Aerospace & Automotive industries make extensive use of composite structures, often with complex geometries. Ultrasonic guided waves are attractive for long-range inspection of large-scale structures. However surface based transducers that are typically used, lead to two-dimensional wave propagation, limiting the applicability of guided wave methods. This work explores the use of embedded waveguides for monitoring delamination type defects in composites. These waveguides confine the wave transmission in one dimension and waves leak only through the opening provided, which enhances the capability to inspect large composite structures with very low attenuation rate. Inaccessible areas can be inspected and inter-laminar delamination detection can be achieved. Live monitoring and assessment of discontinuities can be accomplished effectively by using this mechanism. © 2017 Author(s).

Prabhu Rajagopal

Department of Mechanical Engineering

Krishnan Balasubramaniam

Harsh Shah

Fulltext

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

Guided waves for online monitoring of composites

AIP Conference Proceedings

Ultrasonic guided waves based non-destructive testing (NDT) is attractive due to its potential for long range inspection. In NDT, fiber Bragg gratings (FBG) sensor is widely adopted due to its rugged wavelength encoded information and immunity to electromagnetic interference (EMI). In this paper we discuss the reception of ultrasonic guided waves in a glass fiber reinforced plastic (GFRP) composite plate using a surface bonded FBG sensor. Experimentally deduced values for wave velocity and attenuation are compared with the theoretical values. © 2018 IEEE.

Proceedings of IEEE Sensors

Detection of Guided Waves in a Composite Plate Using Surface Bonded Fiber Bragg Gratings Sensor

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.

Ultrasonics

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

The influence of bends constituting annular polygonal structures on ultrasonic guided waves propagating along their axis is investigated. Considering a single bend as a bent plate connects this problem to the better-understood physics of guided waves in straight plates. Using a three-dimensional finite element simulation validated with experiments, bends in plates are shown to act as features that can concentrate and guide ultrasonic energy along their length. Two interesting 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 faster traveling mode has properties similar to, but travels at group velocities lower than, the S0 (fundamental symmetric) Lamb mode in flat plates. This paper however focuses on the slower bend-guided mode that is similar to the A0 (fundamental anti-symmetric) Lamb mode in flat plates. This mode is shown to be more strongly generated in smaller angle bends where it has a low attenuation. The results are discussed in light of simple modal studies performed using the Semi-Analytical Finite Element method. © 2013 Acoustical Society of America.

Journal of the Acoustical Society of America

Antisymmetric feature-guided ultrasonic waves in thin plates with small radius transverse bends from low-frequency symmetric axial excitation

Structural health monitoring (SHM) of plate-like structures used in aerospace industries, using transducer arrays located suitably on the structure, such as the single-transmitter multiple-receiver (STMR) array [Wilcox PD, Lowe M, Cawley P. Lamb and SH wave transducer arrays for the inspection of large areas of thick plates. Review of progress in quantitative nondestructive evaluation, vol. 19A. Melville, NY, USA: American Institute of Physics; 1999. p. 1049-56; Wilcox PD. Guided wave beam steering from omni-directional transducer arrays. Review of progress in quantitative nondestructive evaluation, vol. 22A. Melville, New York, USA: American Institute of Physics; 2002. p. 761-8], has been demonstrated here. The reconstruction of the material state was carried out by utilizing a phased addition reconstruction algorithm. In addition to the signals from damage sites, the ultrasonic guided wave-based reconstruction procedures also need the complete set of elastic moduli as a continuous input throughout the SHM process. In the present study, two flexible printed circuit board (PCB)-based patches: ((i). single-quadrant, double-ring STMR material characterization (MC) array and (ii). Full-ring STMR SHM array) were developed for accomplishing both objectives, i.e. (a) online MC and (b) SHM of anisotropic plate-like structures, respectively. Experiments were conducted on 3.15 mm graphite-epoxy composite plate using PCB-based STMR arrays, the feasibility of accomplishing both objectives was demonstrated. © 2008 Elsevier Ltd. All rights reserved.

NDT and E International

Structural health monitoring of anisotropic plates using ultrasonic guided wave STMR array patches

A new compact sensor configuration comprising a single transmitter and multi-receivers (STMR) is presented for the in situ structural health monitoring (SHM) of large plate-like isotropic structures. The STMR exploits the long-range propagation characteristics of ultrasonic guided Lamb waves and a phase reconstruction algorithm to provide defect detection and location capability under non-dispersive as well as dispersive regimes of guided waves. Simulations are performed on defect-free and defective finite plates of aluminum to demonstrate the various features of the STMR system. Experiments were carried out on 1mm thick aluminum plates initially using a pair of individual sensors and subsequently using a prototype STMR array. The simulated results of the STMR performance were validated well through these experiments. Features of the STMR system such as its small footprint, the relatively simple data acquisition and processing discussed here have applications in the SHM of plate-like structures, and particularly of aerospace structures. © 2006 IOP Publishing Ltd.

Smart Materials and Structures

A single transmitter multi-receiver (STMR) PZT array for guided ultrasonic wave based structural health monitoring of large isotropic plate structures

The paper provides a state of the art review of guided wave based structural health monitoring (SHM). First, the fundamental concepts of guided wave propagation and its implementation for SHM is explained. Following sections present the different modeling schemes adopted, developments in the area of transducers for generation, and sensing of wave, signal processing and imaging technique, statistical and machine learning schemes for feature extraction. Next, a section is presented on the recent advancements in nonlinear guided wave for SHM. This is followed by section on Rayleigh and SH waves. Next is a section on real-life implementation of guided wave for industrial problems. The paper, though briefly talks about the early development for completeness, is primarily focussed on the recent progress made in the last decade. The paper ends by discussing and highlighting the future directions and open areas of research in guided wave based SHM. © 2016 IOP Publishing Ltd.

Journal	Data powered by TypesetAIP Conference Proceedings
Publisher	Data powered by TypesetAmerican Institute of Physics Inc.
ISSN	0094243X
Open Access	Yes