Applied Mechanics and Materials Vols. 397-400

Abstract: In this paper, a model of an engine case is designed in Pro/Engineer for fatigue simulation. The meshing is created by the way of Abaqus. According to the working conditions, the boundary restriction of the simulation is defined. By the simulation, the heat distribution of the engine case is given, the causes of relatively high temperature areas are discussed, and the heat-stress distribution is drawn too. The high stress area in the engine case is discovered. The simulation result shows that the steady working stress is about 60MPa, the transient stress is between 90MPa to 120MPa, and the maximal stress is 136MPa. Based on the heat stress the fatigue life of the engine case is analyzed. The research result is a reference of the engine case safe working.

Abstract: Fatigue fracture of the intermediate shaft in a transmission was analyzed by finite element method.The solid model has advantages of centrifugal force and spin softening effects over beam models.The results show that the fatigue fracture of the shaft is mainly due to the torsional vibration,the stress stiffening and spin softening have strong influence on the bending vibration medes,and torsional vibration modes do not changed at different speeds.There is accounting for the effects by an adjustment of the stiffness matrix.By using of solid models,the vibration modes of the intermediate shaft were researched,then the model was optimized in order to avoid resonance.

Abstract: In this paper, we studied a smart base isolation system based on magnetorheological elastomers (MRE), which is a new class of smart materials whose elastic modulus or stiffness can be adjusted by changing the magnitude of the applied magnetic field. The main goals of this study are to demonstrate the use of MREs as field-dependent element in a smart base isolation system and investigate the dynamic performance of the smart base isolation system in mitigating excessive vibrations of the building structure under dynamic loadings. To this end, we designed some MRE samples working in compressive mode and measured their properties under various magnetic fields in which the elastic modulus varied by up to 250%.Compared with the structure installing traditional base isolation system, the dynamic performance of the structure installing smart base isolation system is much better under the dynamic loadings.

Abstract: Taking a 660MW turbine generator shaft system as a target system, the torsional stresses responses are calculated under two-phase short-circuit fault by the finite element (FE) method which can obtain torsional stresses in local areas accurately. The results show that torsional stresses threaten the safety of shafts appear at the first several cycles of the vibration. And the amplitude of stress in weak cross sections located between the low pressure cylinder and the generator is much greater. In addition, the proportion of torsional stresses frequency components in different sections is distinct. The results are helpful to improve the safety management level of the unit.

Abstract: The quasi-Green function method (QGFM) is applied to solve the free vibration of clamped orthotropic thin plates with parallelogram boundary shape on Winkler foundation. Firstly the model governing differential equation of the problem is reduced to the boundary value problem of the biharmonic operator, and then it is reduced to the Fredholm integral equation of the second kind by Greens formula. A quasi-Green function is established by using the fundamental solution and the boundary equation of the problem. This function satisfies the homogeneous boundary condition of the problem. The singularity of the kernel of the integral equation is overcome by choosing a suitable form of the normalized boundary equation. The comparison with ANSYS finite element solution shows a good agreement. The proposed method is a novel and effective mathematical one.

Abstract: Based on existing analytical models, an improved model was developed to predict load distribution of ball screw more accurately. In this model, variation of contact angle is considered. The results of this model demonstrate that the load distribution of ball screw is not uniform and load distribution curve falls from the position near the load to further. Downward trend is more marked when the variation of contact angle is introduced into the model. The larger ratio of helical pitch to screw diameter is, the worse the nonuniformity of load distribution is. This will impair the stiffness of ball screw. It is found that the calculated results are significant to ball screw design.

Abstract: The traditional dynamic calibration method for dynamic characteristics testing of hydrodynamic journal bearing is difficult to guarantee the consistency of the calibration condition and test condition and is hard to achieve. This method can affect the precision and accuracy of test result directly. So a novel method was put forward to solve this problem in this paper. Its core is to directly adopt the test bearing as the attached mass block to calibrate the test system, and then the frequency response function for each channel of test system under specific conditions can be got based on the related algorithm. Following, the implementation procedure and key technologies of the new method were introduced in detail. Finally, it is shown by an example that the proposed method is feasible.

Abstract: According to the less-teeth gear design theory, the FEM model of less-teeth gear system was established, and its dynamic contact characteristic was analyzed, then dynamic contact simulation was realized. Laws of contact area, contact stress and tooth stress change over time were got, which can be used for the gear profile modification and dynamic characteristics optimization design of the less-teeth gear system.

Abstract: According to the characteristics of the quasi zero stiffness (QZS) system, a dynamics approximation model is established. The effect of excitation force amplitude, frequency and stiffness on the dynamic characteristics of the system is studied by continuation algorithm. The global bifurcation diagram with a wide range of parameters is achieved by using Poincaré mapping method. Results show that when the exciting force amplitude increases to a certain extent, the system will come into multi-cycle and chaos motion state. When exciting force frequency is lower, the system dynamic behavior is complicated, which is helpful for the engineering optimization design.

Abstract: In close to the rigid body condition,to solve the binding force of multiple pairs of bars space RCCR mechanism,first, starting from solving main binding force of three-pair bars space RCCR mechanism by the theoretical analysis, to have obtained the change law of the main binding force without the inertial force (extremely low speed) by using the computational multibody dynamics software ’COSMOSMotion’ and then summed up the equivalent tangential force through the investigation of the simulation data. Finally the concept of equivalent tangential binding force was expanded to 4, 5, 6 pairs of bars space RCCR mechanism.