This study explored the feasibility and potential benefits provided by the addition of
through-the-thickness reinforcement to foam core sandwich structures. Through-the-thickness
stitching is proposed to increase the interlaminar strength and damage tolerance of composite
sandwich structures. A low-cost, out-of-autoclave processing method was developed to produce
composite sandwich panels with carbon fiber face sheets, a closed-cell foam core, and
through-the-thickness Kevlar stitching. The sandwich panels were stitched in a dry preform state,
vacuum bagged, and infiltrated using Vacuum Assisted Resin Transfer Molding (VARTM)
processing. For comparison purposes, unstitched sandwich panels were produced using the same
materials and manufacturing methodology. Five types of mechanical tests were performed: flexural
testing, flatwise tensile and compression testing, core shear testing, and edgewise compression
testing. Drop-weight impact testing followed by specimen sectioning was performed to characterize
the damage resistance of stitched sandwich panels. Compression after impact (CAI) testing was
performed to evaluate the damage tolerance of the sandwich panels. Results show significant
increases in the flexural stiffness and strength, out-of-plane tensile strength, core shear strength,
edgewise compression strength, and compression-after-impact strength of stitched sandwich
structures.
Damage characteristics and residual strength of composite sandwich panels impacted with and without a compression loading
