In a NASA-funded project, CRG engineers developed a reflexive system for increasing vehicle survivability of advanced systems, such as manned and unmanned air vehicles, spacecraft, and habitats for space exploration missions. Building on previous development with reflexive composites and morphing structures, CRG’s engineers developed an integrated reflexive composite structural system that senses and adapts to damage, increasing inherent survivability and damage tolerance of composite structures integrated into these advanced systems.
Healable Resin Development
At the core of the reflexive system is CRG’s healable composite. The composite uses a healable shape memory polymer (SMP) resin, Veriflex® EH, to restore up to 85% of original mechanical performance. The shape memory effect inherent in CRG’s tailorable thermoset restores the pre-damaged shape and brings fractured surfaces back into contact. Polymer chain diffusion across these fractured surfaces then enables local healing of the damaged composite matrix in a process called reptation. Both these mechanisms are thermally activated and are achieved in less than three minutes.
The reflexive system is a bio-inspired concept, designed to mimic the body’s response to injury using four primary components. CRG incorporated a commercial off-the-shelf structural health monitoring (SHM) technology to enable the system to “sense,” or detect, damage. When damage is detected by the SHM system, an intelligent control system, developed by CRG and a partner, analyzes the results from the SHM system, prioritizes damage, and generates custom healing cycles for each damage incident without requiring user input.
A discrete activation system then heats the reflexive composite above its activation temperature, beginning the healing process. Only the damaged sections of the structure are affected during the repair. Using discrete activation when large areas are damaged ensures that the vehicle is capable of maintaining current loading conditions by segmenting the damaged area into multiple sections and conducting sweep healing; that is, the system will activate heaters sequentially, in one portion of the damaged area at a time, until the entire area is repaired.
The system is capable of healing damage caused by punctures, bird strikes, hail, ground damage, and fatigue failure. Applications for this patent-pending technology include repairing primary composite structures in aircraft, such as loaded wing skins, spars, ribs, and stringers; repairing composite watercraft hulls, superstructure, and decking; and repairing composite automotive and other transport structures.