Applied Mechanics and Materials Vols. 303-306

Abstract: To meet the demand for high precision measurements of radar cross section (RCS) in microwave anechoic chamber, the effect of angle repeatability of position servo system in background cancellation technology is analyzed and its error mathematical model is presented. Then a method of high speed synchronization angle measurement based on CPLD is proposed, which improves the precision of synchronization angle measurement in any fixed angle interval. The experiment results show that this method can effectively solve the accuracy of target RCS when rotating.

Abstract: Since oil palm fruit produces highest yields per cultivated area and its product can be used for many consumer products, it will thus significantly impact to the global economics. This paper proposes a simple technique to determine oil extraction rate of palm fruit. Based on the dielectric constant measurement at microwave frequency, oil extraction rate of palm fruit is found to be inversly proportional to dielectric constant of the palm fruit. This leads to a mathematical model for determining OER in palm fruit. Validity of the model capability for determining OER is proven by predicintg OER of several palm fruit samples. The technique can achieves accuracy of 95.63% for OER determination.

Abstract: This paper proposed a new method of gear fault diagnosis in gearbox. Mainly it stresses on the combination of time synchronous average (TSA) and envelope analysis, using TSA technique to eliminate the random noises in the gearbox. Then, the clear rotation frequency, gear mesh frequency and their harmonics can be obtained through the envelope spectrum analysis. Simulation study indicates that this method can effectively detect the gear faults with a high accuracy.

Abstract: Acoustic emission detection principle was used in testing the working status of Gezhouba Dam ship lock mechanical hoist reducer. According to wavelet analysis technology, high frequency signals of the acoustic emission is decomposed and reconstructed so as to eliminate noise and improve the signal-to-noise ratio. Then the Hilbert envelope transformation analysis is adopted to identify fault information. The results show that wavelet envelope spectrum analysis of the acoustic emission signals can be effectively used in fault diagnosis of reduction gearbox.

Abstract: Abstract: A detection method for the internal defect of the part based on the lever balance principle was presented; the defect method realized indirectly the nondestructive measurement through the relation of the volume and mass of the part’s internal pore or crack and the force change in the lever balanced system. On the basis of the relation of the part’s weight and the balances of the forces and the moments, the forces of the different position was measured in the lever balanced system after the part moved the minute distance through the fulcrum according to a certain directions. It calculated the every lamellar mass of the part and the coordinate values of the corresponding lamellar. Combined the equations of every lamellar masses and the equations of the center of gravity, and established the database of the every lamellar masses, it can realize the non-destructive detection for the internal defect of the part by computer. The measure principles, the mathematical theory basis and the detection method for the part’s internal pore or crack were introduced in details about the detection method based on the lever balance principle. The detection method can be operated simply and feasible and credible.

Abstract: Exploring a proper wavelet base function to characterize fault information of mechanical equipment is a big problem when wavelet analysis is applied into the field of fault diagnosis.Improper wavelet base function can dilute fault information, which will cause difficulties in fault diagnosis , based on the principle that the wavelet domain oscillation waveform are similar to the detected signal components, a proper wavelet base function was selected; through wavelet transform on the acceleration signals of the fault bearing, the spectrum chart of fault signals and the frequency characteristics of fault bearing were obtained. The experimental result shows that this method has a great advantage over extracting character signals.

Abstract: The purpose and meaning of bridge health monitoring is sketched in this paper. In order to study of the structure of the bridge health monitoring problems, First of all, a finite element model for simply supported steel beam is set up on the basis of the Finite Element Theory and the software ANSYS in response to laboratory of the finite Element Theory and the software ANSYS in response to laboratory experient. Identify the different injury by comparing the index value and the rate of change. Through adding instantaneous excitation to the mid-span, do Harmony Response analysis for different injury of steel bridge model to reveal the frequency amplitude diagrams, from these diagrams can be found on the "peak" response. We can identify the different injury by comparing the index value and the rate of change.

Abstract: This paper presents the results of using the system GPR (Ground Penetrating Radar), as an alternative that uses radio waves at frequencies from 10 to 2500 MHz to get data that enable non-destructive conduct inspections of underground or concrete structures in real time. The research aims to investigate asphalt pavements, analyzing the variations in the responses, which can reveal the presence of pathologies or defects. A case study was made acquiring data, at the State University of Campinas - UNICAMP, in Campinas – SP – Brazil, with antennae 270 and 1600 MHz, in pavements with visible defects of patching and alligator cracks, initially with the dry structure and later, wet. The results were processed in specialized software (Radan 7.0) to generate terrain profiles. The GPR showed effective when there is a change in material employed as in the case of patching, because it was possible to detect layers compromised by intensive request of traffic, the start and end of application of the patching and even deformations in the new layer. In contrast, the alligator cracking did not reach the same result, not presenting accuracy in recognizing the defect. The extent of defect was the only well defined feature in the images.

Abstract: A measurement method for loss factor of viscoelastic material was researched. When acoustic wave incident to the surface of submerged elastic plate coated with viscoelastic damping layers, according to boundary conditions of interfaces relationship between reflection acoustic wave in water and loss factor of viscoelastic material was derived. The change of loss factor as frequency goes was also simulated. Loss factor is related to frequency and other parameters of viscoelastic material.

Abstract: Phased array theory was utilized in the unmanned aerial vehicle (UAV) wing box to identify the screw loosening in the structure. Phased array theory could well control the beam steering of Lamb wave to the desired directions to scan the structure for damage recognition. The time delay in special direction was calculated for the beam steering of the signal. The recognition result was shown on a mapped image.