Yuantao Sun

Multiple Failure Modes Reliability Modeling and Analysis in Crack Growth Life Based on JC Method

The fatigue crack growth (FCG) phenomenon generally exists in large mechanical structures. Due to the influences of varied kinds of random factors, the safety evaluation of structure in FCG is under great uncertainty. In this paper, based on the reliability theory, the limit state equations of fracture failure and static strength failure were derived firstly, and the parameters in those equations were regarded as random variables that follow the normal distribution or log-normal distribution. According to the limit state equations, the JC method (equivalent normalizing method) was used to calculate the reliability indexes under the different failure modes of structure in every stress cycle. Based on the reliability indexes and correlation of the two failure modes, the joint failure probability was obtained. In the end, a specific computation example was given, and the curve of joint failure probability in multiple failure modes was used for comparison with the result of single failure mode. The results indicated that the reliability analysis based on multiple failure modes was more reasonable, and the evaluation of reliability could be obtained in fatigue crack growth process.

A two-stage feature selection and intelligent fault diagnosis method for rotating machinery using hybrid filter and wrapper method

Abstract Selecting the most discriminative features from the original high dimensional feature space and finding out the optimal parameters for recognition model both have vital influences on the accuracy of fault diagnosis for complicated mechanical system. However, as these two important processes are interactional, conducting them separately may result in inferior diagnostic accuracy. This paper presents a feature selection and fault diagnosis framework which can select the optimal feature subset and optimize the parameters of SVM classifier synchronously and dynamically with the ultimate objective of achieving the highest diagnostic rate. The proposed method is based on a hybrid Filter and Wrapper framework. Since the original feature dimensionality is high which may lead to a lower computation efficiency of the process of synchronous feature selection and SVM parameters optimization, ReliefF is applied for preliminarily selecting some optimal feature candidates. Furthermore, in the reselection process, the reselection state of feature candidates and the values of classifier parameters are all encoded into BPSO particles. The optimal feature subset and the SVM model can be synchronously obtained for fault diagnosis with a high performance. Moreover, in the original feature extraction stage, intrinsic time-scale decomposition (ITD) is utilized to preprocess the nonstationary vibration signal into several PRCs. The statistical parameters in time and frequency domain of PRCs are extracted as the multitudinous original features for each signal sample. Two experimental cases including rolling bearing fault and rotor system fault are implemented to evaluate the proposed scheme. The results demonstrate that compared with some existing methods the proposed one can obtain a better comprehensive performance in the number of optimal features, training time and testing accuracy.

Research on crack discontinuous interface simulation method based on the meshfree diffraction criterion

Meshfree method is a new numerical method whose solution domain only discredited into independent nodes. To model crack discontinuous interface in practical, the equivalent distance for the weight function arguments is adapted. Firstly, the paper analysis the feature of the function, which point out that the methods have their own disadvantages. And then the paper put forward new binary linear equation, which is used to the weight function arguments to dispose of the crack’s noncontiguous interface. The function can simulate the displacement field around crack tip or crack closure line and also avoid the value overflow phenomenon which the node and a computation superposition occurs in the present processing method. The method has provided new mentality and idea for the present meshfree method in crack analysis. Finally three typical crack theoretical models are established as example. The comparison with the analytical solution shows that the displacement value the crack and the stress intensity factors has a better precise based on the new method, and also verified the method is valid. DOI: http://dx.doi.org/10.5755/j01.mech.24.3.19009

Fault diagnosis using locality sensitive discriminant analysis for feature extraction

Extracting the most sensitive and effective characteristics from original high dimensional feature space is significant for accurately identifying the condition of machinery. This paper presents a locality sensitive discriminant analysis (LSDA) based feature dimensionality reduction approach. Different from locally preserving projection (LPP) that only preserves the local structure of data manifold, LSDA can also employ the discriminant information at each local area when conducting the projection. In the proposed fault diagnosis approach, various multi-domain features are calculated aimed at exploring the machinery condition information roundly from different perspectives. LSDA is applied to discover the representative information contained in the high dimensional feature set. Then a lower informative feature space can be constructed with LSDA. Finally, the effective KNN classifier is used to recognize the condition of machinery with the most representative eigenvectors. A bearing fault experiment is conducted to verify the proposed method. The comparison study with PCA, LPP and KLPP indicates that LSDA has advantages in dimensionality reduction and the proposed fault diagnosis approach is effective.

A Consistent Relationship between the Stress and Plastic Strain Components and Its Application in Deep Drawing Process

As von Mises yield criterion and associated flow rule (AFR) are widely applied in metal forming field, a semitotal deformation consistent relationship between the stress and plastic strain components and the rule of dimensional changes of metal forming processes in a plane-stress state are obtained on the basis of them in this paper. The deduced consistent relationship may be easily used in forming interval of the workpiece. And the rule of dimensional changes can be understood through three plastic strain incremental circles on which the critical points can be easily determined on the same basis. Analysis of stress and plastic strain evolution of aluminum warm deep drawing process is conducted, and the advantage of nonisothermal warm forming process is revealed, indicating that this method has the potential in practical large deformation applications.

Dynamic Efficiency of a Container Crane’s Hoisting Transmission System under Hoisting Dynamic Load

The dynamic efficiency of hoisting transmission system on a container crane is fundamental for accurate efficiency prediction, while the dynamic efficiency of hoisting transmission system has not been investigated sufficiently. This paper will focus on dynamic efficiency of hoisting transmission system under hoisting dynamic load. A power loss model of gearbox was built. Then the dynamic model of gear transmission was developed including time-varying mesh stiffness and hoisting dynamic load was studied. Power loss, dynamic efficiency, and equivalent static efficiency were conducted in hoisting and lowering working conditions. The result shows that dynamic efficiency which consists of the significant lower frequency component coincided with hoisting load torque of the higher frequency component which is directly related to dynamic mesh and bearing force. And in two processes, the equivalent static efficiency in constant speed stage is min, whereas maximum value occurs in different stage. The research results lay a foundation for hoisting gear transmission dynamic efficiency analysis.