Our Publications

  • Fracture toughness of X70 pipeline steel at different temperatures. Zheng Yang, Wanlin Guo, and Chunyong Huo. Acta Metallurgica Sinica, 2003, 39(9), 908-913.

    Zheng Yang, Wanlin Guo, and Chunyong Huo.

    Acta Metallurgica Sinica, 2003, 39(9), 908-913.

    The fracture toughness of X70 pipeline steel was investigated experimentally by use of the 3-point bending fracture toughness sample with different thicknesses and initial crack lengths at different temperatures. The crack tip fields and out-of-plane stress constraint of the specimens were analyzed using three dimensional elastic-plastic theory. It is found that the out-of-plane stress constraint affects the crack tip fields and fracture toughness significantly. Delamination cracks appear on the fracture surface, and the size and amount of delaminated cracks depend closely on the thickness of specimen. The geometry of delamination cracks relates with the initial crack length and the test temperature. At lower temperature the delamination occurs at some distance from the initial crack front with smaller size; while at higher temperature the delamination occurs at the initiation stage with larger size. Delamination decreases the effective thickness of the specimens so that increases the thoughness. Consequently, when using the test standards of plain strain toughness the couple effects of thickness of specimen, size of crack and temperature must be taken into account.

  • Giant axial electrostrictive deformation in carbon nanotubes. Wanlin Guo, and Yufeng Guo. Phys Rev Lett., 2003, 91(11), 115501.

    Wanlin Guo, and Yufeng Guo.

    Phys Rev Lett., 2003, 91(11), 115501.

    An exceptionally large axial electrostrictive deformation is demonstrated in single walled carbon nanotubes using Hartree-Fock and density functional quantum mechanics simulations. Armchair and zigzag open-ended tubes and capped tubes are studied and in all of them the external electric field induced axial strains can be greater than 10% for a field strength within 1 V/A. The corresponding volumetric and gravimetric work capacities are predicted to be three and six orders higher than those of the best known ferroelectric, electrostrictive, magnetostrictive materials and elastomers, respectively.

  • Energy Dissipation in Gigahertz Oscillators from Multiwalled Carbon Nanotubes. Wanlin Guo, Yufeng Guo, Huajian Gao, Quanshui Zheng, and Wenyu Zhong. Phys. Rev. Lett., 2003, 91, 125501.

    Wanlin Guo1, Yufeng Guo1, Huajian Gao2, Quanshui Zheng3, and Wenyu Zhong1

    1. Institute of Nano Science, Nanjing University of Aeronautics and Astronautics, Nanjing 210016, China
    2. Max-Planck Institute for Metals Research, Heisenbergstrasse 3, D-70569 Stuttgart, Germany
    3. Department of Engineering Mechanics, Tsinghua University, Beijing 100083, China

    Phys. Rev. Lett. 91, 125501 (2003) [4 pages]

    Received 5 March 2003; published 15 September 2003

    Using atomistic models and molecular dynamics simulations, interlayer corrugation and resistant force in a biwalled carbon nanotube are shown to be strongly dependent upon the morphology combination of the bitube. Consequently, energy dissipation in a commensurate (e.g., armchair/armchair or zigzag/zigzag) bitube oscillator is found to be much larger than that in an incommensurate (e.g., zigzag/armchair) oscillator, resulting in a decay of oscillation amplitude within a few nanoseconds in the commensurate bitube and several tens of nanoseconds in the incommensurate bitube.

  • Stress intensity factors for elliptical surface cracks in round bars with different stress concentration coefficient. W. Guo, H. Shen and H. Li. International Journal of Fatigue, 2003, 25, 733–741.

    W. Guo, H. Shen and H. Li

    Department of Aircraft Engineering and Astronautics, Nanjing University of Aeronautics and Astronautics, Nanjing 210016, People's Republic of China

    International Journal of Fatigue, 2003, 25, 733–741.

    Received 15 July 2002; revised 11 October 2002; accepted 22 January 2003. ; Available online 11 April 2003.

    Stress intensity factors (SIFs) of elliptical surface cracks in notched tensile round bars are calculated by using three-dimensional finite element analysis (FEA) models with singular 20-node elements arranged around the crack tip. Systematic analyses are performed for semi-circular type, V-type and U-type annular notches with theoretical stress concentration coefficient Kt ranging from 1–5. It is shown that the SIFs are strongly dependent on Kt, and the influence of notch geometry is negligibly weak for a given stress concentration coefficients in the analyzed range. An empirical expression for the SIF as a function of crack geometry and Kt is then obtained by fitting the numerical results. Comparison of present results with available numerical results in the literature shows good agreement. Application of the empirical expression to a screw bolt yields good coincidence with experimental results of SIFs by using a modified James-Anderson method. Therefore, the empirical expression of SIFs can be used conveniently in integrity assessment of various notched bars, at least in the analyzed range in this paper.
    Author Keywords: Stress intensity factor; Surface crack; Stress concentration coefficient; Notch; Three-dimensional finite element analysis

  • Mechanical and electrostatic properties of carbon nanotubes under tensile loading and electric field. Yufeng Guo, and Wanlin Guo. J. Phys. D: Appl. Phys., 2003, 36, 805–811.

    Yufeng Guo1 and Wanlin Guo1,2,3

    1 Institute of Nanoscience, Nanjing University of Aeronautics and Astronautics, Nanjing 210016, People's Republic of China
    2 The State Key Laboratory of Mechanical Structural Strength and Vibration, Xian Jiaotong University, Xian 710049, People's Republic of China
    3 Author to whom correspondence should addressed.

    J. Phys. D: Appl. Phys., 2003, 36, 805–811.

    Received 28 May 2002 , in final form 6 November 2002
    Published 19 March 2003

    Coupled mechanical and electronic behaviours of single walled open carbon nanotubes (CNTs) under applied electric field and tensile loading are investigated by the use of quantum mechanics as well as quantum-molecular dynamics techniques based on the Roothaan–Hall equations and the Newton motion laws. Different failure mechanisms and mechanical properties are found for CNTs subjected to electric fields and that subjected to tensile load. The electric field induced breaking in CNT begins from the outmost carbon atomic layers while the tensile load breaks the nanotube near its middle at 300 K. Electronic polarization and mechanical deformation induced by an electric field can significantly change the electronic properties of a CNT. Under electric field, the CNT can be stretched but the toughness is much lower than that under mechanical loading. Applied tensile loading causes no electronic polarization even in a metallic tube but it indeed changes the energy gap of the tube, thus exhibits influence on field-emission properties of CNTs. When a tube is tensioned in an electric field, the critical tensile strength of the tube may decrease significantly with increasing intensity of electric field. The coupling of mechanical and electrical behaviours is an important characteristic of CNTs.