Xiuqin Bai

Study on wear behaviour and wear model of nitrile butadiene rubber under water lubricated conditions

Nitrile Butadiene Rubber (NBR) is widely used to make water-lubricated rubber stern tube bearings in the marine field. Its tribological properties, which significantly influence its reliable life, directly affect the safe navigation, covert performance and operating costs of a ship. This study aimed to investigate the tribological properties and wear model of NBR under water-lubricated conditions. A CBZ-1 tribo-tester was used to conduct sliding wear tests between NBR pins and 1Cr18Ni9Ti stainless steel discs under water-lubricated conditions. The surface morphologies of the worn NBR pins were examined using laser-interference profilometry and scanning electron microscopy. In addition, the friction coefficients, ageing times and wear rates were analysed and compared to study the tribological properties of NBR and to identify the factors that affect its wear mass loss. The results demonstrated that different ageing times, velocities and loads had a significant effect on the friction and wear properties of the NBR specimens. The ageing times positively correlated with the friction coefficients and the wear mass losses between the rubbing pairs. The anti-tear properties of NBR deteriorated when the material was aged at a high temperature for an extended period of time, which reduced its wear-resistance. The main wear mechanism between the rubbing pairs was severe adhesion tearing wear under the water-lubricated conditions. A comprehensive empirical model for its wear rate estimation was established based on the wear and friction power. The model revealed the relationships between wear and velocity, as well as load and shore hardness. The result produced by the model was largely consistent with the experimental results. The knowledge gained in this study is anticipated to provide the theoretical data for a wear theory study of NBR and be useful for the optimisation of water-lubricated rubber stern tube bearings.

Tribological Properties of Water-lubricated Rubber Materials after Modification by MoS2 Nanoparticles.

Frictional vibration and noise caused by water-lubricated rubber stern tube bearings, which are generated under extreme conditions, severely threaten underwater vehicles’ survivability and concealment performance. This study investigates the effect of flaky and spherical MoS2 nanoparticles on tribological properties and damping capacity of water-lubricated rubber materials, with the aim of decreasing frictional noise. A CBZ-1 tribo-tester was used to conduct the sliding tests between rubber ring-discs and ZCuSn10Zn2 ring-discs with water lubrication. These materials’ typical mechanical properties were analysed and compared. Coefficients of friction (COFs), wear rates, and surface morphologies were evaluated. Frictional noise and critical velocities of generating friction vibration were examined to corroborate above analysis. Results showed that spherical MoS2 nanoparticles enhanced rubber material’s mechanical and tribological properties and, in turn, reduced the friction noise and critical velocity. Flaky MoS2 nanoparticles reduced COF but did not enhance their mechanical properties, i.e., the damping capacity, wear resistance property; thus, these nanoparticles did not reduce the critical velocity obviously, even though increased the frictional noise at high load. The knowledge gained in the present work will be useful for optimizing friction pairs under extreme conditions to decrease frictional noise of water-lubricated rubber stern tube bearings.

Protein engineering of a new recombinant peptide to increase the surface contact angle of stainless steel

Biofouling seriously affects the properties and service life of metal materials. A number of studies have shown that the initial bacterial attachment to the metal surface and the subsequent formation of biofilm are dependent on the surface characteristics of the substratum, including metal surface free energy, roughness and metallurgical features. In this study, a novel recombinant fusion protein, which consists of receptor binding domain protein (RBD), truncated protein fragment of MrpF and alkaline phosphatase (PhoA) domains, has been constructed in an attempt to increase the surface contact angle of stainless steel. It has been confirmed that RBD has a strong affinity to 304 stainless steel; the truncated protein fragment of MrpF has high hydrophobicity and anchoring features, which can improve the contact angle of the material surface, whilst PhoA is an effective detection tool to monitor the expression and secretion of fusion protein. Multiple assays including FTIR, XPS, SEM-EDS and contact angle measurement revealed the existence of nitrogen and sulfur elements, binding energy shifts of nitrogen, carbon and oxygen atoms, and new FTIR peaks in treated stainless steel samples with increased contact angles at about 50°, confirming that a new organic steel material has been produced responding to these surface property changes. Using novel recombinant peptides to react with steel could become a new technique to increase the surface contact angle of the stainless steel for diverse applications.

Preparation and analysis of a new bioorganic metallic material

Biofouling on metal surfaces is one of the main reasons for increased ship drag. Many methods have already been used to reduce or remove it with moderate success. In this study, a synthetic peptide has been utilized to react with 304 stainless steel aiming to generate a bioorganic stainless steel using a facile technique. After the reaction, white matter was found on the surface of the treated stainless steel via SEM, whilst the nontreated stainless steel had none. Elemental analysis confirmed that excessive N existed on the surface of the treated samples using an integrated SEM-EDS instrument, implying the presence of peptides binding on the surface of the bioorganic stainless steel. The FTIR spectra showed amide A and II peaks on the surface of the bioorganic stainless steel suggesting that either the peptides grafted onto the steel surface or the polypeptide composition accumulated on the steel samples. XPS analysis of the treated steel demonstrated that there was nitrogen bonding on the surface and it was a chemical bond via a previously unreported chemical interaction. The treated steel has a markedly increased contact angle (water contact angle of 65.7 ± 4.7° for nontreated steel in comparison to treated, 96.4 ± 2.1°), which supported the observation of the wettability change of the surface, i.e. the decrease of the surface energy value after peptide treatment. The changes of the surface parameters (such as, Sa, Sq, Ssk and Sku) of the treated steel by surface analysis were observed.

Study of Simulation Tester for Key Rubbing Pairs in Internal-Combustion Engine

A simulation tester was designed which could be used to simulate the wear and vibration of the key rubbing pairs in an internal-combustion engine, such as cylinder liner-piston ring, crankshaft and sliding bearings. Its pivotal innovation is that high pressure air was adopted to simulate the explosive pressure and pressure evolution in a cylinder to accord with the real conditions. Pressure sensors, vibration accelerations sensors, oil monitoring sensors and temperature sensors were installed at many points and directions on the tester support to form an on-line condition monitoring system via the developed software, which could simultaneously monitor the real-time wear and vibration condition for key rubbing pairs in internal-combustion engine. It is believed that the successful application of the tester for both tribological and dynamic characterization will be very significant to study the key rubbing pairs in internal-combustion engine.

Effects of Contaminants on Skid Resistance of Asphalt Pavements

Skid resistance is one of the most important properties of asphalt pavements. Contaminants in asphalt pavements affect skid resistance at a certain extent. The detailed effects of contaminants on skid resistance of asphalt pavements were investigated. The core samples of AC-13, SMA-13, SHRP -12.5 and OGFC-13 compressed by the Superpave Gyratory Compactor (SGC) in the laboratory were used as pavement samples, which were usually applied in China. The lube oil, sand, earth, grit and water were chosen as contaminants. By testing skid numbers by British Pendulum Tester of the clean samples and the samples with contaminants in three contamination situations (little-covered, half-covered and all-covered), the effects of contaminants on skid resistance of dry and wet asphalt pavements were analyzed. It was proved that contaminants affected skid resistance of asphalt pavements distinctly. The knowledge gained in this study would provide guidance for the maintenance of asphalt pavements.

Coupling mechanism between wear and oxidation processes of 304 stainless steel in hydrogen peroxide environments

Stainless steel is widely used in strongly oxidizing hydrogen peroxide (H2O2) environments. It is crucial to study its wear behaviour and failure mode. The tribological properties and oxidation of 304 stainless steel were investigated using a MMW-1 tribo-tester with a three-electrode setup in H2O2 solutions with different concentrations. Corrosion current densities (CCDs), coefficients of frictions (COFs), wear mass losses, wear surface topographies, and metal oxide films were analysed and compared. The results show that the wear process and oxidation process interacted significantly with each other. Increasing the concentration of H2O2 or the oxidation time was useful to form a layer of integrated, homogeneous, compact and thick metal oxide film. The dense metal oxide films with higher mechanical strengths improved the wear process and also reduced the oxidation reaction. The wear process removed the metal oxide films to increase the oxidation reaction. Theoretical data is provided for the rational design and application of friction pairs in oxidation corrosion conditions.

A numerical study of drag reduction of superhydrophobic surfaces in shipping industry

As energy-conservation and emission-reduction become more and more severe, the concept of Green Ship has been proposed. And drag reduction is a realizable method to achieve this goal. Superhydrophobic surfaces (SHSs) whose contact angle is greater than 150° have attracted much attention because of the ability of realizing drag reduction in turbulent flows. However, few researchers focus on the application of SHSs in shipping industry. In this paper, a numerical study of turbulent channel flows and turbulent boundary layers developing over SHSs are performed. In the simulation, the VOF multiphase flow model is used for the gas-liquid phase flow, and a superhydrophobic surface microstructure grid with local encryption technology is adopted. The results show that within the range of ship economic speed, a stable gas vortex can form in the upper part of microstructure, and the drag reduction ratio of SHSs has a close relationship with size of velocity, gas-liquid contact area, and soaking time.

Study on influencing factors for wear of water-lubricated rubber stern tube bearing

The water-lubricated rubber stern bearing is one of the key components of ships. Investigating the influence of factors on its wear life has an important significance to guarantee the safety navigation of ships. This study aimed to explore how the lubrication state, load and rotational speed influence on the wear mass loss of the water-lubricated rubber stern tube bearing. A CBZ-1 tribo-tester was used to conduct the sliding wear tests between rubber disc and brass disc rubbing pairs under the water-lubricated conditions or dry conditions. The orthogonal tests was used to quantitate how the different lubrication states, loads and rotational speeds influence on the wear life, and were analyzed and compared based on calculations of orthogonal test. The results showed that only the lubrication states had significant influence on the wear life. Compared with the lubrication state, the influence of the load on the wear mass loss was almost negligible. The lubrication states, rotational speeds and loads affected the wear mass loss of stern tube bearing gradual decline. In actual operation, it is most important to ensure the good lubrication for the water-lubricated rubber stern tube bearing, the imparters of load and rotational speed are considered followed.

Reducing surface energy to improve energy efficiency of ships

Attachment of marine organisms leads to a significant increase of the friction of the hull surface which will reduce the reliability and energy efficiency of ships. The adhesion of destructive organisms can be decreased effectively via reducing the surface energy of the hull. A new type of material was produced using a peptide to bond with 304 stainless steel samples for improving the energy efficiency of ships. It is known that some N-containing substances generated on the surface of the samples by SEM equipped with EDS, which suggested that a new substances obtained by bonding between the peptide and 304 stainless steel. Contact angles of the surface of samples were measured utilizing a contact angle meter, and the value revealed that contact angles of the samples surface have been significantly increased after treating with peptide, and the Youngs equation shows that the surface energy of samples surface have been significantly reduced. The new material provided a way for drag reduction of ships.