A Study On Nonlinear Ultrasonic Testing Of Micro Defects

With the development of the industrial level,more and more metal materials are used in products and equipment that are in a harsh environment such as high speed,high temperature and high pressure for a long time.Product equipment in harsh working environments is increasingly demanding performance for metal materials.Even the presence of tiny defects in the material can cause it to fail and also can cause serious economic losses.In order to avoid material failure,the detection of small defects is of great significance.Conventional ultrasonic testing is limited by the wavelength of the ultrasonic wave,and the acoustic reflection and acoustic attenuation of the acoustic wave to the micro defect are extremely weak.Therefore,the detection of micro defects by traditional ultrasound is highly prone to miss detection.Nonlinear ultrasonic testing technology uses the nonlinear effects of tiny defects on ultrasonic waves and is more sensitive to small defects.Therefore,this paper used nonlinear ultrasonic testing technology to detect lamellar defects and fatigue damage.The nonlinear ultrasonic detection signal was extracted,and the detected time domain signal was subjected to spectrum analysis.Nonlinear ultrasonic detection characteristic parameters were defined to characterize lamellar micro defects and fatigue damage.The specific research contents were as follows:First,based on the modular instrument design method,a suitable nonlinear ultrasonic detection system was built with the RITEC SNAP RAM-5000 high-energy emission receiver as the core.And the special fixtures for layered micro defects and nonlinear ultrasonic testing of fatigue damage micro defects were designed respectively,so that the coupling force between the transducer and the tested sample was consistent in every test.In addition,the test system was tested for calibration before each non-linear ultrasonic test.Secondly,the nonlinear ultrasonic detection technology of lamellar defects was studied,and the detection area was divided with reference to the C-scan image.The nonlinear ultrasonic area detection method was designed.The nonlinear ultrasonic detection characteristic parameters capable of characterizing the defects were extracted by the finite amplitude method.The sensitivity of nonlinear characteristic parameters to lamellar defects was analyzed by Spearman rank correlation.The influence of defect types on nonlinear ultrasonic response wass analyzed by metallographic test and conventional C-scan imaging,and revealed the nonlinear ultrasonic detection mechanism of lamellar defects.Finally,the nonlinear ultrasonic detection technology of fatigue damage was studied.The nonlinear ultrasonic detection characteristic parameters extracted by finite amplitude method were compared with the ultrasonic C-scan image.The variation of nonlinear characteristic parameters with the degree of fatigue crack propagation was analyzed,and the mechanism of nonlinear ultrasonic detection for fatigue damage was revealed.The nonlinear ultrasonic testing technology used in this study is suitable for the non-destructive testing of micro-layered defects and fatigue damage.It plays an important role in improving the ability of detection in lamellar micro defects and fatigue damage micro defects,the practicality of engineering testing and the detection efficiency.