Papers by Author: You Tang Li

Abstract: Taking the mode I crack of finite width plate as the research object, the nodal displacement extrapolation method of type I stress intensity factor is discussed, and the stress intensity factor expressed by nodal displacement is obtained. Taking A7N01 aluminum alloy as the research object, the finite element software ABAQUS was used to numerical simulation and analysis. The effect of stress ratio on stress intensity factor K _I was discussed. The results showed that in the same crack size ratio a/W, the stress intensity factor increases with the increase of the stress ratio; at the same stress ratio R, the stress intensity factor increases with increasing crack size ratio. At the same time, change law of the stress intensity factor increase: under the condition of different stress ratio, when a/W≤0.6, the increase of stress intensity factor is almost consistent; when a/W>0.6, the increase of stress intensity factor will increase obviously.

Abstract: This Based on the elastic theory of a crack perpendicular to and terminating at bimaterial interface, a generalized expression of the stress intensity factor is provided for a crack in single material and a crack perpendicular to bimaterial interface, finite element methods are used to calculate the stress intensity factors. The influences of the material combination and crack length on the the stress intensity factors were investigated. Results show that when the crack terminates at bimaterial interface, singular order of K_Iis different from that of single material, and the values of K_I increase with increasing E₁/E₂ and μ₁/μ₂.

Abstract: A numerical method to simulate the crack propagation based on the maximum circumferential stress theory is presented in this paper. The FEM method is used to estimate the influence of the material discontinuous zone on the propagation path of the crack placed in close to it in the matrix. When the crack grows, the FEM method uses the maximum circumferential stress theory to determine the propagation direction and the elements re-meshing program to ensure the accuracy of the crack-tip stress field. The crack propagation paths in the matrix with different material zone are simulated by the method. The simulation results show that the property of the material discontinuous zone influences the maximum deflection angle and its size influences the length of the deflected crack path.

Abstract: A numerical method to simulate the crack propagation is presented in this paper. The FEM is used to estimate the influence of the material discontinuous zone on the propagation behavior of the crack placed in close to it in the matrix. The crack propagation paths in the matrix with different material discontinuous zone are simulated. The simulation results show that the crack propagation path will deviate toward the material discontinuous zone when the crack grows in closed to it and the property of the material discontinuous zone influences the deflection angle and the crack propagation rate.

Abstract: A series multi-axial tension and torsion low cycle fatigue life experiments of Ti-6Al-4V alloy were conducted on the MTS tension and torsion joint testing machine, in which the torsional strain control and non proportional cyclic loading method under the loading paths of circular, rectangular, square, oval and diamond were successively used. The experimental results are compared and analyzed with the results that calculated by the equivalent strain model, the energy method model and the critical plane method model. The results show that the critical plane method is the accurate prediction model to predict the multi-axial low cycle fatigue life of Ti-6Al-4V alloy.

Abstract: A generalized expression of the stress-singularity function at the tip of artificial crack is proposed, and a formula to calculate the stress intensity factor of artificial crack is obtained in the paper. The solutions of stress singularity of a cracked bi-materials beam under uniform tension and bending were computed. The results show that the degree of stress-singularity is determined by the exponent λ at the tip of artificial crack, and the exponent λ is, not only determined by materials parameter of artificial crack but also by angle. Key words: artificial crack; bi-material; stress singularity; eigen value; stress extrapolation method

Abstract: The low cycle fatigue behaviors of TI-6AL-4V alloy controlled by strain were investigated by experiment. The fatigue tests were performed at room temperature, and cyclic strain and stress ratio are 0.1 with triangle load wave. The results show that TI-6AL-4V alloy is soften rapidly under the cyclic tensile stresses and it is harden rapidly under the cyclic compressive stresses during the initial-stage of strain controlled fatigue, and the rates of cyclic soften and cyclic harden are decreased with the fatigue progress. The soften rate is related to the cyclic strain but little to the cyclic stress during the overall fatigue progress. The change of cyclic stress is related to the macro friction stresses. The results of experiment show that obvious cyclic creep occurs under the stress controlled low cycle fatigue conditions, and the magnitude of cyclic creep strain is related to the maximum cyclic stress. The softening of tensile friction stresses is the main factor of cyclic creep.

Abstract: the nonlinear bending problem of the shallow spherical shells with rectangular bottom was studied under the boundary condition of moved fixed-edges based on the nonlinear deformation foundational equations of shallow reticulated shells, the trigonometric series solution satisfies boundary condition of the deflection was derived first, the stress function was solved by substitution of the solution into the nonlinear compatibility equation, the nonlinear characteristic formula of the loads and the deflection was obtained by the energy equation, then the critical point was given. The critical load was given by the characteristic curves. The nonlinear characteristic formula in the paper can be reference by the engineering designers.

Abstract: The nonlinear dynamical equations are established by using the method of quasi-shells for three-dimensional shallow spherical shells with circular bottom. Displacement mode that meets the boundary conditions of fixed edges is given by using the method of the separate variable, A nonlinear forced vibration equation containing the second and the third order is derived by using the method of Galerkin. The stability of the equilibrium point is studied by using the Floquet exponent.

Abstract: The tip radius ρ, depth t and field angle α of notch and the geometrical sizes a and b of shaft are looked as descriptive parameters in the annular notched shaft. Taken the crack, blunt crack and notch as breach, the stress field and displacement field near the tip of breach which serve dimensionless factor f_α(a/b) as descriptive parameter are obtained. The effects of parameters ρ, t and α to f_α(a/b) are analyzed. The connections between stress intensity factor of crack and stress concentrator factor of notch, between sharp V-notch and crack, between V-notch and U-notch have been founded.