Abstract
There has been an increase in the use of ultrasonic arrays for the detection of defects in composite structures used in the aerospace industry. The response of a defect embedded in such a medium is influenced by the inherent anisotropy of the bounding medium and the layering of the bounding medium and hence poses challenges for the interpretation of the full matrix capture (FMC) results. Modeling techniques can be used to understand and simulate the effect of the structure and the defect on the received signals. Existing modeling techniques, such as finite element methods (FEM), finite difference time domain (FDTD), and analytical solutions, are computationally inefficient or are singularly used for structures with complex geometries. In this paper, we develop a novel model based on the Gaussian-based recursive stiffness matrix approach to model the scattering from a side-drilled hole embedded in an anisotropic layered medium. The paper provides a novel method to calculate the transmission and reflection coefficients of plane waves traveling from a layered anisotropic medium into a semi-infinite anisotropic medium by combining the transfer matrix and stiffness matrix methods. The novelty of the paper is the developed model using Gaussian beams to simulate the scattering from a Side Drilled Hole (SDH) embedded in a multilayered composite laminate, which can be used in both immersion and contact setups. We describe a method to combine the scattering from defects with the model to simulate the response of a layered structure and to simulate the full matrix capture (FMC) signals that are received from an SDH embedded in a layered medium. The model-assisted correction total focusing method (MAC-TFM) imaging is used to image both the simulated and experimental results. The proposed method has been validated for both isotropic and anisotropic media by a qualitative and quantitative comparison with experimentally determined signals. The method proposed in this paper is modular, computationally inexpensive, and is in good agreement with experimentally determined signals, and it enables us to understand the effects of various parameters on the scattering of a defect embedded in a layered anisotropic medium.
Highlights
We develop a model to simulate the scattering from an Side Drilled Hole (SDH) that is embedded in a layered carbon fiber-reinforced plastic (CFRP) laminate
This paper proposes a modeling technique based on the Gaussian beam and the recursive stiffness matrix method to simulate the scattering from an SDH embedded in a CFRP laminate
The modeling technique takes into consideration the diffraction, anisotropic velocity, and inspection frequency effects while simulating the scattering from the SDH embedded in a layered medium
Summary
There has been a rapid increase in the ultrasonic phased array testing of composite structures used in the aerospace industry [4]. The testing of such structures is complicated due to the inherent anisotropy of composites and the presence of multiple layers. The output ultrasonic signal from defects in such structures is influenced by the anisotropy and layering present in them. Sensors 2021, 21, 4640 a layered medium from/into a generally anisotropic semi-infinite medium. It is followed by the theory for Gaussian beam modeling of transducers and for calculating the equivalent homogeneous properties of a layered medium.
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