Research On Lamb Wave Monitoring Technology For Plate Structures Based On Non-contact Laser Interferometry

Plate and shell structures are widely used in aerospace,transportation,power and other fields of engineering structures,in order to ensure the safe and reliable operation of engineering structures,their health status monitoring is particularly important.However,traditional piezoelectric sensors and accelerometers used for health monitoring of the surface of plate structures are affected by their contact measurement method and narrow bandwidth,which reduces the accuracy of the monitoring process.The paper addresses this technical problem by investigating a non-contact vibration measurement method based on the laser interference principle for Lamb wave health monitoring on the surface of plate structures.The research work includes the analysis of Lamb wave propagation characteristics and impact damage mechanism,the design and construction of the laser measurement system,and the study of impact monitoring as an example,non-contact signal acquisition of impact response signals,optimal parameter extraction,characterisation of the impact damage degree,and finally the integration of the laser measurement system into a portable measurement device,and the completion of the corresponding tests.The main research elements of this paper are as follows:Firstly,the propagation characteristics of Lamb waves in plate structures and the principle of Lamb wave-based monitoring techniques are analysed,and the basic theory of wavelet transform methods for filtering interference signals is described.Secondly,the principle of laser interferometric vibration measurement method is studied and a laser interferometric measurement system is designed,which optimises and improves the optical path structure and utilises the linear polarisation characteristics of the laser to improve the interference effect.The design of the supporting circuit and the construction of the overall monitoring system are completed around the laser measurement system.Thirdly,a monitoring method to characterise the degree of impact damage is investigated and analysed in relation to the mechanism of impact damage.The impact monitoring experiments were carried out on the plate structure,and the peak value,centre frequency and phase of the damage signal were extracted to characterise the degree of impact damage,which verified the impact damage characterisation method and eliminated the singularity and limitation of characterising the degree of damage by signal intensity alone.Finally,the whole laser measurement system is systematically integrated and made into a portable measurement device,which can measure signals with frequencies of 200-500 k Hz and successfully captures Lamb waves with a centre frequency of 200 k Hz propagating in the plate structure,verifying the accuracy and practicality of the measurement of this device.The experimental results show that the laser measurement system studied in this paper has better system sensitivity,and combined with the monitoring method proposed in this paper,it can accurately complete the measurement tasks in the health monitoring of plate structures,which has good engineering application value.