Longitudinal guided waves confined in radius filler regions of composite joints.
15 Jul 2016-Journal of the Acoustical Society of America (Acoustical Society of America)-Vol. 140, Iss: 1, pp 334-343
TL;DR: Semi-analytical finite element simulations are used to demonstrate the existence of a longitudinal guided ultrasonic mode confined or trapped in the Noodle regions, and reveal that this mode has attractive properties for rapid screening of Noodle joints, including strong energy concentration, low dispersion, and attenuation.
Abstract: This paper studies the feasibility of using ultrasonic guided waves for fast inspection of conformal deltoid radius filler or “Noodle” regions of joints in stringer composite structures. Semi-analytical finite element simulations, supported by experiments and three-dimensional finite element models, are used to demonstrate the existence of a longitudinal guided ultrasonic mode confined or trapped in the Noodle regions. Studies reveal that this mode has attractive properties for rapid screening of Noodle joints, including strong energy concentration, low dispersion, and attenuation. Discussing the physics of mode confinement in light of material differences and geometry, the phenomenon is shown to be related to feature-guiding effects noted in literature recently.
Citations
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TL;DR: The feasibility of detection of delamination is experimentally demonstrated, whose size is comparable to the ultrasonic wavelength with probability of detection better than 90% using <1% of the total number of samples required for conventional imaging, even under conditions wherein the SNR is as low as 5 dB.
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Cites background from "Longitudinal guided waves confined ..."
...In recent years, one particular branch of guided waves confined to local structural variation - feature guided waves (FGW) have received much attention and been discussed in the literature extensively [5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15]....
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TL;DR: In this paper, a feature guided wave (FGW) was used for rapid screening of the bond line between a stiffener and a carbon fiber reinforced polymer (CFRP) composite panel.
Abstract: Adhesive bonding is widely used in aerospace composite structures. A continuous well-cured bond can offer good joint strength and improved fatigue and impact resistance, and is therefore crucial to the performance of the entire structure. This paper explores the feasibility of using feature guided waves (FGW) for rapid screening of the bond line between a stiffener and a carbon fiber reinforced polymer (CFRP) composite panel. Such FGWs are capable of focusing the wave energy along the stiffener and the bond layer, with limited radiation to the adjacent plate. The Semi-Analytical Finite Element (SAFE) approach is employed to understand the modal properties of FGWs that exist in the structure, and criteria are suggested to choose proper mode-frequency combination that is sensitive to adhesive defects. A shear horizontal type FGW mode is identified to be well suited, as it is easy to excite, and propagates with little dispersion and relatively low attenuation, while it retains sufficient energy around the bond layer. Both 3D Finite Element (FE) simulations and experiments are performed to study the interaction of the selected FGW mode with defects in the adhesive bond, and the results show excellent agreement. The reflection behavior and the wave-defect resonance phenomenon are investigated, which demonstrate the capability of the FGW for the bond line inspection.
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References
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TL;DR: The studies reveal that even a small degree of ovalness can affect mode shapes and velocities in thin pipes, and this may be important for practical inspection applications.
Abstract: This paper studies the influence of cross-section ovalness or ellipticity on lower order axisymmetric guided wave modes in thin pipes. The second longitudinal mode L(0,2) and the fundamental torsional mode T(0,1) are studied, as these are of interest to current pipe inspection. The semi-analytical finite element (FE) method is mainly used, with three-dimensional FE simulations for visualization and cross-validation of results. The studies reveal that even a small degree of ovalness can affect mode shapes and velocities. The effect is more pronounced on the L(0,2) mode than on T(0,1) and this may be important for practical inspection applications.
14 citations
TL;DR: The studies show that even a small eccentricity in the pipe can cause a loss in the L(0,2) mode axisymmetry, leading to its confinement in the thinned side of the pipe cross-section and also a reduction in mode velocities.
Abstract: This paper studies the effect of axially uniform eccentricity on the modal structures and velocities of the lower order axisymmetric guided wave mode L(0,2) in circular tubes or pipes. The semi-analytical finite element method is mainly used, supported by fully three-dimensional finite element models and validated using experiments. The studies show that even a small eccentricity in the pipe can cause a loss in the L(0,2) mode axisymmetry, leading to its confinement in the thinned side of the pipe cross-section and also a reduction in mode velocities. The physics of this phenomenon is related to the feature-guiding and mode confinement effects noted in recent years in the literature, particularly studies on waveguides with local cross-section variations and curvature.
13 citations
TL;DR: In this paper, it was shown that in a bar with an equilateral triangular cross-section longitudinal, torsional, and bending modes of wave propagation are possible, and the first few branches of the dispersion curves for each of these modes were calculated using the collocation method.
8 citations