Numerical Simulation and Experimental Study on Sealing Performance and Frictional Property of Rotary Lip Seal

The hydrodynamic theoretical lubrication model of the friction pair between the rotary shaft and the lip seal under the state of full film lubrication was established in this paper. The Reynolds equation was solved by using the finite difference method, and the influence of the viscosity-temperature characteristics of the lubricant was taken into account in the solution process. The distribution of the film thickness and the hydrodynamic pressure in the sealing area was obtained. At the same time, the bench test was carried out and the correctness of the model was verified by comparing the simulation results and test results of reverse pumping rate and friction torque under different rotational speed of the shaft. The microasperity of the lip surface is a necessary condition for achieving the sealing effect. Therefore, the influences of the contact load of the seal and the root mean square deviation of the lip surface on the sealing performance and frictional property were analyzed by using the theoretical model. The analysis results show that the sealing performance and frictional property can be changed by changing the contact load and surface roughness of the lip, but a single increase in the influence of a certain factor cannot achieve good results, and comprehensive consideration is required in product design.

Experimental research on the wall-wetting effects on the frictional property of the cylinder liner–piston ring pair

The application of novel injection strategies (high-pressure injection, early injection, retarded injection, etc.) in combustion engines has made the wall-wetting problem severer. As the splashed fuel dilutes the lubricating oil, the tribological performance of the cylinder liner–piston ring pair will be affected. In this research, the viscosity and wettability tests were conducted firstly by mixing diesel into lubrication oil. It was found that the dynamic viscosity of the mixture drops with more fuel diluting the oil, and a small quantity of diesel mixed will cause a remarkable decline in lubricant viscosity; also, the contact angle shows a downward trend with the increasing diluting ratio. Then based on several typical diluting ratios, the reciprocating friction tests were carried out to measure the instantaneous friction force of the production ring/liner pair. The experimental results showed that under a mixed lubrication state, the peak friction force of the ring/liner pair occurs around the dead centers, while the minimum force occurs at the middle position of the reciprocating stroke; with more fuel diluting the oil, the bearing capacity of oil film degrades, resulting in the increase of friction force. In addition, the average friction coefficient of the ring/liner pair shows an upward trend with the increasing diluting ratio, and the Stribeck curve moves toward the upper-left, which means the lubrication condition of this pair tends to transit from mixed lubrication to boundary lubrication, causing negative effects on the frictional property of the cylinder liner–piston ring pair. Therefore, the diluting ratio should be controlled under 20%.

Rupture Propagation along Stepovers of Strike-Slip Faults: Effects of Initial Stress and Fault Geometry

ABSTRACT Large earthquakes on strike-slip faults often rupture multiple fault segments by jumping over stepovers. Previous studies, based on field observations or numerical modeling with a homogeneous initial stress field, have suggested that stepovers more than ∼5 km wide would stop the propagation of rupture, but many exceptions have been observed in recent years. Here, we integrate a dynamic rupture model with a long-term fault stress model to explore the effects of background stress perturbation on rupture propagation across stepovers along strike-slip faults. Our long-term fault models simulate steady-state stress perturbation around stepovers. Considering such stress perturbation in dynamic rupture models leads to prediction of larger distance a dynamic rupture can jump over stepovers: over 15 km for a releasing stepover or 7 km for a restraining stepover, comparing with the 5 km limit in models with the same fault geometry and frictional property but assuming a homogeneous initial stress. The effect of steady-state stress perturbations is stronger in an overlapping stepover than in an underlapping stepover. The maximum jumping distance can reach 20 km in an overlapping releasing stepover with low-static frictional coefficients. These results are useful for estimating the maximum length of potential fault ruptures and assessing seismic hazard.

Investigation on the Fabrication and Properties of the Cu Base Friction Composites

Cu-based friction materials were prepared by powder metallurgy technology. The effect of Fe content on friction and wear properties of Cu-based friction materials has been investigated. The results indicate that Fe content has great effects on the wear ability of Cu-based friction materials. Fe works as frictional component in copper-based friction materials, influening the mechanical and frictional property of materials. With increasing Fe content, the hardness and friction coefficient of Cu-based friction materials stability increase, the wear rate of the friction materials decreases. When Fe content is 6%, the materials posses stably high friction factors, as well as good wear ability.

Experimental Study on the Complex Contact Frictional Property of an Ultralong Distance Large-Section Concrete Pipe Jacking and Prediction of Pipe String Stuck

Line 2 of the Guanjingkou Pipe Jacking Project in Chongqing encountered a pipe sticking problem, whose occurrence was inevitably attributed to the higher total frictional resistance of pipe strings rather than the maximum jacking force. Line 1, which is about to start construction, has basically the same construction environment as Line 2 using the same microshield and pipe string sizes. To avoid repeating the pipe sticking problem of Line 2, the mutual friction characteristics between the surrounding rocks and jacked pipe strings are studied for Line 1 by adopting the same test method under seven complex contact conditions (the presence or various combinations of three substances, i.e., extrapipe string field debris, bentonite slurry, and sand-laden waste slurry, on the jacked pipe string-surrounding rock contact surface are mainly considered). The results show that sufficient bentonite slurry can effectively reduce the frictional resistance, and when the amount of bentonite is insufficient, the average friction coefficient (AFC) of the later contact surface increases by 50%∼70%. The comparison of the monitored versus predicted jacking forces indicates that the value predicted by the test is slightly higher than the monitored force and the variation trends of the two match well, thus proving the correctness of the test results. It is possible to continue predicting the variation trends of the jacking force and frictional resistance based on the contact situation outside the pipe string wall, which greatly lowers the probability of re-encountering pipe sticking. The test results not only explain the important role of bentonite slurry in reducing the pipe string wall frictional resistance but also suggest that an increase in the pipe string wall frictional resistance resulting from the complex contact inflow into the overexcavation gap is the root cause of pipe sticking; moreover, the number of jacked pipe strings matching a single IJS is the second cause of pipe string sticking. The methodology of this study can provide a reference for other studies concerning the jacking force of long-distance rock microshield tunnelling.