<title>Composite materials stiffness determination and defects characterization using enhanced leaky Lamb wave dispersion data acquisition method</title>

Abstract

The leaky Lamb wave (LLW) technique is approaching a maturity level that is making it an attractive quantitative NDE tool for composites and bonded joints. Since it was first observed in 1982, the phenomenon has been studied extensively, particularly in composite materials. The wave is induced by oblique insonification using a pitch-catch arrangement and the plate wave modes are detected by identifying minima in the reflected spectra to obtain the dispersion data. The wave behavior in multi-orientation laminates has been well documented and corroborated experimentally with high accuracy. The sensitivity of the wave to the elastic constants of the material and to the boundary conditions led to the capability to measure the elastic properties of bonded joints. Recently, the authors significantly enhanced the LLW method's capability by increasing the speed of the data acquisition, the number of modes that can be identified and the accuracy of the data inversion. In spite of the theoretical and experimental progress, methods that employ oblique insonification of composites are still not being applied as standard industrial NDE methods. The authors investigated the issues that are hampering the transition ofthe LLW to industrial applications and identified 4 key issues. The current capability of the method and the nature of these issues are described in this paper.

Lamb Waves-based Impact Damage Monitoring of a Stiffened Aircraft Panel using Piezoelectric Transducers

“…However, the intensive use of these kinds of materials as primary structures remains limited, in particular in the field of civil aviation, because the presence of internal defects can severely degrade their mechanical properties. The second limitation to widespread use of composite materials is their cost, which is more than their metallic equivalents, and the cost of inspections, which accounts for %30% of the total investment for a carbon fiber reinforced plastic (CFRP) structure (Bar-Cohen et al, 1999). Hence, the aptitude to quickly evaluate the health of a structure becomes an economic objective of first importance.…”

An Optimisation Scheme Based on the Local Interaction Simulation Approach and Lamb Waves for Elastic Property Estimation in Multi-Layered Composites

“…7 shows very clearly that the propagation is by guided waves and the results of the inversion show that the increased complexity of the propagation allows the waveform to carry enough information to fix the material properties. The exception to latter statement is the overall density of the plate, although the density ratio between the two materials was estimated accurately; density has always presented problems [15], and the matter will clearly bear further thought. In terms of the optimisation strategy, the dynamic time warping approach applied here appears to be necessary in order for the optimisation scheme to effectively avoid local minima.…”

“…perimental data in aluminium plates is given in the recent work [14]. The idea of inversion based on dispersion curves was exploited in a considerable body of work in the 1990s using measurements of leaky Lamb waves; the paper [15] marks an interesting point at which the technology was starting to make the transition to established procedure. A blind inversion scheme utilising fundamental Lamb wave mode velocities and a genetic algorithm has also been used to estimate material properties in a quasi-isotropic graphite-epoxy composite plate [16].…”

Evaluation of effect changing temperature on lamb-wave based structural health monitoring

“…Conditions sustaining such as; high loads, fatigue cycles and extreme temperature differentials can cause defect in aircraft structures. Inspection of aircraft, play a very important role in aviation safety [1][2][3]. Non-destructive testing (NDT) methods are used to ensure the safe operation of aircraft structures.…”