Abstract
In order to detect the early fatigue crack of mechanical components simply, this paper puts forward the ultrasonic testing technology of different side collinear mixing. Firstly, based on the nonlinear ultrasonic theory, the method of calculating the difference frequency and sum frequency nonlinear coefficients of mixing ultrasonic is deduced. Then, the ram-5000 SINAP ultrasonic system is used to detect the aluminum alloy specimens with five different depth fatigue cracks, and the corresponding spectrum diagram is drawn. From the experimental results, we get that the crack depth is positively correlated with the nonlinear coefficients of difference frequency and sum frequency within a certain crack depth. Finally, by analyzing and fitting the experimental data, the prediction models of the difference frequency and sum frequency nonlinear coefficients on the crack depth are established. Through the analysis and combination of the above two prediction models, the prediction model of the mixing relative nonlinear coefficient is established, and the average error of the three prediction models is compared. The results show that the mixing relative nonlinear model has better results. The research work in this paper makes a useful exploration for crack detection and crack depth prediction.
Highlights
Nowadays, metal materials have become the main force of industrial materials
The non-linear high-energy ultrasonic system RAM-5000 SINAP acts as a signal generator and the trigger inside the system acts as a reference trigger
The frequency selection of the two excitation signals in the co-line mixing test is reasonable. It can be seen from the local amplified frequency domain diagram corresponding to the difference frequency and sum-frequency of the upper end of Fig.4.The amplitude of the differential frequency signal A is (ω2 −ω1) = 0.042V while that of sum-frequency signal is A(ω1−ω2 ) = 0.04V, which is not equal
Summary
Metal materials have become the main force of industrial materials. Due to the long-term influence of different loads or high temperature and high pressure environment, the key metal parts of common pressure vessels, transportation pipelines and various engines are very easy to form fatigue cracks on the surface and inside, leading to component fracture failure, and even disaster accidents [1,2,3]. It is very important to detect the early fatigue cracks of key metal parts. Nondestructive testing is the most commonly used and important means to detect material damage Ultrasonic nonlinear technology can detect and characterize the early defects of metal parts, and the second harmonic technology is the most commonly used detection method [5]. In the process of the second harmonic test, the test equipment, sensors and couplants will produce higher harmonic, so it is difficult to distinguish the measured ultrasonic nonlinear coefficient effectively. For the conventional ultrasound can not effectively extract the nonlinear coefficient, mixing ultrasonic detection perfectly makes up for this defect. At present, mixing detection method has become a hot direction in the field of ultrasonic nonlinear detection
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