Damage Detection In Composite Laminates Research Articles

A refined Lamb wave reciprocity-based method with enhanced sensitivity for damage detection in composite laminates

The Lamb wave reciprocity-based method is an effective candidate for the health monitoring of composite plates. However, if the damage is located symmetrically between the transmitter–receiver pair, the reciprocity still holds true and the method misjudges its presence. In the present work, a new method for computing the reciprocity index (RI) from Lamb wave signals with extended data length is proposed. This method exploits extra indirect waves that bounce one or more times between the damage and other reflectors. These waves probe the damage through different paths and from different directions. Thus, the damage missed by the direct wave may be exposed by the indirect waves. Benefiting from that, two modified RIs are defined and their performance is validated by two experimental examples. As expected, both indices demonstrate excellent sensitivity to damage even in the middle of the transmitter–receiver pair and ensure a low threshold for the pristine condition, illustrating an excellent ability to distinguish between health and illness.

Damage detection in composite laminates using nonlinear guided wave mixing

This paper presents a delamination damage detection technique based on the nonlinear response of Lamb waves in composite laminates. In the approach, a network of transducers is employed to sequentially scan the structure by actuating and receiving dual guided waves. Using combined frequency waves originated due to contact nonlinearity when the incident dual frequency wave interacts with the damage, a damage localization imaging algorithm is proposed to locate the damage and determine the damage location. The proposed damage localization imaging algorithm is based on analysing the cross-correlation of the signal envelope at combined frequency wave with the excitation pulse envelope at incident waves for each transducer pair, the damage localization image is constructed. A numerical study using an experimentally validated finite element model is used to verify the proposed damage detection technique. The results of the numerical study show that, despite the small amplitude of the nonlinear components, the proposed method can effectively predict the damage location, and it does not require baseline measurements, which makes it potential to be a baseline-free damage detection technique.

Influence of Sensor Position and Low-Frequency Modal Shape on the Sensitivity of Vibro-Acoustic Modulation for Impact Damage Detection in Composite Materials

Very sensitive structural health monitoring methods are needed to detect barely visible impact damage in composite materials. Based on extracting non-linear modulated components from the frequency response of the damaged system, vibro-acoustic modulation (VAM) has shown to be effective in identifying the presence of damage at its early stage. A decisive role in the success of this technique is played by the choice of the high-frequency probe and the low-frequency pump sinusoidal signals that simultaneously excites the system. This study explores how the position of the sensing transducer, with respect to the modal shape of the pump excitation, may influence the sensitivity of the VAM technique for impact damage detection in composite laminates. This aspect has been scarcely investigated in previous research works, as other studies have focused more on the role of the probe frequency. Here, VAM tests were performed on a composite beam by using a frequency-swept pump vibration simultaneously with a high frequency probe excitation. The results of the experimental tests indicate that the VAM technique is capable of clearly revealing the presence of impact damage only when the sensor is placed on appropriate locations, which are directly related to the shape of the deformation activated by the applied excitation. These results suggest the adoption of low frequency excitations that activate multiple modal shapes to improve the effectiveness and reliability of VAM approaches.

Guided wave based localization and severity assessment of in-plane and out-of-plane fiber waviness in carbon fiber reinforced composites

Waviness is a common geometrical defect in carbon fiber reinforced plastics (CFRP) plates, characterized by local misalignment of an otherwise region of straight fibers. Presence of fiber waviness is a potential source of non-linearity and affects the relative strength of the composite structure. Recently, guided wave (GW) based in situ NDE techniques have been extensively used for damage detection in composite laminates, albeit for damages other than fiber waviness. This work pertains to the numerical investigation of fiber waviness interactions with S0 mode in a bonded composite structure (BCS) panel. The fiber waviness is modeled in curvilinear physics framework in a commercially available finite element (FE) solver, COMSOL Multiphysics. The change in group velocity due to waviness predicted by the FE model developed in this work agrees well with analytical calculations based on change in elastic modulus. This feature is used for localization of fiber waviness region within a network of PZT sensors by utilizing a recently developed damage index (DI) mapping algorithm. The efficacy of DI mapping is demonstrated using noise-augmented FE generated GW data set for a composite panel with a network of lead zirconate titanate (PZT) sensors, for in-plane and out-of-plane fiber waviness with varying severity factors.

Damage detection in Composite laminates by Fiber optic sensors

Fiber optic sensors, both FBG point sensors and distributed sensors based on OFDR, are accepted and validated as temperature and strain sensors, enjoy a high TRL and are already in use in many industrial applications. The determination of occurrence of damage from strain measures is a technique still not mature, its TRL can be 2-3. A local crack can greatly weaken a structure, it will be the point of initiation of the catastrophic failure, but until the failure has occurred, the crack only causes very small changes in the overall behavior of the structure (stiffness, natural frequencies, strain field, etc.). Therefore, and unless the position of the crack coincides with the predetermined position of the sensors, it is not easy to detect the existence of damage from strain measurements. In this work two parallel techniques, experimentally validated, are presented. The first one is to use distributed measurement, with an optical fiber placed in the area where the damage is expected. It is verified that a delamination causes residual strains in the delaminated area, of  significant value, and that will be detected by the fiber, if it crosses the delamination zone. The second technique is to compare the strains measurements obtained at different points, when the structure subjected to external loads. Although the changes are going to be very small, local damage causes a redistribution of the rigidity of the structure, and of the load paths, and therefore the strains readings, may be slightly different. Results of the application of the model are presented to actual composite elements, such as an isogrid structure, and a small wind turbine blade.

Enhanced wavefield imaging method for impact damage detection in composite laminates via laser-generated Lamb waves

Full wavefield processing techniques are promising for damage detection and imaging. However, the high measuring requirements in space are labor-consuming. To improve the imaging quality of wavefields with limited scanning points, 2D interpolation methods are investigated with simulating wavefields. To detect the defects, a damage index called first-to-residual energy ratio (FRER) is introduced with considering the amplitude signatures of the first arrived Lamb waves and the residual wave components. It shows a remarkable sensitivity to the barely visible impact damage (BVID). Besides, to further improve the damage imaging resolution, a data fusion technique is employed by multiplying the sub-frequency features extracted from the broadband Lamb waves. Hence, the implicit information of broadband Lamb waves can be efficiently used. Finally, an experimental investigation was carried out on a T300 composite laminate with artificial impact damage. The results verified the efficiency of the proposed method.

An Efficient Time Reversal Method for Lamb Wave-Based Baseline-Free Damage Detection in Composite Laminates

Time reversal (TR) concept is widely used for Lamb wave-based damage detection. However, the time reversal process (TRP) faces the challenge that it requires two actuating-sensing steps and requires the extraction of re-emitted and reconstructed waveforms. In this study, the effects of the two extracted components on the performance of TRP are studied experimentally. The results show that the two time intervals, in which the waveforms are extracted, have great influence on the accuracy of damage detection of the time reversal method (TRM). What is more, it requires a large number of experiments to determine these two time intervals. Therefore, this paper proposed an efficient time reversal method (ETRM). Firstly, a broadband excitation is applied to obtain response at a wide range of frequencies, and ridge reconstruction based on inverse short-time Fourier transform is applied to extract desired mode components from the broadband response. Subsequently, deconvolution is used to extract narrow-band reconstructed signal. In this method, the reconstructed signal can be easily obtained without determining the two time intervals. Besides, the reconstructed signals related to a series of different excitations could be obtained through only one actuating-sensing step. Finally, the effectiveness of the ETRM for damage detection in composite laminates is verified through experiments.

Analysis of elastic nonlinearity for impact damage detection in composite laminates

This paper concerns the experimental analysis of nonlinear response features of a composite laminate plate for impact damage detection. The measurement procedure is based on the Scaling Subtraction Method (SSM) and consists in exciting the damaged specimen with two sinusoidal signals at different amplitude. The linearly rescaled response signal at low amplitude excitation is subtracted from the response at large amplitude excitation to extract the nonlinear signatures. The latter are analysed in the time domain to infer the presence of damage. Results are compared with frequency domain analyses using the nonlinear vibro-acoustic modulation technique (NWMS). Changes in amplitude and phase as well as modulation effects of the acquired responses are also monitored. Surface-bonded, low profile piezoceramic transducers are used for excitation and sensing. Both measurements techniques are applied to detect barely visible impact damage in laminate composite plate. Non-destructive penetrant-enhanced X-ray inspections are carried out to characterize the extent of internal damage. The behavior of the nonlinear features and the sensitivity of each technique are also investigated in the paper.

Sensor requirements for in situ imaging of multiple damage by Lamb waves

Lamb waves are guided waves that propagate in plate-like structures. These waves are well suited for wide-area inspection, such as aircraft wing skins, because of their relatively slow geometrical decay with propagation distance. Recently, a computationally efficient algorithm for in situ imaging was derived based on the multi-static data matrix. Here, previous work on imaging a single circular inhomogeneity is extended to the case of structural damage spread over two distinct sites. Detailed results are presented for the rank and bandwidth of the data matrix, showing the dependence on the overall size of the damage cluster. The implications of these results for the practically important problem of determining minimum sensor requirements for image reconstruction are discussed. References C. T. Ng and M. Veidt. A Lamb-wave-based technique for damage detection in composite laminates. Smart Mater. Struct. , 18(7):074006, 2009. doi:10.1088/0964-1726/18/7/074006 J. E. Michaels and T. E. Michaels. Guided wave signal processing and image fusion for in situ damage localization in plates. Wave Motion , 44(6):482–192, 2007. doi:10.1016/j.wavemoti.2007.02.008 J. S. Hall and J. E. Michaels. Multi-path guided wave imaging for in situ monitoring of complex structures. AIP Conf. Proc. 1511:707-713, 2013. doi:10.1063/1.4789115 Z. Q. Su, L. Cheng, X. M. Wang and L. Yu. Diagnostic imaging for structural damage. Adv. Mater. Res. , 47–50:1157–1160, 2008. doi:10.4028/www.scientific.net/AMR.47-50.1157 L. R. F. Rose and C. H. Wang. Mindlin plate theory for damage detection: Source solutions. J. Acoust. Soc. Am. , 116(1):154–171, 2004. doi:10.1121/1.1739482 L. R. F. Rose and C. H. Wang. Mindlin plate theory for damage detection: Imaging of flexural inhomogeneities. J. Acoust. Soc. Am. , 127(2):754–763, 2010. doi:10.1121/1.3277217 C. H. Wang and L. R. F. Rose. Imaging damage using Mixed Passive and Active Sensors. 4th Asia-Pacific Workshop on Structural Health Monitoring, 2012 , Melbourne, Australia. C. H. Wang and L. R. F. Rose. Minimum Sensor Density for Quantitative Damage Imaging. 9th International Workshop on Structural Health Monitoring, 2013, Standford, USA . E. Chan, C. H. Wang and L. R. F. Rose. Characterisation of Part-through Damage in a Stiffened Panel by a Time-reversal Based Imaging Method. 9th International Workshop on Structural Health Monitoring, 2013, Standford, USA . Abaqus/Explicit 6.10 Dassault Systemes http://www.3ds.com/products-services/simulia/portfolio/abaqus/abaqus-portfolio/abaqusexplicit/

Impact damage detection in laminated composites by non-linear vibro-acoustic wave modulations

The paper presents an application of nonlinear acoustics for impact damage detection in composite laminates. Two composite plates were analysed. A low-velocity impact was used to damage one of the plates. Ultrasonic C-scan was applied to reveal the extent of barely visible impact damage. Finite element modelling was used to find vibration mode shapes of the plates and to estimate the local defect resonance frequency in the damaged plate. A delamination divergence study was performed to establish excitation parameters for nonlinear acoustics tests used for damage detection. Both composite plates were instrumented with surface-bonded, low-profile piezoceramic transducers that were used for the high-frequency ultrasonic excitation. Both an arbitrary frequency and a frequency corresponding to the local defect resonance were investigated. The low-frequency modal excitation was applied using an electromagnetic shaker. Scanning laser vibrometry was applied to acquire the vibro-acoustic responses from the plates. The study not only demonstrates that nonlinear vibro-acoustic modulations can successfully reveal the barely visible impact damage in composite plates, but also that the entire procedure can be enhanced when the ultrasonic excitation frequency corresponds to the resonant frequency of damage.

Damage detection in composite laminates aeronautics structures through accelerometers network

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Impact damage detection in composite laminates using nonlinear acoustics

The paper demonstrates the application of nonlinear acoustics for impact damage detection in composite laminates. A composite plate is monitored for damage resulting from a low-velocity impact. The plate is instrumented with bonded low-profile piezoceramic transducers. A high-frequency acoustic wave is introduced to one transducer and picked up by a different transducer. A low-frequency flexural modal excitation is introduced to the plate at the same time using an electromagnetic shaker. The damage induced by impact is exhibited in a power spectrum of the acoustic response by a pattern of sidebands around the main acoustic harmonic. The results show that the amplitude of sidebands is related to the severity of damage. The study investigates also the effect of boundary conditions on the results.

A Lamb-wave-based technique for damage detection in composite laminates

This paper presents the application of Lamb waves to inspect damage in compositelaminates. The proposed methodology employs a network of transducers that are used tosequentially scan the structure before and after the presence of damage by transmittingand receiving Lamb wave pulses. A damage localization image is reconstructed byanalyzing the cross-correlation of the scatter signal envelope with the excitation pulseenvelope for each transducer pair. A potential damage area is then reconstructed bysuperimposing the image observed from each actuator and sensor signal path. Bothnumerical and experimental case studies are used to verify the proposed methodology forcomposite laminates. Three-dimensional finite element models with a transducer networkconsisting of four transducer elements are used in the numerical case studies. Theexperimental case studies employ a transducer network using four piezoelectrictransducers as transmitter elements and a laser vibrometer to measure the responsesignals at four locations close to the transducers. The results show that the methodenables the reliable detection of structural damage with locating inaccuracies ofthe order of a few millimeters inside as well as outside of an inspection area of100 × 100 mm2.

Guided Wave and Damage Detection in Composite Laminates Using Different Fiber Optic Sensors

Guided wave detection using different fiber optic sensors and their applications in damage detection for composite laminates were systematically investigated and compared in this paper. Two types of fiber optic sensors, namely fiber Bragg gratings (FBG) and Doppler effect-based fiber optic (FOD) sensors, were addressed and guided wave detection systems were constructed for both types. Guided waves generated by a piezoelectric transducer were propagated through a quasi-isotropic carbon fiber reinforced plastic (CFRP) laminate and acquired by these fiber optic sensors. Characteristics of these fiber optic sensors in ultrasonic guided wave detection were systematically compared. Results demonstrated that both the FBG and FOD sensors can be applied in guided wave and damage detection for the CFRP laminates. The signal-to-noise ratio (SNR) of guided wave signal captured by an FOD sensor is relatively high in comparison with that of the FBG sensor because of their different physical principles in ultrasonic detection. Further, the FOD sensor is sensitive to the damage-induced fundamental shear horizontal (SH0) guided wave that, however, cannot be detected by using the FBG sensor, because the FOD sensor is omnidirectional in ultrasound detection and, in contrast, the FBG sensor is severely direction dependent.

Damage detection in composite laminates using coin-tap method

The "coin-tap" test has the ability to indicate damage in a composite structural element due to a localized change of stiffness. The change in vibration signature may be detected by ear or more precisely by measurement of the dynamic contact force. It has been shown that the characteristics of radiated sound from a structure during a tap are changed by the presence of defect beneath the surface of the composite structure. For structurally radiated noise, the sound field is directly coupled to the structural motion. Therefore, impact response analysis should be computed. In this study, the radiated sound induced by impact is obtained by solving the Rayleigh integral equation. Experimental results for the delaminated composite structure are presented and correlations between analytical predictions and measured data are shown. It is shown that the sound based tap test is useful and practical diagnostic tool for detecting localized delamination in composite laminates

Impact Damage Detection in Composite Laminates Using PVDF and PZT Sensor Signals

Low-velocity impact damage is a major concern in the design of structures made of composite materials, because impact damage is hidden and cannot be detected by visual inspection. Piezoelectric sensors can be used to detect variations in structural and material properties for structural health monitoring. In this study, polyvinylidene flouride (PVDF) and lead zirconate titanate (PZT) sensors are used for monitoring impact damage initiation and propagation in composite laminates to illustrate this potential benefit. Several tests for monitoring the stress wave signals including acoustic emission due to failure modes, such as matrix cracking, delamination, and fiber breakage are performed. A series of impact tests at various impact energies by changing the impact mass and height is performed on the instrumented drop weight impact tester. The wavelet transform (WT) and short time fourier transform (STFT) are used to decompose the piezoelectric sensor signals in this study. Test results show that the particular waveform of sensor signals implying the damage initiation and propagation are detected above the damage initiation impact energy. It is found that both PZT and PVDF sensors can be used to detect the impact damage.

Assessment of NDT interferometric techniques for impact damage detection in composite laminates

In this paper, the feasibility of using optical methods to detect impact damage in thin laminates is investigated and discussed. Specimens impacted with different energy levels were analysed by a holographic procedure and by an electronic speckle pattern interferometry technique; the results obtained with the two techniques were compared with those acquired by a pulse-echo full-volume ultrasonic technique. The investigation showed that both optical methods were able to identify the presence of impact damage, with an efficiency dependent on the through-thickness location of the delaminations produced by impact. The adoption of the ESPI technique allowed significant reductions in inspection times, but quantitative estimates of impact damage were drastically impaired by the high level of speckle noise typical of the technique.

Damage detection in composite laminates with built-in piezoelectric devices using modal analysis and neural network : Chukwujekwu, Okafor, A.; Chandrashekhara, K.; Jiang, Y.P. Smart Structures and Materials 1995: Smart Sensing Processing and Instrumentation, San Diego, California (United States), 27 Feb. – 1 Mar. 1995. pp. 314–325. Edited by W.B. Spillman. SPIE Vol. 2444 (1995)

Damage detection in composite laminates with built-in piezoelectric devices using modal analysis and neural network : Chukwujekwu, Okafor, A.; Chandrashekhara, K.; Jiang, Y.P. Smart Structures and Materials 1995: Smart Sensing Processing and Instrumentation, San Diego, California (United States), 27 Feb. – 1 Mar. 1995. pp. 314–325. Edited by W.B. Spillman. SPIE Vol. 2444 (1995)