Papers by Author: K.M. Liew

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Authors: Yu Zhou Sun, Jin Yan Wang, K.M. Liew
Abstract: This paper introduces a multiscale modeling approach for carbon nanotubes (CNTs), in which a fine continuum model that has been developed by the present authors is employed to implement the continuum modleing. The entire domain is decomposed into a continuum modeling region and an atomic region with an overlapping region. For the atomic region, the atomic finite element method (AFEM) is used to trace the individual atomic motion. Whereas, the continuum region is viewed as the higher-order continuum media, and the mesh-free method is adopted to implement the continuum numerical discrization. For the overlapping region, the bridging domain method is used to efficiently couple two scales. Numerical computation is carried out and several examples are discussed.
Authors: L.W. Zhang, K.M. Liew
Abstract: A regulatory network of G2/M phase transition influenced by different intensities of DNA damage is modeled. It contains the sub-modules of P53-Mdm2 feedback loop and G2/M phase transition process. To investigate the robustness of the regulatory network, a sensitivity analysis of kinetic parameters in the proposed mathematical model is implemented to select the most significant kinetic parameters, which are relevant to key proteins involved in G2/M phase transition. Subsequently, the statistical hypothesis testing is employed to evaluate the influence of perturbations on the G2/M regulatory network. The results indicate that G2/M regulatory network is robust to DNA damage signal when perturbations are very small that is consistent with the experimental observations.
Authors: Wei Guang An, Lin Jiang, Jin Hua Sun, K.M. Liew
Abstract: An experimental study on downward flame spread over extruded polystyrene (XPS) foam at a high elevation is presented. The flame shape, flame height, mass loss rate and flame spread rate were measured. The influences of width and high altitude were investigated. The flame fronts are approximately horizontal. Both the intensity of flame pulsation and the average flame height increase with the rise of sample width. The flame spread rate first drops and then rises with an increase in width. The average flame height, mass loss rate and flame spread rate at the higher elevation is smaller than that at a low elevation, which demonstrates that the XPS fire risk at the higher elevation area is lower. The experimental results agree well with the theoretical analysis. This work is vital to the fire safety design of building energy conservation system.
Authors: K.M. Liew, C.H. Wong, Ming Jen Tan, P.D. Chuang
Abstract: Compressive and tensile properties of non-twisted and twisted carbon nanotube (CNT) bundles are studied using molecular dynamics (MD) simulations. The results reveal that non-twisted CNT bundles exhibit better compressive and tensile properties than twisted CNT bundles. When the twist angle of a CNT bundle is greater than 60°, its buckling load dropped considerably due to the significant curve geometries of the surrounding single-walled carbon nanotubes (SWCNTs). Twisted CNT bundles also do not demonstrate good tensile properties. During tensile loading, the intertube distance in CNT bundle with twisting angle greater than 75° will decrease as the strain increases. This gives rise to increasing intertube van der Waals forces until the intertube distance falls below 2.0Å. At this time, the repulsive force between the SWCNTs suddenly increases causing the SWCNTs to repel one another at junction areas where they overlap. As a result, twisted CNT bundles tend to fail at these junction areas with lower failure load and strain.
Authors: Ming Jen Tan, X.J. Zhu, S. Thiruvarudchelvan, K.M. Liew
Abstract: This work reports the influence of oxidation on the superplasticity of commercially pure titanium at high temperatures. Uniaxial tensile tests were conducted at temperatures in the range 600-800°C with an initial strain rate of 10s-1 to 10s-3. This study shows that oxidization at the surface of the alloy causes oxide film on the surface of commercially pure titanium alloy, and the thickness of oxide film increase with increasing exposure time and temperature. XRD analysis shows that the oxide film consists of TiO2. Because this oxide film is very brittle, it can induce clefts and degrade the ductility of the titanium at high temperatures. The mechanism of the initial clefts was investigated and a model for the cleft initiation and propagation during high temperature tensile test was proposed.
Authors: Fei Zhou Huo, Wei Guo Song, Wei Lv, K.M. Liew
Abstract: In this paper, an extended lattice gas model is proposed to simulate pedestrian flow on floor-stair interface by considering inner-side walking preference, turning behavior and different desired speeds. The effects of different injection rates for pedestrians from corridor on the mean velocity and occupancy are investigated, and the merging behavior, which happened on floor-stair interface, is analyzed. The simulation results show that the extended model can reproduce some essential features of pedestrian flow on stairs, such as transition of movement state at higher injection rate, merging behavior on floor-stair interface. The effects of two kind of typical structures of the floor-stair interface on pedestrian merging behavior are discussed, and merging process simulated by the model appears biased to that the corridor is connected opposite to the incoming stair.
Authors: X.J. Zhu, Ming Jen Tan, K.M. Liew
Abstract: In this work, studies were carried out to investigate the superplasticity of a commercially pure (CP) titanium alloy during high temperature deformation. Uniaxial tensile tests were carried out at 600, 750 and 800°C with an initial strain rate from 10-1s-1 to 10-4s-1. It was found that the alloy do not show good superplasticity due fast grain growth at high temperature and cavity. The effects of temperature on the grain growth and cavity phenomena as well as the dynamic recrystallization of the alloy were studied and a ‘two-step-method’ was introduced to increase the superplasticity of the alloy.
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