Research Progress of Nano Copper Lubricant Additives on Engineering Tribology

Nanoparticles have as characteristics super sliding, extreme pressure, self-healing, etc., which can improve the friction reduction and anti-wear performance of sliding components, when used as lubricating oil additives. Nano-copper particles have a good synergistic effect with other antifriction agents, anti-wear agents, antioxidants and grease additives because of their low shear strength and grain boundary slip effect, showing a better anti-friction and anti-wear effect. However, nanoparticles are prone to conglomerate, and this causes a bottleneck in the application of dispersant for nano-copper in a lubricating oil system. The regulation of nanosized effect and surface properties has great engineering significance in compensating for the precision in manufacturing accuracy. This paper comprehensively reviews the tribological research progress of nano-copper as a lubricant additive, which provides a reference to the application of nano-copper particles as lubricating oil additives on engineering tribology.

Strength Model of Backfill-Rock Irregular Interface Based on Fractal Theory

In the two-step open stope subsequent filling mining method, the determination of the strength model for the backfill-rock interface is of great engineering significance to study the stress distribution and stability of the backfill in the stope. Considering the deformation mechanism of the interface and the interaction of the asperities, a strength model for backfill-rock with irregular interface has been proposed based on fractal theory, which can effectively describe the shear mechanical behavior of interfaces with random roughness. The model has been compared with the two-body mechanistic model and good agreements have been achieved. The results show that the shear strength of the interface changes non-linearly with increasing fractal dimension D, when the fractal dimension D is in the range of 1∼1.12. The complete relationship between the interface shear strength and the fractal dimension is given, as the fractal dimension increases from 1 to 2 based on the presented model. At the same time, the quantitative relationship between the interface and backfill friction angles during direct shear testing is analyzed.

Response of Floc Networks in Cemented Paste Backfill to a Pumping Agent

Cemented paste backfill is critical for the development of green mines, the safe exploitation of mineral resources deep underground, and the efficient disposal of solid wastes produced by mining. In this paper, the mechanism underpinning how the pumping agent works was studied. The number, area, and fractal dimension of pores in the microstructure of fresh paste were quantitatively analyzed using scanning electron microscopy (SEM), image processing, and fractal theory, and the response of flocs was investigated. The results show that floc networks disintegrated and the liquid network became the dominant structure under the action of the pumping agent, which enhanced the lubrication and promotion of multi-scale particles. In addition, the force chains became fragile and scattered, diminishing the yield stress of the paste. The pores had a more homogenized dimension and the porosity was 15.52% higher. The increase in the fractal dimension of the pores indicated that there was a higher self-similarity, in terms of microstructure, with a strengthened liquid network. The migration of floc structures contributed to the enhancement of the fluidity and rheology of the paste. This study provides insights into the effects of floc and liquid networks on the performance of paste, and it is of engineering significance in terms of realizing safe and efficient CPB operations.

Analysis and Revision of Torque Formula for Hydro-viscous Clutch

Hydro-viscous clutch is a speed-regulating device for heavy fans and water pumps. It has important engineering significance in the fields of soft-start for rotating machinery. More and more attention has been paid to its torque and control characteristics. This paper is focused on the torque formula for hydro-viscous clutch (HVC), assuming that multi-friction plates distribute ununiformly with different oil film thickness. A mathematical model of friction plates was constructed, then the distribution formula of the oil film thickness was obtained. A new expression was presented using a modified factor. Parameters such as pressure, viscous torque, and oil film thickness were obtained. The results show that each clearance of friction plates is not the same and the distribution of oil film thickness is influenced by pressing force, groove depth, angular ratio of groove/non-groove, and static friction force. To verify the proposed expression, relevant experiments were carried out on an HVC with multi-friction plates, and the experimental results indicate that the new expression is more accurate compared to the original one.

Research on the Calculation Method of Harmonic Contribution in the Case of Dominant System-side Harmonics

Existing methods for quantifying the responsibility of harmonic sources assume a dominant user side and use a harmonic source equivalence circuit to calculate the equivalent system impedance and background harmonic voltage, which in turn assesses the harmonic contribution of that source to the bus of concern. For users who actively participate in harmonic governance, it is very important to evaluate the responsibility of injecting harmonics into users. This paper assumes system-side is dominant, constructs a partial linear regression model and a constant impedance model, and tracks the regression error. The equivalent fundamental impedance is doubly screened to calculate the harmonic impedance for the corresponding number of times, which in turn quantifies the harmonic voltage duty. The results of simulation and the analysis of measured data show that this method has simple calculation model, small regression error (0.0037), high accuracy and practical engineering significance.

Optimisation analysis of reinforced cable distribution on the airship

Reinforced cables are usually installed on flexible airship structures to enhance their load-bearing capability. However, reinforced cables also increase the total weight of the airship. In order to find a balance between large loading-bear capability and light weight, a multi-objective optimisation scheme based on the genetic algorithm NSGA-II is put forward for the reinforced cable distribution on the airship. Firstly, different cable distribution schemes are presented according to engineering experience and the optimal one is determined by load analysis. Then, the CAE method and optimisation analysis are combined to achieve structure design optimisation. The parametric model of the airship structure with reinforced cables is established by ABAQUS secondary development and the load analysis is carried out. Parameter passing and optimisation algorithm are operated by Isight software and the optimisation analysis is conducted based on the NSGA-II algorithm. Finally, we draw some conclusions of the rules of optimised reinforcing cable distribution. The work of this paper has crucial engineering significance for improving performance of the airship structure design.

BIM research vs BIM practice: a bibliometric-qualitative analysis from China

PurposeUnderstanding the frontier difference between building information modeling (BIM) research and practice is a top priority to guarantee the engineering significance and feasibility of academic achievements, yet such research gap has not been well-explored. The purpose of this paper is to provide an objective and accurate analysis of BIM knowledge using 551 published BIM-related papers and 68 documents of frontier BIM projects in China.Design/methodology/approachThis paper adopts the mixed method, combining the bibliometrics method with the qualitative method. Bibliometrics was used to analyze 551 BIM-related literatures from China with Citespace 5.0. Qualitative research was used to analyze 68 project documents from China with Nvivo. Finally, the analysis results are compared to obtain the final conclusion.FindingsThe analysis results of the collected BIM-related papers, given by bibliometrics analysis, show that the subject categories of engineering, civil engineering, and construction and building technology, and 8 key research clusters are extremely important for development of BIM knowledge. The analysis results of the collected project documents, given by qualitative analysis, indicate that visualization, aided management, intelligent construction, simulation and analysis are the hot applications of BIM practice.Originality/valueThrough comparison, certain research gaps between the research and practice community in China was identified, which are useful for identification of research trends and practice frontier in BIM community. This study offers useful and new insights to summarize the status quo of BIM and can be used as a reference to integrate future BIM developments.

Study on the Friction and Wear Performance of Lightly Loaded Reciprocating Carbon/Aramid-Based Composites

The preparation methods of T300 carbon cloth- and aramid cloth-reinforced epoxy resin and cyanate ester were proposed, and four kinds of composite samples were obtained. The friction coefficient and wear rate under different test times and loads were obtained using a reciprocating pin-disk tribology tester. The tribology pairs included pins or sliding blocks made from different metals (45 steel and brass) and the disk samples of the composites. The test results showed that the friction coefficients of the T300 carbon cloth- (T300/4211 and T300/BS-4) and aramid cloth- (aramid/4211 and aramid/BS-4) reinforced epoxy resin or cyanate ester changed from 0.09 to 0.3 and were low under dry friction conditions. Under 75 N, aramid/BS-4 coupled with 45 steel pins was the lowest friction coefficient, which was 0.09. In particular, the friction coefficient and wear rate of the composite-reinforced cyanate ester were the lowest, which meant that this composite may be more suitable for use under lightly loaded and reciprocating running conditions in space engineering. By comparing the surface morphologies of composites before and after the test, the wear mechanism of the composites was discussed and the lower friction coefficient and wear rate may originate from the abrasive wear effects occurring between the tribology pairs. The research results have important engineering significance for guiding the use of composites in the deployable mechanisms used in space engineering.

Producing Hollow Shafts in a New Horizontal Mill by Novel Flat-Knifing Cross-Wedge Rolling With Single Guide

To meet the requirement of lightweight, there are increasing solid shafts being designed to be hollow in transportation industry. In this study, a novel method of flat-knifing cross-wedge rolling (FCWR) with single guide is proposed including a modified roller, a horizontal mill and a single-guide structure, and its key problems are studied by numerical simulations and experimental tests. A mathematical model of FCWR roller is established, which reveals the wedge length of rollers is effectively reduced by modifying knifing wedge from normalized roller. Further, a horizontal multifunctional mill is invented and constructed to carry out the FCWR experiment with single guide. According to the results from the numerical simulations and corresponding experiments, it is observed that the typical defects of hole expansion and knifing groove are absolutely avoided because the improved flat-knifing wedge produces a radial force to shrink the inner hole and avoid the deformation concentration of the outer surface during knifing stage. Moreover, the single guide rolling performed in the horizontal mill efficiently improve rolling stability because the workpiece is restricted into a smaller workspace. To the authors’ knowledge, all these integrated improvements of FCWR roller, single guide rolling and horizontal mill are innovative, which are of great engineering significance to manufacture hollow shafts on account of the advantages of avoiding forming defect, reducing roller diameter, improving rolling stability and simplifying mill structure.