Research On Damage Localization And Imaging Algorithm Based On Laser Ultrasonic Testing Technology

The laser ultrasonic detection technology is based on the thermo-elastic effect.A high-energy laser pulse emitted by the laser excites an ultrasonic wave in the structure.The ultrasonic wave can propagate in the structure and be affected by the damage in the structure.The ultrasonic signal is received by the sensor,and the damage information in the structure can be obtained by signal analysis and processing.Laser ultrasonic detection technology has the advantages of no couplant,non-contact and suitable for curved surface structure detection,and has a wide range of applications.However,the current laser ultrasonic damage imaging algorithm based on wavefield reconstruction relies on intensive measurement points,which has the problem of long detection time and low efficiency.For the detection of large-size structures,this paper presents a damage localization algorithm and damage imaging algorithm based on laser ultrasonic detection technology.The main contents of this paper include:Firstly,the principle of laser ultrasonic testing technology is introduced,including the excitation principle of Lamb wave by laser and the propagation characteristics of Lamb wave in the structure.The hardware part and the software part of laser ultrasonic testing system in laboratory are introduced respectively.Next,the principle of wavefield reconstruction and the damage imaging algorithm based on wavefield reconstruction are introduced.The effect of increasing the distance between measuring points on the damage imaging is analyzed.It is found that the damage imaging based on wavefield reconstruction algorithm relies on dense measurement points.Then,the damage localization algorithm based on S₀ modal anomaly energy is studied to realize the damage localization under the large measuring point spacing,and the influence of the damage parameters on the damage localization effect is studied.Finally,the damage imaging algorithm based on the incident wave anomaly energy is studied.Compared with the wave field energy flow method and the anomalous energy method,this method has higher reliability and accuracy.Meanwhile,the effect of damage parameters on imaging performance is studied,and through multi-sensor fusion imaging,the SNR of imaging result and the ability to detect damage of different angles are improved.