Available at: https://digitalcommons.calpoly.edu/theses/2934
Date of Award
12-2024
Degree Name
MS in Mechanical Engineering
Department/Program
Mechanical Engineering
College
College of Engineering
Advisor
Eltahry Elghandour
Advisor Department
Mechanical Engineering
Advisor College
College of Engineering
Abstract
Composite structures have demonstrated great potential to improve mechanical performance in various applications, including ballistics protection. This study demonstrates that the integration of geometrically optimized composites into core-face sheet assemblies provide great impact resistance. The research investigated the performance of two composite manufacturing methods under low-velocity impact through residual strength and damage comparisons. Corrugated core composites were produced with traditional manufacturing methods, namely compression molding, using twelve stacking sequences. These stacking sequences were chosen to represent four laminate groups, where a unique fiber orientation scheme was employed across three laminate thicknesses (6, 8, and 12 layers). In contrast, honeycomb and auxetic cell cores were produced using continuous fiber-reinforced 3D printing. To maintain consistency, both the corrugated cores and the advanced cell cores were produced with para-aramid fibers, though the matrix differed between the two manufacturing methods. The cores were subjected to a consistent drop-weight impact event under various impact cases where the makeup of the assembly differed. The findings of this testing showed that external damage decreased as layer count increased for the laminates and that the addition of a silica damping material significantly improved post-impact, out-of-plane compressive response. In addition, testing proved that the cross-ply, longitudinally dominant laminates & the honeycomb printed composite exhibit exceptional out-of-plane compressive strength prior to and after impact. The cross-ply core retained 58.0% of its pre-impact stiffness & 68.3% of its pre-impact strength while the honeycomb core retained 88.0% of its pre-impact stiffness and did not fail under the maximum compressive load. Aside from impact testing, theoretical and numerical analyses were performed. Classic Laminate Plate Theory was employed to predict laminate engineering constants, while finite element models were created to simulate the in-plane response of the cores. The theoretical approach roughly approximated the longitudinal modulus, though the error was significant. In contrast, the finite element models developed closely mirrored experimental tensile behavior, with peak stress predicted within 5% of experimental results. The compressive response was also well captured by the model, though the displacement to buckling onset was underpredicted by 38.0%.