Applied Mechanics and Materials Vols. 29-32

Abstract: Geometric models often contain small features that we would like to remove, including small extrusions and holes. Feature removal can be desirable for many reasons, including finite element simulation, analysis of feature purpose and so on. In this study, an algorithm based on level set method is proposed to remove the small features. First, we initialize the zero level set in such a way that the zero level set includes the input model. And then the zero level set evolves towards the input model based on a novel speed function. When zero level set stops moving, a simplified model without small features can be got. The method receives approval from the experimental results.

Abstract: In free-form surface machining, it is essential to optimize the feedrate in order to improve the machining efficiency. This work is the first of a two part paper on cutting force prediction and feedrate optimization for five-axis milling. Conservative cutting parameters have been mostly used since there was a lack of physical models and optimization tools. Part and tool deflections under high cutting forces may result in poor part quality. The extracted cutter workpiece engagements are used as input to a force prediction model. The predicted cutting forces are shown to be in reasonable agreement with those collection during a roughing operation on a dual blades part.

Abstract: This paper presents process optimization for the five-axis milling based on the mechanics model explained in Part I. The process is optimized by varying the feed as the tool-workpiece engagements. The linear and angular feedrates are optimized by sequential quadratic programming. Sharp feedrate changes may result in undesired feed-marks on the finished surface. The adopted step is to update the the original CL file with optimized and filtered feedrate commands. The five-axis milling process is simulated in a virtual enviroment, and the resulting feedrate outputs are stored at each position along the tool path. The new feedrate profiles are shown to considerably reduce the machining time while avoiding process faults.

Abstract: During identifying the natural frequency of the rolling bearing rotor system, due to the complex non-linear relationship between the factors which influence the natural frequency, it is hard to establish a complete and accurate theoretical model. Based on the self-learning ability and approximation of non-linear mapping capability of the artificial neural network (ANN) and the powerful ability of global optimization of the genetic algorithm (GA), the paper establishes combined genetic neural network (GA–ANN) through optimizing the ANN by GA. This method establishes the mapping between a rolling bearing rotor system natural frequency and the various parameters, which reduces the calculation of the workload greatly for the study of the similar rotor structure’s natural frequency. Through using the network model to predict the natural frequency of rolling bearing rotor system under different parameters, we finally find that the predicted values are in good agreement with the experimental data, which indicates that the method is powerful in identification.

Abstract: In order to meet the demand of designing the waste gas efflux self-sucking device simply and practicably, based on the single-phase isentropic gas flow theory, a more effective theory analysis and design method was presented. The device’s main working parameters and characteristic indexes that had a signification effect in practice application were analyzed and given. And their calculating means were put forward. Some model was designed by this way and the parameters were analyzed by comparison with experiments. The result of the calculating case shows that the calculated data accord with the experimental data. And the method has good reliability with simpleness and practicality, which provides a good way of designing the self-sucking device.

Abstract: Based on the theory of two-dimensional (2-D) orthogonal polynomials, the function of dynamic load is fit by using the primary functions sequence. The identification of the distributed dynamic load can be transformed into the solution of the fitting coefficients. For the finite element model of the rotating Timoshenko beam, the unknown distributed force is identified by the load identification theory of the continuous beam in time domain. Numerical simulation shows that the method is precise as long as enough data of feedback points are collected; and it is simple and effective for engineering applications.

Abstract: Using the logarithmic hoop strain，a nonlinear dynamic equation governing the axisymmetric radial motion of an axially compressed cylindrical shell subjected to radial disturbance is derived. By means of Bubnov-Galerkin approach the partial differential equation can be transformed into an ordinary differential equation containing second-order nonlinear term. The qualitative analysis indicates that the autonomous dynamic systems corresponding to two cases of pre-buckling and post-buckling has the form-same homoclinic orbits and two orbits locate different positions on the horizontal axis of phase plane. The threshold condition for the occurrence of Smale horseshoe-type chaos in disturbed system is obtained by Melnikov’s method. Finally, the bifurcation diagram, time-history curve, phase portrait and Poincare’s map are calculated.

Abstract: Plasma assisted deposition technology with an advanced plasma source and its application in the field of optical coating fabrication are investigated. In this paper, MgF2, Al2O3 and TiO2 single layer films are prepared by this technology, and the measure results show that they all have good optical parameter.

Abstract: An improved model has been developed to predict fatigue crack initiation life using the criterion of minimizing the Gibbs free energy change considering plastic energy. The prediction process was described in this paper and used to predict the fatigue crack initiation life of notched GH4169 superalloy rolled bar at room temperature and 450°C. The results are acceptable for fatigue crack initiation life prediction in engineering experience and show that the improved model for predicting fatigue crack initiation life as an extension of the concept of minimizing the Gibbs free energy change considering plastic energy is adoptable to some superplastic materials such as GH4169.

Abstract: In low-cycle fatigue process, plastic strain takes place at notch root vicinity fast appears induced by high stress concentration. Plastic strain makes material non-uniform and the change of distribution of local stress. The approximation to stress concentration point of Neuber’s rule is not suitable for some plastic materials in engineering practice. In this paper, the average strain of fatigue process zone was considered to substitute Neuber strain for predicting fatigue life. Prediction results indicated that average strain range of fatigue process zone is more suitable than Neuber strain range for predicting low-cycle fatigue life of LY12CZ.