Investigation of damages in impacted thick composite panels by NDI methods

Composite structures widely used in advanced sectors as in the automotive and aeronautical fields, during their useful life are usually subject to dynamic events responsible for apparently invisible failures which, over time, extend and severely compromise their performance. In this regard, a huge amount of experimental results, also validated by theoretical considerations, is available on the behaviour to damage caused by low velocity impacts (LVI) on laminate systems in polymeric composite and on their residual strength. However, until now the research interest has been mainly focused on thin composite laminates (less than 4 mm) and only very few experimental works are available concerning thick laminates (thickness higher than 4 mm) generally used in the skin of airplane wings, stringers, highly loaded components. This study aims to investigate simulated defects in carbon fiber reinforced polymers (CFRP) and of the damage deriving from LVI events, particularly peculiar to structures with higher bending stiffness such as thick ones and, therefore, to fill the current knowledge gap for a more appropriate use of the latter. To this end, thick carbon epoxy resin composite laminates, kindly supplied by Leonardo SpA and impacted at the Department of Industrial Engineering of the University of Naples Federico II, will be systematically investigated with well-established skills on infrared thermography, air coupled ultrasonic tests and shearography at the Institute of Applied Science and Intelligent Systems of the National Research Council. The combined results for both panels with simulated defects and impacted panels provided an accurate description of the different defects present in the thick panels involved in their damage process.