eleven-roll bar straightening process and provide reliable theoretical support and technical reference for the optimization of straightening process parameters.

The reinforcement mechanism of functionalized graphene nanosheets (GNS) on the mechanical properties of polyetheretherketone (PEEK)/polytetrafluoroethylene (PTFE) composites was investigated. Composite specimens were fabricated using PGNS, as well as GNS grafted with hydroxyl, carboxyl (-COOH) and amino functional groups, and mechanical characterizations were conducted on the prepared specimens. The results demonstrated that carboxyl-functionalized GNS (COOH-GNS) exhibited the most remarkable reinforcing effect on PEEK/PTFE composites, with its elastic modulus, tensile strength, yield strength and compressive modulus increased by 47.09%, 31.1%, 45.16% and 20.91%, respectively, compared with PGNS-reinforced composites. Combined with experimental measurements and molecular dynamics simulations, the reinforcement mechanism of this composite system was elucidated. The functional groups on the surface of GNS can induce interfacial interactions with the PEEK/PTFE matrix, by which the mobility of polymer molecular chains is restricted, the deformation and slippage of molecular chains are suppressed, and the interfacial bonding between GNS and the polymer matrix is simultaneously strengthened. The enhancement of interfacial binding energy, the reduction in free volume in the composite system, and the restriction of polymer molecular chain mobility were identified as the critical atomic-scale mechanisms responsible for the improvement of the macroscopic mechanical properties of the composites.

Grafting different functional groups on the graphene has emerged as a powerful method to precisely regulate the wear behaviors of graphene/polymer composites. However, experimental approaches are often time-consuming and costly, restricting the efficiency of the design of new materials. In this study, molecular-dynamics-derived energy descriptors were coupled with a random forest regression (RFR) framework to systematically and quantitatively elucidate the wear mechanisms of functionalized graphene-reinforced nitrile butadiene rubber (FGNS/NBR) composites. Four FGNS/NBR matrices were simulated under shear conditions to establish a dataset containing 264 samples for constructing the RFR prediction model. To identify critical influencing factors, Feature Importance and Permutation Importance were applied to sift the optimal model for further interpretation analysis. The results showed that Bond energy and Angle energy were the most critical parameters influencing the abrasion rate, with a significant interaction observed between the two. The functionalization significantly increased the bond and angle energies of composites, consequently reducing their abrasion rate. In particular, the nitrophenyl-functionalized composite exhibited the lowest abrasion rate among all functionalized composites studied, showing a strong synergistic interaction between Bond energy and Non-bond energy interactions compared to carboxyl- and amino-functionalized graphene composites, significantly enhancing its wear resistance. Further molecular dynamic analyses elucidated that the enhancements in these key energy parameters originated from the introduction of functional groups onto the graphene surface. These findings provided clear theoretical insights and practical guidelines for designing and developing high-performance, wear-resistant polymer composites.

Thermo-oxidative aging is the primary degradation pathway governing the service life and reliability of recycled rubber, as it impairs mechanical properties and limits reutilization. Combined experimental and molecular dynamics (MD) simulations were employed to examine the microstructural evolution and mechanical response of styrene-butadiene rubber (SBR) and ground tire rubber (GTR) during the thermo-oxidative aging process. Furthermore, the influence of various modified GTRs on the performance of recycled rubber was also investigated. Accelerated aging at 100 degrees C led to a decrease in tensile strength and elongation at break, accompanied by an increase in hardness. Acid oxidation and incorporation of nanomaterials effectively improved the mechanical and friction properties of aged recycled rubber. Notably, composites containing graphene oxide demonstrated superior performance compared to those with hydroxylated carbon nanotubes, showing a 3.38% enhancement in elastic modulus and a 14.19% reduction in the coefficient of friction. MD simulations were employed to elucidate the influence of thermo-oxidative aging on the tensile and frictional properties of recycled rubber, and the calculated results were found to be in good agreement with the experimental observations. This work establishes a quantitative oxidation-property nexus for recycled rubber and provides design guidelines for sustainable, aging-resistant elastomers.

Rubber has a wide range of application prospects as an important material in the field of oil extraction and sealing rings. The effect of molybdenum disulfide (2H-MoS2) on the properties of the composites of antioxidant 4020 and nitrile butadiene rubber (NBR) was investigated. Two sets of composites, 4020/NBR and MoS2/4020/NBR, were modeled using molecular dynamics simulations. The mechanical, thermal-oxidative aging and tribological properties of 2H-MoS2 on NBR composites were investigated at 298 and 398 K, respectively, and the adsorption ability and reinforcement effect of 2H-MoS2 on NBR were analyzed from an atomic perspective. The mechanical studies showed that Young’s modulus of MoS2/4020/NBR composites was improved by about 28

A comprehensive and comparative study of the thermal-oxygen aging and tribological properties of antioxidant 6PPD synergized with carbon nanotubes (CNTs) and graphene (GE)-reinforced hydrogenated nitrile rubber (HNBR) composites was performed using molecular simulations and experiments. The results indicated that GE exhibits superior capabilities in inhibiting the volatilization and migration of the antioxidant 6PPD compared to CNTs and enhancing the thermal and oxygen aging resistance of HNBR. The surface morphology of the HNBR composites was characterized using scanning electron microscopy (SEM) and X-ray spectroscopy (XPS), which revealed the different enhancement mechanisms of CNTs and GE. The mechanical and tribological properties of the HNBR composites were experimentally investigated before and after the thermal-oxygen aging. The results revealed that the tensile and tear strengths of the 6PPD/HNBR composites with added GE increased by approximately 4% compared to those of the 6PPD/HNBR composites with added CNTs. The coefficient of friction decreased by approximately 7%. Finally, the wear surface morphologies of the HNBR composites were characterized using SEM and energy dispersive spectrometer (EDS). These results further indicate that the larger specific surface area of GE can be better combined with HNBR, improving its overall thermal-oxygen aging and tribological properties.

A novel functional carbon nanofiller CNTs-COOH-RD resistant to thermal-oxidative aging was prepared by grafting 1,2-dihydro-2,2,4-trimethyl-quinoline (antioxidant RD) onto the surface of carboxylated carbon nanotubes (CNTs-COOH) using gamma-(2,3-epoxypropoxy) propytrimethoxysilane (KH560). Five groups of nitrile butadiene rubber (NBR) composites were prepared by mechanical blending, and the effects of CNTs-COOH-RD on the mechanical and tribological properties of NBR composites were investigated. The results showed that compared to pure NBR and free antioxidant RD-loaded samples, the tensile and tear strengths increased by approximately 23%, 5%, 18%, and 4%, respectively. The wear surfaces of the NBR composites were characterized using scanning electron microscopy and X-ray energy spectroscopy, which revealed the reinforcing mechanism of CNTs-COOH-RD. Molecular dynamics simulations were used to explain the thermal-oxidative aging mechanism of CNTs-COOH-RD from an atomic mechanism perspective. The results showed that the mobility of CNTs-COOHRD within the NBR matrix was significantly reduced compared with that of the free antioxidant RD. The proposed functional carbon nanofiller enabled the NBR composites to exhibit superior mechanical and thermaloxidative aging properties during the aging failure process.

The mechanical and tribological properties as well as the microstructural characteristics of five groups of nitrile butadiene rubber (NBR)/graphene (GE)/phenolic resin (PF) composites were systematically investigated using a combination of experimental and molecular dynamics (MD) simulation methods. Experiments confirmed that PF effectively enhanced the mechanical properties of NBR, including the crosslinking density, hardness, and compression permanent deformation, along with its tribological performance under various working conditions. MD simulations further clarified the tribological mechanism of the NBR/GE/PF composites from a microscopic perspective, highlighting the pivotal role of the hydrogen-bonding network. PF15 exhibited low wear and mobility during friction owing to its robust hydrogen-bonding network.Highlights Combined experiments and simulation for NBR performance analysis. Investigated the tribological properties of NBR/GE/PF under various conditions. Hydrogen bonding in NBR/GE/PF was achieved via simulation. A good correlation was found between experimental results and simulation data.