Research On Detection For Interface Debond Of CFRP T-joints Under Tensile Load

Carbon fiber composite glued T-joint is one of the typical pattern of aerospace compositeintergrated structure used for load transfer in orthogonally vertical direction. In service, T-joint ismainly bearing tensile load and easy to produce interface debond damage. In this paper, the initiationand extension of typical damage(debond) in T-joint(T700/QY8911) was studied from three aspects,tensile experiment, active Lamb wave monitoring experiment and mechanics numerical simulation.The main works and results are as follows:(1) In tensile experiment, PZT sensors were selected and their arrangement was designed, thetensile experiments in two steps, intermittent and continuous loading,were carried on. The resultsshowed that the PZT sensors located on the path of the debond damage extension was good foranalysis of damage extension. The T-joint specimen generated visual debond damage when the tensileload reached about12.339kN with time interval of0.5ms. The horizontal and vertical debond cracksize was11.34mm and31.09mm.(2) In active Lamb wave monitoring experiment, the monitoring signals by Lamb excitation ofdifferent center frequences were analyzed. Vppof direct wave was selected as characteristic parameterand amplitude damage index was defined by using time-domain signal process method. Thecharacteristic parameter and damage index was used to analyze the change of T-joint specimen’sadhesive interface. The results showd the monitoring signals remaind unchanged in healthy state. Vppreflected four states of T-joint specimen, healthy status, filler break, interface debonding, structuralfailure. The amplitude damage index first appeared greater than or equal to10could warn that thestructure damage was about to generate.(3) In mechanical numerical simulation, the CFRP T-joint was modeled by numerical method.The results was compared to the results in above two aspects as reference. The model of L-layer andSkin-layer was simplified by simplified theory of laminated plates. The damage criterion of adhesivelayer and filler choosed secondary nominal stress criterion and Mises criterion. The results showedwhen the tensile load reached the limit the layer near th arc zone cracked first. After the failure offiller the aera of stress concentration transfered to adhesive layers between laminated plate. Thesimulated results was closer to experimental results. They had a similar change rule. The error of mainparameter values(tensile load,tensile displacement) in three states(before and after visual debonddamage generation, structural failure) ranged0.48%~7.13%.