Hirsekorn, S.S.Hirsekorn2022-03-092022-03-092001https://publica.fraunhofer.de/handle/publica/338380The load capacity of composite materials is often limited by the quality of the bonded interfaces. Therefore, an important task in nondestructive materials testing is the development of techniques to characterize the bond quality or even to measure the bond strength of adherent joints. Binding forces are nonlinear and cause a nonlinear modulation of transmitted and reflected ultrasonic waves. As a consequence, the generated higher harmonics of an insonified monochromatic wave will give informations about the adhesive bonds. It has been shown by theory and experiment that local binding force curves of thin bonded interfaces can be imaged by the measured amplitudes of the ultrasonic waves of the insonified frequency and its higher harmonics transmitted through the interface. Additional phase measurements will enable the evaluation of the full hysteretic interaction force curve. The theoretical fundamentals of this method are described. Experimental results on aluminium plates joined by thin epoxy layers are presented. Sources of error as e.g. the nonlinear behavior of the measuring system or of the bonded components themselves are considered. Systematic experimental and theoretical investigations still necessary to assess the potentials and limitations of this nonlinear technique and to develop methods to minimize the error effects are discussed.enNonlinear ultrasoundultrasonic technique620658670conference paper