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Now showing items 33 - 48 of 53

  • Effects of the fiber releasing on step-climbing performance of the articulated tracks robots

    Liu, Yuanyuan   Chu, Chengcheng   Fang, Haifeng   Ge, Shirong   Li, Yunwang  

    For a robot used to deliver optical fiber for communication; its center of mass and load change over time. This may affect the robot's obstacle-surmounting capability. In this paper; step-climbing performance of articulated tracks robots was discussed; regarding the maximum height of the step in term of the length of fiber releasing that the robot carries and the swinging angle of the swinging tracks. Two kinds of tracked mobile robots were studied; which were four-track mobile robot with two swinging arms and six-track robot with four swinging arms. The relation equations of the step height; the released fiber length; swinging angles of the swing tracks and the evaluation angle of the main body were founded and the conditions of the maximum step height were deduced. The theoretical relation curve of the maximum height of step and the released fiber length could be obtained; and the curve could be a good reference to the robot's obstacle-surmounting control.
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  • One-year biodegradation study of UHMWPE as artificial joint materials: Variation of chemical structure and effect on friction and wear behavior

    Ge, Shirong   Kang, Xueqin   Zhao, Yujie  

    Ultra-high molecular weight polyethylene (UHMWPE) has been the most commonly used bearing materials in the total joint replacement. The biodegradation of implanted UHMWPE components has notable influence on wear and fatigue resistance. Although accelerated aging protocols in vitro have been developed to evaluate the oxidation behavior of the UHMWPE materials, the mechanism still remains not accurately understood. Thus, the biodegradation of UHMWPE in simulated body fluid (SBF) was performed for up to 12 months and the chemical structure (i.e. oxidation and crystallinity) and scratch resistance, punch shearing strength, friction and wear behavior of biodegraded UHMWPE samples were investigated in this work. The results provided strong evidence that oxidation degradation significantly reduced the crystallinity and in consequent decreased the wear and scratch resistance of UHMWPE. It was found that the oxygen content on UHMWPE surface increased by almost two times and the crystallinity degree decreased by 16%, resulting in the reduction of scratch coefficient and peak breaking load by 30% and 15%, respectively, after one-year biodegradation. Also, significant wear rate increase up to 6 times for the one-year degraded UHMWPE sample was noticed in this study, and an exponential decay relation for the wear rate of UHMWPE to the crystallinity was identified. A bi-linear behavior of the crystallinity and oxidation index on UHMWPE sample was discovered, which corresponded to the two-stage wearing volume growth of degraded UHMWPE. The preliminary study suggested the necessity of a full-scale biodegradation test for UHMWPE materials including oxidative, hydrolysis and biodeterioration and even dynamic rubbing process. Moreover, it was indicated scratch test as an effective method to evaluate the superficial properties of UHMWPE samples which may be used as an important tool on comparing friction and wear behavior of this material. (C) 2011 Elsevier B.V. All rights reserved.
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  • Investigation of mechanical responses to the tactile perception of surfaces with different textures using the finite element method

    Tang, Wei   Zhang, Jiankai   Shi, Xiaolu   Zhang, Shaogang   Liu, Songyong   Zhu, Hua   Ge, Shirong  

    Tactile perception is essential for humans to perceive the world, and it usually results in mechanical responses from the finger. In this study, a nonlinear, viscoelastic, and multilayered finite element model of the finger was developed. The relationship between the mechanical responses within the finger and tactile perception while the finger scanned different surface textures was studied. The results showed that the sensitivity of tactile perception is affected by the peak value of von Mises stress, which is itself determined by the shape and density of a given texture. The von Mises stress varies periodically with time, and this variation depends on the periodicity of the texture. Displacement signals around Pacinian corpuscles have periodic variation. The period of displacement decreases as the density of the texture increases. The spectral centroid increases as the spacing of the texture decreases. The related mechanisms are discussed in this article.
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  • Study on the variation of 3D topography of specific spot on sliding wear surface

    Liu, Hongtao   Cao, Shoufan   Ge, Shirong   Jin, Jing  

    The study of topography of wear surface is an effective method to determine the mechanism of material's wear. So, in this article, the process of materials' sliding wear at room temperature was simulated based on the pin-on-disk wear test. The change of three-dimensional surface topography of a specific spot on the sliding wear surface was studied. Then the wear mechanism was analyzed. The results indicated that friction coefficient can reflect the interfacial properties of the wear of materials in real-time. The change of three-dimensional surface topography of a specific spot can directly reflect the change of material's surface structure during the wear process, providing an important experimental evidence for the analysis of material's wear mechanism. (C) 2011 Elsevier B.V. All rights reserved.
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  • Alterations in Three-dimensional Knee Kinematics and Kinetics during Neutral, Squeeze and Outward Squat

    Han, Shuyang   Ge, Shirong   Liu, Hongtao   Liu, Rong  

    The squat exercise was usually performed with varying feet and hip angles by different populations. The objective of this study was to compare and contrast the three-dimensional knee angles, moments, and forces during dynamic squat exercises with varying feet and hip angles. Lower extremity motions and ground reaction forces for fifteen healthy subjects (9 females and 6 males) were recorded while performing the squat with feet pointing straight ahead (neutral squat), 30 degrees feet adduction (squeeze squat) and 30 degrees feet abduction (outward squat). Nonparametric procedures were used to detect differences in the interested measures between the conditions. No significant difference in three-dimensional peak knee angles was observed for three squat exercises (p>0.05), however, the overall tendency of knee rotations was affected by varying feet and hip positions. During the whole cycle, the outward squat mainly displayed adduction moments, while the neutral and squeeze squat demonstrated abduction moments. Peak abduction moments were significantly affected by feet positions (p<0.05). Moreover, the tibiofemoral and patellofemoral joint forces progressively increased as knee flexed and decreased as knee extended, yet peak forces were not affected by varying feet positions (p>0.05). In conclusion, a neutral position is recommended to perform the squat exercise, while the squeeze squat and outward squat might contribute to the occurrence of joint pathologies.
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  • Kinematic Modeling of a Combined System of Multiple Mecanum-Wheeled Robots with Velocity Compensation

    Li, Yunwang   Ge, Shirong   Dai, Sumei   Zhao, Lala   Yan, Xucong   Zheng, Yuwei   Shi, Yong  

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  • Fretting wear behaviors of steel wires in coal mine under different corrosive mediums

    Zhang, Dekun   Shen, Yan   Xu, Linmin   Ge, Shirong  

    The failure of steel wire rope mainly resulted from rust, wear or broken of steel wires. Effects of various corrosive mediums (dry friction, three kinds of corrosive solutions) on fretting wear behaviors of steel wires were investigated on the self-made fretting wear rig under varied normal forces (from 10 N to 30 N) and displacement amplitudes (from 5 mu m to 200 mu m). The fretting running behaviors, wear mechanisms and the effects of different corrosive mediums were analyzed by using scanning electron microscope and X-ray energy spectrum analysis. The results reveal that the fretting running regimes of fretting wear can be determined according to the curves of friction force versus displacement amplitude and damage morphologies. And finally the running condition fretting map (RCFM) was established. It was found that corrosive mediums could affect the friction behaviors, wear mechanisms and RCFM. Compared with the dry friction condition, three corrosive mediums not only transform the boundaries of partial slip regime (PSR)/mixed fretting regime (MFR) and MFR/slip regime (SR) obviously to the smaller displacement amplitudes, but also reduce friction coefficient and increase the materials loss. The fretting wear mechanisms are mainly delamination, abrasive wear and oxidative wear in the three fretting regimes under dry friction, whereas abrasive wear and electrochemical corrosion dominates the wear in three kinds of corrosive solution. It is observed that slight damage appears at the contact edges in PSR, strong plastic deformation accompanied with the damage occurs in MFR, and severer degradation on the wear scars appears in SR. (C) 2011 Elsevier B.V. All rights reserved.
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  • Finite element analysis of fretting fatigue behavior of steel wires and crack initiation characteristics

    Wang, Dagang   Zhang, Dekun   Ge, Shirong  

    The effects of fretting parameters on stress distributions of contacting wires during the initial stage of fretting fatigue of steel wires were investigated using the finite element method. The roles of fretting parameters on crack initiation characteristics were discussed employing the multiaxial fatigue criteria of Fatemi-Socie and Smith-Watson-Topper, and three-dimensional coordinate transformation. Non-uniform stress distributions on contact surfaces and ring-shaped stress distributions near the contact zone on the symmetric plane are observed. Different fretting parameters induce distinct fretting regimes, stress distributions and abrupt changes of stress near the trailing edge. Crack initiation becomes more difficult with increasing contact load as compared to the increased possibility of crack initiation with increasing relative displacement. (C) 2012 Elsevier Ltd. All rights reserved.
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  • Effect of micro-surface defect on tribological property of UHMWPE

    Liu, Hongtao   Cao, Shoufan   Ge, Shirong  

    The article studied the friction and wear properties of UHMWPE when the surface was probed with micro-defect. The results indicated that the friction coefficient decreased when the micro-defect holes were gradually distributed on the friction surface uniformly. That was mainly because the uniform micro-defect holes formed regular texture, increasing the balance of friction and wear. The wear loss of UHMWPE decreased gradually with the increase of the amount of micro-defect holes, and there was a good linear relationship between them. When the friction surface was filled with uniformly distributed micro-defect holes, not only the wear loss decreased, but also wear debris with ideal size distribution was obtained. So, the theoretical and experimental basis was provided for the idea of the surface texturization of artificial arthrosis.
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  • Fretting-fatigue behavior of steel wires in low cycle fatigue

    Wang, Dagang   Zhang, Dekun   Ge, Shirong  

    The effect of strain amplitude on fretting-fatigue behavior of steel wires in low cycle fatigue was investigated using a fretting-fatigue test rig which was capable of applying a constant normal contact load. The fretting regime was identified based on the shape of the hysteresis loop of tangential force versus displacement amplitude. The variations of the normalized tangential force with increasing cycle numbers and fretting-fatigue lives at different strain amplitudes were explored. The morphologies of fretting contact scars after fretting-fatigue tests were observed by scanning electron microscopy and optical microscopy to examine the failure mechanisms of steel wires. The acoustic emission technique was used to characterize the fretting-fatigue damage in the fretting-fatigue test. The results show that the fretting regimes are all located in mixed fretting regimes at different strain amplitudes. The increase in strain amplitude increases the normalized tangential force and decreases the fretting fatigue life. The abrasive wear, adhesive wear and fatigue wear are main wear mechanisms for all fretting-fatigue tests at different strain amplitudes. The accumulative total acoustic emission events during fretting-fatigue until fracture of the tensile steel wire decrease with increasing strain amplitude. An increase of the strain amplitude results in the accelerated crack nucleation and propagation and thereby the decreased life. (C) 2011 Elsevier Ltd. All rights reserved.
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    Liu, Houguang   Ge, Shirong   Cheng, Gang   Yang, Jianhua   Rao, Zhushi   Huang, Xinsheng  

    Several types of middle ear implants (MEIs) have been invented as an alternative to conventional hearing aids for the rehabilitation of sensorineural hearing loss. Temporal bone and clinical studies have shown that the implantation of MEIs' transducers influences middle ear transfer function. But there is little comparative data available about these influences. We conducted comparative studies on the influences of three principal types of MEI transducers in respect to their attachment points on the ossicular chain. To aid the investigation, a human middle ear finite element model was constructed. The model was built based on a complete set of micro-computerized tomography section images of a human ear by reverse engineering technology. The validity of the developed model was verified by comparing the motions obtained by this model with published experimental measurements on human temporal bones. The results show that the eardrum driving transducer (EDT) and the floating mass transducer (FMT) decrease stapes displacement prominently at high frequencies. The greater these transducers' mass, the smaller is the displacement of the stapes footplate. In contrast, the incus body driving transducer (IBDT) decreases stapes displacement severely at low frequencies, and its adverse effect on residual hearing increases with increasing stiffness of the IBDT's driving rod.
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  • Microtribological and micromechanical properties of the skin stratum corneum

    Tang, Wei   Liu, Songyong   Zhu, Hua   Ge, Shirong  

    The stratum corneum is the outermost layer of mammalian skin, serves as a penetration, dehydration, and protection barrier against various environmental hazards. In this article, the microtribological and dynamic micromechanical properties of stratum corneum are studied. The rat stratum corneum is chosen as the animal model. In the microtribological tests, it is found that the coefficient of friction of stratum corneum decreases with the increasing of normal load and a linear viscoelastic contact model of stratum corneum is developed. In the dynamic micromechanical tests, the results show that there are initial maxima in storage (E') and loss (E '') moduli with both increasing of frequency and penetration depth. After the maxima, there are marked decreases in storage and loss moduli with increasing of frequency and penetration depth. It is suggested that this decrease is due to a water gradient across the stratum corneum. In addition, although the loss modulus is less than the storage modulus, there is a gradual increase in their ratio with increasing of displacement into stratum corneum. This indicates a shift toward more viscous behavior. This study provides key stratum corneum tribological and mechanical properties when moving on and penetrating into stratum corneum for the exploitation of drug delivery systems, artificial skin, textile, skin care production, and other studies related to stratum corneum.
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  • The friction and wear behavior of WC coating on medical grade titanium alloys

    Luo, Yong   Yang, Li   Tian, Maocai   Ge, Shirong   Wang, Qingliang  

    The clinical success of artificial joints has provided remarkable benefit to patients with joint disorders. However, the long-term success of total joint prostheses has been frustrated by an unacceptable rate of aseptic loosening, the osteolysis induced by joint wear, metal ion release, and high risk of toxicity. In this article, a hard and wear resistance WC coating was formed on the surface of medical grade titanium alloys, using a plasma spraying system in order to solve the above clinic problems. The WC phase and micro-hardness were characterized with X-ray diffraction and Vickers hardness tester to evaluate the plasma spraying process and the mechanical properties of the coatings. Then, the friction and wear tests of WC coatings were performed on M-2000 block-on-ring tribological testing machine. After that, the tribological behavior of the modified titanium alloys was investigated by means of scanning electron microscopy. It was observed that a graded structure was formed on the surface of titanium alloy and exhibited good bonding between the coating and substrate. In addition, it was noticed that WC phase could significantly harden the surface of titanium alloys and decreased the wear factor from 38.5x10(-11) to 1.66x10(-11)kg/Nm. Finally, it was proved that adhesion and abrasive wear dominated the damage of titanium alloy, while the wear of WC coating was controlled by adhesion wear. All of the results indicated WC coating on titanium alloys with good bonding strength after plasma spraying was a potential candidate for the application of artificial joints from the understanding of wear resistance. Further investigation regarding biocompatibility and artificial joint simulation need to be conducted.
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  • Microstructure analysis and wear behavior of titanium cermet femoral head with hard TiC layer

    Luo, Yong   Ge, Shirong   Liu, Hongtao   Jin, Zhongmin  

    Titanium cermet was successfully synthesized and formed a thin gradient titanium carbide coating on the surface of Ti6Al4V alloy by using a novel sequential carburization under high temperature, while the titanium cermet femoral head was produced. The titanium cermet phase and surface topography were characterized with X-ray diffraction (XRD) and backscattered electron imaging (BSE). And then the wear behavior of titanium cermet femoral head was investigated by using CUMT II artificial joint hip simulator. The surface characterization indicates that carbon effectively diffused into the titanium alloys and formed a hard TiC layer on the Ti6Al4V alloys surface with a micro-porous structure. The artificial hip joint experimental results show that titanium cermet femoral head could not only improve the wear resistance of artificial femoral head, but also decrease the wear of UHMWPE joint cup. In addition, the carburized titanium alloy femoral head could effectively control the UHMWPE debris distribution, and increase the size of UHMWPE debris. All of the results suggest that titanium cermet is a prospective femoral head material in artificial joint. (C) 2009 Elsevier Ltd. All rights reserved.
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  • The impact wear-resistance enhancement mechanism of medium manganese steel and its applications in mining machines

    Ge, Shirong   Wang, Qingliang   Wang, Junxiang  

    In order to obtain higher wear resistance steel for the application in mining machines, new modified medium manganese austenitic steel( MMAS) was developed. The impact abrasive wear properties were investigated on MLD-10 impact wear test equipment. The wear resistant and strengthening mechanisms of MMAS were analysed by SEM, TEM and XRD observation. Our research results show that the wear mass loss of MMAS decreases about 30% in comparison to that of martensitic steel, which suggests that medium manganese austenitic steel has the higher impact abrasive wear resistance than the martensitic steel. It is found that 1mm thick hardened layer is formed on the MMAS abrasive surface. In this harden layer, the highest Vickers hardness is about 531HV, and the highest Rockwell hardness is about 52HRC at the layer of 50 mu m from the surface. It is proved that the harden layer substantially enhances wear resistance of MMAS. The wear resistance strengthening mechanism of MMAS is found to be dependent on the impact energy. For the lower impact energy, the strengthening mechanism is controlled by the composite reinforcement of martensitic transformation, dislocation and stacking fault. For the high impact energy, the strengthening mechanism is controlled by the martensitic transformation, deformation twin and dislocation. The field wear tests of MMAS were done on the scraper convey or machines in coal mines, the test results indicated that the wear duration of MMAS transportation slots could be double of the martensitic wear resistant steel slots. (C) 2017 Elsevier B.V. All rights reserved.
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  • Effect of Fomoral Head Shape on Mechanical Behaviours of Artificial Hip Joint

    Han, Shuyang   Ge, Shirong  

    The human femoral head is not a perfect sphere, but the artificial femoral head is made spherical due to simple manufacturing. The shape may significantly affect the mechanical characteristics of artificial hip joint. This paper is aiming at studying the shape effect of femoral head on mechanical behaviors of artificial hip joint. Three hip joint models with different shapes femoral head were proposed in the finite element analysis software Ansys (version 11.0). Mechanical properties, such as acetabular deformation, were investigated under static and dynamic conditions. In static condition, the acetabular deformation of spherical model is 8.8x10(-5) m, and the deformation for ellipsoidal model and conchoidal model are 3.2x10(-5) m and 3.4x10(-5) m. The acetabular peak stresses are 1.718x10(7) Pa, 8.87 x 10(6) Pa and 9.52 x 10(6) Pa respectively. In the spherical model, peak value occurs in the bottom of the socket, while peak values of the second and third model are obtained at a circle region away from the socket bottom. In dynamic condition, both deformation and peak stress change abruptly. The acetabular deformations are 1.045x10(-3) m, 1.143x10(-3) m and 1.151x10(-3)m, the peak stresses are 3.313x10(8) Pa, 3.260x10(8) Pa and 3.277x10(8) Pa. The mean stresses of the second and third model along the sliding direction are lower than the first model. And less deformation is generated near the rim of the acetabulum for the second model.
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