Our Publications

  • Three-parameter description of the stress field near the border of an embedded elliptical crack. Junhua Zhao, Wanlin Guo, and Chongmin She. Acta Mechanica, 2007, 190, 29–44.

    Junhua Zhao, Wanlin Guo, and Chongmin She

    Acta Mechanica, Volume 190, Numbers 1-4, May 2007 , pp. 29-44(16)

    Received June 11, 2006; revised August 22, 2006; Published online: December 21, 2006

    The elastic T-stress and stress intensity factor K for embedded elliptical cracks have been investigated in elastic plates by detailed three-dimensional finite element calculations. The distributions of normalized K and T-stress have been obtained along the crack front with aspect ratios (a/c) of 0.2, 0.4, 0.5, 0.6, 0.8 and 1.0, and far-field tension and the effect of Poisson's ratio have also been considered. The normalized K increases and the normalized T-stress decreases with the increase of Poisson's ratio ν. For ν=0.3, the normalized K gradually increases in the range of crack face angle Φ≥22.5° and decreases in the range of Φ≤22.5° with increasing a/c. When Φ rises to 90°, the K values tend to maximum for various a/c. The normalized T-stress increases in the beginning and then decreases with the increase of Φ except for a/c = 1.0. By fitting the numerical results with the least squares method, empirical formulae have been given for the convenience of engineering applications. Combining with the corresponding out-of-plane constraint factor T z , the three-parameter K-T-T z approach has been provided, which can accurately describe the stress field around the crack front.

  • Two Distinct Buckling Modes in Carbon Nanotube Bending. Xiaojie Duan, Chun Tang, Jin Zhang, Wanlin Guo, and Zhongfan Liu. Nano Lett., 2007, 7(1), 143–148.

    Xiaojie Duan, Chun Tang, Jin Zhang, Wanlin Guo, and Zhongfan Liu

    Nano Lett., 2007, 7(1), 143–148.

    By using controlled SPM manipulation, carbon nanotubes have been continuously bent into a series of increasing angles, and two distinct buckling modes corresponding to “abrupt” and “gradual” buckle formation were observed through recording the height increment at the bend site during the loading process. Molecular dynamics simulation also found the two buckling modes in different types of carbon nanotubes, and their atomistic mechanism was revealed. Finally, the dependence of the critical buckling condition on diameters of carbon nanotubes was tentatively studied.

  • Modeling the Damage Progression in the Composite Structure Subjected to Static Contact Crush. Yunpeng Jiang, and Wanlin Guo. Key Engineering Materials, 2006, 324-325, 831-834.

    Yunpeng Jiang, and Wanlin Guo

    Key Engineering Materials, 2006, 324-325, 831-834.

    Based on the classic laminate theory, a progressive damage model has been incorporated into the composite structure analysis by using a commercial code, ABAQUS, via one of its user-defined subroutine, UGENS. The developed user subroutine can be applied to simulate fiber and matrix damage processes in the general composites structures. The responses of flat laminate subjected to static contact crush have been studied to verify the efficiency of the presented damage method. The predicted load-displacement relationships, damage distribution were obtained and compared with the corresponding experiments, and the results were found to be in good agreement.

  • A new method for quantifying residue conservation and its applications to the protein folding nucleus. Xinsheng Liu, Jing Li, Wanlin Guo, and Wei Wang. Biochemical and Biophysical Research Communications, 2006, 351, 1031–1036.

    Xinsheng Liua,1, Jing Li2, Wanlin Guo1 and Wei Wang2

    1. Institute of Nanoscience, Nanjing University of Aeronautics and Astronautics, Nanjing 210016, China
    2. National Lab of Solid State Microstructure, Department of Physics and Institute of Biophysics, Nanjing University, Nanjing 210093, China

    Biochemical and Biophysical Research Communications, 2006, 351, 1031–1036.

    Received 26 October 2006. Available online 7 November 2006.

    The conservation of residues in columns of a multiple sequence alignment (MSA) reflects the importance of these residues for maintaining the structure and function of a protein. To date, many scores have been suggested for quantifying residue conservation, but none has achieved the full rigor both in biology and statistics. In this paper, we present a new approach for measuring the evolutionary conservation at aligned positions. Our conservation measure is related to the logarithmic probabilities for aligned positions, and combines the physicochemical properties and the frequencies of amino acids. Such a measure is both biologically and statistically meaningful. For testing the relationship between an amino acid’s evolutionary conservation and its role in the Φ-value defined protein folding kinetics, our results indicate that the folding nucleus residues may not be significantly more conserved than other residues by using the biological-relevance weighted statistical scoring method suggested in this paper as an alternative to entropy-based procedures.

    Keywords: Evolutionary conservation; Physicochemical property; Multiple sequence alignment (MSA); Folding nucleus

  • Molecular Physical Mechanics and Multiphysics-Scale Studies. Wanlin Guo, and Chun Tang. Int. J. Multiscale Computational Engineering, 2006, 4, 115-126.

    Wanlin Guo, and Chun Tang

    Institute of Nano Science, Nanjing University of Aeronautics and Astronautics, Nanjing, 210016, China

    Int. J. Multiscale Computational Engineering, 2006, 4, 115-126.

    When size goes down to nanoscale or molecular scale, besides the widely known spatial and temporal multiscale problems, new physical properties and coupling effects between mechanical motion and physical, biochemical properties may become dominant, and multiphysics-scale problems arise. Under the interdisciplinary framework that combines continuum mechanics and quantum mechanical theory, here we present several selected problems, including nanointelligent behaviors, the energy dissipation mechanism, the temperature treatment strategy, bond switching, and ion channels, among others, to demonstrate some of the most common concerns in molecular physical mechanics. The examples mainly cover the range of multidisciplines from classical mechanics to quantum mechanics, etc., although for more complex phenomena such as in life science the multiphysics scale may not stop at quantum mechanics. The results show that except for the size scale and the time scale, the physical scale is also spanned in these multiscale investigations. The molecular physical mechanics needs to extend to a larger range of multiphysical scale when research goes deeper into the nature of molecular systems, certainly with greater challenges, but more arresting findings.

  • On the study of the effects of notch shape on creep damage development under constant loading. Y.P. Jiang, W.L. Guo, Z.F. Yue, and J. Wang. Materials Science and Engineering A, 2006, 437, 340–347.

    Y.P. Jiang1, W.L. Guo1, Z.F. Yue2, and J. Wang3

    1. Institute of Nano-science, Nanjing University of Aeronautics and Astronautics, Nanjing 210016, PR China
    2. Department of Engineering Mechanics, Northwestern Polytechnic University, Xi’an 710072, PR China
    3. School of Mechanical & Aerospace Engineering, Queen's University Belfast, Ashby Building, Stranmillis Road Belfast BT9 5AH, UK

    Materials Science and Engineering A, 2006, 437, 340–347.

    Received 8 April 2006; revised 21 July 2006; accepted 13 August 2006. Available online 20 September 2006.

    Numerical calculations with the K-R damage law have been performed to study the creep damage development of different notched specimens (circumferential, U-type and V-type notched) under constant loading. Emphasis was placed on the roles of notch shape, material parameter α and applied stress. The numerical results show that the distributions of creep stress in the notch cross-section are different from those in the previous studies. Different notched specimens have different creep damage distributions. The development of creep damage in the minimum cross-section varies with notch shape and notch radius. For the circumferential notched specimen, the maximum creep damage lies at the point inside from the notch tip; for the U-type notched specimen, the maximum creep damage appears at the point in from notch root in the notch surface; for the V-type notched specimen, the maximum creep damage appears from the notch tip. The development of creep damage is clearly affected by applied stress, material parameter α and notch shapes. Larger stress and material parameterα can cause the creep damage to develop faster.

    Keywords: Creep; User subroutine; Stress; Damage; Finite element analysis; Notched specimen

  • Structural transformation of partially confined copper nanowires inside defected carbon nanotubes. Yufeng Guo, and Wanlin Guo. Nanotechnology, 2006, 17, 4726.

    Yufeng Guo and Wanlin Guo

    Nanotechnology, 2006, 17, 4726.

    Received 24 May 2006 , in final form 8 August 2006
    Published 1 September 2006

    The encapsulated copper atoms inside a defected single-walled carbon nanotube escape from the tube through the defect hole as the temperature increases. This causes the partially confined copper nanowires (CNWs) to undergo special structural transformations from a solid to a distinguishable helical layered structure and finally to the liquid state. The defect has a vital function in automatically adjusting the internal pressure and copper atom density. The critical structural transformation temperature of the CNW is significantly influenced by the confinement conditions of the carbon nanotube.

  • Stress concentration at an elliptic hole in transversely isotropic piezoelectric solids. Longchao Dai, Wanlin Guo, and X. Wang. International Journal of Solids and Structures, 2006, 43, 1818–1831.

    Longchao Dai, Wanlin Guo, and X. Wang

    Institute of Nano Science, Nanjing University of Aeronautics and Astronautics, Nanjing 210016, China

    International Journal of Solids and Structures, 2006, 43, 1818–1831.

    Received 6 December 2004; revised 26 May 2005. Available online 20 July 2005.

    Two-dimensional electroelastic analyses have been performed theoretically on a transversely isotropic piezoelectric material containing an elliptic hole, subjected to a uniform stress field and a uniform electric displacement field at infinity while the surface of the hole is free of traction and electrically open. Solutions are obtained by using the exact electric boundary condition based on the complex variation method. Explicit solutions for the distributions of the mechanical and electrical components on the rim of the elliptic hole are obtained. An interesting relationship between the stress concentration factor of an elliptic hole (Kt) and that of a circular hole (Ktt=1), , is found in both elastic and piezoelectric materials. It is shown that the electromechanical coupling effect is helpful to reduce the stress concentration. And the influence of the dielectric parameter of the medium inside the hole on the stresses and the concerned stress concentration factor at the surface of the hole is weak in a wide range of the dielectric parameter. Comparisons with available results show good coincidence.

    Keywords: Elliptical hole; Transversely isotropic piezoelectric; Stress concentration; Complex variation method; Electric boundary condition

  • Electrostrictive effect on electronic structures of carbon nanotubes. Chun Tang, Wanlin Guo, and Yufeng Guo. Appl. Phys. Lett., 2006, 88, 243112.

    Chun Tang, Wanlin Guo, and Yufeng Guo.

    Appl. Phys. Lett., 2006, 88, 243112.

    Received 7 March 2006; accepted 16 May 2006; published online 15 June 2006

    The effect of axial electrostrictive deformation on the electronic properties of single walled carbon nanotubes (SWCNTs) is studied by the density functional theory. We find that the band structures of SWCNTs change in electric fields, and the change can be significantly enhanced by the electrostrictive deformation. The polarization of the orbital charge densities and the variation of the dipole moment are also enhanced by the electrostriction. The influence of chirality and size effect on these properties are also analyzed.

  • Advances in Three-Dimensional Fracture Mechanics. Wanlin Guo, Chongmin She, Junhua Zhao, and Bin Zhang. Key Engineering Materials, 2006, 312, 27-34.

    Wan Lin Guo,1, Chongmin She,1, Jun Hua Zhao,1, Bin Zhang,1

    1. Institute of Nano Science, Nanjing University of Aeronautics & Astronautics, Nanjing 210016, China

    Key Engineering Materials, 2006, 312, 27-34.

    The historical developments of the fracture mechanics from planar theory to threedimensional (3D) theory are reviewed. The two-dimensional (2D) theories of fracture mechanics have been developed perfectly in the past 80 years, and are suitable for some specific cases of engineering applications. However, in the complicated 3D world, the limitation of the 2D fracture theory has become evident with development of the structure toward complication and micromation. In the 1990’s, Guo has proposed the 3D fracture theory with a 3D constraint factor based on the deformation theory and energy theory. The proposed 3D theory can predict accurately the fracture problems for practical and complicated engineering structures with defects, by integrating the 3D theory of fatigue, which has been developed to unify fatigue and fracture. Our efforts to develop the 3D fracture mechanics and the unified theory of 3D fatigue and fracture are summarized, and perspectives for future efforts are outlined.

  • Nanointelligent Materials And Systems. Wanlin Guo, Chun Tang and Yufeng Guo. International Journal of Nanoscience, 2006, 5(6), 671-676.

    Wanlin Guo, Chun Tang and Yufeng Guo

    Institute of Nano Science, Nanjing University of Aeronautics and Astronautics, Nanjing, 210016, P. R. China

    International Journal of Nanoscience, 2006, 5(6), 671—676.

    Domain switch, phase transition and electrochemical mechanisms introduced traditional smart materials to various technologies such as piezoelectric ceramics, shape memory alloys and elastor/polymer used in actuators, sensors, etc. From the studies on carbon nanotues, graphite and other nanoscaled materials, we show that due to the quantum effect induced response at atomic or molecular level, all matters in this scale would exhibit intelligent behaviors, and buildings based on this are expected to construct nanointelligent systems which can be believed to improve the current technologies.

    Keywords: Nanointelligent; smart material; function material; quantum effect; size effect; multi-scale; bio-mimic; local field

  • Investigation of the three-dimensional micromechanical behavior of woven-fabric composites. Y. P. Jiang, W. L. Guo, and Z. F. Yue. Mechanics of Composite Materials, 2006, 42(2), 141-150.

    Y. P. Jiang,*,** W. L. Guo,* and Z. F. Yue**

    *Institute of NanoScience, Nanjing University of Aeronautics and Astronautics, Nanjing 210016, P.R.C.
    **School of Me chanics, Building, and Architecture, North western Polytechnical University, Xi’an 710072, P.R.C.

    Mechanics of Composite Materials, 2006, 42(2), 141-150.

    Russian translation published in Mekhanika Kompozitnykh Materialov, Vol. 42, No. 2, pp. 209–220, April–May, 2006.

    A three-dimensional representative volume-element model is presented to study the micromechanical behavior of woven-fabric composites. The effects of the fiber undulation zone and the fiber braid angle on the elastic modulus of the composites are taken into account in the unit cell. Based on isostrain and isostress assumptions, a standard homogenization procedure is used to calculate the effective elastic properties of woven-fabric composites, and all the final stiffness components are expressed in an explicit form. The results obtained by the model considered agree with published experimental results very well. The relationship between the geometric parameters, such as fiber width, thickness, volume fraction, etc., and the macromechanical behavior of the composites can be obtained by this model.
    Keywords representative volume element - woven-fabric composites - micromechanics

  • Molecular dynamics simulation of self-assembled carbon nanotubes. Dawei Wei, and Wanlin Guo. International Journal of Nanoscience, 2006, 5(6), 835-839.

    Dawei Wei1, and Wanlin Guo2

    1. Ministry of Education Key Laboratory of Mechanical Structure Strength and Vibration Xi’an Jiaotong University, Xi’an 710049, P. R. China
    2. Institute of Nano Science, Nanjing University of Aeronautics and Astronautics Nanjing 210016, P. R. China

    International Journal of Nanoscience, 2006, 5(6), 835—839.

    Molecular dynamics (MD) was used to study the behaviors of single-walled carbon nanotubes (CNTs) immersed in ethanol liquid (suspension) when assembling tangled and bulky CNTs into a well-controlled fashion. The ends of the CNTs were modified with carboxyl groups in advance,
    and then were put into different electric field to analyses the motion process of the assemblage. We found that CNTs moved to the cathode quickly and aligned parallel to the orientation of the direct current electric field.

    Keywords: Molecular dynamics simulation; carbon nanotubes; self-assemble.

  • Three dimensional K-Tz stress fields around the embedded center elliptical crack front in elastic plates. Junhua Zhao, Wanlin Guo, Chongmin She, and Bo Meng. Acta Mech Sinica, 2006, 22, 148–155.

    Junhua Zhao, Wanlin Guo, Chongmin She and Bo Meng

    Acta Mech Sinica, 2006, 22, 148–155.

    Received: 26 September 2005 / Accepted: 9 December 2005 / Revised:12 December 2005 / Published online: 14 March 2006

    Through detailed three-dimensional (3D) finite element (FE) calculations, the out-of-plane constraints Tz along embedded center-elliptical cracks in mode I elastic plates are studied. The distributions of Tz are obtained near the crack front with aspect ratios (a/c) of 0.2, 0.4, 0.5, 0.6, 0.8 and 1.0. Tz decreases from an approximate value of Poisson ratio ν at the crack tip to zero with increasing normalized radial distances (r/a) in the normal plane of the crack front line, and increases gradually when the elliptical parameter angle ϕ changes from 0° to 90°at the same r/a. With a/c rising to 1.0, Tz is getting nearly independent of ϕ and is only related to r/a. Based on the present FE calculations for Tz, empirical formulas for Tz are obtained to describe the 3D distribution of Tz for embedded center-elliptical cracks using the least squares method in the range of 0.2≤a/c≤1.0. These Tz results together with the corresponding stress intensity factor K are well suitable for the analysis of the 3D embedded center-elliptical crack front field, and a two-parameter K-Tz principle is proposed.

    Keywords Three-dimensional finite element - Out-of-plane constraint Tz - Embedded elliptical crack - Stress intensity factor - T-Stress - Stress field

  • Validation of the non-local elastic shell model for studying longitudinal waves in single-walled carbon nanotubes. Lifeng Wang, Haiyan Hu, and Wanlin Guo. Nanotechnology, 2006, 17, 1408–1415.

    Lifeng Wang1, Haiyan Hu1,3 and Wanlin Guo2

    1 Institute of Vibration Engineering Research, Nanjing University of Aeronautics and Astronautics, 210016 Nanjing, People’s Republic of China
    2 Institute of Nanoscience, Nanjing University of Aeronautics and Astronautics, 210016 Nanjing, People’s Republic of China
    3 Author to whom any correspondence should be addressed

    Nanotechnology, 2006, 17, 1408–1415.

    Received 9 October 2005, in final form 6 January 2006
    Published 16 February 2006

    This study deals with the dispersion of longitudinal waves in a single-walled armchair carbon nanotube, focusing on the effect of the microstructure of the carbon nanotube on the wave dispersion. To reveal the effect analytically, the carbon nanotube is modelled as a non-local elastic cylindrical shell in the study. The dynamic equation of the non-local elastic cylindrical shell is established and the corresponding dispersion relation of longitudinal waves is derived. These analytic results are verified via molecular dynamics simulations, based on the Terroff–Brenner potential, for the propagation of various longitudinal waves in three single-walled armchair carbon nanotubes. The molecular dynamics simulations indicate that the longitudinal wave dispersion predicted by the model of the non-local elastic cylindrical shell shows a good agreement with that of molecular dynamics simulations in a wide frequency range up to the terahertz region. They also show that both the microstructure of the carbon nanotube and the coupling between the longitudinal wave and the radial motion play an important role in the dispersion of longitudinal waves in a single-walled armchair carbon nanotube.

  • Self-healing properties of flaws in nanoscale materials: Effects of soft and hard molecular dynamics simulations and boundaries studied using a continuum mechanical model. Yufeng Guo, and Wanlin Guo. Phys. Rev. B, 2006, 73, 085411.

    Yufeng Guo and Wanlin Guo

    Phys. Rev. B 73, 085411 (2006) [7 pages]

    Received 29 September 2005; published 16 February 2006

    Soft and hard boundary effects on the flaw in self-healing capabilities of the nanoscale copper clusters and biomaterials have been studied using molecular dynamics simulations as well as the theoretical analyses. When the copper nanocluster size decreases to a compatible magnitude to its flaw, different boundary conditions change the flaw self-healing capability and lead to different dislocation generation and atom rearrangement after the copper nanocluster is healed. The theoretical predictions for the copper nanocluster are in good agreement with the molecular dynamics simulations. Further theoretical investigations demonstrate that the mineral layer in biomaterials possess a high flaw self-healing capability because of the nanometer scale and natural soft boundaries caused by the stacking protein and aragonite layered structures.

  • Isothermal atomistic simulations of nano-electromechanical systems. Wanlin Guo, and Chunzhang Zhu. Nanotechnology, 2006, 17, 1370–1374.

    Wanlin Guo and Chunzhang Zhu

    Institute of Nano Science, Nanjing University of Aeronautics and Astronautics, Nanjing, 210016, People’s Republic of China

    Nanotechnology, 2006, 17, 1370–1374.

    Received 6 November 2005, in final form 10 January 2006
    Published 10 February 2006

    Temperature control in non-equilibrium nano-electromechanical systems is a vital issue to both scientific and engineering fields. The effect of temperature control in a specific dynamic system is studied using the concepts of thermodynamic temperature and kinetic temperature in a molecular dynamic model. It is demonstrated that isothermal simulations can be realized by constant thermodynamic temperature control of the system, but a constant kinetic temperature control scheme yields misleading results for the mechanical movements of the system. The isothermal simulations yield
    similar trends as an adiabatic approximation, at least at low temperature.

  • Numerical investigations of maximum stress concentration at elliptic holes in finite thickness piezoelectric plates. Chongmin She, and Wanlin Guo. International Journal of Fatigue, 2006, 28, 438–445.

    Chongmin She and Wanlin Guo

    International Journal of Fatigue, 2006, 28, 438–445.

    Received 14 May 2004; revised 5 March 2005; accepted 14 June 2005. Available online 18 August 2005.

    The through-thickness variations of stress-concentration factors along the wall of elliptic holes in finite thickness plates of transversely isotropic piezoelectric materials subjected to uniaxial remote tensile stress and applied electric field have been systematically analyzed using the finite element method. The three-dimensional stress concentration factor Kt is found to be a function of the thickness to root radius ratio B/ρ and the aspect ratio t (short to long axial length) of the elliptic holes under tensile loading. It is found that the maximum stress-concentration factor through the thickness, (Kt)max, is 20–150% higher than the value on the free surface (Kt)surf when t changes from 1 to 0.01, and the ratio of the surface value (Kt)surf to the corresponding planar solution (Kt)p−σ at the roots is only 0.84–0.44 when t ranges from 1 to 0.01 if B/ρ is large enough. When B/ρ is decreasing to 1, both the ratios are approaching unity. Simple empirical formulae for the relationships between the three values were obtained by fitting the numerical results with good engineering accuracy for large range of B/ρ (from 1 to 100,000) and t (from 0.01 to 1). The proposed formulae will be useful for strength and fatigue designs of engineering structures with notches and holes. Additional applied electric field can cause higher opening stress in the interior and lower opening stress at the free surface of the plate near the hole, and enhance the out-of-plane constraint significantly. Therefore, the three-dimensional effects can be much stronger in piezoelectric ceramics than in metallic materials.

    Keywords: Stress concentration; Piezoelectric plate; Elliptic hole; Three-dimensional; Finite element