Determination of epoxy film parameters in a three-layer metal/adhesive/metal structure

Abstract

The aim of this work is to propose a method to determine the elastic parameters and the thickness of a thin epoxy film located inside a 3-layer aluminum/epoxy/aluminum structure, based on ultrasonic measurements. This study is conducted at low frequencies, to allow the vibration of the whole structure. First, the direct problem is addressed. The sensitivity of the vibration modes to the parameters of interest is studied to select the most sensitive one for a given parameter to be determined. Second, the identification of the parameters with the selected modes is obtained by a minimization of the characteristic equation. This process is applied to experimental data: the longitudinal and shear wave velocities and the thickness of the epoxy film are obtained within a 3% error range.

Lamb Modes for the Characterization of Bonded Structures

“…The model of Jones allows aquantitative evaluation of the bonding quality.From the experimental values of the wavenumber-frequencyp airs, it is possible to deduce the values of K L and K T by solving an inverse problem. The algorithm used [9] is summarized in the following. First, aw ide range of variation of the Jones parameters is assumed.…”

“…Atransducer with ac entral frequencyo f1MHz is fixed on aP lexiglas wedge with 38.5 • angle, placed on the surface of the structure [8]. The transducer is excited by as hort pulse (about 0.5 µs duration)with an amplitude of −300 V. The targeted modes by this type of excitation are the shear and longitudinal vertical modes which are sensitive to the bulk variations of the adhesive [9]. The normal displacement related to the propagation of the generated Lamb waves, is measured using al aser velocimeter,f or several positions on the surface in the propagation direction.…”

Elastodynamic Behaviour of Laminate Structures with Soft Thin Interlayers: Theory and Experiment

“…For visualization of localized macroscopic damage in bonded structures with EGWs, non-contact imaging techniques are being developed based on object surface scanning with a laser source [11], laser interferometer [12] and their combinations [13]. Since guided wave dispersion properties strongly depend on structural material parameters, EGWs are valuable for global assessment of adhesive bonding integrity [8,14] and might be also used for the estimation of adhesive mechanical properties [15,16]. The latter is particularly important for in-and post-manufacturing quality control of bonded structures because the strength properties of adhesives strongly depend on curing conditions [17,18].…”

“…In the EGWs diagnostics of laminate assemblies with soft interlayers, relevant mathematical and computational models describing their elastodynamic behaviour are essential for adequate interpretation of the experimental data. A natural and basic way is to model such waveguides as multilayered objects assuming continuity conditions for displacement and stress components at the interlaminar interfaces [15] (for bonded structures, they are known as tri-layer models). To handle possible imperfectness in interface coupling, such models are further modified by including an additional viscoelastic interfacial layer [19] or assuming the spring-type boundary conditions (SBCs) between the laminae [8,20].…”

Modeling and numerical study of the influence of imperfect interface properties on the reflectance function for anisotropic multilayered structures

“…In this work, the interest is directed towards multilayered structures. The ultrasonic characterization of interfaces in this specific case has been assessed by several researchers [6][7][8][9][10]. For example, Vlasie et al [8] proposed an interface model simulating the damage evolution of a structural joint.…”