A Ultrasonic Time-varying Dynamic Testing Technology Of Stress

In practical engineering applications, the state of stress is to change all the time, the dynamic testing stress state is helpful to study the use of the material being measured; and acquisition equipment dynamic detection accuracy of transit-time difference measurement will be higher, the sampling rate will be bigger too. It makes the detection cost is higher, the dynamic error is larger. So this paper puts forward a kind of material stress testing technology based on ultrasonic wavelength change, to realize the time-varying stress ultrasonic dynamic test, and experimental verification.First part is introducing background and the importance of the stress state detection technology in the industry; then briefly describing the stress of the commonly used detection methods and their respective advantages and disadvantages; at the end of this part,expounding the ultrasonic stress testing methods in domestic and overseas research status and development trend of the stress testing method.Then this paper expounds the basic theory of ultrasonic stress testing technology, this paper introduces the definition of ultrasonic, excitation and the receiving principle; Secondly introduces the ultrasonic propagation characteristic in solid: the classification of the ultrasonic wave and the motion equation of ultrasonic wave in solid, laying a foundation for acoustic elasticity theory in solid; Acoustic elasticity theory is used to derive relationships of the stress variation with ultrasonic longitudinal wave, shear wave;Finally the innovation of the theory of stress testing method is proposed: one stress testing technology based on ultrasonic wavelength changing material, and the formula is derived, at the same time, analyzing on the advantages of the stress test and the traditional method of time difference.Then using MATLAB software for extracting effective components time-varying stress ultrasonic signal is studied. Briefly analyzes and build the models of the incentive of ultrasonic signal, the initial receive ultrasonic signal, and loading stress ultrasonic signal of the received signal; Signal denoising processing methods are introduced, and emphatically describing the structure of the sparse decomposition denoising method; Then introduces the signal phase extraction method; By using the MATLAB software to the simulation of signal, the orthogonal matching pursuit(MP) is used to denoise and reconstruct the signal;using fast Fourier transform on the reconstructed signal phase extraction, extracted the phase are compared with those of the original phase.Finally set up a time varying stress ultrasonic dynamic detection system. Build a simple test platform, using the sparse decomposition OMP algorithm and FFT phase extraction method to test the stress testing technology which is based on ultrasonic wavelength change material, the experiment error is analyzed, and summarized the disadvantage of experiment; And the experiment compared with the traditional ultrasonic stress testing time difference method, in advantages and disadvantages and puts forward improvement methods.