Cure monitoring through time–frequency analysis of guided ultrasonic waves

Pavlopoulou, S.; Soutis, C.; Staszewski, Wiesław J.

doi:10.1179/1743289811y.0000000052

Cited by 27 publications

(15 citation statements)

References 30 publications

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“…Moreover, a first observation is that as the cure level increases, the peak‐to‐peak amplitude of the IF increases. For the purpose of the current analysis, after the decomposition of the original time signals, the power spectrum of each corresponding IMF was plotted and the optimum one was selected according to how close its carrier peak was to the excitation frequency . The optimum IMF for all cure levels was IMF5, which was used for the subsequent analysis.…”

Section: Resultsmentioning

confidence: 99%

“…Many methods have been successfully used to monitor the cure level, either based on the cure temperature measurement or on the molecular level assessment. An extensive literature review as well as a preliminary assessment of this approach can be found in literature . Damage detection on the other hand refers to the monitoring of the repair integrity for the estimation of flaws or damage of critical size.…”

Section: Introductionmentioning

confidence: 99%

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Evaluation of instantaneous characteristics of guided ultrasonic waves for structural quality and health monitoring

Pavlopoulou

Staszewski

Soutis

2012

Struct. Control Health Monit.

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The analysis and extraction of the appropriate signal's features in structural health monitoring applications is one of the major challenges on which the robustness of the designed systems relies. Many strategies have been developed in the past, which utilise the identification of amplitude-based parameters for the evaluation of structural integrity. However, these parameters usually require a baseline reference, which might be extensively affected by noise, environmental or mounting conditions. This paper illustrates the applicability of Hilbert transform and Hilbert-Huang transform on the postprocessing of guided ultrasonic waves for evaluating the condition of relatively complex structural health monitoring applications. Two case studies are presented to demonstrate the suitability of the techniques, namely, the damage monitoring of an aluminium repaired panel and the cure level monitoring of symmetric carbon fibre-epoxy composite laminates. In the first case study, the technique exhibits sensitivity in propagation paths within damaged areas and shows good agreement with the developed damage, enabling the identification of critical areas. In the second study, the technique demonstrates a significant advantage over the traditionally adopted approaches and predicts accurately the cure level of the polymeric composite system. Inspection with guided ultrasonic waves is a wave-propagation-based method, which has lately attracted the attention of the scientific community, offering various industrial applications in monitoring pipes, pipelines and rails [7]. Guided waves propagate in a bounded media, which interacts with the boundaries of the structure and propagate through its thickness in two possible modes; symmetric (S n ) and antisymmetric (A n ). The mathematical equations that describe their behaviour are the same with bulky waves. The only difference is that, in the case of guided waves, the equations should satisfy the boundary conditions. The most widely used technique for health monitoring is inspection with Lamb waves. Lamb waves are elastic perturbations that occur in solid plates with free boundaries. Those perturbations are a combination of displacements that occur both in the direction of wave propagation and perpendicularly to the plane of the plate [8]. Lamb waves have been extensively used for health monitoring of advanced, complex structures. The scope of the current investigation concentrates on aspects of Lamb wave's application for health monitoring of two case studies, the first on damage monitoring of bonded patch repairs and the second on monitoring the cure process of a composite laminate.Adhesively bonded repair patches have lately received a considerable amount of interest for their potential repair applications for temporary (emergency or field) solutions to structural damage. In the aerospace industry, the interest in bonded patches emerges from the need to increase the operational life of ageing aircrafts. Such aircrafts are estimated to be approximately 30% of the worldwide fleet [9]....

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Section: Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Evaluation of instantaneous characteristics of guided ultrasonic waves for structural quality and health monitoring

Pavlopoulou

Staszewski

Soutis

2012

Struct. Control Health Monit.

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“…Bulk wave contact ultrasound, usually conducted in pulse-echo mode in the low megahertz frequency range, can monitor the completion of resin cure based on when the time delay plateaus/ultrasonic velocity becomes constant value in graphite/epoxy composites [8] and epoxy resins [9]. Other ultrasonic phenomena have also been used for monitoring degree of cure including, attenuation (i.e., amplitude of signal) [7,8,[10][11][12][13], instantaneous phase, and the "mean value of each frequency curve weighted by the maximum corresponding spectral amplitude" [14].…”

Section: Introductionmentioning

confidence: 99%

Automated In-Process Cure Monitoring of Composite Laminates Using a Guided Wave-Based System With High-Temperature Piezoelectric Transducers

Hudson

Fang

2018

Journal of Nondestructive Evaluation, Diagnostics and Prognostics of Engineering Systems

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An in-process cure monitoring technique based on “guided wave” concept for carbon fiber reinforced polymer (CFRP) composites was developed. Key parameters including physical properties (viscosity and degree of cure) and state transitions (gelation and vitrification) during the cure cycle were clearly identified experimentally from the amplitude and group velocity of guided waves, validated via the semi-empirical cure process modeling software RAVEN. Using the newly developed cure monitoring system, an array of high-temperature piezoelectric transducers acting as an actuator and sensors were employed to excite and sense guided wave signals, in terms of voltage, through unidirectional composite panels fabricated from Hexcel® IM7/8552 prepreg during cure in an oven. Average normalized peak voltage, which pertains to the wave amplitude, was selected as a metric to describe the guided waves phenomena throughout the entire cure cycle. During the transition from rubbery to glassy state, the group velocity of the guided waves was investigated for connection with degree of cure, Tg, and mechanical properties. This work demonstrated the feasibility of in-process cure monitoring and continued progress toward a closed-loop process control to maximize composite part quality and consistency.

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“…A widely used and accepted technology in the structural health monitoring (SHM) of thin‐walled structures is to deploy the propagation of guided elastic waves for damage detection purposes . Named after their discoverer, Horace Lamb , they refer to elastic perturbations propagating in plate‐like structures.…”

Section: Introductionmentioning

confidence: 99%

Numerical analysis of Lamb waves using the finite and spectral cell methods

Duczek

Joulaian

Düster

et al. 2014

Int. J. Numer. Meth. Engng

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SUMMARYAn accurate and efficient simulation of wave propagation phenomena plays an important role in different engineering disciplines. In structural health monitoring, for example, ultrasonic guided waves are used to detect and localize damage and to assess the structural integrity of the component part under consideration. Because of the complexity of real structures, the numerical simulation of structural health monitoring systems is a computationally demanding task. Therefore, to facilitate the analysis of wave propagation phenomena, the authors propose to combine the finite cell method with the spectral element method. The ensuing novel method is referred to as the spectral cell method. Because it does not rely on body‐fitted meshes, the resulting approach eliminates all discretization difficulties encountered in conventional finite element methods. Moreover, with the aid of mass lumping, it paves the way for the use of explicit time‐integration algorithms. In the first part of the paper, we show that using a lumped mass matrix instead of the consistent one has no detrimental effect on the accuracy of the spectral element method. We introduce the spectral cell method in the second part, showing that, when applied to wave propagation analysis, the spectral cell method yields results comparable with other standard higher order finite element approaches.Copyright © 2014 John Wiley & Sons, Ltd.

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Cure monitoring through time–frequency analysis of guided ultrasonic waves

Cited by 27 publications

References 30 publications

Evaluation of instantaneous characteristics of guided ultrasonic waves for structural quality and health monitoring

Evaluation of instantaneous characteristics of guided ultrasonic waves for structural quality and health monitoring

Automated In-Process Cure Monitoring of Composite Laminates Using a Guided Wave-Based System With High-Temperature Piezoelectric Transducers

Numerical analysis of Lamb waves using the finite and spectral cell methods

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