Barely Visible Impact Damage Evaluation of Composite Sandwich Structures

Abstract

The nature of quasi-static indentation damage is st udied in aluminum honeycomb core sandwich panels with eight ply, quasi-isotropic, graphite/epoxy fac e sheets. Parameters that are varied include the co re thickness, core density, face sheet layup and inden tor diameter. The majority of induced damage is in the vicinity of the barely visible threshold. The perma nent dent in the panel is found to always be larger than the contact area of the indentor, and specimens with de nser cores exhibit smaller dent diameters for a giv en dent depth. Regardless of specimen layup, delaminations occur essentially only at the 3 rd , 5 th , 6 th and 7 th interfaces. Stiffer cores, either in terms of a higher density or, for those cores considered, a smaller thickness , result in more face sheet delamination for a given indentatio n event. Regardless of the core, larger delaminatio ns occur in face sheets that contain only 90° angle ch anges between adjacent plies in comparison to those that contain only 45° angle changes. Thus, when delamination area is considered as a damage resistance metr ic, a low density core with a [45/90/-45/0] s face sheet will provide the best results of those geometries considered. However, if dent area or dent depth is chosen as th e damage metric, this geometry will provide the lea st damage resistance, and a high density core with a [ ±45/0/90] s face sheet is best. These and similar results are discussed in the context of choosing the most damag e resistant structural configuration and how this translates to damage tolerance.