Fiber-reinforced polymeric (FRP) composites are eminent engineering materials for structural applications due to their high strength-to-weight ratios. During their service life, FRP composites are often exposed to severe conditions leading to fatigue-induced damage. This damage mode is complex and difficult to detect and repair before eventual catastrophic failure. Continuous fibers are typical reinforcements for FRP composites which provide excellent axial strength and stiffness in the fiber direction. Owing to this directionality, the fatigue-induced damage first creates matrix cracks and fiber/matrix interfacial debonding near the off-axis fibers and evolve into fiber failures and delaminations. Therefore, failure of the FRP composite can be retarded by repairing microscale flaws at the initial stage.
Self-healing materials have been developed to autonomously detect and repair the damage. One method of self-healing in a material is to incorporate microcapsules which sequester healing agents. These healing agents are autonomously released and wick into the fracture planes upon rupturing by a damage. Yet, little has been done on capsule-based self-healing FRP composites due to the difficulties in the fabrication process. Existing composite manufacturing processes cause microcapsules to agglomerate or often rupture because of the presence of fiber-reinforcements. As a result, the capsule-based self-healing FRP composites inherently possess a low fiber volume fraction < 40 vol% and agglomerated microcapsules.
Another method for creating a self-healing material is to embed microvascular channels which can deliver healing agents from an external reservoir. These pervasive channels can transport large amounts of healing agents to fracture planes with the aid of an external pump, but segregated channels can suffer from blockage. Three-dimensional (3D), inter-connected microvascular networks provide redundant networks improving the flow distribution and minimizing the effects of individual microchannel failure. However, fabricating 3D microvascular networks within a FRP composite is a major challenge for existing rapid and large-scale manufacturing processes.
In this thesis, the manufacturing difficulties listed above will be addressed to effortlessly fabricate a high-performance self-healing FRP composite. Microcapsule-containing unidirectional (UD) prepreg fabrics were developed to uniformly distribute the microcapsules at the fiber interstitial spaces. Self-healing FRP composites were fabricated from the microcapsule-containing prepregs and the healing of fatigue-induced damage was demonstrated. In addition, UD prepreg fabric containing sacrificial fibers were developed to create 3D microvascular networks within a FRP composite.
This study will drive the adoption of self-healing FRP composites into commercial industries that need high-performance materials with the enhanced reliability. Moreover, the development of multi-functional FRP composites will be facilitated as it guides a solution to uniformly distribute functional fillers without compromising their mechanical integrity
