Study On Phased Array Ultrasonic Testing Technology For Aerospace Disk

Aerospace turbine disk is the core component of aeroengine.Fluctuation of manufacturing parameters may lead to various defects such as segregation,inclusions,holes and cracks.Moreover,the fatigue crack defects are often generated because of force complex and harsh conditions,and fatigue crack defects are often generated during the course of service.It may also cause serious consequences if there has a small defect in the aviation turbine disk.Thus,it is necessary to test the turbine disk which is minted and in service by nondestructive.Phased array ultrasonic detection technology is a kind of non-destructive testing technology which can complete the change of the angle of acoustic beam and the change of the depth of focus,this technology avoids the missed detection defect which caused by the limitation of the moving range and the sound beam angle.Phased array ultrasound detection technology with a high control of the sound field and high energy,can effectively improve the detection accuracy and detection efficiency.According to the characteristics of the Phased array ultrasonic detection technology,it is expected to accurately and efficiently detect all kinds of defects of high temperature alloy aeronautical turbine discs which have complex structure.Phased array ultrasonic detection technology was used to test the aeronautical turbine discs,when the micro defects are located near the surface,the bottom surface,and the complex structure area of the aeronautical turbine discs with the large size,complex structure and coarse organizational structure,the defect is prone to missing or false detection because the easy confusing defect signal and the low signal to noise ratio of the defect signal.Therefore,the detection parameters were optimized by the analysis of phased array ultrasonic sound field distribution characteristics and its influencing factors,the corresponding signal processing algorithm for the detection of signal and image noise reduction was the major research contents through the analysis of detection signals in the aerospace turbine phased array ultrasound testing technology.First of all,the influence of the parameters such as array element number,array element spacing and frequency on the aviation turbine disk phased array ultrasonic sound field is analyzed by theory,The results show that the energy of phased array ultrasound focused sound field increases with the increase of array number andfrequency,the amplitude of phased array ultrasonic grating increases with the increase of element spacing.Secondly,the characteristics of the ultrasonic phased array sound field in the disk is analyzed,the width of ultrasonic beam focusing area and amplitude of signal was measured by changing the number of arrays.It suggested that phased array ultrasonic focal zone width decrease with the increase of the number of array element,increase with the increase of the depth of focus.The interval transverse holes on the 50 mm arc ware detected by phased array ultrasonic slant probe and the effects of resolution by different number of array elements and different position of probe was analyzed.The results show that the detection resolution was improved as the lager intersection of the scanning line angle interval by increasing the number of elements,the appropriate adjustment of the probe position.Thirdly,the groove type defect in aviation turbine disk was detected by phased array ultrasonic slant probe,ultrasonic phased array imaging method and image feature of area type defect in aviation turbine disk was thoroughly analyzed and at the base of orientation and size that had been detected by separated strips,come from narrow slots' diffraction echo,the influence of accuracy of detection caused by the array number and the position of the probe is analyzed.The results show that the length measure by phased array ultrasound are generally larger than actual value,detection near surface narrow slot should choose a small number of elements and long-range detection should use more elements.Fourthly,the phased array ultrasonic oblique probe was used to study the micro defects of the complex area of the aerodynamic turbine disk.The phased array ultrasonic parameters were optimized and the characteristic signals of the aeronautical turbine disk were analyzed.The results show that the 5MHz frequency phased array ultrasonic oblique probe,exciting 32 array elements,with the excitation signal pulse width of100 ns,the depth of focus is 102 mm can effectively detect the defect.Finally,in order to improve the signal-to-noise ratio of phased array ultrasonic micro detection signal of aeronautical turbine disk and the image quality of aviation turbine disk sweep,the signal of the aerodynamic turbine disk detected by phased array ultrasonic detection is analyzed,wavelet packet decomposition is used to understand the time-frequency characteristics of the phased array ultrasonic detection signal in the aerodynamic turbine disk,the wavelet threshold and the noise-reducing effect of the wavelet-based detection signal are compared and the wavelet packet threshold is optimized to obtain the optimal wavelet packet noise reduction parameters.To further improve image quality,after the wavelet packet processing,the ultrasonic phased array detectionsignal is further processed by the singular value decomposition technique,the Hankel matrix dimension selection and how the singular value to process the effect of noise reduction are compared.The optimal singular value noise reduction parameters are obtained.The results show that the small defect signal in the aeronautical turbine disk is close to the aeronautical turbine disk structure signal.The defect characteristic signal is not concentrated in a certain frequency range,so filtering for a specific frequency band will cause noise loss at the same time as the loss of the characteristic signal.Selecting the partial decomposition signal according to the wavelet packet analysis result and combining the improved the threshold decreased the noise,which can effectively extract the defect feature image,the structural feature image and even the noise stripe caused by the material structure.Optimized parameters of the singular value decomposition technology is used to further process phased array ultrasound detection data and to image,defect signal to noise ratio and resolution to be further improved.In summary,the use of phased array ultrasonic testing technology for high-temperature alloy aviation turbine disk safety and effective non-destructive testing to ensure the quality and safety of turbine disk,it's great significant to save manufacturing costs,improve turbine performance,to avoid safety accidents and other aspects.