Optical Methods for Experimental Stress Analysis of CFRP Structures

Interest in adoption of Carbon Fibre Reinforced Polymers (CFRP) for manufacturing of structures and components for aerospace applications has increased more and more along the years. In fact, due to the inherent properties of CFRPs, in particular to their high strength to density ratio, their implementation has impact in terms of relevant reduction of the weight of the structure as well as in reduction of fuel consumption and CO2 emissions [1-3]. However, due to the anisotropy of CFRP, classical mechanical characterization can fail to describe the complex behaviour of such materials. Optical methods constitute a powerful class of experimental stress analysis methodologies [4]. They allow obtaining full-field displacement, strain and stress map so that they are of great appealing in order to capture the whole mechanical behaviour of the CFRP components or structures under testing. In this paper an overview of the application of those techniques will be presented. In particular, the buckling analysis of a panel subjected to a compression test will be presented as obtained by implementing the moiré projection method. In this approach a fringe pattern is projected in triangulation over the surface under analysis. This allows retrieving the out-of-plane displacement field and analysing, as a consequence, the buckling behaviour of the structure. Moreover, a stress analysis as obtained by photoelasticity will be presented for the case of a CFRP stringer panel. Finally, the approach based on stereo digital image correlation [5] will be shown as applied to CFRP samples under compression allowing to determine the occurrence of buckling phenomena and to identify anticipately, based on the local increment of the shear strain, the point of failure of the structure. Potentialities and future perspectives concerning with adoption of these methods will be outlined at the end of the paper.