Ultrasonic Measurement Method For Defect And Stress Of Stiffened Panel Under Wing Skin

The performance of R-zone components of stiffened panels under wing skin has a significant impact on the overall flight performance and safety reliability of aircraft.Therefore,it is of great significance to use accurate and reliable nondestructive testing technology to detect defects and stresses in R-zone.Ultrasonic testing technology is a kind of non-destructive testing technology with considerable prospect in the application of aviation industry at home and abroad.In the ultrasonic testing of complex shaped components such as stiffened panels under wing skin,the placement of probes,scattering and focusing of ultrasonic beams have become problems to be solved.In this paper,the synthetic aperture dynamic full focus imaging method is used to measure the front defects of L-shaped R-zone components and the back defects of T-shaped R-zone components.Combined with the acoustic elastic effect and Mohr’s circle theory,the stress measurement scheme of R-zone components is determined.Based on COMSOL simulation platform,the defect and stress measurement scheme of R-zone component is simulated and verified.Finally,the experimental systems of L-shaped R-zone component front defect measurement,T-shaped R-zone component back defect measurement and stress measurement are built to characterize the defects qualitatively and quantitatively and measure the stress numerically.The main research work of this paper is as follows.In this paper,the focal synthetic aperture,delay rule and propagation path are determined for the front defect measurement of L-shaped R-zone component and the back defect measurement of T-shaped component respectively.In this paper,the synthetic aperture dynamic full focus method is selected as the imaging algorithm of R-zone component defect measurement.According to the acoustoelastic effect,the relationship between wave velocity and stress in different modes and the corresponding stress sensitivity are analyzed.In this paper,the longitudinal wave along the stress propagation direction is selected as the measurement mode,and combined with the Mohr circle stress theory,the stress measurement scheme of R-zone components is derived.At the same time,the wavelet packet decomposition and reconstruction,cross-correlation acoustic time delay estimation methods are analyzed and elaborated.Based on COMSOL simulation platform,the material setting,physical field simulation selection,mesh generation and solution step are determined according to the actual detection requirements.In order to achieve the minimum energy leakage,the best frequency resolution and the maximum signal-to-noise ratio,the sinusoidal signal modulated by Hanning window is selected as the excitation signal of ultrasonic phased array transducer and single element transducer.The simulation results can clearly distinguish the position of interface echo signal and defect echo signal,and verify the relationship between acoustic time difference and stress.Finally,the test specimens with the same parameters as the simulation are made,and the experimental systems of L-shaped R-zone component front defect measurement,T-shaped R-zone component back defect measurement and stress measurement are built respectively.In this paper,the circular defect with a diameter of 2mm and the circular defect with a 1mm×4mm crack defect measurement.The stress coefficient is 6.58MPa/ns and the resolution of stress measurement is 1.36 MPa.The straight probe,K1 angle probe and calibrated stress coefficient are used to realize the stress measurement of R-zone components,and the measurement error is ±17.91 MPa.The experimental results show that the measurement method is effective.