On the use of Lockin Thermography to Monitor Delamination Growth in Composite Panels under Compression

The success of composites in automotive, aerospace and naval applications, is mainly related to their aptitude to be tailored to obtain a final product perfectly fulfilling the design requirements. However, during both manufacturing processes and maintenance, some flaws, like delaminations (which may flee from simple visual inspection), may be induced in composite structures. The presence of delaminations is of major concern for the load carrying capability of Carbon fiber reinforced polymers (CFRP) panels. Indeed delaminations can strongly affect the structural strength and may grow under in-service loads, leading, sometimes, to catastrophic failures. The aim of this work is to explore the use of lockin thermography for the monitoring of delaminations propagation in composite structures when subjected to generic multi-axial loading conditions. Indeed, a stiffened composite panel with an embedded skin delamination subjected to compressive loading has been taken as benchmark to assess, experimentally, the effectiveness of lockin thermography for monitoring the delamination propagation in-situ during the compressive mechanical test. The delamination size as a function of the applied load, observed by lockin thermography during the execution of the compressive test, has been used to validate the results of preliminary numerical computations