Self-Repair and Damage Mitigation of Metallic Structures

The central goal of this research program was to design self-healing in lightweight metallic materials. This technology has the potential to significantly reduce cost, space and weight, and with the value-added characteristic of self-healing for increased reliability, structures can be designed with unprecedented and revolutionary abilities. The design composite consists of an alloy matrix with Shape Memory Alloy (SMA) reinforcements. During operation, when a force I applied to the composite that is large enough to initiate a crack, crack nucleation and propagation occur. The SMAs instantaneously provide crack closure by applying a clamping force. When the composite reaches its final healing temperature, the matrix will partially liquefy and cause crack filling. Following healing, the composite displays its original strength. The proposed composite consists of an alloy matrix and SMA wires as the reinforcements. The objectives of this research program were to 1) understand the fundamental relationship, in metal-matrix composites reinforced with SMAs, between the martensitic phase transformations in the SMAs and the fracture toughness of the composite; 2) characterize the healing efficacy of in-situ self-fluxing reactive elements in a high specific strength aluminum (Al) alloy composite; 3) explore the feasibility of passive fiber optic sensing to monitor strain localization and damage accumulation in the composite. Understanding the influences of these sub-systems to the macroscopic mechanical and sensing behavior of the composite provides new pathways to design smart structures. Bridging these components into a self-healing lightweight metallic material is transformative and is expected to fill the critical needs NASA’s future vehicle fleet. This program produced the first demonstration of a aluminum-based shape memory alloy reinforced composite self-repairing technology that can heal after monotonic and fatigue loading applications. Additionally, a reactive element self-fluxing technology was implemented to improve healing and reduce surface oxidation, while a high strength shape memory alloy was designed to enhance composite strength and crack closure mechanisms. The program addresses TA12: Materials, Structures, Mechanical Systems and Manufacturing area.