Structural health monitoring (SHM) has seen significant growth over the past few years due to the safety and performance enhancing benefits as well as the potential life saving capabilities offered by the technology. Current advances in SHM systems have lead to a variety of techniques capable of identifying damage; however, few strategies exist for using this information to quickly react to the environmental or material conditions to repair or protect the system. Unlike these modern SHM systems, biological systems can not only detect the presence of damage but react to heal it through stimulus responsive behavior. This research plan focuses on the use of advanced composite materials to mimic the response of biological systems to damage. This effort will provide a bridge between structural health monitoring and autonomic structural materials such that the SHM system can detect and respond to damage in a controlled fashion. Existing healing techniques are problematic because they cannot be controlled and provide no sensing response to report the presence of damage, the initiation of healing, or the strength recovered. A unique combination of materials and sensors will be used to mimic the one of the toughening responses exhibited by bone when subjected to cracking. The autonomous system developed here will use optical fibers to sense the presence of damage and autonomously initiate healing. Responsive behavior will occur by using the energy released from the optical fiber in the presence of damage as stimulus and the recent advances in thermally activated shape memory polymers (SMPs). The outcome of the research will be a material system that can sense the presence of damage, arrest its propagation and initiate controlled healing through stimulus. The work will 1) model and characterize recently developed reactive polymers, 2) characterize the crack blunting from a localized modulus change at the crack tip, and 3) use cyberengineering to fabricate a composite material with integrated sensor networks, computing and logic to allow the system to respond to damage without human intervention. The research program will advance SHM from damage detection to an integrated material system which can identify and react to damage in an autonomous manner as biological systems do.
