The S0 Lamb mode can propagate over distances of the order of 1 m in composite laminates and so has the potential to be used in long‐range nondestructive inspection. This paper discusses the interaction of the S0 Lamb mode with delaminations. The dispersion curves and the corresponding stress and displacement mode shapes of the lower order Lamb modes are obtained analytically and the interaction of the S0 mode with delaminations at different interfaces in a composite laminate is then studied both by finite element analysis and by experiment. It is shown that the amplitude of the reflection of the S0 mode from a delamination is strongly dependent on the position of the delamination through the thickness of the laminate and that the delamination locations corresponding to the maximum and minimum reflectivity correspond to the locations of maximum and minimum shear stress across the interface in the S0 mode.

The interaction of Lamb waves with delaminations in composite laminates

It is imperative to study the damage detection methods of steel truss structures that are always employed in extreme environment. Accurate structural damage localization is still a challenge due to...

An algorithm for damage localization in steel truss structures: Numerical simulation and experimental validation:

Structural Health Monitoring (SHM) of aerospace structures has received significant interest as a core component of Condition Based Maintenance (CBM). An Acousto-Ultrasonic method based on high frequency structural vibrations using piezoelectric transducers has been developed to perform damage detection on metallic and composite aerospace structures. Tests were performed on laboratory specimens to evaluate the sensitivity of crack detection and ballistic damage using this method. The Bell 407 tail boom structure was chosen to demonstrate the capability a system, designed to employ the developed method, to detect common structural damage related to fatigue cracking and battle damage.

Structural Health Monitoring for Bell 407 Tail Boom

Flexible ultrasonic transducers (FUTs) which have the on-site installation capability are presented for the non-destructive
evaluation (NDE) and structural health monitoring (SHM) purposes. These FUTs consist of 75 μm thick titanium membrane, thick (> 70 μm) thick piezoelectric lead-zirconate-titanate (PZT) composite (PZT-c) films and thin (< 5 μm) thick top electrodes. The PZT-c films are made by a sol-gel spray technique. Such FUT has been glued onto a steel pipe of 101 mm in diameter and 4.5 mm in wall thickness and operated up to 200°C. The glue served as high temperature
ultrasonic couplant between the FUT and the external surface of the pipe. The estimated pipe thickness measurement accuracy at 200°C is 34 μm. FUTs also were glued onto the end edge of 2 mm thick aluminum (Al) plates to generate
and receive predominantly symmetrical and shear-horizontal (SH) plate acoustic waves (PAWs) to detect simulated line defects at temperature up to 100°C. FUTs glued onto a graphite/epoxy (Gr/Ep) composite are also used for the detection of artificial disbonds. An induction type non-contact method for the evaluation of Al plates and Gr/Ep composites using FUTs is also demonstrated.

/pdf/flexible-ultrasonic-transducers-for-structural-health-3qb8y2k8wy.pdf

Flexible ultrasonic transducers for structural health monitoring of metals and composites

Extensive studies have been conducted to examine the use of piezoelectric transducers and other ultrasonic devices for structural health monitoring applications due to their high electroacoustic efficiency and simple operation principles. Most studies use guided Lamb wave inspection methods to detect, locate, and characterize damage in relatively simple plate-like structures. These studies have proven that this type of technique is useful for structural health monitoring in the simple structures, but little work has shown feasibility when using more realistic test articles. In our study, we present a sparse array technique using multiple piezoelectric transducers mounted to an external composite panel on a legacy F/A-18 wing section to investigate its capabilities for more realistic structural health monitoring applications. The panel is secured to the wing by a series of bolts surrounding the panel, and as the main method of simulating damage to the wing, these bolts are loosened by a specified torque in several different cases. The guided Lamb wave pitch-catch inspection method is used to identify such simulated damage by comparing baseline and damaged trials using differential analysis and a spatial mapping approach. This approach requires an estimate of the Lamb wave mode group velocities in the composite panel along with the geometry of the transducer array and the transducers location metrics. Despite the complexities of using a realistic test article, the sparse piezoelectric array combined with the Lamb wave inspection method shows promise in its ability to accurately detect, locate, and characterize the simulated damage to the airframe.

Structural health monitoring of a composite F/A-18 wing section using a sparse piezoelectric transducer array

The study addresses experimental detection and quantitative interrogation of damage in a jointed composite structure. To construct a cohesive structural health monitoring system for the jointed composite panel, the wave propagation method was used with smart piezoelectric transducers for excitation and sensing. The smart sensor system was configured using four piezo patches located at the four quadrants of the composite panel, and provided multiple actuation/sensing scenarios to capture time and frequency response signals for a variety of bolt damage configurations. Signal information was compressed into non-dimensional damage indices at each excitation configuration. The collected information was used in a pattern recognition algorithm. Based on pattern recognition, a damage discriminator was generated which indicated location and amount of damage information automatically. Using simulated bolt torque loss damage on a jointed composite structure, the damage detection performance of the damage discriminator was evaluated.Copyright © 2008 by ASME

/pdf/experimental-detection-and-quantitative-interrogation-of-20yy9ec5dq.pdf

Experimental Detection and Quantitative Interrogation of Damage in a Jointed Composite Structure

This study addresses experimental detection and quantitative interrogation of damage in a jointed composite structure. To construct a cohesive structural health monitoring system for the jointed composite panel, the wave propagation method was used with smart piezoelectric transducers for excitation and sensing. The smart sensor system was configured using four piezo patches located at the four quadrants of the composite panel, and provided multiple actuation/sensing scenarios to capture time and frequency response signals for a variety of bolt damage configurations. Signal information was compressed into non-dimensional damage indices for each excitation configuration. The collected information was used in a pattern recognition algorithm. Based on pattern recognition, a damage discriminator was generated which indicated location and amount of damage information automatically. Using simulated bolt torque loss damage on the jointed composite structure, the damage detection performance of the damage discrim...

/pdf/experimental-detection-and-quantitative-interrogation-of-50kt9b60k3.pdf

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Experimental Detection and Quantitative Interrogation of Damage in a Jointed Composite Structure

Experimental Detection and Quantitative Interrogation of Damage in a Jointed Composite Structure