Additively Manufactured Self-Healing Structures with Embedded Healing Agent Reservoirs

Abstract

Self-healing materials with the ability to partially or completely restore their mechanical properties by healing the damage inflicted on them have great potential for applications where there is no or only limited access available to conduct a repair. Here, we demonstrate a bio-inspired new design for self-healing materials, where unit cells embedded in the structure are filled with a UV-curable resin and act as reservoirs for the self-healing agent. This design makes the repeated healing of mechanical damage possible. When a crack propagates and reaches one of these embedded reservoirs, the healing agent is released into the crack plane through the capillary action, and after polymerization through UV light exposure, bonds the crack faces. The structures here were fabricated using a stereolithography technique by a layer-by-layer deposition of the material. "Resin trapping" as a unique integration technique is developed for the first time to expand the capability of additive manufacturing technique for creating components with broader functionalities. The self-healing materials were manufactured in one step without any needs for any sequential stages, i.e. filling the reservoir with the healing agent, in contrast with the previously reported self-healing materials. Multiscale mechanical tests such as nanoindentation and three-point bending confirm the efficiency of our method.

Figure 1

(a) A CAD model of the self-healing structure (front view). The inset shows the geometry of the straight notch, (b) an actual 3D printed specimen with hollow reservoirs and trapped resin, (c) a schematic of the structure with an optical image inset, showing the leaked healing agent from a crack, (d) curing the leaked UV-photocurable resin, using multi-directional UV LEDs.

Figure 2

Force-displacement curves of three different types of specimens under the tensile loads.

Figure 3

Nanoindentation test results. (a) The elastic modulus of different locations on a cured specimen after 9 min exposure to a 405 nm UV light, (b) elastic modulus and hardness versus the exposure time for a cured specimen under the UV light.

Figure 4

(a) Force-displacement curves from the 3-point bending of the specimens before and after healing process (Cycle 1, Cycle 2, respectively) as well as that for manually repaired and virgin samples, (b) a schematic of the experimental procedure for the crack detection using an acoustic sensor, (c) force-displacement curves for one specimen exhibiting four continuous healing cycles before fracture, (d) a schematic and an optical image of the self-healing structure after a crack is formed and the healing agent leaked out to the surface. The inset shows a zoomed-in OM image of the first and second crack.

Figure 5

The healing efficiency of the specimens for each cycle of loading, compared with reported data from microcapsule (black), single network (blue), and dual network (green).