Yun Xin Wu

Inner Leakage Fault Diagnosis of Hydraulic Cylinder Using Wavelet Energy

Inner leakage of hydraulic cylinder is a very serious failure in the hydraulic system and it can lead to many problems.A important fault diagnosis way is to detect the pressure signal.But the pressure signal is seriously influenced by pressure fluctuation and other noises.It is difficult to extract features from pressure singal. Aiming at the difficulty in extracting feature from pressure singal in fault diagnosis for leakage of hydraulic cylinder,a fault diagnosis approch based on monitoring preesure singal and wavelet energy is proposed in this article.According to the method, the enegry of different frequency bands after wavelet decomposition costitutes the eigenvectors at first, then these eigenvectors are input into BP network to identify faults. The experimental results show that three modes of no leakage, slighter leakage and severe leakage were correctly identified.This approach can be used in the leakage fault diagnosis of hydraulic cylinder.

Surface Yield Strength Gradient versus Residual Stress Relaxation of 7075 Aluminum Alloy

Different distributed residual stresses were introduced by quenching and two shot-peening treatments on 7075 aluminum alloy. The residual stress distributions and micro-hardness profiles in surface layers were measured. Pre-stress coefficient characterizing contribution of local residual stresses to local yield strength is introduced to analyze residual stress relaxation under cyclic loading. Load testing shows that re-distribution of residual stresses and proportional decrease of the pre-stress coefficient would occur in the non-uniform structural residual stresses introduced by quenching, while great stress relaxation and non-linear decrease of the pre-stress coefficient would occur in the uniform surface residual stresses introduced by shot-peening. Additionally, advantages of surface compressive residual stress and micro yield strength on anti-fatigue property and on restraining initiation and propagation of surface micro cracks should be considered in the usually conservative engineering design.

Study of Concrete Pump Truck Structural Health Monitoring

Concrete pump truck is a kind of mobile construction machinery, with the characteristic of complex structure, poor working condition and difficult to maintenance. Therefore, adopting appropriate health monitoring methods, and accurate grasping the running status information of the pump truck is significant to the pump truck’s safety use and pre-judgment maintenance plan arrangement. In this paper, the traditional structural health monitoring methods was studied. And the structure, load and work environment characteristics of concrete pump truck were analyzed. Taking into account the economy and reliability of the structural health monitoring system, the technical route of the concrete pump truck structural health monitoring system and health evaluation criteria were proposed. The evaluation criteria takes into account both the cumulative health effect and timely health status of concrete pump truck structure.

A Mathematical Model for Predicting Residual Stresses in Pre-Stretched Aluminum Alloy Plate

A mathematical model has been developed to predict the residual stresses level in pre-stretched aluminum alloy plate. This is based on force balances of the residual stress, theory of plastoelasticity and a new conception of free length. The model is relatively simple because only rolling direction residual stress is taken into account, but provides a clear illustration of stress relief mechanism in stretching process. With this model, residual stress distributions of stretched beam can be determined directly by knowing the specimen dimensions, material properties and the original stress. The model offers an useful tool to show the effect of varying tension ratio on the final residual stress level, thus makes it possible to predict stress relief and control residual stresses. An example of using the model is presented by applying published data while showing mechanism of stress relief during stretching. Analysis indicates that it is stretch-caused convergence of the free lengths of strips in beam that lead to reduction in the residual stresses.

Study of Damage Limit for Aluminum Alloy Plates with Surface Cracks under Cross-Thickness Bending

A damage limit prediction model was built due to fracture failure problems of aluminum alloy plates. Based on the global plastic collapse of the entire cross-section containing the defect, the relationships of crack width and depth of fracturing 7075 aluminum alloy plates with either shallow crack or deep crack was analyzed by using reference stress method. The damage limit curves of 7075 aluminum alloy plates with crack was drew, and safety zone of crack propagation under corresponding bending load was confirmed. Then the experimental verification was carried out, results show that calculated results are in good agreement with the test results during the shallow crack stage, while in the deep crack stage experimental results are slightly less than calculated results.

Effect of Cladding Material on Residual Stress in Quenched Aluminum Alloy Plate

Using finite element method, a quenching analysis of 7075 aluminum alloy thick plate is carried out. The effect of surface heat transfer coefficient and plate thickness on residual stress, and the effect of cladding material on residual stress are discussed. It shows that the bigger surface heat transfer coefficient or thickness is, the bigger the residual stress is, and the residual stress significantly reduces while the cladding material exists. Experiments validated the simulation results.

Research of Correctness on Internal Stress Measurement in Aluminum Alloy Thick Plate

It’s necessary to research and analyze the correctness of internal stress measurement, in order to effectively deal with the measurement problem of stress field and rightly describe the distribution character of stress in aluminum alloy thick plate. Firstly, the total uncertainty of stress calculation in layer removal method (LRM) is determined by experimental error and model error, and less than ±10MPa, in which the accuracy of experiment is high. Secondly, in the integral calculation of LRM, a modified function is proposed by the multi-methods of simulation and experiment, and can compensate the deviation resulted from unpredictable error for experimental conditions. Then the multi-methods achieve the value of X-ray surface stress, simulation calculation and experimental results to consistent, the correctness of experimental calculation is enhanced. The research presents that the LRM can exactly describe distribution of internal stress in thick plate under special experiment conditions.

Influence of Specimen Sampling on Internal Residual Stress Test

Using Finite Element Method, the changing rules of residual stresses in the test specimen cut out from a quenched plate were analyzed, and suitable dimensions of the specimen for crack compliance method test was recommended. The results show that cutting has great influences on residual stresses in the specimen edge areas to a range of about one thickness, while it has little influences on stresses at the center part of the specimen; cutting mainly influences stresses normal to the cutting plane, while it has little effect on stresses parallel to the cutting plane; specimen with length bigger than 2.67 times the thickness and width bigger than 2 times the thickness is suitable for crack compliance method test, under these conditions peak stresses losing in crack compliance method results is less than 5% compared with surface stress X-ray diffraction results.

Parameter Simulation for Quenching and Pre-Stretching about Aluminum Alloy Thick Plates Based on MARC Finite Element

To predict the three-dimensional residual stress distribution of 7075 aluminum alloy thick plates, the quenching and pre-stretching process were simulated by using MARC finite element software. In order to simulate quickly according to different reality conditions, the parametric model was realized by using defining parameters and selecting objects by inputting coordinate value with the box mode. In the quenching process, a non-linear thermo-mechanical direct coupled analysis of the aluminum alloy thick plates was carried out, by taking into account of the temperature dependence of the thermo-physical properties. In the pre-stretching process, the clamp and release of the clamp of pre-stretch machine were simulated by using life and death element technology. The study demonstrates that the theoretical predictions agree well with the experimental values of residual stresses measured by the X-ray diffraction method. The simulation results provide the user a tool for analyzing and studying on quenching and pre-stretching technique using virtual reality method.

Higher Order Harmonic Wave and its Effect on Thermosonic Bond System

Thermosonic bond is widely used in package of semiconductor chip due to its advantages, such as simple process, high efficiency, and no pollution. Ultrasonic play important role inspired interconnection interface atomic energy and soften metallic materials in thermosonic bond. The vibration of bond tool is nonlinear and bond strength is unstable with contact interface condition changing due to discontinuity characteristic parameters of contact interfaces. In order to improve bond strength of chip, model of ultrasonic propagation across a rough contact interface was established. Aluminium wire bond was performed on a thermosonic bond test platform. The harmonic waves of bond tool and the bond strength were measured. The experiment results show that the best bond strength and the less higher order harmonic is achieve when the contact interface pressure is in moderate range.