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The nonlinear ultrasonic detection method is presented for the issue of difficulty in detecting metal-non-metal bonding adhesive defect detection by conventional ultrasonic testing methods.A solid rocket motor(SRM)model containing gap defect has been produced in this paper.The fundamental amplitude and second harmonic amplitude of nonlinear ultrasonic response are measured effectively by the nonlinear ultrasonic testing system.The effectiveness of nonlinear ultrasonic testing method in the bonding interface defect detection was demonstrated.A relationship between acoustic nonlinearity coefficient and the interface gap defects is established.Experiment results show that the nonlinear effects are mainly fiom the contact nonlinear,which were caused by defects and the ultrasound relative nonlinear coefficient has an overall monotonously increasing trend.