Laminated composites are susceptible to delamination due to their weak transverse tensile and interlaminar shear strengths as compared to their in-plane properties. Delamination damage can occur internally, where it is not visible to the naked eye. Development of reliable, quantitative techniques for detecting delamination damage in laminated composite components will be imperative for safe and functional optimally designed next-generation composite structures. In this article, we study the potential of using Lamb waves for delamination detection and quantification, using model-assisted data acquisition. Novel wavenumber analysis approaches are developed and discussed to show how they can be used to investigate Lamb wave interactions with delaminated plies. Ultrasonic wave simulations are implemented to provide both in-plane and out-of-plane wave motion for the wavenumber studies. The out-of-plane results are verified against data obtained from experimental tests. It is found that the wavenumber methods can not only determine the delaminated region of the plate and its length, but can also identify the plies between which the delamination occurs. We envision that the wavenumber approaches can lead to a complete delamination quantification in the future.
The continued and expanded use of composite materials in aerospace applications necessitates structural health monitoring and/or nondestructive evaluation techniques that can provide quantitative and detailed damage information for layered plate-like components (such as composite laminates). Guided wavefield methods are at the basis of a number of promising techniques for the detection and the characterization of damage in plate-like structures. Among the processing techniques that have been proposed for guided wavefield analysis, the estimation of instantaneous and local wavenumbers can lead to effective metrics that quantify the size and the depth of delaminations in composite laminates. This article reports the application of both instantaneous and local wavenumber damage quantification techniques to guided wavefield data for delaminated composite laminates. The techniques are applied to experimental data for a simple single delamination case and to simulated data for a more complex multi-ply delamination case. The two techniques are compared in terms of accuracy in damage characterization and computational demand. The proposed methodologies can be considered as steps toward a hybrid structural health monitoring/nondestructive evaluation approach for damage assessment in composites.
Ultrasonic wave methods constitute the leading physical mechanism for nondestructive evaluation (NDE) and structural health monitoring (SHM) of solid composite materials, such as carbon fiber reinforced polymer (CFRP) laminates. Computational models of ultrasonic wave excitation, propagation, and scattering in CFRP composites can be extremely valuable in designing practicable NDE and SHM hardware, software, and methodologies that accomplish the desired accuracy, reliability, efficiency, and coverage. The development and application of ultrasonic simulation approaches for composite materials is an active area of research in the field of NDE. This paper presents comparisons of guided wave simulations for CFRP composites implemented using four different simulation codes: the commercial finite element modeling (FEM) packages ABAQUS, ANSYS, and COMSOL, and a custom code executing the Elastodynamic Finite Integration Technique (EFIT). Benchmark comparisons are made between the simulation tools and both experimental laser Doppler vibrometry data and theoretical dispersion curves. A pristine and a delamination type case (Teflon insert in the experimental specimen) is studied. A summary is given of the accuracy of simulation results and the respective computational performance of the four different simulation tools.
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