A NEW TECHNIQUE FOR ULTRASONIC NONDESTRUCTIVE EVALUATION OF ADHESIVE JOINTS .1. THEORY

In this paper we propose a new technique for ultrasonic nondestructive evaluation (UNDE) of adhesively bonded joints. We report an exact solution to the problem of reflection and transmission of a plane, time-harmonic, longitudinal wave through an N-layered medium. The solution is valid for perfectly elastic as well as linear-viscoelastic materials, and for isotropic as well as anisotropic materials (for example, fiber-reinforced composites) so long as the wave-propagation vector coincides with one of the material coordinates. The transfer function, H*(omega) is defined as the transmitted (or reflected) field normalized with respect to the Incident field. A closed-form solution for H*(omega) for the case of an adhesive joint (consisting of two adherends joined by an adhesive layer) immersed in an elastic fluid is derived. A detailed analysis of the sensitivity of H *(omega) to the wave speed and thickness of the adherends and the adhesive is carried out. An experimental verification of the analysis is the subject of Part II of this paper.