Our Publications

  • The charpy notch impact test of X70 pipeline steel. Zheng Yang, Chun Yong Huo, and Wanlin Guo. Acta Metallurgica Sinica, 2003, 39(2), 159-163.

    Zheng Yang, Chun Yong Huo, and Wanlin Guo.

    Acta Metallurgica Sinica, 2003, 39(2), 159-163.

    The effects of thickness, notch orientation and delamination cracks on the impact toughness of X70 pipeline steel are investigated experimentally by use of the instrumented Charpy impact tests at different temperatures. The couple effect of delamination cracks, thickness, notch orientation and temperature is discovered. The delamination cracks have certain direction, and their amount and size are related to the temperature and the specimen thickness. Though the delaminating orientations of T-S and T-L specimen are not same, the reasons for both T-S and T-L specimen delaminating are that the weak interfaces in the specimens are pulled apart by the stress perpendicular to them. The delamination cracks can improve the actual impact toughness of X70 pipeline steel both T-L and T-S specimens. The effect of delamination cracks on the actual impact toughness changes with the thickness and the temperature. The couple effect of wall thickness, defect orientation and working temperature of pipeline must be taken into account in safe assessment of pipeline.

  • Mechanism of delamination and its effects on fracture of surface crack bodies in ductile pipeline steel. Hui Ru Dong, Wanlin Guo, and Zheng Yang. Advances in Fracture and Strength, 2005, 297-300, 1235-1240.

    Hui Ru Dong, Wanlin Guo, and Zheng Yang.

    Advances in Fracture and Strength, 2005, 297-300, 1235-1240.

    The effects of three-dimensional crack configurations and delaminations on fracture mechanism and fracture toughness Jc of pipeline steel were investigated experimentally by use of tensile specimens having surface cracks of different depth to length ratio. Comparison with test results of through-thickness cracks and mechanism analyses are made as well. When 3D stress constraint is larger than the strength in the thickness direction the delamination forms. As no delamination occurs in the interior of a surface crack, the constraint is higher and the fracture toughness is lower than that of the through-thickness cracks. Therefore, the nominal fracture toughness obtained from through-thickness cracked specimens is not a real material constancy, and not suitable for safety assessment of pipelines.

  • Lifecycle safety guarantee of structures. Wanlin Guo, Bin Zhang, Qian Feng, and Chun Li. Chinese Journal of Mechanical Engineering, 2005, 18(2), 279-285.

    Wanlin Guo, Bin Zhang, Qian Feng, and Chun Li.

    Chinese Journal of Mechanical Engineering, 2005, 18(2), 279-285.

    The principles for lifecycle safety guarantee of engineering structures are proposed, and theconception is developed for developing the safety guarantee system by integrating the monitoringsystem, analysis system and maintenance system together on the basis of multi-sensor, distribu-tion-measurement, data fusion and digital-signal-processor (DSP) technologies as well asthree-dimensional (3D) fatigue fracture unified theory. As all the systems should work in situs and inreal-time, micromation and integration are important. Damage detectability is introduced to clarify therelationship of life prediction and healthy monitoring or faulty diagnosis. The research work to realizethe lifecycle safety guarantee system is summarized and perspectives for future efforts are outlined.

  • Plane strain problem of piezoelectric solid with elliptic inclusion. Longchao Dai, Wanlin GUo, and Chongmin She. APPLIED MATHEMATICS AND MECHANICS, 2005, 26(12), 1615-1622.

    Wanlin GUo, and Chongmin She.

    APPLIED MATHEMATICS AND MECHANICS, 2005, 26(12), 1615-1622.

    By using the complex variables function theory, a plane strain electro-elastic analysis was performed on a transversely isotropic piezoelectric material containing an elliptic elastic inclusion, which is subjected to a uniform stress field and a uniform electric displacement loads at infinity. Based on the present finite element results and some related theoretical solutions, an acceptable conjecture was found that the stress field is constant inside the elastic inclusion. The stress field solutions in the piezoelectric matrix and the elastic inclusion were obtained in the form of complex potentials based on the impermeable electric boundary conditions.

  • Optimized Bearing and Interlayer Friction in Multiwalled Carbon Nanotubes. Wanlin Guo, and Huajian Gao. Computer Modeling in Engineering & Sciences, 2005, 7(1), 19-34.

    Wanlin Guo1 ,2 and Huajian Gao2

    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.

    Computer Modeling in Engineering & Sciences, 2005, 7(1), 19-34.

    A systematic investigation is performed on energy dissipation related interaction force associated with interlayer motion of sliding, rotation and telescoping between any two possible neighboring carbon nanotubes. In particular, we analyze the interlayer corrugation energy and sliding, rotation and telescoping resistance force associated with the Lennard-Jones potential as well as a registry-dependent graphitic potential. It is found that the interlayer resistance associated with both of these potentials can vary with the morphology, length and diameter of the two tubes. Energy dissipation related fluctuation of the resistant force can be as low as 10$^{ - 18}$N/atom between the most optimistic tube pairs, but can be as large as 10$^{ - 11}$N/atom in the widely investigated zigzag/zigzag orientations. In most cases, the fluctuation of interlayer sliding resistance force increases with the tube length in a commensurate pair of tubes, but can remain unchanged in an incommensurate pair. These findings may be significant for the design of nanotube-based devices.

  • Radial compression of carbon nanotubes: deformation and damage, super-elasticity and super-hardness. Chunzhang Zhu, Wanlin Guo, T X Yu, and C H Woo. Nanotechnology, 2005, 16, 1035–1039.

    Chunzhang Zhu1,2, W Guo1,2, T X Yu2 and C H Woo

    1 Institute of Nano Science, Nanjing University of Aeronautics and Astronautics, Nanjing, People’s Republic of China
    2 Department of Mechanical Engineering, Hong Kong University of Science and Technology, Hong Kong, People’s Republic of China
    3 Department of Electronic and Information Engineering, Hong Kong Polytechnic University, Hong Kong, People’s Republic of China

    Nanotechnology, 2005, 16, 1035–1039.

    Received 1 February 2005 , in final form 7 April 2005
    Published 12 May 2005

    Molecular dynamics (MD) simulations of nanoindentation of multiwalled carbon nanotubes (MWCNTs) are carried out to study the deformation mechanism and the mechanical properties of MWCNTs in the radial direction. The MWCNT is found to be soft in its radial direction, with nanohardness rising slowly from about 6 to 15 GPa. The soft phase persists until all spaces between adjacent layers of the MWCNT are compressed beyond a critical value of about 1.9 Å. Beyond the critical stage the formation of new bonds between different layers starts to increase, producing a super-hard amorphous phase with a hardness of up to 94 GPa. Though locally compressed to a large radial strain of about 63%, the amorphous phase with a mixture of sp3 and sp2 bonds is completely reversible upon unloading, showing super-elasticity. Further indentation afterwards leads to permanent sp3 and even sp rehybridization, the MWCNT is badly damaged and the hardness fluctuates with a maximum of about 124 GPa which is comparable to the microhardness of diamond.

  • Monochiral tubular graphite cones formed by radial layer-by-layer growth. G. Y. Zhang, X. D. Bai, E. G. Wang, Y. Guo, and Wanlin Guo. Phys. Rev. B, 2005, 71, 113411.

    G. Y. Zhang, X. D. Bai, and E. G. Wang*
    Institute of Physics, Chinese Academy of Sciences, Beijing 100080, China

    Y. Guo and Wanlin Guo
    Institute of Nano Science, Nanjing University of Aeronautics and Astronautics, 210016, China

    Phys. Rev. B 71, 113411 (2005) [4 pages]

    Received 28 December 2004; published 28 March 2005

    Multiwalled carbon nanotubes in the form of tubular graphitic cones (TGC) are grown at high yield. Structure analysis reveals that chirality of the multiple walls in a TGC are nearly identical to each other and preferentially zigzag. The formation of such TGCs is explained by two separate processes along radial and axial directions, respectively. The root-based radial growth is via a layer-by-layer mode that controls the chirality of tubes. The axial growth extends the tubules with nearly identical chiral angles. Total energy calculations indicate that the inner tube with near zigzag chirality is favored to template the growth of monochiral multiwalled structures, in good agreement with experiments.

  • Cracking diamond anvil cells by compressed nanographite sheets near the contact edge. Bin Zhang, and Wanlin Guo. Appl. Phys. Lett., 2005, 87, 051907.

    Bin Zhang and Wanlin Guo

    Appl. Phys. Lett. 87, 051907 (2005)

    Received 29 March 2005; accepted 7 June 2005; published online 26 July 2005

    Uniformly cold-compressed nanographite sheets in diamond anvil cells (DAC) are found to transform from soft into hard phase at about 17 GPa using molecular dynamics simulations. The hard phase can reach the compressive strength of about 150 GPa. Finite element analyses show that high stress concentrations occur along the boundary of interface on the diamond-anvil culets contacted with the nanographite sheets. The concentrated compressive stress can exceed the strength of diamond in a ring region with the width about 0.2 μm, when the average pressure in the graphite sample is 17 GPa as in [ W. L. Mao et al., Science 302, 425 (2003) ]. Within the narrow ring, superhard carbon phase can be formed from the nanographite sheets, which leads to cracking of the DAC near the contact edge.

  • Deflection and stability of membrane structures under electrostatic and Casimir forces in microelectromechanical systems. C. Wang, W. Guo, and Q. Feng. Acta Mechanica, 2005, 180, 49–60.

    C. Wang, W. Guo, and Q. Feng.

    Acta Mechanica, 2005, 180, 49–60.

    The deflection and stability of microfabricated rectangular membrane strips driven electrostatically are analyzed theoretically in this paper with the attractive Casimir force between the conducting surfaces under consideration. The analytical results of the deflection of the membrane strip under the combined electrostatic and Casimir forces show that the effect of the Casimir force on the deflection is dependent on the values of the initial gap between the membrane and the substrate w0, the applied voltage V and the fourth power of span to thickness ratio L4/h. The Casimir effect on the membrane system is dominant for smaller gap w0 and lower voltage V, yet it decreases with the gap width and the voltage increasing. When the value of w0and V is large enough, it is feasible to neglect the Casimir force. The Casimir effect on the deflection increases with the increasing L4/H as well. The static stability of the membrane structure can be determined by a dimensionless parameter K related to the geometrical parameters of the membrane structure. The critical value KC, over which the system will become unstable and the membrane strip will collapse to the substrate, is solved through numerical calculations, and it is found that an electrostatically driven membrane structure can be designed to avoid the potential instability with a high aspect ratio (L/h).

  • Influence of scanning velocity on the tribology performance of hard disk. Yan Jiang, and Wanlin Guo. Chinese Science Bulletin, 2005, 50(17), 1829-1833.

    Yan Jiang, and Wanlin Guo

    Chinese Science Bulletin, 2005, 50(17), 1829—1833.

    The dependence of tribology behavior of hard disk on scanning velocity was investigated by friction force microscopy in both air and vacuum. It is found that the surface friction force decreases with increasing scanning velocity in air as well as in vacuum. In vacuum, due to the capillary force disappearing, the adhesive energy decreases significantly, and the friction force is much smaller than that in air.

  • Coupled defect-size effects on interlayer friction in multiwalled carbon nanotubes. Wanlin Guo, Wenyu Zhong, Yitao Dai, and Sunan Li. Phys. Rev. B, 2005, 72, 075409.

    Wanlin Guo, Wenyu Zhong, Yitao Dai, and Sunan Li.

    Phys. Rev. B, 2005, 72, 075409.

    Received 20 July 2004; published 3 August 2005

    Systematical molecular statics and dynamics simulations are performed on the interlayer friction and energy dissipation of biwalled carbon nanotubes of different chirality and size, with and without defects. The interlayer friction force of perfect bitube systems is strongly dependent on commensuration and independent of the tube length in incommensurate systems at very low temperature. However, the existence of defects can ruin the perfect-geometry controlled interlayer interaction and lead to a sharp increase in friction and energy dissipation rate. The oscillating energy dissipation rate increases monotonically even in an incommensurate bitube system with increasing tube length and defect density. The coupled effects of system registration, size, and defects are demonstrated, which can explain how an ultrasmooth nano-bitube system leads to a rougher longer tube system and provides a new mechanism for multiscale tribology. Simulations on the influence of attachments and terminal conditions at the end of the tubes show that H terminations lead to a higher rate of energy dissipation in a bitube oscillator than capped and freely open cores in the systems. The findings of these important effects can provide a fundamental understanding with which to create novel nanosystems from multiwalled carbon nanotubes.

  • Buckling of multiwalled carbon nanotubes under axial compression and bending via a molecular mechanics model. Tienchong Chang, Wanlin Guo, and Xingming Guo. Phys. Rev. B, 2005, 72, 064101.

    Tienchong Chang1,3,*, Wanlin Guo2, and Xingming Guo1

    1. Shanghai Institute of Applied Mathematics and Mechanics, Shanghai University, Shanghai 200072, China
    2. Institute of Nano Science, Nanjing University of Aeronautics and Astronautics, Nanjing 210016, China
    3. Department of Civil Engineering, Tongji University, Shanghai 200092, China

    Phys. Rev. B 72, 064101 (2005) [11 pages]

    Received 24 March 2005; revised 10 June 2005; published 1 August 2005

    Based on a molecular mechanics model, analytical solutions are obtained for the critical buckling strain of multiwalled carbon nanotubes (MWNT’s) under axial compression and bending. We show that only part of the outer layers buckles first while the remaining inner part remains stable in a very thick MWNT, which is quite different from the initial buckling mode of a relatively thin MWNT in which all individual tubes buckle simultaneously. Such a difference in the initial buckling modes results in quite different size effects on the critical buckling strain of thin and thick MWNT’s. For instance, inserting more inner individual tubes may increase the critical buckling strain of a thin MWNT, but cannot increase the critical buckling strain of a thick tube. The effects of tube size on the initial buckling wavelength are also examined, and it is shown that the initial buckling wavelength is weakly dependent on the thickness of the MWNT.

  • Fusion analyses of lifecycle safety and damage tolerance for cracked structures. Chun Li, and Wanlin Guo. International Journal of Fatigue, 2005, 27, 429–437.

    Chun Li, and Wanlin Guo.

    International Journal of Fatigue, 2005, 27, 429–437.

    Received 22 December 2003; revised 19 June 2004; accepted 2 August 2004. Available online 19 November 2004.

    The important problem of damage detectability is proposed and the relationship between fatigue life and damage detectability of cracked structures is elucidated through cracked gear tooth models with detailed analyses of the fatigue fracture properties and vibration modes and frequencies. It is shown that the detectability of the damage or faults in a large portion of fatigue life of the structures is poor, where the crack is relatively small. The damage detectability of a structure depends not only on the size of the crack, but also on the location and structure details of the crack and the diagnosis techniques used. It is pointed out that damage monitoring or diagnosing techniques can only be used to structures with enough damage tolerant capability and enough long detectable life duration for safety guarantee. Through the whole text, an integrated description on fusion technology of lifecycle safety guarantee of mechanical structures is provided.

    Keywords: Damage tolerance; Fatigue life; Damage detectability; Safety guarantee

  • Modified James–Anderson method for stress intensity factors of three-dimensional cracked bodies. Haijun Shen, and Wanlin Guo. International Journal of Fatigue, 2005, 27, 624–628.

    Haijun Shen, and Wanlin Guo.

    International Journal of Fatigue, 2005, 27, 624–628.

    Received 8 October 2003; revised 15 October 2004; accepted 9 December 2004. Available online 2 March 2005

    James and Anderson have proposed a method for the determination of stress intensity factors for three dimensional cracked bodies from experimentally-measured two-dimensional fatigue crack growth data. In the present work, the method is improved through the use of 3D fatigue crack closure theory, and it is shown that the modified method can accurately evaluate stress intensity factors for 3D cracks. The explicit procedures given in the paper provide a convenient method for the determination of stress intensity factors for 3D cracked bodies.

    Keywords: James–Anderson method; Three-dimensional cracks; Stress intensity factor; Constraint; Fatigue crack closure

  • Electric-Field-Enhanced Assembly of Single-Walled Carbon Nanotubes on a Solid Surface. Zhuo Chen, Yanlian Yang, Zhongyun Wu, Gang Luo, Liming Xie, Zhongfan Liu, Shaojie Ma and Wanlin Guo. J. Phys. Chem. B, 2005, 109(12), 5473–5477.

    Zhuo Chen, Yanlian Yang, Zhongyun Wu, Gang Luo, Liming Xie, and Zhongfan Liu
    Center for Nanoscale Science and Technology (CNST), College of Chemistry & Molecular Engineering, Peking University, Beijing 100871, PRC

    Shaojie Ma and Wanlin Guo
    Institute of Nano Science, Nanjing University of Aeronautics and Astronautics, Nanjing 210016, PRC

    J. Phys. Chem. B, 2005, 109 (12), pp 5473–5477

    We report a novel electric-field-enhanced chemical assembly approach for fabricating highly aligned SWNT arrays on a solid surface with remarkably improved efficiency and packing density, which is very important for the real applications of carbon nanotube arrays. With the enhancement of the electric field, the assembling kinetics of SWNTs is remarkably speeded up to effectively decrease the assembling time, and the packing density can even exceed the saturated density of conventional assembly method by four times within only half an hour. The molecular dynamics simulation results illustrated the alignment of SWNTs with their long axes along the electric flux in solution, leading to the increase of packing density and efficiency through overcoming the steric hindrance of the “giant” carbon nanotubes.

  • Tz constraints of semi-elliptical surface cracks in elastic plates. Bin Zhang, and Wanlin Guo. International Journal of Fracture, 2005, 131, 173–187.

    Bin Zhang, and Wanlin Guo.

    International Journal of Fracture, 2005, 131, 173–187.

    The out-of-plane constraints Tz around the semi-elliptical surface cracks in an elastic plate subjected to uniform tension loading have been investigated through detailed three-dimensional (3D) finite element (FE) analyses. The distributions of Tz are obtained in the vicinity of the crack border with aspect ratios of 0.2, 0.4, 0.5, 0.6, 0.8 and 1.0. Tz drops from Poisson’s ratio at the crack tip to approximate zero beyond certain radial distance in the normal plane of the crack front line, and increases gradually from the free surface to the mid-plane at the same radial distance. By fitting the numerical results, empirical formulae are obtained to describe the 3D distributions of Tz for semi-elliptical surface cracks with a sufficient accuracy in the wide aspect ratio range of 0.2a/c 1.0 except very near the free surface, where Tz is extremely low. Tz, combining with the corresponding K and T or J and Q, can be applied to establish the three-parameter dominated stress field, which can characterize the 3D crack front field completely as an attempt.

    Keywords: Out-of-plane constraint Tz; semi-elliptical surface crack; three-dimensional finite element

  • 3D constraint effect on 3D fatigue crack propagation. Haijun Shen, and Wanlin Guo. International Journal of Fatigue, 2005, 27, 617–623.

    Haijun Shen, and Wanlin Guo.

    International Journal of Fatigue, 2005, 27, 617–623.

    Received 9 April 2004; revised 15 October 2004; accepted 9 December 2004. Available online 25 February 2005.

    As typical examples, tensile round bars with elliptical surface cracks are used to illustrate the three-dimensional (3D) constraint effect and the characteristics of 3D fatigue crack propagation. Based on the latest plastic constraint theory and the concept of equivalent thickness Beq, a practical 3D crack closure model, which can be as well used to obtain material da/dN−ΔKeff curves, is developed to eliminate the 3D constraint effect on 3D fatigue crack propagation. Further, in order to verify the present Beq based 3D crack closure model, the fatigue crack propagation lives of 20CrMo steel round bars with elliptical surface cracks and 7475-T761 aluminum alloy sheets with corner cracks in edge region of their holes are predicted in this paper. The analytical results based on the present 3D model show that the 3D constraint effect on 3D fatigue crack growth can be eliminated, and fatigue crack propagation lives for both 20CrMo steel round bars and 7475-T761 aluminum alloy sheets with straight holes can be predicted accurately. The Beq based 3D crack closure model in the present paper can also be applied to analyze other complicated 3D fatigue cracks.

    Keywords: Fatigue crack propagation; 3D constraint effect; Equivalent thickness Beq; Crack closure model