Technique For Detection Of Delamination Research Articles

Fatigue damage evolution using NDT techniques for Health Monitoring of CFRP laminates

In this work, an experimental method based on ultrasonic measurements with piezoelectric transducers (PZTs) was proposed for monitoring the evolution of fatigue damage on a batch of carbon fabric Open Hole specimens. The amplitudes of the recorded ultrasonic sinusoidal waves in packets were evaluated with pitch-catch modality during the different phases of the fatigue life and correlated to the applied loads.The examination of the ultrasonic data showed high sensitivity of the UT signal respect to stiffness decay and to fatigue damage associated with delamination near the hole. Occasional ultrasound measurements with the consolidated pulse-echo Phased Array technique were carried out by the authors at regular time intervals during the tests to evaluate the state of damage in relation to the degradation of the signal detected with the PZT sensors.The results have shown the potential capability of the applied experimental technique for real-time detection of delamination on composite elements subjected to time-varying loads.

Delamination detection at web/flange junction of I-section composite beam with fiber optical interferometer sensor

The identification of delamination location at the web/flange junction of I-beams is an important aspect of any structural inspection program. However, there are currently no published experimental results of it. This paper presents the results of an experimental investigation on the use of fiber optic based technique for early detection of delamination at the web/flange junction of a GFRP I-beam. A PZT transmitter was employed to create the stress waves in the beam element, and an optical fiber interferometric sensor with high sensitivity and long sensing arm was attached to the surface of the beam to serve as an ultrasonic receiver. From the laboratory validation, the proposed technique successfully captures the presence of delamination. Additional frequency component was observed at the delamination location and at the resonant frequency relating to the defect depth. The results also show a close correlation between the experiment and the theory.

Optimal Excitation Frequency of Lamb Waves for Delamination Detection in CFRP Laminates

To improve the reliability of delamination detection techniques based on Lamb waves for carbon fibre reinforced plastics (CFRP) composite laminates, the influence of excitation frequency of Lamb waves on the intensity of reflected waves from a delamination in cross-ply CFRP delaminated beams was investigated. The A0 Lamb wave mode was chosen although the conclusion in this work is also applicable to S0 mode. A Chebyshev pseudospectral Mindlin plate element proposed by authors was employed to simulate the A 0 mode propagation and the interaction of the A0 mode with the delamination. Numerical results show that the sensitivity of A0 mode to the delamination at different frequencies is remarkably different. Each delamination with different lengths or different locations along the through-thickness direction of the laminates generally has at least one or more optimal excitation frequencies which can generate the strongest reflected wave signals from the delamination. The reason for this phenomenon was also investigated by analyzing the natural vibration of the local upper- and lower-delaminated regions. The optimal excitation frequencies were identified to be close to the resonant frequencies of the local delaminated regions with pure flexural vibration modes similar to the deformation pattern of A0 mode.

A sensor charge output deviation method for delamination detection using isolated piezoelectric actuator and sensor patches

Delamination is one of the most prevalent failure mechanisms for laminated composites. To secure the safety of composite structures, it is required and necessary to develop cost-effective and efficient delamination detection techniques and methods. In this paper, a dynamic analytical model, namely sensor charge output deviation method is proposed to identify a delamination embedded in a cantilever laminated composite beam bonded with isolated piezoelectric actuator and sensor patches. Two pairs of collocated piezoelectric patches are bonded on top and bottom surfaces of the beam and used as actuators for exciting the composite beam. Another piezoelectric patch with gridding electrode pattern on its top surface is bonded on the top surface of the host beam and is employed as a sensor to record the required voltage and thus the sensor charge output along the beam. The effects of some major geometric parameters and the type of applied electric voltage on the sensor charge output distribution and delamination detection sensitivity are discussed in this paper. A comparison between the analytical models using isolated piezoelectric actuator and sensor patches and that using integrated piezoelectric sensor/actuator layer, which was developed previously, is conducted. For the baseline case considered here, there is an excellent agreement of the first three order frequencies between the present finite element analysis and analytical models.

EFFECTS OF DELAMINATIONS ON THE DAMPED DYNAMIC CHARACTERISTICS OF COMPOSITE LAMINATES: ANALYSIS AND EXPERIMENTS

Analytical and experimental work is presented on the damped free vibration of delaminated laminates and beams. A laminate theory is developed in which the unknown kinematic perturbations induced by a delamination crack are treated as additional degrees of freedom. The generalized stiffness, inertia and damping matrices of the laminate are formulated. An analytical solution is developed for the prediction of natural frequencies, modes and modal damping in composite beams with delamination cracks. Evaluations of the mechanics on various cantilever beams with a central delamination are performed. Experimental results for the modal frequencies and damping of composite beams with a single delamination are also presented and correlations between analytical predictions and measured data are shown. The effects of delamination vary based on crack size, laminate configuration and mode order. The implications of the mechanics in developing delamination detection techniques are also discussed.