Our Publications

  • The coupled effects of thickness and delamination on cracking resistance of X70 pipeline steel. Wanlin Guo, H. Dong, M. Lu, and X. Zhao. International Journal of Pressure Vessels and Piping, 2002, 79(6), 403-412.

    Wanlin Guo,1,2, H. Dong,2, M. Lu,3, and X. Zhao,3

    1. Department of Aircraft Engineering, 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. Tubular Goods Research Center of China National Petroleum Corporation, No. 21, Dianzier Road, Xian 710065, People's Republic of China

    International Journal of Pressure Vessels and Piping, 2002, 79(6), 403-412.

    Received 11 November 2000; revised 17 April 2002; accepted 29 April 2002. ; Available online 4 December 2002.

    The effects of thickness and delamination on the fracture toughness and stable crack growth behaviour of high-toughness pipeline steels were investigated experimentally by use of compact tension specimens with thicknesses of 3–15 mm cut from a 17 mm-thick wall pipe. Material resistance curves were generated based on the stress intensity factor (SIF) K and the J-integral. The critical SIF Kc and the J-resistance curves are found to be independent of thickness as the delaminations near the crack tip within the material reduce the out-of-plane constraint in thicker specimens. Both fracture mechanism and mechanics analyses shown that the fracture behaviour of the steel is controlled by the strong-coupled effects of thickness and delaminations. With increasing thickness, the out-of-plane stress constraint increases and causes the inclusion separation, growth and coalescence to form delaminations of different sizes before the main crack initiates. The delaminations in turn, reduce the out-of-plane constraint and thus, the thickness effect upon fracture. The advantages and disadvantages of delaminations in a safety assessment of pipelines are also discussed based on three-dimensional fracture theory.

    Author Keywords: Fracture toughness; Crack growth resistance; Thickness; Delamination; Pipeline steel; J-Integral; Stress intensity factor; Three-dimensional fracture theory

  • Corrosive fatigue of structures with dimple holes under spectrum loading. Haijun Shen, Wanlin Guo, and G. Lu. Fatigue & Fracture of Engineering Materials & Structures, 2002, 25(5), 489-498.

    Haijun Shen1, Wanlin Guo1, and G. Lu2

    1: School of Aeronautics and Astronautics, Nanjing University of Aeronautics and Astronautics, Nanjing, 210016.
    2: Aircraft Department of Northwestern Polytechnic University, Xi'an, 710072, P.R. China

    Fatigue & Fracture of Engineering Materials & Structures, 2002, 25(5), 489-498.

    Experimental investigation and life prediction are made for structures with straight holes and dimple holes in both laboratory ambient conditions and 3.5% NaCl solution under spectrum loading. With the aid of acoustic emission, label loading and fractography technique, the crack-growth data are obtained in both environments. Stress-intensity factors for the corner crack emanated from the dimple hole are evaluated by three-dimensional (3D) finite element (FE) method. Life prediction of the tested structures is made by using the modified FASTRAN-II code on the basis of corresponding fatigue crack-growth rate curves. It is shown that once the initial defect size a0 is determined by one set of test data, it can be used together with the 3D crack-growth method in order to provide accurate life prediction in alternative structure and loading condition. By comparison, life prediction by the traditional local strain method is also made which is shown to be less reliable than the 3D crack-growth method.

  • Theoretical investigation of elastoplastic notch fields under triaxial stress constraint. Wanlin Guo. International Journal of Fracture, 2002, 115(3), 233-249.

    Wanlin Guo.

    International Journal of Fracture, 2002, 115(3), 233-249.

    In this paper, an exact elastic-plastic solution has been obtained based on the J2-deformation theory of plasticity for a plate having a circular hole under biaxial tension and triaxial stress constraint in linear elastic strain-hardening materials. The theoretical solution shows that a linear elastic solution of the equivalent strain can be used to linear elastic-power hardening plastic situation just by a simple variable replacement. Then a strain equivalent rule (SER) is proposed to predict the elastoplastic notch fields by use of the elastic solution. Validations against theoretical analyses and finite element calculation for various combinations of material properties, triaxial stress constraints, load levels show that the SER can be used to predict stress-strain distributions in the whole plastic zone effectively and conveniently.

    Keywords: elastoplastic material; strain equivalent rule; stress concentration; triaxial stress constraints

  • Freezing atom method in molecular dynamics simulation. Wanlin Guo, and T.Z. Chang. International Journal of Nonlinear Sciences and Numerical Simulation, 2002, 3(3-4), 717-720.

    Wanlin Guo, and T.Z. Chang.

    International Journal of Nonlinear Sciences and Numerical Simulation, 2002, 3(3-4), 717-720.

  • The influence of plasticity mismatch on the growth and coalescence of spheroidal voids on the bimaterial interface. Zhenhuan Li, and Wanlin Guo. International Journal of Plasticity, 2002, 18(2), 249-279.

    Zhenhuan Li,1, and Wanlin Guo,2,3

    1. Department of Mechanics, Huazhong University of Science and Technology, Wuhan 430074, PR China
    2. The National Key Laboratory of Mechanical Structural Strength and Vibration, Xi'an Jiaotong University, Xi'an 710049, PR China
    3. Department of Aircraft Engineering, Nanjing University of Aeronautics and Astronautics, Nanjing 210016, PR China

    International Journal of Plasticity, 2002, 18(2), 249-279.

    Received in final revised form 28 June 2000. Available online 19 January 2002.

    To investigate the macro-mechanical response and micro-mechanism of damage by void growth and coalescence on the interface in a bimaterial system, detailed finite element computations of a representative cylindrical cell containing a spherical void are performed. By comparison with the response of a homogeneous material cell model, significant effects of the matrix plasticity mismatches due to the yield stress and the strain hardening exponent on the void growth and coalescence are revealed: (1) The growth rate of the void on the bimaterial interface is much faster than that in the homogeneous material, and the critical coalescence strain of the void on the interface is only about half of that in homogeneous material. (2) Due to the difference in the deformation resistance of the matrix materials in the bimaterial system, all computations indicate that deformed voids are seriously distorted and the linking of adjacent voids takes place in the softer matrix material. Comparison of the computational results with the classical Rice–Tracey (R-T) model shows that the R-T model cannot make good prediction for the growth of the void on the bimaterial interface. On the basis of large numbers of numerical simulations, a correction coefficient is introduced to improve the R-T model.

    Author Keywords: A. Voids and inclusions; B. Porous material; C. Finite element; Plasticity mismatch; Interface