Fractography of Aeronautical Composite Structures Submitted to Mode I Interlaminar Fracture Toughness Characterization

Many components of modern aircrafts are now manufactured from polymer composites. Reinforced laminates with continuous carbon fibers and modified epoxy resin are employed in primary and secondary structures to reduce weight and improve the aircraft performance. However, if a circumstantial failure happens, the complex fracture process of the laminates may involve interlaminar damage mechanisms. The delamination is the interlaminar discontinuity which may propagate catastrophically with the application of mechanical loads. The Double Cantilever Beam (DCB) is the most used method to determine the Mode I fracture toughness of structural composites. In this work samples prepared from a plain weave fabric laminate were submitted to Mode I delamination under static load at room temperature. The analysis of the delaminated surfaces was performed with scanning electron microscopy (SEM). The results show that the fracture process initiates at the resin pockets after a Teflon (R) insert and propagates along the resin rich areas at the crossing of weft and warp tows. The main fractographical aspects revealed are identified, reported and discussed.