Low Velocity Impact Response of Composite Sandwich Structure with Hybrid Honeycomb Core

Abstract

Lightweight design is one of the key characteristics of engineering design, as light weight not only reduces operational cost but also reduces the impact on environment due to lesser fuel consumption. The use of sandwich structures is an important advancement in this regard, as sandwich structures use geometrically efficient design to reduce weight and offer superior properties like increased specific strength and stiffness, better fatigue and impact resistance, thermal conductivity and corrosion resistance as compared to their metallic counterparts. Sandwich structures, specifically with honeycomb core and fiber reinforced composite face sheets have been extensively used in aerospace, ship building, rail industry, military and auto motives. Impact loading, especially low velocity impact, is one of the most critical loading scenario for sandwich structures, as impact can cause strength degradation and barely visible damage, which can compromise the structural integrity. In recent times, most of the research has focused on improving the impact resistance of honeycomb sandwich structures by filling honeycomb with a filler material because the porous structure of honeycomb cells is the weakest region against impact loads, especially against oblique impact. This research also focuses on improving the impact resistance of conventional honeycomb by addition of aluminum grid and foam in honeycomb (HC) to produce a hybrid honeycomb (HHC) core sandwich panel. Impact tests are carried out using drop weight method at 30J and 45J for both conventional HC and HHC core and results are recorded in the form of force-displacement, force-time and energy time-response. The testing shows that HHC sustained higher peak force and lower displacement as compared to conventional HC core. The performance index, which compares the performance of HHC with conventional HC, for HHC-foam impact was 1.31 and 1.26 times for 30J and 45J respectively while for HHCgrid impact was 1.14 and 1.16 times for 30J and 45J respectively, highlighting the improved impact resistance of HHC core sandwich panels. Damage characterization through macroscopic damage analysis for damage on surface as well as internal damage was also performed highlighting the various damage modes like delamination, matrix cracking, core crushing and core buckling among other.