Papers by Author: Tao Yu

Abstract: Based on the safety and durability in the cement soil engineering about the pits anti-seepage, embankment impermeable walls and subgrade strengthening in the frozen regions and the retaining walls in foundation pits, the experiments on the compressibility about the cement soil under freezing-thawing cycle, infiltrated and other environmental-action conditions have been carried out and the influential laws of environmental actions on the compression parameter of cement soil have been obtained. The results show that the various environmental actions may have influences on compressibility of cement soil at different levels, and the environmental effects on the compressibility of cement soil in the engineering applications and designs, such as impermeable walls or in the frozen regions, should be taken into account; and the void ratio and the compression parameter will increase with the increase of freezing-thawing cycle times and infiltration time but the compression modulus will decrease with the increase of freezing-thawing cycle times and infiltration time so that the curve regression equation about the void ratio, the compression parameter and compression modulus varying with the freezing-thawing cycle times and the infiltration time has been established. The results are significant and valuable to the safety and the durability of cement soil engineering.

Abstract: In structural welded joints after long-term service under elevated temperature, fracture occurred mainly in the heat affected zone (HAZ). Recently, the nucleation and growth of creep voids in the fine-grained HAZ of weldments, recognized as Type IV fracture, has become an important problem for ferritic heat resisting steel. In this paper, a new computational model was presented to analyse the void growth induced creep damage development in HAZ. The new constitutive model based on continuum damage mechanics (CDM) equations is combined with a micromechanism-based model in order to account for the void growth process, which is different from the previous studies of creep damage. Material properties used for the creep damage computations are fitted from actual creep test data. Basic benchmark tests were performed to verify the new computational model. Then the model was used to study the creep damage development in the welded joints where four different material properties, base material, coarse-grained HAZ, fine-grained HAZ, and weld material, are taken into account. The numerical simulation results for creep lifetimes agreed well with the experimental results.

Abstract: Rotating machinery, such as steam turbo, compressor, and aeroengine etc., are widely used in many industrial fields. Among the important rotor faults, the fatigue crack fault, which can lead to catastrophic failure and cause injuries and severe damage to machinery if undetected in its early stages, is most difficult to detect efficiently with traditional methods. In the paper, based on the truth of the change of the mode shapes of the cracked structure, a new method by combining accurate finite element model of rotor with multi-crack in shaft and artificial neural network (ANN) is proposed to identify the location and depth of cracks in rotating machinery. First, based on fracture mechanics and the energy principle of Paris, the accurate FE model of the rotor system considering several localized on-edge non-propagating open cracks with different depth, is built to produce the specific mode shapes. Then a set of different mode shapes of a rotor system with localized cracks in several different positions and depths, which will be treated as the input of the designed ANN model, can be obtained by repeating the above step. At last, with several selected crack cases, the errors between the results obtained by using the trained ANN model and FEM ones are compared and illustrated. Meanwhile, the influences of crack in the different position on the identification success are analyzed. The method is validated on the test-rig and proved to have good effectiveness in identification process.

Abstract: In this paper, the theory of fractal geometry was used to study the barrel-rifle surface topography and correlation dimension method was adopted to calculate the fractal dimensions of the projectile worn marks shot from the barrels with different worn. The study showed that the different wears of barrel-rifle surface resulted in different fractal dimensions of the projectile wear surface and there was a correlation between the fractal dimensions of the projectile wear surface and the change of the barrel rifle surface. Therefore, through the rifle marks on the projectiles, not only the wear of the barrel’s internal surface can be analyzed, but the gun life also can be further estimated. The paper provided a new tool for analyzing the barrel-rifle surface wear.

Abstract: Mechanical model and rubbing force model of a dual-disc overhung rotor-bearing system are set up respectively. By using an experiment rig to simulate rubbing fault, the nonlinear dynamic characteristics of rubbing rotor system are investigated and the dynamic characteristics of mid-disc and overhung disc are analyzed respectively. The numerical simulation results coincide with the experiment results and the research in this paper has practical reference value to the safe and stable run of the practical rotating machinery.

Abstract: The nonlinear chatter in grinding machine system is discussed analytically in the paper. In higher speed grinding process, the self-excited chatter vibration is mostly induced by the change of grinding speed and grinding wheel shape. Here the grinding machine tool is viewed as a nonlinear multi-D.O.F. autonomous system, in which hysteretic factors of contact surfaces are also introduced. Firstly, the DOFs of the above system are reduced efficiently without changing its dynamic properties by utilizing the center manifold theorem and averaging method. Then, a low dimensional system and corresponding averaging equations are obtained. The stability and bifurcation of chatter system are discussed on the base of deduced averaging equations. It is proved that chatter occurs as a Hopf bifurcation emerging from the steady state at the origin of system. The theoretical analyses on the multi-DOF chattering system will lead to further understanding of the nonlinear mechanisms of higher speed grinding processes.

Abstract: Model based fault identification techniques can be used to diagnose local faults in rotating machinery; the equivalent loads that represent fault forces can be used to identify the fault location. But in some cases the equivalent loads smeared over many nodes, and make it hard to identify accurate fault location and transient fault force. In this paper, the fault location is identified using least squares fitting approach by the system’s vibration shape when the fault signal is periodic or quasi-periodic. And after the fault location is ascertained, the transient fault forces can be identified by transient residual vibration using simple matrix multiplications and additions. Numerical simulations and experiment on rotor to stator rub are used to test the method, which proved the efficiency of the method.

Abstract: A quantitative identification procedure for local rubbing fault in rotor systems based on a hybrid model is proposed. The hybrid model combines finite element model of rotor and rigid discs, online identified oil film stiffness and elastic supports. The identification algorithm of oil film parameters is stated in detail. The hybrid model based diagnosis process for local rubbing fault is described with assumption of periodic rubbing forces. With the help of modal expansion technique, the estimated rubbing forces at each node along rotor are checked for the rubbing position. The estimated rubbing forces at ascertained position are then used in fault severity assessing quantitatively next. These approaches have been tested successfully on a test rig with single rotor double discs.