Fatigue behavior of impacted composite structures

The aim of this study was to compare the mechanical behavior of different impact-damaged composite materials. Three composite materials were realized using the Liquid Resin Infusion process (LRI) according to three different cycles of polymerization. Thus the temperature of the glass transition of the resin was controlled and the influence of this parameter was then determined.In accordance with the aeronautical use of composite materials, the plates were subjected to Barely Visible Impact Damage (BVID). Two experimental methods were developed to ensure that impact conditions were respected. The first method, using the numerical digitalization of surfaces made it possible to reconstruct the defect. Thus the residual indentation could be measured. This indentation had to be lower than 0.3 mm. The second method, using passive infrared thermography, enabled the thermal cartography on the surface to be determined. The size of the damage area was then obtained.Through the use of these two methods, the best cycle of polymerization was determined and fatigue tests were carried out to estimate the evolution of the defect. For this purpose and in compliance with impact and fatigue testing standards, a new and adapted sample was imagined (FAI sample). The fatigue testing conditions were determined to avoid buckling effects and to limit the rise of the temperature of the sample. An experimental method using infrared thermography was then developed to follow the size evolution of the defect. This real time evolution was then compared to the loss of rigidity of the sample.