Response of Impacted Sandwich Panels with Integral Stiffeners

Abstract

A study was conducted to determine the effect of integral stiffeners on the damage growth and ultimate strength of sandwich panels with impact damage. A total of 18 specimens with IM7/8552 [90/0]S facesheets cocured to 25-mm thick Nomex honeycomb core were impacted and tested in compression. All of the specimens were nominally 152 mm in width and 356 mm in length and were impacted at the center of the front facesheet. Damage growth was monitored via strain gages, and ultimate strength was compared against sandwich panels without integral stiffeners. When the integral stiffeners involved redistributing material in the facesheet, the damage in the resulting thinner facesheet often grew sooner and the ultimate strength was unaltered. When the internal stiffeners involved additional material, damage growth was delayed and the ultimate strength was increased to the point where the ultimate failure initiated away from the impact site.