The compressive residual strength and behavior of impact damaged sandwich panels are governed by the amount of non-visible core damage underneath the facesheets. The failure modes under in-plane compressive loading are either due to crack precipitation from the damage zone or unstable dimple propagation across the width. In both cases, the local bending of facesheet (dimple) triggers the final failure sequence. Thus, containment of this local bending by reinforcing the core cell(s) in the damage region will mitigate the failure initiation and thus increase residual properties. A repair technique involving the containment of local bending of sandwich facesheet by strategically filling honeycomb core cells has been explored to improve the damage tolerance of impact damaged sandwich panels. The experimental results indicate that filling honeycomb cells at the center of the damage region in addition to those at the edge of the damage region produces the maximum benefit. The test data and final failure mode of the repaired specimen under in-plane compression loading indicated that the present repair technique can help recover the undamaged strength of the sandwich panels.

Thesis [M.S.] - Wichita State University, College of Engineering, Dept. of Aerospace Engineering