Key Engineering Materials Vols. 324-325

Abstract: In this paper the Fractional Spline Wavelet Transform (FrSWT) is introduced based on the definitions and properties of the fractional B-spline and the symmetric fractional B-spline. Then the computation process and approximation properties of the FrSWT are also discussed and especially, the truncation error of computation is obtained analytically. At last, the FrSWT is applied to detect the abrupt information in the simulated and measured signal of fault gear system.

Abstract: Three-dimensional finite element simulations were carried out to investigate the hydraulic progressive damage and associated flow behavior in rock. In this study cohesive elements were used to simulate the damage of rock. A three-dimensional coupled pore fluid flow and stress model was proposed. The commercial engineering software ABAQUS is employed to simulate the damage process in rock along several predefined paths. A user-subroutine named FLOW was developed to enhance the capability of ABAQUS to deal the moving loadings. With the proposed coupling model, we studied the stress distribution, the pore pressure, the fluid loss, the geometry of the progressive damage. The results show that the length and the width of the path of the progressive damage are strongly influenced by both the hydraulic pressure and the injection time. The results provide good interpretation and understanding of the mechanism of hydraulic progressive damage in rock. This study is very useful and important to the oil engineering and some other rock engineering fields.

Abstract: A fatigue crack growth model under constant amplitude loading based on the total plastic energy dissipation per cycle ahead of the crack was proposed. With the energy balance concept, the crack growth rate was correlated with the total plastic dissipation per cycle, and the total plastic dissipation per cycle was obtained through 2-D elastic–plastic finite element analysis of a stationary crack under constant amplitude. The predictions of the model were in good with the experimental results.

Abstract: Numerical simulation of hydraulic fracturing propagations in the permeable reservoirs was carried out with the finite element analysis software (ABAQUS). A model of coupling the stress equilibrium and fluid continuity equations was proposed and implemented. The nonuniform of sink pore pressure on the fracture surfaces which changes associated with the propagation of fracture was described by a self-developed subroutine through the FLOW in ABAQUS. Samples under different conditions were conducted for studying the rules of the propagation of hydraulic fracturing. The results show that the permeability at the fracture tip is more serious than any other places of the fracture face. The model also illustrates that the fracture geometry is mainly determined by the minimal in-situ stress. The model can be used to simulate the effects of hydraulic fracturing pressures and injection rates on fracture propagation. The results are of much significance for the design of hydraulic fracturing treatments.

Abstract: Major nuclear components have been designed by conservative codes to prevent unanticipated fatigue failure. However, more realistic and effective assessment is necessary in proof of continued operation beyond the design life. In the present paper, three-dimensional stress and fatigue evaluation is carried out for pressurizer employing complex full geometry itself instead of conventional discrete subcomponents. For this purpose, temperature and mechanical stress transfer Green’s functions are derived from finite element analyses and applied to critical locations of pressurizer. In accordance with comparison of resulting stresses obtained from the Green’s function and detailed finite element analysis, suitability of the specific Green’s function is investigated. Finally, prototype of fatigue life assessment results is provided along with relevant ongoing activities.

Abstract: Based on ANSYS/LS-DYNA code, the finite-element models were created to simulate the response of the aircraft panel structure impacted by high velocity projectile. The models proved to be effective through the comparison between the results of simulation and relative experiments. Then the impact process was simulated respectively considering the states of various types of stress in the panel. Through analyzing the simulation results, the influence of various stress states in the panel on impact response and damage mechanism was summed up. The conclusions indicated that the stress and particularly compression stress in aircraft panel structure can facilitate much more deformation and damage when the panel suffers high velocity impact.

Abstract: A 3D finite element model of bolt composite joint has been established to determine the stress distribution on the contact surface. The effects of clamping torque and friction on the contact stress and interlaminar normal stress are considered. From the analysis results, contact stress is bared mainly by the 0° layer. The distribution and magnitude of contact stress are conducted by friction. The effect of clamping torque on interlaminar normal stress is very strong. A 3D damage user subroutine is added to the FEM to simulate the damage of joint. By the means of damage simulation, the initiation and progression direction of three types damage are predicted. Matrix cracking and fiber-matrix shear occur at first, and fiber buckling is founded subsequently. The matrix cracking and fiber-matrix debonding initiate at circumferential angle 45°and 135°, and fiber buckling initiate at the 0° layer on the bearing plane. The friction and bolt clamping torque can restrain damage initiation and development.

Abstract: Based on Reissner plate theory and using Hamilton variational principle, the nonlinear equations of motion are derived for the moderate thickness rectangular plates with transverse surface penetrating crack on an elastic foundation under the action of periodic load. The suitable expressions of trial functions satisfied all boundary conditions and crack’s continuous conditions are proposed. By using the Galerkin method and the Runge-Kutta integration method, the nonlinear equations are solved. The possible bifurcation and chaos of the system are analyzed under the action of external load. In numerical calculation, the influences of the different location and depth of crack and external load on the bifurcation and chaos of the rectangular moderate thickness plates with freely supported boundary are discussed.

Abstract: Based on the analytical solution for an elliptical cavity and the self-consistent method, the exact solutions for a crack in a two-dimensional magnetoelectroelastic medium is derived. The strain energy density factors are calculated for mixed mode cracks in a composite made of BaTiO3 as the inclusion and CoFe2O4 as the matrix.

Abstract: This paper is aimed at investigating the damage and remaining life of a whole HP-Nb hydrogen reformer tube serviced for 12 years. The damage and remaining life evaluation of different parts of the tube were made using metallographic examination, ambient and high temperature uniaxial tensile tests, creep rupture tests and damage mechanics analysis. The results showed that different parts of the tube have the different damage and remaining life due to different service temperature, higher the service temperature, severer the damage and shorter the remaining life. Based on these research results, a case of local maintenance of the reformer tube was introduced.