CLoVER: an alterntive concept for damage interrogation in structural health monitoring systems

Abstract

NOMENCLATUREb substrate half-thickness c j complex Fourier coefficients of shear tractions c g group velocity C capacitance d ij piezoelectric coupling coefficient (i, j = 1,2,3) D dispersion equation for Rayleigh-Lamb waves H k(2) hankel function of the second kind and order k i I electric current J m bessel function of the first kind and order m L rectangular actuator dimension n number of half-cycles in toneburst signal p capacitance function r radial position R radius R I transducer inner radius R O transducer outer radius s(t) toneburst signal S(ω) fourier transform of toneburst signal t time t thickness T substrate-actuator thickness ratio T period u(.) unit step function u displacement vector V voltage x, y cartesian co-ordinates Γ coefficient matrix used in theoretical solution δ(.) dirac delta function ABSTRACT Structural Health Monitoring (SHM) is the component of damage prognosis systems responsible for interrogating a structure to detect, locate, and identify any damage present. Guided wave (GW) testing methods are attractive for this application due to the GW ability to travel over long distances with little attenuation and their sensitivity to different damage types. The Composite Long-range Variable-direction Emitting Radar (CLoVER) transducer is introduced as an alternative concept for efficient damage interrogation in GW SHM systems. This transducer has an overall ring geometry, but is composed of individual wedge-shaped anisotropic piezocomposite sectors that can be individually excited to interrogate the structure in a particular direction. The transducer is shown to produce actuation amplitudes larger than those of a similarly sized ring configuration for the same electric current input. The electrode pattern design used allows each sector to act as an independent actuator and sensor element, decreasing the number of separate transducers needed for inspection. The fabrication and characterisation procedures of these transducers are described, and their performance is shown to be similar to that of conventional piezocomposite transducers. Experimental studies of damage detection demonstrating the proposed interrogation approach are also presented for simulated structural defects.

Guided wave structural health monitoring using CLoVER transducers in composite materials

“…The CLoVER transducer has been introduced by the authors [23][24][25][26] as an alternative concept for damage interrogation in GW-based SHM systems. The device is composed of independent anisotropic piezocomposite sectors that induce directional GW fields on the surface where they are bonded.…”

Guided Wave Structural Health Monitoring Using CLoVER Transducers in Composite Plates

“…The CLoVER transducer has been introduced by the authors 11,13,14,21 as an alternative concept for damage interrogation in GW-based SHM systems. The device is composed of independent anisotropic piezocomposite sectors that induce directional GW fields on the surface where they are bonded.…”

“…The CLoVER transducers used in this study were fabricated in-house following the manufacturing procedure presented earlier by the authors. 11,13 Two different electrode designs were employed, which will be referred to as CLoVER 1 and CLoVER 2 and are illustrated in Fig. 8.…”

“…These angles were chosen so that the width of the fibers at the inner radius position is similar to that used in the prismatic rectangular fibers used in conventional piezoceramic devices. 13,22 The cure of the device was conducted following a procedure similar to the one described previously by the authors. 11,13 The poling of the finalized transducers was conducted at a temperature of 50 • C and an electric field of 2.92 kV/mm for 30 minutes.…”

“…The directionality of these transducers and their effectiveness in damage detection has been previously shown in metallic structures. [11][12][13][14] The paper begins with a brief review of the theory of GW in composite materials, to illustrate how the changing elastic properties introduce a directional dependence on the wave propagation parameters. The GW field excited by circular piezoelectric wafers is then analyzed through laser vibrometry and finite element simulations to provide a baseline for comparison with the CLoVER transducers.…”