Damage Detection in Complex Composite Material Structures by using Elliptical Triangulation Method

Abstract

This paper is concerned with the detection and characterization of impact damage in stiffened composite panels using elliptical triangulation method and high frequency Lamb waves. Laminated composite materials, used in many aerospace and aircraft structures, often contain a variety of hidden internal flaws which occur during manufacturing and processing of the material or while the structure is subjected to service loads. In order to avoid quick failure of structural components, a special attention was given to the damage detection in complex structures. More specifically, structural health monitoring based on the vibration of structures has been at the focus of attention of many researchers in order to obtain very efficient damage detection techniques. In this way, few nondestructive techniques based on measurement of Lamb waves were developed. On the same approach is based the elliptical triangulation method presented in this paper. Through the calculation of the Time of Flight of the signals and the knowledge of the actuator-sensor positions, the method allows to identify position and dimension of the damage. The effectiveness of the elliptical triangulation method was highlighted through a preliminary numericalexperimental correlation on flat plates. Subsequently, the method is applied to a stiffened structures in composite material affected by the impact damage. Upon the numerical characterization of the damage entities generated by low-velocity impacts at 15J and 30J on the stiffened structures, the waves propagation analysis were performed on both undamaged and damaged structures. The feasibility of the ellipse triangulation method on the evaluation of the position and the damaged area on complex structures realized in composite material has been characterized. The potential applications of the methods in developing health monitoring systems in defects-critical structures and in complex composite material structures are discussed.