Delamination Growth and Residual Strength of Compressively Loaded Sandwich Panels with Stiffness Tailored Face Sheets

This study shows that a simple approach to stiffness tailoring of composite face sheets can improve the performance of sandwich panels under compressive loading when delaminations are present. The simple stiffness tailoring concept used here is to reposition of all 08 material (aligned with the loading direction) into regions of certain width near the edges of the sandwich panel. This concept has been shown to improve the buckling and postbuckling performance of solid plates and to offer control of delamination growth. To evaluate this tailoring design concept in sandwich panels, numerical simulations of onset and propagation of the delamination growth were conducted with uniform face sheets and tailored face sheets. The delamination front tracing method previously developed by the authors was used to perform the delamination growth analysis. The interfacial elements, which allow the growth of the delamination front to be traced, are placed at the interface between the top face sheet and the core in the undelaminated region. They enable calculation of the strain energy release rates and application of a fracture mechanics delamination growth criterion. Gap elements were used to avoid interfacial overlap. Based on the numerical study, the improvement in the ultimate load provided by the simple stiffness tailoring concept ranges from 80% to 100%, depending on the extent of tailoring. Substantial improvements in the residual strength and stiffness, after significant delamination growth, can also be observed. Therefore, this article provides a potential design concept that can improve the damage tolerance of sandwich panels without adding weight.