Compression After Impact Testing of Sandwich Composites for Usage on Expendable Launch Vehicles

Abstract

Composite material usage is necessary on NASA’s future launch vehicles in order to obtain a low mass vehicle. While aircraft and launch vehicles that utilize load-bearing composite components have many similar damage tolerance requirements, the distinct differences between a part that has a lifetime of ∼500 s (one launch) and can be inspected in detail before use and one that has a lifetime of many tens of thousands of flight hours and can only undergo a ‘walk around’ inspection before each flight (commercial transport) needs to be taken into account. This article presents these differences and uses data from the ARES I composite interstage as an example of how to arrive at preliminary compression after impact strength values for the sandwich structure in the acerage of this part using residual strength curves. Results show that if severity of damage can be quantified by a nondestructive method (other than dent depth), the mass of the structure can be reduced due to better characterization of the damage.

Experimental study on the compression-after-impact behavior of foam-core sandwich panels

“…However, the damage states due to larger impactor produced buckling failures which were triggered by the unzipping of the localized face-sheet bending over the core. A procedure was established in [16] to produce a preliminary damaged compression strength design value for two types of honeycomb sandwich construction used in the acreage area of the ARES I interstage. From the tests, a CAI strength design curve which plots the reduction in compressive load carrying capability as a function of increasing damage severity was generated.…”

Compressive strength of honeycomb-stiffened graphite/epoxy sandwich panels with barely-visible indentation damage

“…11 The compressive strength of sandwich panels often exhibits significant scatter when examined as a function of a particular damage metric. 7,19 The source of scatter can be difficult to determine definitively; however, scatter is likely attributed to manufacturing induced variations and flaws, differences in the post-impact damage state, and variations in the test method, to name a few. Nevertheless, when the compressive strength is evaluated over a large range of damage, the scatter becomes small compared to the overall reduction in strength, and the compressive strength generally decreases with the increasing impact energy or the resulting planar damage area.…”

Compression after impact strength of out-of-autoclave processed laminates

“…These results coupled with the similarity in damage morphology between the three fiber/resin systems make a comparison of the damage resistance difficult based on the data presented. In a previous study, 6 it was determined that damage width was a better indicator of CAI strength than damage length. If this holds true then the CAI strength of the IM7/8552 fiber/resin system should be slightly lower than the other two fiber/resin systems at the 1.1 and 2.3 J impact energy levels if all three fiber/resin systems have the same tolerance of damage.…”