Drilling Damage and Dynamic Response of Carbon/Glass Hybrid Nomex Sandwich Composites

Nomex honeycomb core sandwich composites are attractive for lightweight structural applications because of their high specific stiffness. However, drilling required for mechanical joining can introduce both surface and subsurface damage and may change the mechanical and dynamic response of the structure. This study examines Nomex aramid honeycomb sandwich composites with C/C/C, C/G/C, G/C/G, and G/G/G face-sheet configurations using three-point bending, drilling, image analysis, ultrasonic C-scan, and acoustic impact measurements. The C/C/C configuration reached an average bending load 36.05% higher than G/G/G and reduced the entry and exit side delamination areas by 88.91% and 78.89%, respectively. Although C/C/C produced the highest thrust forces during drilling, it also showed the smallest surface and internal damage regions, indicating that thrust force alone does not fully describe hole quality. C/G/C also exhibited less damage than G/C/G; however, these two hybrid configurations differ in both carbon/glass content and ply position, so the contribution of each factor cannot be separated independently. After drilling, the natural frequency decreased, and the damping ratio increased in all configurations. Overall, the carbon-rich face sheets provided higher bending resistance and more effectively limited drilling-induced damage.