Stick-slip behaviours of water lubrication polymer materials under low speed conditions

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.

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Tribological Properties of Water-lubricated Rubber Materials after Modification by MoS 2 Nanoparticles

Tribological behaviour of carbon filled hybrid UHMWPE composites in water

Study on tribological properties of novel biomimetic material for water-lubricated stern tube bearing

Influence of local bush wear on water lubricated sliding bearing load carrying capacity

A new rubber/UHMWPE alloy for water-lubricated stern bearings

Bioceramic scaffolds for repairing mandibular bone defects have considerable effects, whereas pore architecture in porous scaffolds on osteogenesis in specific structures is still controversial. Herein 6 mol% magnesium‐substituted calcium silicate scaffolds were fabricated with similar porosity (∼58%) but different cylindrical pore dimensions (Ø 480, 600, and 720 μm) via digital light processing‐based three‐dimensional (3D) printing technique. The mechanical properties, bioactive ion release, and bio‐dissolution of the bioceramic scaffolds were evaluated in vitro, and the facilitation of scaffolds on bone formation was investigated after implanting in vivo. The results showed that as the pore dimension increased, the scaffolds indicated similar surface microstructures, but their compressive strength was enhanced gradually. There was no significant difference in vitro bio‐dissolution between the 480 and 600 μm groups, whereas the 720 μm group showed a much slower dissolution and ion release. Interestingly, the two‐dimensional/three‐dimensional (2D/3D) micro‐CT reconstruction analysis of rabbits' mandibular bone defects model showed that the 600 μm group exhibited evidently higher ratio of the newly formed bone volume to total volume (BV/TV) and trabecular number (Tb. N) values and lower ratio of the scaffolds residual volume to total volume (RV/TV) compare to the other two sizes. Furthermore, the histological analysis also revealed a considerably higher new bone ingrowth rate in the 600 μm group than the other two groups at 4–12 weeks post‐implantation. Totally, it is proved from these experimental studies that the DLP‐based accurately fabricated calcium (Ca) silicate bioceramic scaffolds with appropriate pore dimensions (i.e., 600 μm in pore size) are promising to guide new bone ingrowth and thus accelerate the regeneration and repair of cranial maxillofacial or periodontal bone defects.

3D printed bioceramic scaffolds: Adjusting pore dimension is beneficial for mandibular bone defects repair


Purpose
The purpose of this paper is to propose a wheel/rail mixed lubrication model to study the water lubrication behavior of wheel/rail contact interface.


Design/methodology/approach
The numerical simulation method is applied in this paper. A deterministic mixed lubrication model considering surface roughness and transient state is established. The quasi-system numerical and finite difference method are used for numerical solution. The model is verified by comparing with the experimental data in the literature under the same conditions.


Findings
Under wet conditions, the change of train speed will change the lubrication state of the wheel/rail contact interface. With an increasing speed, the average film thickness and the film thickness ratio increase, while the adhesion coefficient, the contact load ratio and the contact area ratio decrease. When the creep ratio increases from 0% to 0.5%, the wheel/rail adhesion coefficient and subsurface stress increase sharply. With the increase of axle load, the average film thickness decreases and the adhesion coefficient increases.


Practical implications
This paper aims to improve the mixed lubrication theory by analyzing the characteristics of wheel/rail friction and lubrication, so as to provide some guidance and theory for train driving behavior.


Originality/value
Using the deterministic model, the lubrication state of the wheel/rail contact interface affected by various external factors and the adhesion behavior of wheel/rail progressive process from boundary lubrication to mixed lubrication are studied.


Hong-ling Qin

Papers

A new rubber/UHMWPE alloy for water-lubricated stern bearings

3D printed bioceramic scaffolds: Adjusting pore dimension is beneficial for mandibular bone defects repair

Study on the adhesion behavior of wheel/rail under water conditions by using mixed lubrication model