Ultrasonic evaluation of ply and interleaf layer properties of interleaved composite laminates.

An ultrasonic nondestructive evaluation procedure is presented for the ply and interleaf layer properties of carbon/epoxy composite laminates having interleaf resin layers at their interlaminar interfaces. It is shown that the material properties of plies (density, thickness, and transversely isotropic complex elastic moduli) and elastic interleaf layers (density, thickness, Young's modulus, and Poisson's ratio) can be identified by best fitting the theoretical energy transmission spectra of longitudinal waves through the laminate immersed in water to those obtained in ultrasonic measurement. It is also demonstrated that compared to the mass-less and null-thickness spring-type interlaminar interface model employed in the previous works, the present finite-thickness interleaf layer model can better reproduce the experimental transmission spectra of a unidirectional interleaved composite laminate containing ultrasonic bandgaps.

Second-harmonic generation of the lowest-order antisymmetric Lamb wave at a closed parallel crack.

The second-harmonic generation of the fundamental antisymmetric Lamb wave at a closed parallel crack in an elastic plate is studied by numerical analysis. The closed crack is modeled as a spring-type interface with quadratic nonlinearity. Based on a perturbation method, the problem of nonlinear Lamb wave scattering is decomposed into two linearized problems, i.

Analytical modeling of the interaction of an ultrasonic wave with a rough bone-implant interface.

Quantitative ultrasound can be used to characterize the evolution of the bone-implant interface (BII), which is a complex system due to the implant surface roughness and to partial contact between bone and the implant. The determination of the constitutive law of the BII would be of interest in the context of implant acoustical modeling in order to take into account the imperfect characteristics of the BII. The aim of the present study is to propose an analytical effective model describing the interaction between an ultrasonic wave and a rough BII.

Transmission of Lamb waves across a partially closed crack: Numerical analysis and experiment.

The transmission characteristics of Lamb waves across a partially closed through-thickness crack in a plate are investigated numerically and experimentally. In the numerical analysis, the spectral element method is used to simulate the transmission of the lowest-order symmetric (S0) and antisymmetric (A0) Lamb modes across a crack in a low-frequency range. The analysis is carried out for an open crack with traction-free surfaces as well as for a partially closed crack modeled as a spring-type interface characterized by normal and tangential stiffnesses.

Damage localization method for plates based on the time reversal of the mode-converted Lamb waves.

A damage localization method based on the time reversal focusing of the mode-converted scattered Lamb wave is proposed for plate structures with a non-symmetric defect in the thickness direction. Dual transducers are attached symmetrically on the upper and lower surfaces of the plate to selectively emit and receive the lowest-order symmetric (S0) and antisymmetric (A0) modes. The localization of damage is achieved by the numerical time-reversed (TR) simulation of the mode-converted Lamb wave generated at the defect.

Transmission characteristics of the S0 and A0 Lamb waves at contacting edges of plates.

In order to gain basic insight into the interaction between ultrasonic guided waves and structural discontinuities with contacting surfaces, the transmission characteristics of Lamb waves at contacting edges of two plates are studied experimentally. The edges of two 2.5-mm thick aluminum alloy plates are mated together to constitute a contacting interface of plates and subjected to different levels of compressive loading.

Ultrasonic wave transmission and bandgap in multidirectional composite laminates with spring-type interlayer interfaces.

The ultrasonic wave transmission through multidirectional composite laminates is studied theoretically by accounting for the effect of thin interlayer resin-rich regions based on the spring-type interface model. Using the stiffness-matrix method, the energy transmission spectrum of the longitudinal wave impinging obliquely on cross-ply and quasi-isotropic laminates immersed in water is calculated. The location and bandwidth of the frequency ranges where the transmissivity becomes vanishingly small are shown to be significantly influenced by the incident angle, the laminate lay-up, and the interlayer interfacial stiffnesses.

Transmission of Lamb waves and resonance at an adhesive butt joint of plates.

The transmission behavior of Lamb waves and the possible occurrence of resonance at an adhesive butt joint of plates are studied experimentally. To this purpose, two 2.5-mm thick aluminum alloy plates are bonded at their edges using cyanoacrylate-based adhesive.

Transmission of ultrasonic waves at oblique incidence to composite laminates with spring-type interlayer interfaces.

The transmission characteristics of ultrasonic waves at oblique incidence to composite laminates are analyzed theoretically by the stiffness matrix method. The analysis takes into account the presence of thin resin-rich regions between adjacent plies as spring-type interfaces with normal and shear stiffnesses. The amplitude transmission coefficient of longitudinal wave through a unidirectional laminate immersed in water is shown to be significantly influenced by the frequency, the interlayer interfacial stiffnesses, and the incident angle.

Resonance of an imperfect joint of plates by the lowest-order symmetric Lamb mode.

Resonance behavior of an imperfect joint of elastic plates subjected to the incidence of the lowest-order symmetric (S0) Lamb mode is numerically analyzed in the frequency domain by the hybrid finite element method. To this purpose, the reflection and transmission characteristics of the S0 mode are calculated for the frequency range in which the S0 mode is the only symmetric mode that can propagate in the plates. The imperfect joint is modeled as a linear spring-type interface characterized by the normal and tangential stiffnesses.

Evaluation of interlayer interfacial stiffness and layer wave velocity of multilayered structures by ultrasonic spectroscopy.

An ultrasonic evaluation procedure for the interlayer interfacial normal stiffness and the intralayer longitudinal wave velocity of multilayered plate-like structures is proposed. Based on the characteristics of the amplitude reflection spectrum of ultrasonic wave at normal incidence to a layered structure with spring-type interlayer interfaces, it is shown that the interfacial normal stiffness and the longitudinal wave velocity in the layers can be simultaneously evaluated from the frequencies of local maxima and minima of the spectrum provided that all interfaces and layers have the same properties. The effectiveness of the proposed procedure is investigated from the perspective of the sensitivity of local extremal frequencies of the reflection spectrum.

Influence of axle-wheel interface on ultrasonic testing of fatigue cracks in wheelset.

For the ultrasonic testing at the wheel seat of railway axles, quantitative investigation of the reflection and transmission phenomena at the axle-wheel interface is important. This paper describes the influence of the axle-wheel interface on the ultrasonic testing of a fatigue crack in a wheelset by applying the spring interface model. The normal and tangential stiffnesses were identified experimentally for an as-manufactured wheelset at the normal incidence, and the reflection coefficient for the shear-wave oblique incidence was calculated.

Stiffness evaluation of contacting surfaces by bulk and interface waves.

This paper describes ultrasonic measurements of normal and tangential stiffnesses of the contacting interface between polished aluminum blocks subjected to nominal contact pressures up to about 3.8 MPa. These stiffnesses were evaluated by ultrasonic spectroscopy methods for the bulk (longitudinal and transverse) wave reflection coefficients and the anti-symmetric mode interface wave velocity.