Abstract
Laminate structures composed of stiff plates and thin soft interlayers are widely used in aerospace, automotive and civil engineering encouraging the development of reliable non-destructive strategies for their condition assessment. In the paper, elastodynamic behaviour of such laminate structures is investigated with emphasis on its application in ultrasonic based NDT and SHM for the identification of interlayer mechanical and interfacial contact properties. A particular attention is given to the practically important frequency range, in which the wavelength considerably exceeds the thickness of the film. Three layer model with spring-type boundary conditions employed for imperfect contact simulation is used for numerical investigation. Novel effective boundary conditions are derived via asymptotic expansion technique and used for analysis of the peculiar properties of elastic guided waves in considered laminates. It is revealed that the thin and soft film influences the behaviour of the laminate mainly via the effective stiffnesses being a combination of the elastic moduli of the film, its thickness and interface stiffnesses. To evaluate each of these parameters separately (or to figure out that the available experimental data are insufficient), a step-wise procedure employing the effective boundary conditions is proposed and tested versus the laser Doppler vibrometry data for Lamb waves in Aluminium/Polymer film/Alumunium structure. A good agreement between theoretical and experimental data is demonstrated for a certain symmetric laminate specimen. The possibility of using film-related thickness resonance frequencies to estimate the film properties and contact quality is also demonstrated. Additionally, the rich family of edge waves is also investigated, and the splitting of fundamental edge waves into pairs is revealed.
Highlights
Laminate thin-walled structures composed of stiff plates and soft polymeric interlayers are typical for many industrial applications
Since guided wave dispersion properties strongly depend on structural material parameters, elastic guided waves (EGWs) are valuable for global assessment of adhesive bonding integrity [8,14] and might be used for the estimation of adhesive mechanical properties [15,16]
With extensive analytical and numerical analysis, it is illustrated that mechanical properties of the thin soft interlayer and the interface contact quality have a sufficient influence on the EGWs properties in a three-layered laminate structures
Summary
Laminate thin-walled structures composed of stiff plates and soft polymeric interlayers are typical for many industrial applications. The aim of the current study is to comprehensively investigate and explain the influence of thin and soft interlayers on the behaviour of EGWs in laminate isotropic structures with particular emphasis on the application of the obtained results for the identification of mechanical properties of such sublayers and evaluation of interlaminar contact integrity For this purpose, extensive numerical analysis of EGW characteristics in a three-layered geometrically symmetric laminate with a thin film is performed while elastic constants and thickness of the latter as well as contact quality are serving as input.
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