Papers by Author: Qing Gao

Abstract: Based on the time-dependent deformation behavior of solder alloy 63Sn-37Pb at room temperature, a damage-coupled unified visco-plastic multi-axial fatigue model and its failure criterion were proposed. In the evolution equation of damage for the model, the time-dependent effect of damage was taken into account. The model was used to predict the fatigue life under different loading paths. The comparison between the predicted and experimental results demonstrated that the time-dependent failure model can simulate the deformation behavior and predict the fatigue life well under different nonproportional strain paths.

Abstract: A multiple fields’ coupled model of new magnetic controlled DC plasma torch, which was used for CVD diamond film, was presented. In this model, the effects of electric field and magnetic field on the flow field and temperature field were taken into account, and the fluid dynamics equations were modified by the addition of some source terms relating to electromagnetic field, such as Lorentz force, joule heating, and radiative cooling. Conversely, the generalized ohm’s law was used to solve the current density, which reflected the effects of flow field and temperature field on the electric field and magnetic field. In addition, the rest Maxwell’s equations and external solenoid magnetic field equation were also modeled. In order to know the effect of external magnetic field on the torch, the current intensity of external solenoid was chosen to simulate its influence on the flow and heat transfer in the torch. Results show that external magnetic field plays a part in stirring the plasma, which is advantageous for the preparation of diamond film. The larger the external solenoid current intensity is, the better the uniformity of the temperature and velocity of plasma is.

Abstract: Uniaxial ratchetting-fatigue interaction of tempered 42CrMo alloy steel was observed by various cyclic stressing tests at room temperature. The ratchetting deformation and low cycle fatigue (LCF) property of the material as well as their interaction occurred in cyclic stressing were discussed. It is shown that progressive ratchetting deformation causes the decrease of fatigue life, and the fatigue life of the material depends greatly upon the applied mean stress, stress amplitude, maximum stress and stress ratio. Since tempered 42CrMo steel presents significant cyclic softening feature, a tertiary ratchetting is observed. Based on the experimental results, a simple and reasonable failure model convenient to engineering application was constructed to predict the fatigue life of the material in uniaxial cyclic stressing. The basic variables of the model are maximum stress and stress ratio, and the effect of cyclic softening feature on the ratcheting-fatigue interaction is also included in the model by introducing a new variable. It is shown that the predicted lives are in fairly good agreement with the experimental ones.

Abstract: First, the characteristics of thermal residual stress in randomly oriented short δ-Al2O3 fiber reinforced aluminum alloy composites were analyzed by an elasto-plastic finite element method regarding the effect of the variation in short fiber orientation. Then, the effective moduli and initial tensile stress-strain curves of the composites were simulated by finite element method with the thermal residual stress taken into account. It is concluded that the simulated results obtained with thermal residual stress contained agree with corresponding experimental results better than those obtained in thermal residual stress-free cases.

Abstract: The tests of 63Sn-37Pb under cyclic strain and stress were conducted to investigate the material’s time-dependent behavior. A damage-coupled viscoplastic model and its failure criterion are proposed. The prediction of the proposed viscoplastic model implies that the model can describe the cyclic strain and cyclic stress ratcheting behavior, and the fatigue lives very well.