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. © 2016 Acoustical Society of America.

Prabhu Rajagopal

Department of Mechanical Engineering

Krishnan Balasubramaniam

Prabhakaran Manogharan

Fillers

Guided electromagnetic wave propagation

STRINGERS

Ultrasonic applications

COMPOSITE JOINT

ENERGY CONCENTRATION

GUIDING EFFECT

LOW DISPERSIONS

RAPID SCREENING

SEMI-ANALYTICAL FINITE ELEMENT

Three dimensional finite element model

ultrasonic guided wave

finite element method

IIT Madras is a public technical and research university located in Chennai, Tamil Nadu. Founded in 1959, it is recognised as an Institute of National Importance.

IIT Madras has been ranked as the top engineering institute in India for four years in a row by the National Institutional Ranking Framework of the MHRD

It currently offers undergraduate, postgraduate and research degrees across 16 disciplines in Engineering, Sciences, Humanities and Management. About 596 faculty belonging to science and engineering departments and centres of the Institute are engaged in teaching, research and industrial consultancy.

IIT Madras

Longitudinal guided waves confined in radius filler regions of composite joints.

Journal of the Acoustical Society of America

This article demonstrates a rapid, fully non-contact inspection technique for a full-scale complex composite structural component using air-coupled ultrasonic guided waves. The presence of different features such as stiffeners, stringers and geometric variations in skin-stiffened structures makes the received guided wave signal cumbersome and difficult to interpret. Experiments, supported by three-dimensional finite element models, are used to demonstrate the physics of guided wave interaction with complex features and defect configurations. B-scans are used to detect geometric variations in skin, and also disbonds in the skin-stiffener interface. Correlation between the numerically simulated and experimentally obtained B-scans is established. Different regions in the B-scan images could be used to locate and identify the defects and geometric variations in the test sample. The size of the disbond can also be computed from the B-scan. © 2018 Elsevier Ltd

Composite Structures

Rapid guided wave inspection of complex stiffened composite structural components using non-contact air-coupled ultrasound

Numerical models based on the Semi Analytical Finite-Element method are used to study the characteristics of guided wave modes supported by bone-like multi-layered tubular structures. The method is first validated using previous literature and experimental studies on phantoms mimicking healthy and osteoporotic conditions of cortical bone, and later used to study a trilayer marrow–bone–tissue system at varying mechanical degradation levels. The results show that bone condition strongly affects the modal properties of axially propagating guided waves and indicates that L(0,3) and F(1,6) are suitable modes for assessing the mechanical condition of the bone. The work here reports suitable modal selection and their dispersion properties which would the aid in development of a transduction mechanism for mechanical assessment of bones. © 2017 The Author(s).

Fulltext

International Biomechanics

Semi-analytical finite-element modeling approach for guided wave assessment of mechanical degradation in bones

This paper reports the experimental demonstration of deep subwavelength ultrasonic imaging of defects in metallic samples with a feature size of λ/25 using holey-structured metamaterial lenses. Optimal dimensions of the metamaterial’s geometric parameters are determined using numerical simulation and the physics of wave propagation through holey lenses. The paper also shows how the extraordinary transmission capacity of holey structured metamaterials comes about by the coupling of higher frequencies in the incident ultrasonic wave field to resonant modes of the lens. © 2017, The Author(s).

Scientific Reports

Deep subwavelength ultrasonic imaging using optimized holey structured metamaterials

Antisymmetric and symmetric Lamb-type feature guided waves (FGW) have recently been shown to exist in small angle plate bends. This paper reports Semi-Analytical Finite Element (SAFE) method simulations revealing the existence of a new family of Shear Horizontal (SHB) type of FGW mode in 90° bends in plate structures. Mode shapes and velocity dispersion curves are extracted, demonstrating the SH-like nature of a bend-confined mode identified in studies of power flow across the bend. The SHB mode is shown to have reduced attenuation in the higher frequency range, making it an ideal choice for high-resolution inspection of such bends. Further modal studies examine the physical basis for mode confinement, and argue that this is strongly related to FGW phenomena reported earlier, and also linked to the curvature at the bend region. Wedge acoustic waves discussed widely in literature are shown as arising from surface-limiting of the SHB mode at higher frequencies. The results are validated by experiments and supported by 3D Finite Element (FE) simulations. © 2015 Elsevier B.V. All rights reserved.

Ultrasonics

Shear horizontal feature guided ultrasonic waves in plate structures with 90° transverse bends

The authors have recently reported on the attractive properties of shear-horizontal type feature guided (SHB) waves for the inspection of 90° plate bends. Further to this, here the interaction of the SHB mode with transverse and longitudinal defects in the bend region is studied using 3D finite element simulations validated by experiments. Trends are discussed in light of the underlying wave mechanics principles. The results show that the SHB mode yields improved through-thickness defect resolution capabilities as compared to regular plate guided SH waves in view of mode confinement and higher frequencies used. © 2015 Elsevier Ltd. Allrightsreserved.

NDT and E International

Interaction of shear horizontal bend (SHB) guided mode with defects

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. © 2015 Acoustical Society of America.

Low frequency axisymmetric longitudinal guided waves in eccentric annular cylinders

Recent research by the authors shows that bends in plates can act as features that can concentrate and guide ultrasonic energy along their axis. At low frequencies, two feature-guided modes are identified when the bent plate is subjected to 'in-plane' or axial excitation applied uniformly along a through-thickness line bisecting the bent edge. Of these, the slower mode has properties similar to the A0 (fundamental antisymmetric) Lamb mode in flat plates. This paper focuses on the faster bend-guided mode that is similar to the S0 (fundamental symmetric) Lamb mode in flat plates. Using 3D finite element (FE) simulation validated with experiments, this mode is shown to be more strongly generated in smaller angle bends. Features of the mode including velocity, attenuation and modal structure are considered in detailed studies. Results are discussed in light of simple modal studies using the Semi Analytical Finite Element (SAFE) method, suggesting a relationship of bend-guided waves to modes of curved bars. © 2014 Elsevier B.V. All rights reserved.

Symmetric low-frequency feature-guided ultrasonic waves in thin plates with transverse bends

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. © 2015 Acoustical Society of America.

Journal	Journal of the Acoustical Society of America
Publisher	Acoustical Society of America
ISSN	00014966
Open Access	No