| Although the sandwich structures currently occupy a considerable place in all the industrial sectors including aerospace, their high sensitivity to low velocity impact raises some concerns among aircraft manufacturers and tends to limit their scope. The aeronautical structures are likely to be exposed to accidental shocks of various origins (falls of tools during maintenance, shocks between two panels during the assembly, impact of birds during the service life,...) whose consequences are often undesirable. For that, a damage tolerance approach is adopted for the certification of these structures. The aim of this method is to evaluate the residual resistance of a damaged structure and thus to quantify the effect of the damage on the mechanical performances of these structures. This will allow us to make structures more damage tolerant. Accordingly, we were interested to study the impact behavior of sandwich panels made with laminated skins glass-E/vinyl-ester and a rigid PVC foam core.;To carry out the tests of impact, various sandwich panels (17 x 45 po 2) were manufactured by resin infusion and vacuum molding. For research testing purposes, two core densities were retained (58.5 kg / m3 and 92 kg / m3). The facesheets were made up with two different thicknesses (2 and 3 plies) respectively according to the following stacking sequences [0/90/-45/+45]s and [0/90/-45/+45/90/0]s. The impact loading was simulated by a drop-weight tower on samples measuring 4 po x 6 po, using three impactor diameters (½, 1 and 1 ¾ po). The results of impact tests (force-time signal) associated with visual inspection of samples impacted, have allowed to evaluate the severity of damage caused by the impact. In addition, with reference to the energy-time curves, we have determined the damage index (ID) for each impacted sample. The results are subsequently presented in the form of curves where the abscissa is the percentage of absorbed energy and the ordinate is the supplied energy. These curves were used to determine the critical value of impact energy at which a transition between different categories of impact damage is observed. Thus, we could determine the effect of various structural parameters (density of core and thickness of facesheets) and experimental (diameter of impactor) on the response to the impact of our samples, especially in the transition zone. In addition, tests of compression after impact (CAI) were conducted on a conventional MTS fatigue machine. The main objective of these tests was to measure the compressive strength of sandwich structures containing barely visible impact damage. To achieve this goal, the residual compressive strength are standardized compared to the strength of virgin specimens and are presented in terms of damage index. Finally, the results of tests of dynamics impacts encourage us for realization of statics ones. Through a static approach, these tests reproduce the same types of damage induced during the dynamic impact loading. In light of these results, we were able to identify the transition zone in terms of depth.;Keywords: sandwich structure, impact, damage tolerance, CAI, BVID, foam core, glass-E, diameter impactor, static impact... |
