REAL-TIME DELAMINATION MONITORING IN DCB SPECIMENS USING MFC SENSORS

Abstract

Laminated composites when subjected to high-cycle fatigue loading, undergo delamination and the damage due to fatigue delamination can be detrimental to structural health. Hence, it is necessary to develop a way to detect the damage and then explore novel methods to repair it without need of mechanical fasteners. With this objective, double cantilever beam (DCB) specimens were fabricated, and macro fiber composite (MFC) elements were attached to the top and bottom surfaces. The MFC elements serve a dual purpose- First, they can be used as sensors to detect damage; secondly, they can be used to generate heat to actuate the self-healing process where damage is detected, as proven and presented in our previous studies. The main objective of this study is to detect the damage due to fatigue loading, i.e., crack size and location, with the help of MFCs so that the same network of MFCs can be used to heal the crack in situ. Tests were carried out on baseline DCB specimens with a pre-crack of 38.1 mm and specimens with crack growth in the interval of 2.5 mm beyond the pre-crack end. The DCB specimen with an array of 8 MFCs was used to perform damage detection initially with a single 5-cycle tone-burst actuation signal and then with the actuation signal as antisymmetric Lamb wave excitation. The signal difference coefficient (SDC) was used as a delamination detection metric and calculated for different actuator and sensor location combinations. The preliminary results of lamb wave actuation showed significant increase in SDC with the delamination crack growth for the selected actuator combination. The other objective of this study was to simulate the experimental results for the MFC actuator-sensor setup using the commercially available finite element (FE) analysis software ABAQUS, with fully dynamic simulation of Lamb wave propagation in the composite DCB specimens.