A new self-healing smart material is in the making at Switzerland’s Ecole Polytechnique Federale de Lausanne (EPFL). The concept is ready, but some fine-tuning works are still required so that the material can successfully and autonomously heal itself. The carbon composite material is among the strongest and most resistant, unfortunately it has the tendency to separate internally, causing cracks parallel to its surface upon collision, in a process called delamination.

But doctoral student Eva Kirkby from EPFL is undergoing operations in order to build a material that would cope with that by itself, with no human intervention. Used in Formula 1 cars and Boeing 787 planes, carbon fiber composites are made of a large number of layers of epoxy and light carbon fibers, providing a weight-strength ratio far superior to other materials of a similar weight. In order to deal with cracking, tiny healing liquid monomer bubbles are added at a rate of about 10 per cubic centimeter of material and accompanied by even smaller catalyst bubbles.

 

When delamination occurs, the bubbles in the affected area break, spilling the monomer which hardens under the effect of the catalyst upon covering the crack. But for maximal material strength, the number and size of bubbles should be kept to a minimum, which, in turn, might mean that they won't wholly fill the cracks. But Kirby added shape-memory alloy (SMA) wires into the composite, so when electricity is induced, they regain their initial shape, forcing the cracks to narrow (from 120 micrometers to about 17 µm, according to tests). Then, the bubbles can fill them entirely and heal them completely.

 

In order to make the process autonomous, first it is required that the material figures out where the crack occurs for only sending electricity there. The newly added optical fibers detect where the damage has been done and a pulse tracking system allows for instant recognition of the problem zone with an error margin of a few centimeters. Still, there is a lot of work ahead in order to improve the process, as researchers claim. But when it's done, we'll have a strong material that will always be as good as new.