“Fiber-reinforced composites are popular due to them being both strong and lightweight, ideal for aircraft or satellites, but the risk of internal micro-cracks can cause catastrophic failure”, – explained Yongjing Wang, PhD student at the University of Birmingham. “These cracks are not only hard to detect, but also to repair, hence the need for the ability to self-heal.”
Similarly to how some animals in the natural world maintain a constant body temperature to keep enzymes active, the new structural composite maintains its core temperature. According to the researchers, 3D hollow vessels, with the purpose of delivering and releasing the healing agents, and a porous conductive element, to provide internal heating and to defrost where needed, are embedded in the composite.
“Both of the elements are essential. Without the heating element, the liquid would be frozen at -60°C and the chemical reaction cannot be triggered”, – explains Wang. “Without the vessels, the healing liquid cannot be automatically delivered to the cracks.”
The healed fiber-reinforced composite, or host material, would, therefore, have higher interlaminar properties – that is the bonding quality between layers. The higher those properties, the less likely it is that cracks will occur in the future.
The team ran two tests: either by using a copper foam sheet or a carbon nanotube sheet as the conductive layer. The latter of the two was able to self-heal more effectively with an average recovery of 107.7% in fracture energy for laminates reinforced with glass fiber. However, the researchers state that the method can be applied to a large range of self-healing composites, including basalt fiber reinforced materials.
Find the full research paper here, please.