Lamb waves from microfractures in composite plates (original) (raw)
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The purpose of the present report consists in studying an opportunity of use of devices for registration of complex signals in thin- walled details of structures. Lamb's wave properties were used for explanation of dynamic reaction of thin plate surface when in some place there is some source of impulse loading. The experiment on the study of some parameters of propagation of elastic waves in the plate from the Al-Cu aluminum alloy was carried out. Using the Lamb's waves' dispersion property, the formal simulation of waves interference was carried out. It was shown that dynamic reaction of thin plate surface can be explained as effect of several waves' interference. More detailed researching of the structure and the parameters of signals, excited with the impact loading, composes the basis of this work.
Long range damage assessment through Lamb waves in large plate-like composite structures
Journal of Advanced Science, 2000
The health of a structure depends on both the homogeneously distributed degradation of its mechanical properties during its life cycle and the presence of localised defects such as cracks or delaminations. The proposed non-destructive health monitoring method allows recovering both kinds of information using ultrasonic waves. To avoid traditional techniques limitations, such as coupling reproducibility for instance, we propose here to integrate a piezoelectric element into the plate-like composite structure. The element dimensions are determined in order to uncouple the frequency ranges of the thickness and radial vibration modes. The thickness mode is used to monitor the homogeneous ageing of the structure through electrical impedance measurement. As for the radial vibrations, they are used to generate and detect Lamb waves, which have the advantage of propagating over long distances and offering specific sensitivity of various modes to different kinds of defects. The present work focuses on this last application and studies the ability of the proposed technique to detect and identify defects such as low speed impact-induced delaminations and cracks in composite plate-like structures.
Linear and non-linear analysis of composite plates using guided acoustic waves
2019
Guided acoustic wave techniques have been found to be very effective for damage detection. In this investigation Lead Zirconate Titanate (PZT) transducers are used to generate guided acoustic waves for structural health monitoring of a variety of composite specimens. Multiple sets of composite plate specimens are inspected for impact induced damage detection using PZT transducers. Composite samples are divided into two groups for comparative studies i.e. glass fiber composites and basalt fiber composites. They are damaged by impactors having different levels of impact energy. A chirp signal is excited and propagated through the specimens in a single sided excitation/detection setup to investigate the damages induced by impacts of varying intensity. Signal processing of the recorded signals for damage analysis involved both linear and nonlinear analyses. Linear ultrasonic analysis such as change in the time-of-flight of the propagating waves, Fast Fourier Transform and S-Transform of the recorded signals were tried out while the nonlinear ultrasonic analysis involved the Sideband Peak Count or the SPC technique.
Four vectors of Lamb waves in composites: Semianalysis and numerical simulation
For source location in composites based on Lamb wave techniques using direction-dependent piezoelectric rosettes sensors, the source is usually located by the intersection of wave propagation directions identified by the sensors. However, the rosettes do not measure the direction of group velocity directly. Instead, they measure the direction of principal strain. Hence, in order to accurately predict the sources in anisotropic plates, it is essential to investigate the relationship between the direction of principal strain and that of group velocity. In this study, the four vectors, namely, phase velocity, group velocity, displacement, and principal strain associated with propagating waves in anisotropic plates, are computed using semianalytical methods. The analytical results agree very well with the results of finite element method based on Abaqus, including those of the complicated SH 0 mode. Moreover, it is found that the four vectors exhibit some symmetrical properties. When Lamb waves propagate along the symmetry axes, the directions of the four vectors are all the same.
Advanced Materials Research, 2015
Among Non-Destructive Testing, guided ultrasonic Lamb waves are particularly suitable for Structural Health Monitoring (SHM) applications for composite structures because of their sensitivity to damage. This paper presents a numerical simulation technique for guided waves propagation in damaged composite laminates by using the finite element code Abaqus®. The damage modeling has been achieved by lowering the elastic material properties of the area affected by damages. Lamb waves propagation have been performed on both undamaged and damaged laminate, in order to investigate the detection criteria. In particular, the influence of different parameters such as the shape, size and extend of damage on the damage reflected wave has been studied.
In the present study the influence of microscopic elastic properties and the geometry of the acoustic emission (AE) source are investigated by finite element simulation. We investigate the formation process of Lamb waves in isotropic and anisotropic plate specimen by simulation of five different AE source configurations. As reference a microscopically and macroscopically homogeneous, isotropic aluminum specimen with point force couples is used. For fiber-reinforced materials, the elastic properties are typically anisotropic. A comparison is made be-tween the Lamb wave formation of the anisotropic, homogeneous model specimen and those of an anisotropic, microscopically inhomogeneous model. It is demonstrated, that the microscopic elastic properties of the AE source have significant influence on the excitation of distinct Lamb wave modes. This can be used to distinguish between failure mechanisms like fiber breakage or resin fracture in fiber reinforced materials.
Acoustic structural health monitoring of composite materials
Composites Science and Technology
The characterisation of the damage state of composite structures is often performed using the acoustic behaviour of the composite system. This behaviour is expected to change significantly as the damage is accumulating in the composite. It is indisputable that different damage mechanisms are activated within the composite laminate during loading scenario. These ''damage entities'' are acting in different space and time scales within the service life of the structure and may be interdependent. It has been argued that different damage mechanisms attribute distinct acoustic behaviour to the composite system. Loading of cross-ply laminates in particular leads to the accumulation of distinct damage mechanisms, such as matrix cracking, delamination between successive plies and fibre rupture at the final stage of loading. As highlighted in this work, the acoustic emission activity is directly linked to the structural health state of the laminate. At the same time, significant changes on the wave propagation characteristics are reported and correlated to damage accumulation in the composite laminate. In the case of cross ply laminates, experimental tests and numerical simulations indicate that, typical to the presence of transverse cracking and/or delamination, is the increase of the pulse velocity and the transmission efficiency of a propagated ultrasonic wave, an indication that the intact longitudinal plies act as wave guides, as the transverse ply deteriorates. Further to transverse cracking and delamination, the accumulation of longitudinal fibre breaks becomes dominant causing the catastrophic failure of the composite and is expected to be directly linked to the acoustic behaviour of the composite, as the stiffness loss results to the velocity decrease of the propagated wave. In view of the above, the scope of the current work is to assess the efficiency of acoustic emission and ultrasonic transmission as a combined methodology for the assessment of the introduced damage and furthermore as a structural health monitoring tool.
Detection of multiple low-energy impact damage in composite plates using Lamb wave techniques
Composites Part B: Engineering, 2015
This work concerns the assessment of the suitability of the Lamb wave method, in particular of the two zero-order Lamb modes (A 0 and S 0), to detect multiple barely-visible impact damage in composite material. Four plates were produced with carbon-epoxy cured pre-preg, using a representative stacking sequence. Three specimens were subjected to multiple impact damage at three different low-energy levels, and one was left as an undamaged reference sample. Ultrasonic Lamb wave modes were selectively generated by surface-bonded piezoceramic wafer transducers in two tuned configurations. A signal identification algorithm in the timescale domain based on the Akaike Information Criterion (AIC) was used to determine the group velocity of the Lamb modes. The effectiveness of the Lamb wave method was successfully verified on all damage scenarios, since the 5 and 10 J damages were undoubtedly detected by the S 0 mode configuration. The results were validated by digital Shearography, ultrasonic C-scan, and optical microscope observations, revealing strong consistency. For the material tested, the detection threshold of the three NDT methods was found to be between 3 and 5 J.