Improved elliptical triangulation method for damage detection in composite material structures

Abstract

In this paper, an improvement of the elliptical triangulation method for damage detection using Lamb waves is presented. The damage is the main cause of structural failure and often occurs on structures. In order to avoid sudden failure, a special attention was given in the past decades to the damage detection in structures. In order to obtain efficient damage detection techniques, the structural health monitoring has been the main research topic of many scientists worldwide. The elliptical triangulation method, proposed in this paper, is a non-destructive method based on measurement of Lamb waves. This method, through the calculation of the time of flight of the signals and the actuator-sensor positioning, allows to identify position and dimension of the damage. The application of the method to the metallic structures and to the composite material structures is presented in this paper. The complexity connected with the uncertainty of the waves’ propagation speed due to the anisotropy of the composite materials has been explored through an iterative approach. The initialization of the wave propagation speed at first tentative iteration is the key issue for the convergence of the method. Seven different conditions were used to validate the method on both metallic and composite structures combining two damage shapes, two damage dimensions (effective damaged area), and three different positions. Upon evaluating the effectiveness, the method has been applied at two composite panels in order to detect by test the post-impact damages. Tests results have been compared with the numerical ones. The feasibility of the elliptical triangulation method to detect the damage (evaluating the damage position and area) has been proved using the ultrasonic C-Scan.

Application of structural health monitoring techniques to composite wing panels

“…The PZT damage detection method herein illustrated is the elliptical triangulation method (ETM), which is based on the propagation of ultrasonic waves within the structure. Sorrentino and De Fenza 21 verified the effectiveness of the method on unstiffened flat composite plates.…”

“…FOS sensors ensure a higher sensitivity to the detection of the debonding and monitoring of its propagation, while PZT sensors/actuators ensure a higher sensitivity to the impact damage detection. 15,16,21,25,43 Higher FOS spatial resolution, distributed very close to the debonding line ensures the possibility to measure a debonding, even of 1 mm. Moreover, the use of both the sensors for the damage detection could also ensure a redundancy of the system that is going to be the object of next activities.…”

“…The reliability method assessment, by both numerical and experimental point of view, in terms of the damage location and the area identification, varying the composite layups and both damage entity and location, was already proposed in Sorrentino and De Fenza 21 on unstiffened flat composite panels.…”

“…19,20 In particular, De Fenza et al 19 applied both methods to highlight the damage detection starting from the damage index knowledge that was calculated on each sensing-path within the whole actuator-sensor network. In the attempt to obtain more accurate results, in the next study phase, 21,22 the time of flight (ToF) of the actuator-sensor positions knowledge (in each sensingpath) has been utilised to draw the probable damage locations.…”

An Impedance Measurement Technique for Composite Materials Moisture Level Detection Devoted to Health Monitoring in Aeronautics

“…Indeed, the next step is the integration of the proposed method with an already developed SHM approach for barely visible impact damage (BVID) identification. This study has been already performed by some authors [17,18]. In addition, a direct relationship between the impedance of moisturized specimen and mechanical strength is to be evaluated in order to establish the "residual strength" of the structures during the operation life of aircraft with respect to the current state of the art in level of safety [1].…”