Study On The Detection Of Delamination Damage For CFRP-steel's Bonding Interface Based On Lamb Wave

Carbon fiber reinforced composites?CFRP?have been widely used in the field of of industry for their mechanical properties of light weight and high strength.When CFRP and metal are used together by bonding,the bonding interface under the influence of various factors is prone to debonding,which will become delamination eventually,so bonding interface is the weakness of adhesive structure,especially in steel structure reinforced by CFRP.Interface delamination will greatly reduce the bearing capacity of the whole structure,therefore,it is very necessary to do nondestructive testing for this delamination.Aiming at Lamb wave detection technology,so far the linear propagation characteristics of Lamb wave in the interface delamination area are not studied clearly,the nonlinear characteristics of Lamb wave caused by delamination and analysis on their influencing factorsits are not perfect,the location detection using Lamb wave on delamination damage also needs further study.Based on this status,aiming at the delamination in the CFRP-steel bonding plate,this paper mainly completed the following work:?1?According to the three-dimensional elasticity theory the phase velocity models of Lamb wave in isotropic and orthotropic plate are established,combining with the transfer matrix the dispersion equation of CFRP-steel bonded plate is derived,which provides a theoretical basis for drawing the dispersion curve of Lamb wave.Using finite element modal analysis method,the dispersion curve of CFRP-steel bonding plate is drawn,which provides a reference for the subsequent signal analysis.?2?The delamination's effect on Lamb wave propagation is studied by simulation,combining the simulation with experiment,the relationship between damage echo and the length of delamination is analyzed.The results show that Lamb wave is separated into two parts in the delaminiation region and the energy is gathered in the upper part of the delamination to form a standing wave,A0 waves are more sensitive to damage and the damage echo mainly reflects in the exit end of the delamination.With the increasing of delamination length,the reflection coefficient of damage echo increases first and then decreases to exhibit an oscillatory trend.?3?The causes of harmonic and harmonic damage signal are analyzed by simulation,through the digital filter and HHT time-frequency transform,the difference of arrival time between second harmonic?2f₀?and direct wave in transmission signal is shown and the reasons are explained.The displacement curves of nodes of the upper and lower interfaces are extracted,the collision process is analyzed detailedly from two aspects:the structural stiffness and nodal motion phase.Aiming at the three key factors:signal excitation amplitude,the length and depth of delamination,their influence on the nonlinear characteristics of Lamb wave is studied and explained.?4?The wavelet packet transform theory is introduced,based on the wavelet packet energy spectrum the damage identification index is established,combining with Reconstruction Algorithm for the Probabilistic Inspection of Damage?RAPID?a method to detect the location of delamination of CFRP-steel bonded plate is proposed.The results of simulation and experiment are compared to analyse the cause of lower precision of esperiment,and then some suggestions are given to optimize the test results.