Mode-Selective Excitation and Detection of Ultrasonic Guided Waves for Delamination Detection in Laminated Aluminum Plates
ABSTRACT Selective modes of guided Lamb waves are generated in a laminated aluminum plate for damage detection using a broadband piezoelectric transducer structured with a rigid electrode. Appropriate excitation frequencies and modes for inspection are selected from theoretical and experimental dispersion curves. Dispersion curves are obtained experimentally by short time Fourier transform of the transient signals. Sensitivity of antisymmetric and symmetric modes for delamination detection are investigated. The antisymmetric mode is found to be more reliable for delamination detection. Unlike other studies, in which the attenuation of the propagating waves is related to the extent of the internal damage, in this investigation, the changes in the time-of-flight (TOF) of guided Lamb waves are related to the damage progression. The mode conversion phenomenon of Lamb waves during progressive delamination is investigated. Close matching between the theoretical and experimentally derived dispersion curves and TOF assures the reliability of the results presented here.
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ABSTRACT: This paper reviews the state-of-the-art in numerical wave propagation analysis. The main focus in that regard is on guided wave-based structural health monitoring (SHM) ap- plications. A brief introduction to SHM and SHM-related problems is given and various numerical methods are then discussed and assessed with respect to their capability of simulating guided wave propagation phenomena. A detailed evaluation of the following methods is compiled: (i) ana- lytical methods, (ii) semi-analytical methods, (iii) the lo- cal interaction simulation approach (LISA), (iv) finite ele- ment methods (FEMs) and (v) miscellaneous methods such as mass spring lattice models (MSLMs), boundary element methods (BEMs) and fictitious domain methods. In the framework of the FEM, both time and frequency domain ap- proaches are covered and the advantages of using high order shape functions are also examined.Applied Mechanics Reviews 01/2015; 67(1):1-20. DOI:10.1115/1.4029539 · 2.00 Impact Factor
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ABSTRACT: Investigations with the aid of longitudinal guided waves in cylindrical structures have been regularly carried out for nondestructive evaluation (NDE) and structural health monitoring (SHM). While earlier works concentrated on the amplitude reduction of the propagating waves due to structural anomalies in this work the change in time-of-flight is investigated. Longitudinal (axisymmetric) modes are excited by a PZT (Lead Zirconate Titanate) transducer for detection of any fluctuation or change in the surface of a steel pipe. Propagating waves are analyzed after proper signal processing. To observe the small change in TOF due to lamination on the surface of a steel pipe, cross-correlation technique is used to attain a higher temporal resolution. The experimental technique is discussed and the obtained results are presented in this paper.SPIE Smart Structures and Materials + Nondestructive Evaluation and Health Monitoring; 04/2013
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ABSTRACT: Damage monitoring under time-varying structural boundary condition is one of the most difficult tasks in piezoelectric transducers (PZTs) and Lamb wave based SHM methods for engineering applications. Because the structural boundary changes such as variations in the tightness of bolts between structures can lead to false monitoring result even the structure is in health state. This paper proposes a Lamb wave based on-line continuous updating Gaussian Mixture Model (GMM) to study the problem. Based on the baseline GMM constructed by features of Lamb wave signals in structural health state, an on-line continuous updating GMM is studied to learn the dynamic changes of Lamb wave monitoring signals without any prior knowledge of damage patterns. The Kullback–Leibler (KL) divergence is used as a degradation index to estimate the structural damage by measuring the difference between the baseline GMM and the on-line GMM. The proposed method is validated on an aircraft steel beam. The validation results show that the method is effective for bolt hole crack growth monitoring under the time-varying changes in the tightness degree of the bolts.EWSHM-7th European Workshop on Structural Health Monitoring; 07/2014