Bistable structures for energy absorption II: Composite structures under tension

Abstract

This paper discusses proof-of-concept experiments of composite bistable structures and is preceded by a companion paper about metallic bistable structures. A bistable structure is characterized by a stress/strain curve with stable branches separated by unstable branches. We were interested in a particular bistable structure: one that, once activated, has a second stronger state with the ability to sustain higher loads. This allows for a better distribution of damage, and in addition the structure keeps its integrity for a longer time. Positive results on metallic configurations under tensile loading have prompted us to try and identify an equivalent composite configuration, able to show directional control of damage through this material-driven mechanism. Chain-like configurations with different reinforcements (T-300 carbon fibers, Kevlar® 49, E-glass and Dyneema®), polyurethane foam core and Kevlar stitching were conceived, designed, fabricated and investigated. Dyneema prototypes turned out to exhibit the desired bistable behavior as well as higher energy absorption than their baselines.