Nonlinear Ultrasonic Detection Of Impact Damage In CFRP Panels Based On Pulse Inversion Technique

Carbon fiber reinforced polymer(CFRP)panels are widely used in critical areas such as aerospace,construction and engineering due to characteristics such as high strength-to-weight ratio and good fatigue resistance.However,impacts from debris and dropped tools during service can cause many forms of impact damage within their structure,which can pose a significant threat to the safety of the structure.Nonlinear ultrasonic detection is widely used in the field of early damage detection by virtue of its sensitivity to micro-damage.In this paper,the ultrasonic nonlinear response of CFRP panels with different impact parameters and detection distances is investigated using experimental and simulation analyses,and a detection method based on the pulse inversion technique is proposed to address the problem of low efficiency of second harmonic generation during the detection process.Firstly,the fluctuation equations of Lamb wave in multilayer composites are derived based on the stress-strain expansion matrix of single-layer anisotropic media,then the propagation characteristics of Lamb waves and the advantages of nonlinear ultrasonic detection are introduced,and the dispersion and multimodal characteristics of Lamb wave are introduced through the dispersion curves of Lamb wave drawn by DC software.At the same time,the principle of the pulse inversion technique is explained and the improved nonlinear parameter is derived and defined.Then,the nonlinear Lamb wave response of CFRP panels with different impact damage is investigated experimentally.Nonlinear ultrasonic detection platform based on pulse inversion technique is constructed and the excitation signal and coupling agent are selected,the stability of the inspection system and the correctness of the pulse inversion technique are verified.Then CFRP specimens containing damage are prepared,and the damage produced by different impact energies is compared by means of the ultra-depth-of-field microscopy system.The results show that the pulse inversion technique can effectively improve the detection amplitude of the second harmonics,while the increase of the impact energy does not significantly affect the amplitude of the fundamental wave,but leads to the increase of the second wave packet amplitude,the second harmonic amplitude as well as the IRANP.Finally,considering the limitations of the test conditions,a finite element model for impact-vibration cancellation-nonlinear detection of CFRP panels is developed in this paper to study the nonlinear ultrasonic response under different parameters.After the introduction to the creation process of the integrated model,the accuracy of the model and the validity of the pulse inversion technique are verified.This model is then used to further investigate the damage caused by impact energy,impact angle in combination with substrate tensile damage and energy absorption and the effect of these impact parameters and detection distance on the nonlinear ultrasonic response.The results show that impact energy is positively correlated with impact damage and impact angle is negatively correlated with impact damage.IRANP is positively correlated with impact damage when performing damage detection,so the magnitude of damage from different impact parameters can be assessed by comparing IRANP.Also,the detection distance has an important influence on IRANP.