Applied Mechanics and Materials Vol. 421

Abstract: As a research hotspot, microwave technology is employed to measure grains moisture. Microwave devices based on various frequency bands appear in some measurement systems. These applications have no a theoretical foundation. This paper provides the principle of microwave technology used in moisture measurement. The factors, detection depth, horizontal and vertical resolutions, which are crucial to select the working frequency, are expounded. This paper also sets forth current application frequencies in moisture measurement systems. At the end, an advisable experiment framework is built to help select the frequency band preliminary for the moisture measurement.

Abstract: This paper presents a novel measurement system for the on-machine estimation of the profiles of a linear slide in the presence of three motion errors, i.e. straightness, yawing and rolling. The system consists of eight displacement sensors, a mounting stage and a data acquisition system. The Fourier Eight Sensor (F8S) method is employed for the error separation with software programs written in MATLAB codes. A prototype is designed, built and fitted to an axis of the precision slide. Experiments are performed to test the repeatability of the profile results under three different slide speeds. Results confirm that the proposed measurement system is capable of determining the profiles with good repeatability in the presence of straightness, yaw and roll errors of the slide.

Abstract: After the technologies of measurement for thin-film thickness were analyzed, the method of real-time measurement for coating thickness based on quartz crystal oscillation was proposed. The principle of the thickness measured by frequency shifting was analyzed on theory, the functional relationship between the resonant frequency shifting and the film thickness changing was deduced. Aim at the complicated working condition in coating machine, the structure of the measuring system for reducing the influence from external pressure and temperature was designed. The circuit for detecting the frequency shift was designed. Final, according to the experiment result, the resolution of thickness measurement can achieve sub-micrometer level.

Abstract: t is difficult to obtain high measurement accuracy in online detecting the thermal geometric parameters of hot large forgings, based on machine vision method. In this paper, firstly, a spectrum selective image acquisition method for high-temperature components is proposed, which can successfully reduced the effect of high temperature on image quality. Then, a measurement method based on the coding feature lines for geometric parameters of hot large forgings is employed, which can effectively improve the extraction efficiency of geometry characteristic information of high-temperature components. Experiments on the forging workshop show that measurement accuracy of diameters for cylindrical forging reaches 0.2% and the measurement time is 2.25 seconds; measurement accuracy of lengths for cuboid forging reaches 0.48% and the measurement time is 5.9 seconds. The experimental results have verified the feasibility and high efficiency of the proposed method for measuring the geometric parameters of hot large forgings.

Abstract: According to the measurement requirements of acoustic fatigue load on aft fuselage structure and the external installation restriction of the acoustic sensor on aircraft surface, an acoustic sensor is installed on the silencing jet test plate with reference to body type of the real aircraft. A dynamic test and analysis system combined hot wire wind speed measurement and acoustic spectrum measurement is built up for the combined experiments with different acoustic sensor height and various boundary layer flow structure at subsonic flow condition. Turbulence development of different boundary layer is analyzed. The test result can be coordinated with the local measurement to aircraft flow structure so as to estimate the effect of acoustic sensor on the flow field.

Abstract: Determination of theflow stress of materials at high strain rate is very important in automotive and military areas.The compressive flow stress at high strain rate can be obtained relativelyexactly by SHPB(Split Hopkinson Pressure Bars) tests. However, it is difficult to determinethe flow stressexactlyin the tensile state by using the SHPB tests. The difficulty in the tensile SHPB tests is how to fix a specimen on two bars. So, the design of a specimen and holders is needed to obtain more accurate measurement of the flow stress. In this study, the accuracy of the tensile SHPB tests results was numerically investigated. Finite element analyses of the tensile SHPB were carried out for various cases of fixing bolt location and bolting force. From the analysis results, a design guide for the fixing structure was obtained and the causes of error were investigated.

Abstract: The methods for Multi-component gas monitoring combination with multi-windows infrared sensor can be to detect and analyze conventional gas such as CO2 in the atmosphere based on the non-dispersive infrared (NDIR) detection technology, and can adapt to multi-task and multi-parameter measurement, convert the monitoring object to complete the different monitoring tasks at any time. First, the principle of the NDIR technology was described in this paper, and proposed a targeted circuit design and key technology solutions. The preliminary experimental analysis was shown that the test result is valid. NDIR infrared gas detection method as rapid and accurate gas analysis techniques can be generally used in the detection of continuous emission monitoring system as well as motor vehicle exhaust.

Abstract: t is important to remove the noise signal effectively in non-destructive ultrasonic testing. Use the wavelet and neural network algorithm in multi-layered structure ultrasonic testing system of the solid rocket-motor, and construct self-adaptive wavelet neural network in the ultrasonic testing in order to restrain the noise. Better fitting signal is achieved by choosing Orthogonal Daubechies wavelet group and optimize the scale parameter by a searching algorithm. The simulation result shows that the wavelet neural network can make the testing system less distortion and better noise cancellation, and the method can be widely applied to ultrasonic detecting.

Abstract: The Alternating Current Field Measurement (ACFM) technique is an electromagnetic inspection method for surface crack detection and sizing. According to signal characteristics of ACFM, a detecting instrument has been designed and fabricated successfully. The ACFM inspection system is composed of signal conditioning circuit and testing system based on DSP and LABVIEW. The functions of generating exciting signal, collecting data, processing data and sending data are realized through DSP, while the functions of displaying data, storing data and calculating are achieved through the LABVIEW software. The function and performance of the instrument has been tested by experiments. It can calculate the length and depth of the crack and can facilitate the quantitative evaluation of crack as well. Its detection accuracy and performance can completely meet the requirement of practical test.

Abstract: A method for computing lines of curvature and umbilical points is proposed. These properties, derived for NURBS surfaces, are useful in shape modeling for both aesthetic and functional characteristics evaluation. Moreover, the application to the ship-hull design and to the progressive additional lens design, of umbilics and lines of curvature are investigated.