Ultrasonic Nondestructive Evaluation Of Debonding Damage In Honeycomb Sandwich Structures Using Guided Waves

Recent years,honeycomb sandwich structures are widely used in trains,marine,aerospace and aeronautics industries due to their high strength/stiffness-to-weight ratio.While the manufacturing processes,repeated or intensive loading,aging can lead to the occurrence of disbond along the skin-core junctions,which may jeopardize the integrity and safety of the whole structure.To avoid such accidents,it is essential to identify and position the damage in honeycomb sandwich structures.The potential of guided waves to travel over long distance,cover a large area and respond quickly to the changes and defects hidden in the structure makes guided waves efficiently used in damage detection and structure health monitoring.Multi-mode and dispersion properties makes it difficult to distinguish and deal with guided wave signals.Therefore,the study on the propagation characteristics of guided waves in honeycomb sandwich structures is not only of certain academic significance,but also of great value for the effective application of guided waves in damage detection of plate and honeycomb sandwich structures.Multi-mode and dispersion properties of ultrasonic guided waves on the basis of its dispersion relations in single plate are introduced.The phase and group velocity dispersion curve are obtained using dichotomy method.Next,a model for plane problems for honeycomb sandwich structure is proposed to introduce the principles of the excitation and reception of guided waves based on piezoelectric elements.Then,simplify the honeycomb sandwich structure using the sandwich theory and model it in FEM software COMSOL Multiphysics,based on the finite element intrinsic frequency method,the dispersion curve of guided waves is obtained.On these foundation,the propagation of guided waves both in perfect and damaged honeycomb sandwich plate structure are simulated through a 3D model by using FEM software COMSOL Multiphysics,the effects of disbond on the propagation of guided waves are carried out.Experimental study on detection of debonding damage within the honeycomb sandwich structure is then conducted,guided waves acquired in the experiment are processed by damage probability imaging algorithm to identification and position for debonding damage hidden in the structure.The main results include:(1)The dispersion curve of guided waves can be obtained by using a simplified honeycomb sandwich plate combined with finite element intrinsic.Guided waves contain symmetric modes S0,S1,S2 and antisymmetric modes A0,A1 at 100kHz,which accords with simulation and experiment results.Meanwhile,the group velocity of each mode of guided waves through this method is close to that of experimentresults.Therefore,the dispersion curve of guided waves can be calculated by using equivalent model.(2)When the frequency is relatively low,guided waves propagate in the whole honeycomb sandwich plate;When the frequency is relatively high,it can be reagarded as leaky guided waves propagation in the upper panel of the structure with a little energy releasing into the core and lower panel.(3)The amplitude of A0 mode of guided waves in debonding structure is larger than that of perfect structure,while the amplitude of other modes will not be obviously different.The specific A0 mode of guided waves is the most sensitive to disbond,which can be the basis for judging disbond in structure,and the amplitude of A0 mode increases along with the area of disbond.The wavelegths of guided waves are too long to identify disbond at a low frequency.(4)The guided waves signals can be captured by the experimental systems based on piezoelectric wafers and Polytec Scanning Vibrometer respectively.It shows that the amplitude of A0 mode changes greatly when guided waves propagate in perfect and damage structure,A0 mode has the highest sensitivity to disbond.The experiment validates the effectiveness of the dispersion curve using the equivalent honeycomb sandwich plate.The damage probability imaging algorithm based on signal difference coefficient(SDC)are proposed to position and restruct the disbond,and the results shows good accuracy with the actual disbond.The amplituede of A0 mode can be a parameter for damage detection and identification,and the results agrees well with the actual disbond.Guided waves testing techniques have a good prospect.