Self-Healing Structural Materials

Abstract

Self-healing materials have been developed since the 1990s and are currently used in various applications. Their performance in extreme environments and their mechanical properties have become a topic of research interest. Herein, we discuss cutting-edge self-healing technologies for hard materials and their expected healing processes. The progress that has been made, including advances in and applications of novel self-healing fiber-reinforced plastic composites, concrete, and metal materials is summarized. This perspective focuses on research at the frontier of self-healing structural materials.

Keywords: mechanical properties; self-healing; self-repair; structural composites.

Figure 1

(a) Self-healing specimen in which microcapsules of the healing agent and the catalyst are embedded in the polymer matrix, and healing is autonomic. Reprinted with permission from [27]. (b) Optical microscopy images of a composite laminate before and after healing. The scalebar is 50 μm. Reprinted with permission from [28]. (c) Optical micrographs of brick-and-mortar structure composites under a bending test. The displacement rates are 1 and 0.1 mm/min. Reprinted with permission from [29]. (d) Snapshot and infrared image of a CFRTP specimen stitched with an electrically conductive thread for Joule heating. Reprinted with permission from [30].

Figure 2

(a) Microscope image of the microcapsules composed by an emulsion (54-wt% mineral oil, 42-wt% sodium silicate, and 4-wt% emulsifier). Reprinted with permission from [45]. (b) Evolution of a crack at the specimen surface containing biomortar. Crack widths are given in the micrograph. Reprinted with permission from [46]. (c) Schematic of the concrete crack closure system of a shape-memory PET tendon. Reprinted with permission from [9]. (d) Schematic of the self-healing cement composite induced by Joule heating. Reprinted with permission from [49].

Figure 3

Illustration of BN precipitation on the creep cavity surface in stainless steel. Reprinted with permission from [56].

Figure 4

Micrographs of the Fe–Mo alloy after creep under a stress of 160 MPa at a temperature of 565 °C demonstrating cavities and precipitation at grain boundaries parallel to the loading direction at selected locations. Reprinted with permission from [59].

Figure 5

Structure of the gaps in Al₂O₃/SiC composites healed at 1473 K. High-resolution transmission electron microscopy of healed cracks at the interface between SiC and SiO₂ and between Al₂O₃ and SiO₂. Reprinted with permission from [66].