Chang Feng Yan

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.

Effect of Wear on the Fatigue Life of Annular Notched Shaft Based on Product Lifecycle Management

Anti-fatigue design is a key content in product lifecycle management and there are many factors to affect the fatigue life of parts. For designing the fatigue life of shaft with a circumferential notch exactly, the influencing factors have been analyzed completely. The mechanics model for assessing the fatigue life of shaft is set up. The assessment method of fatigue life for shaft is set up according to the traditional fatigue life estimation. The effect of wearing parameter to fatigue life is analyzed and the results show that the wear is an important factor to affect the fatigue life.

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.

Effect of parameters of notch on fatigue life of shaft based on product lifecycle management

For designing the fatigue life of shaft with a circumferential notch exactly, the influencing factors have been analyzed completely. The modified mechanics model to estimate the fatigue life of shaft with a circumferential notch is set up. The assessment method of fatigue life for shaft with a circumferential notch is put forward. The effects of notch on stress concentration factor and fatigue life of shaft with a circumferential notch are discussed and the influencing parameters are obtained. The results show that the tip radius of notch has a great effect on fatigue life of shaft; on the other hand, the open angle of notch has a little effect on it. The results will establish the base of anti-fatigue design of shaft.

The Method of Torsional Cylindrical Shaft with Annular Notch in Quadric Coordinate

The notch is not only one of the primary reasons of component fracture, but also the key factor in life assessment of shaft. The stress and displacement field near the tip of annular notch should be obtained at first for safe design and life assessment. A quadric coordinate system suited for annular notch is proposed and the stress and displacement component of cylindrical shaft with annular notch are derived by using the modified Galerkin displacement function. This method can be used to solve various problems of cylindrical shaft with annular notch by selecting an appropriate displacement function and provides the basis for safe design and life assessment of this kind of components. A solution of torsional problems of cylindrical shaft with annular notch is calculated as a demonstration of the method presented.

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.

Fault Diagnosis Expert System of Turbine Generator Sets Based on Rule Reasoning and Case Reasoning

A synthetic fault diagnosis expert system for turbine generator sets based on rule based reasoning and cases based reasoning is built in this paper. The structure of synthetic fault diagnosis expert system is discussed. The rule base and case base for the fault diagnosis of expert system is established based on the domain expert knowledge and relevant fault cases of turbine generator sets. Both the inference flow and case retrieval strategy of diagnosis system are discussed in detail. Finally the expert system is verified by a given application example.

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.

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.