Figure 8. Effect of loading rate and brick length on composite healing.

(a,b) In situ optical micrographs taken during bending tests carried out on composites formed with thicker (1 mm) bricks. Due to the shear-thickening behavior of the interface, fracture is “cleaner” during faster fracture (displacement rate of 1 mm/min) but long capillary bridges form at slow fracture (0.1 mm/min). (c) As a result, the fracture rate affects the strength (maximum in the stress-strain curve), although it does not influence the healing behavior which is above 90% after only 1 day. The capillary bridges bring the structure back together after removing the load without need of external pressure. (d) Evolution of the material’s three point bending strength with time after healing (no external pressure applied). Materials with brick aspect ratio below a critical value exhibit full interfacial fracture and recover all their strength after five days, while recovery is only partial for materials with longer bricks that undergo fracture during the first tests. As for the interfaces the materials can be stronger after healing.