Rui Cheng Feng

Improved Method of Fatigue Life Assessment for TiAl Alloys

For rapid fatigue life assessment of TiAl alloys, the new method was proposed based on qualitative and quantitative analyses. The qualitative analysis was employed to illustrate the microstructure effect for TiAl alloys on their fatigue life. The new formula is derived for estimation of the interaction forces of dislocations, which yields quite satisfactory results. The results of qualitative and quantitative analyses were used to predict the fatigue life improvement by the addition of trace elements producing grain refinement.

Influence of Temperature on Fatigue Crack Propagation in TiAl Alloys

Experimental investigations of fracture toughness for a TiAl-based γ-alloy were performed at different temperatures. The temperature effect on fatigue crack growth behavior is evaluated, the formula describing its rate in range to II (stable propagation) was derived, as well as specific values of equation constants were obtained on the basis of experimental results. Tests were conducted in vacuum at 25, 750, and 850°C. The experimental results demonstrate that temperature exerts great influence on fatigue crack growth rates. With an increase in temperature up to 750°C, the growth rate of such cracks increases, after reaching this temperature, the brittle-ductile transition of a TiAl-based alloy is taking place. A similar relationship is also observed for conventional alloys.

Sparse Representation of Vibration Signals Using Trained Dictionary

The sparsity of a signal is critical for compression and high compression performance is obtained by utterly sparse signal. But real signals are not sparse commonly, so sparse transformation is considered. In addition, the sparse degree of coefficients is mainly determined by the quality of transform base. Therefore, this paper constructs a transform base (trained dictionary) by K-SVD algorithm for rolling element bearing vibration signals and uses the Orthogonal Matching Pursuit (OMP) algorithm to conduct sparse representation and simulation. Results show that the trained dictionary can be more fitted with the features of signals, the residual components are smaller and the reconstruct similarity is higher compared to the untrained dictionaries, obtaining better representation.

Performance Evaluation of Hybrid Production Lines with Multiple Stochastic Failure Modes and Unreliable Limited Buffers

A hybrid manufacturing system which consists of two machines is examined. Unreliable buffers and multiple stochastic failure modes of the machines are introduced to the system. A new method of the system performance evaluation is presented. The states of the system are analyzed in detail based on a discrete model and a new solution technique is given to determine the state probabilities. The method can be used to analyze the cases arising from two or more stochastic events or longer (or more complex)production lines. Numerical results are also offered to testify the method and show some characteristics of the system.

The Micro Crack Nucleation Rule and Fracture Behavior of Titanium Aluminum Alloy

Study on tensile fracture behavior of TiAl alloy by means of the macro fracture theory and micro dislocation block theory. A quantitative analysis method of micro crack nucleation and crack mechanism for TiAl alloy is performed with the help of the dislocation distribution model, and is based on the strain energy density theory and criterion, a crack criterion of TiAl alloy instability is established. The experimental results confirmed that the dislocation model and S criterion on tensile fracture behavior of TiAl alloys are effective.

Calculations for Diffusion Probability and Diffusivity of Interstitial Atom in one Lattice for γ-TiAl Alloy

The motion of interstitial atoms (one of the point defects) in material is random under certain temperature. However, the diffusion of interstitial atoms has priority along some certain directions to the others, so it is necessary to reveal the phenomenon (the phenomenon also can be called anisotropic). In order to illustrate the anisotropic and reveal the magnitude of probability of the micro crack formation along crystal axes, some formulae derived from former literatures have been adopted, and the values of diffusion probability and diffusivity of interstitial atoms-Ti or Al along 〈110〉and〈100〉have been calculated. The conclusion that the diffusion of interstitial atoms along different crystal axis has different diffusivity is verified by the comparison of the results of calculations.

Influence of Microstructure and Stress Ratio on Fatigue Crack Propagation in TiAl Alloy

Based on the fatigue crack propagation experiments did by A.-L. Gloanec et al., the fatigue crack propagation rates of TiAl alloy of two processing routes, namely casting and PM, and stress ratios had been tested, in order to find out the effects of microstructure and stress ratio. An improved fatigue crack propagation formula for region Ⅱ (the expansion region) was derived according to Paris formula. The specific values of the constants in the formula were calculated. Fatigue crack propagation resistance of nearly fully lamellar microstructure is superior to that of equiaxed γ grain. The experimental results present that both microstructure and stress ratio has a significant influence on fatigue crack growth rate.

Coupled Vibration Modal Analysis of Synchronous Dual Ball Screw Feeding System

With the Synchronous Dual Ball Screw Feeding System used in a Milling-Turning compound machining center as the research object. For study the ball screw vibration modal, which using Lagrange established the dynamics equation and using the Lizs series expansion analyzing its various order modal coupling characteristics. Meanwhile using the ANSYS analysis to get the first three order vibration mode diagram and calculate the frequency corresponding to the critical speed for each rank. Through the analysis found that the screw pitch determine the modal coupling axial and corner, the workbench position and load quality changes, the screw vibration frequency also changes. Provide theoretical analysis for the analysis of dynamic characteristics of the next step.

Illustration of Fracture Mechanism in High Temperature for TiAl Alloys

For the shorting of fracture mechanism from the point of high temperature condition, so a new method of illustration, which is carried out under the condition of high temperature, for fracture mechanism will be adopted in this paper. And a more accuracy and more understandability result can be got by this new method. Besides, the performance of TiAl alloys can be improved by making grains refined to decrease the slip plane spacing, which can be got from the mechanics analysis.

The Dynamic Analysis for Special Friction Welder Upsetting System Based on the Finite Element Method

Electrolytic aluminium pre-baked anode conductive device for the special friction Welder upsetting system is the research object. Establish dynamic equation of the upsetting system by its Lagrange equation; analyze the key factors affecting the systems dynamic characteristics; build the systems finite element model to be real by ANSYS Workbench; Set key parameters for the two sets of plans and do analysis for the modal and harmonic response successively. The two plans compared results reveals that the guide spacing and the damping among all the parts can affect the systems dynamic characteristics, which will provide a basis for further improvement and optimization of special friction welding machine bed.