A New Methodology for Structural Health Monitoring Applications

This work presents a combination of vibration-based method and speckle shearography in order to identify, locate and quantify the damage in composite structures. The experiments were carried out on laboratory specimens, which consist in cylinders made of carbon fiber and epoxy resin via filament winding process. Twelve composite specimens were considered in this study. Three different stacking sequence were tested: Type A [90/60/-60/90/60/-60/90]S, Type B [90/30/-30/90/30/-30/90]S and Type C [90/30/-60/60/-60/30/-30]S. Firstly, Frequency Response Functions (FRF's), for intact and damaged structures, were obtained by using the excitation caused by an impact hammer and the signal gathered by two accelerometers sensors attached in suitable positions. The results were analyzed by using a new damage metric, where the metric values were compared in terms of their capability for identifying damage. After identifying the structural damage, there was application of the speckle shearography technique in order to locate and quantify the damage. In this technique, defects are usually detected based on the abnormity of slope fringes due to the fact that out-of-plane displacement derivative at the region with defects is much larger than that at the region without any defect. Finally, it was discussed the advantages and limitations to use vibration based method and damage metric combined to speckle shearography into the context of SHM.