Papers by Author: Cheng Hui Gao

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Authors: Yu Hui Peng, Cheng Hui Gao
Abstract: The generation of boundaries from the triangular meshes of CAD object is very important for successful surface segmentation and subdivision. Considering the characteristics of non-uniformity, sparseness and known facet normal for STL model, which is generated by a CAD system, a new and efficient approach for extracting boundaries on STL model is presented in this paper. Boundaries are classified into sharp feature edge and non-sharp feature edge embedded in the filleting and transitive region. The former is detected based on dihedral edge angle (angle between facets), while the latter is identified by analyzing intrinsic region properties of triangular facets distribution without curvature estimation. By means of unidirectional increment of feature edges, continuous region boundaries are generated. Successful examples are presented to illustrate the feasibility of the proposed algorithm.
Authors: Lian Feng Lai, Cheng Hui Gao, Jian Meng Huang
Abstract: A three-dimensional contact model was established between two isotropic rough surfaces exhibiting fractal behavior,and the equivalent plastic strain was discussed using the finite element analysis. The maximum equivalent plastic strain and its depth are presented with the different paths of rough solid when loading. The result showed that the equivalent plastic strain versus different depth which at different locations showed different laws, in the top area of the asperities versus different depth, the maximum equivalent plastic strain occurs in the subsurface which range about 5 um from the surface. In addition, with different deformation characteristics, the degree of the equivalent plastic strain was different. The contact model between two rough solids will lay a foundation to further research on the substance of the process of friction and wear.
Authors: Lian Feng Lai, Cheng Hui Gao, Jian Meng Huang
Abstract: A FEA model of two-dimensional (2D) sliding between two interfering fractal rough solids was build, and the results was presented. The trends in shear stress between the rough solids were provided by the FEA. Combined with the delaminating theory of wear, the Maximum shear stresses and its distance are presented when loading and sliding. The result showed that the Maximum shear stresses was located in the subsurface which range about 2 to 8 um from the surface. In addition, with different plastic characteristics, the location of Maximum shear stresses were different. With modeling the contact and sliding between rough surfaces, the friction, sub-surface crack initiation and propagation and wear mechanisms can be understood deeply.
Authors: Chao Zhou, Cheng Hui Gao
Abstract: Since the tribology properties of rough surfaces are closely related to its topography, one of the most important ingredients in tribology research is to find an appropriate tool to analyze and characterize rough surfaces. The elementary theory of contourlet which is a good method for multi-scale and multi-direction signal analysis was introduced and an application of contourlet in rough surface analysis was demonstrated. It was found that contourlet is more sensitive to curved features than general two dimensional wavelets; it is possible to become a new powerful tool for rough surface analysis and characterization.
Authors: Zhi Ying Ren, Cheng Hui Gao, Jian Xing Lin, Ding Shen
Abstract: This paper proposes the third generation wavelet--double tree complex wavelet (DT-CWT) transformation used in nanometer roughness rating, based on the explanation of the shortcomings of the current nanometer roughness rating reference and conventional three dimensional datum evaluations due to the insufficient study. The experiment got porous anodic alumina film as the object of surface roughness of nanotechnology study. Through the comparisons of the three generations of the wavelet reconstruction after the maximum reconstruction error, a conclusion can be made that the superiority of DT-CWT in application is very obvious, a result meeting the16% principle of the surface roughness rating on the bases of DT - CWT extracted datum to compute income parameters, which indicates the feasibility of this application to the extraction of the nano3-D roughness evaluation. Keywords: nanometer roughness;dual-tree complex wavelet;three dimensional datum
Authors: Liang Chen, Cheng Hui Gao, Guo Dong Jin
Abstract: The essence of the multidisciplinary collaborative design problem (MCDP) is the coordination of the design variables among multiple disciplines on the basis of the all constraints of all disciplines. There exist some problems such as the early detection of design conflicts and the determination of the consistency domains of the design variables, etc. The resolving of these problems can help designers avoid bad decision-making, reduce the design iteration and improve the design efficiency. Aiming at the problems, this paper proposes a constraint-net model to describe and manage all the design variables and constrains of all disciplines, discusses the reformulating method of the MCDP to improve computation efficiency, and develops the interval propagation algorithm to determine the consistency domains of the design variables, etc. A gear drive is taken as an example to illustrate the effectiveness of the proposed method.
Authors: Fu Shan He, Cheng Hui Gao, Shao Yan Ye
Abstract: In this paper, a novel no-asbestos brake composite reinforced by natural bamboo fibers is studied. The bamboo fibers are modified by heat treatment, alkali treatment and coupling treatment respectively. Tribological performance of different fibers reinforced composites are developed by means of friction test and microstructure observation. The results show that heat treatment of bamboo fibers at 140 for 4 hours makes the friction and wear characteristics of brake composites more stable than the untreated ones, but poor wear resistance at low temperature and heat fade still exist. There is no significant change on fiber surface. The alkali treatment of 17% NaOH solution for 12 hours contributes to desirable combination of higher friction coefficients and lower wear rates, and the surface morphology shows a number of deep grooves that avail the interface bonding. The effect of coupling treatment with KH550 on tribological performance of composites have the similar rule to that of the alkali treated ones except of heat fade, and the fiber surface is evenly coated with the coupling agent, which enhances the bonding of fibers and resin but fails at elevated temperature.
Authors: You Xi Lin, Cheng Hui Gao, Yuan Li
Abstract: The tribological properties of PEEK composites filled with CaCO3 whisker in various content of 0-30%(weight percent) were investigated.The composite specimens were prepared by compression molding. Tribological testing of composites in water lubrication against carbon steel ring was carried out on a MM200 block-on-ring apparatus.Data on neat PEEK were also included for comparison. The morphologies of wear traces were observed by SEM.It was observed that inclusion of CaCO3 whisker significantly improved the wear resistance and reduced the friction coefficient of PEEK composites under water lubricated condition. With an increase in CaCO3 whisker contents, the specific wear rate of composites decreased and showed minima for 20% CaCO3 content as 5.2% of that for PEEK. In terms of friction applications under water lubrication, the optimal content of CaCO3 whisker in PEEK composites should be recommended as 15% to 20%.The SEM observation of the wear traces indicated that the transfer film is not the main reason for the enhancement of wear resistance of the composites in water lubrication.CaCO3 whisker contributed to increase the load-carrying capacity and abate the scuffing and adhesion of PEEK composites, finally led to a significant improvement of the wear resistance.
Authors: Ai Hua Chen, Cheng Hui Gao, Bing Wei He
Abstract: Image stereo correspondence is the core technology of stereo vision. It has been widely studied and applied in the fields such as 3D reconstruction, vision measurement and target recognition. According to characteristics and application of stereo matching technology, the image stereo correspondence methods can be classified into three categories: local stereo correspondence, global stereo correspondence and semi-global stereo correspondence. Some image stereo correspondence solutions and problems are emphatically analyzed. Finally some future research issues on image stereo correspondence are highlighted.
Authors: Cheng Hui Gao, Jian Meng Huang, Lei Dai
Abstract: Sliding velocity has a direct impact on friction heat and contact situation. Frictional heating and associated temperature seriously affects the material chemical and physical - mechanical properties, and is one of the direct factors on the wear mechanism. To analyze the influence of the sliding speed on the maximum contact temperature, contact pressure, stress, etc, a 3D thermo-mechanical coupling model for the rough surface frictional sliding is established. The rough surface is characterized based on fractal theory. The model considers friction contact between an elastic flat plane and an elasto-plastic rough surface. Also, the model integrates the heat flux coupling between the sliding surfaces and allows the analysis of the effects of elastic-plastic deformation of rough body and the interplay among asperities. The numerical results from the analysis and simulation show that the maximum contact temperature increases with the increasing of the sliding velocity. But the maximum VonMises equivalent stress and the maximum contact pressure have few relationships with sliding speed. They may increase or reduce with the sliding velocity increasing. Some results are validated by research’s results available in the literature.
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