Title: Dynamic Crush Testing and Characterization of Elastomeric Honeycomb Structures in Crashworthiness Applications

Authors: Norman Wereley, Colleen Murray

DOI:

Abstract: Hexagonal honeycomb (HHC) structures are cellular structures used in energy absorption applications due to their high strength and low density. Crush force vs. displacement behavior of HHC structures is characterized by an elastic region culminating in a rupture or peak force, followed by a progressive collapse region over which the mean crush force is relatively constant, followed by densification. Densification crush is typically well above 60% crush ratio. In prior work, conventional HHC structures under quasi-static crush exhibited high peak force and relatively low mean crush force and thus had low crush efficiency. The introduction of buckling initiators (BIs), or purposeful stress concentrators, were found to encourage progressive collapse of the HHC walls by reducing the peak force substantially. This results in peak and plateau force values that are similar in value, thereby greatly increasing crush efficiency. However, HHC structures with BIs are challenging to manufacture using conventional honeycomb manufacturing processes. In this study, the samples were manufactured using thermoplastic polyurethane filament such that six hexagons were arranged around a central hexagon. The inscribed diameter of these samples was 30 mm with an overall height of 30 mm. These HHC samples were crushed under quasi-static speed (0.03 mm/s) using a servo-hydraulic test machine. The HHC samples were also subjected to dynamic crush using a drop mass (5 kg) impact tester under sink rates ranging from 1 to 4 m/s. A specific sink rate was realized by dropping the 5 kg mass from a specific height. From these tests, the force vs. crush (as well as acceleration for the drop tests), crush efficiency, and energy absorbed efficiency were determined. Test data demonstrated that the HHC samples tested under dynamic crush exhibited similar failure mechanisms as under quasi-static crush, but with a much greater stroking load. When comparing the dynamic crush efficiency of these tests, the data showed that the HHC samples with BIs exhibited at least a 40% increase in crush efficiency when compared to samples with 0BI. The total energy absorbed by the samples with buckling initiators located half way up experienced six times the amount of energy absorbed due to strain rate effects as opposed to the strain rate independent effects.

References: Microvascular channel networks embedded within composite materials provide a pathway toward multifunctional structural systems capable of active thermal management, damage detection, and self-healing. In this work, a practical sacrificial-filament processing approach is demonstrated for integrating continuous microvascular channels within carbon fiber reinforced epoxy laminates. Polylactic acid (PLA) filaments were embedded at the laminate mid-plane during layup and subsequently removed through a controlled thermal evacuation process combining vacuum extraction with a post-evacuation pressure purge to ensure channel continuity. Mechanical performance of the resulting microvascular laminates was evaluated and compared to neat laminates using tensile, compressive, flexural, and short beam shear testing. Results show that stiffness-dominated properties were largely retained, while strength-dominated properties exhibited greater reductions, particularly under compressive loading. Failure mode analysis indicated predictable damage initiation at channel locations under compressive and interlaminar stresses. The results demonstrate that continuous microvascular channels can be integrated using scalable composite processing methods with quantifiable and manageable mechanical trade-offs.

Conference: SAMPE 2026

Publication Date: 2026/04/27

SKU: 103

Pages: 14

Price: $28.00