European Space Agency develops self-healing materials

Citation

(2006), "European Space Agency develops self-healing materials", Assembly Automation, Vol. 26 No. 3. https://doi.org/10.1108/aa.2006.03326caf.002

European Space Agency develops self-healing materials

European Space Agency develops self-healing materials

Keywords: Spacecraft, Adhesives, Composite materials

Much has been made of the emerging families of smart materials in recent years and one of the more futuristic concepts being studied is “self-healing.” The idea is to develop materials that can repair themselves if damage is sustained and steps towards this becoming a reality are being made by the European Space Agency (ESA). A research group at Bristol University's Department of Aerospace Engineering in the UK are working on an ESA project which aims to develop a self-healing skin for spacecraft. This is a particularly critical requirement, as manned space vehicles and satellites are subjected to extreme and rapid temperature fluctuations and impacts from high velocity micrometeroids which can cause cracks and other surface defects to develop. Over the course of a mission, these accumulate and can ultimately lead to catastrophic structural failure. Further, there are potential economic benefits, as the ESA estimates that doubling the lifetime of an earth-orbiting spacecraft could halve the overall cost of the mission.

The research group fabricated a composite laminate material where a few percent of the fibres were replaced by hundreds of 60 μ-wide, hollow glass filaments, with inner diameters of 30 μ. Half of the filaments were filled with an epoxy polymer or resin and the other half with a curing agent. When damage occurs, the fibres break and release the compounds that fill the cracks, react and solidify and prevent the cracks from developing further (Plate 2).

Plate 2 Performance of the self-healing material

In recent experiments, the team constructed and then intentionally damaged some panels containing the fibres. They were then dismantled to assess how efficiently they had healed, revealing that the process restored about half of the structural strength lost during impact. Further experiments aimed to assess the material's ability to survive and operate in a space-like environment. Trials in a vacuum chamber showed that the material can survive in a vacuum and the resin also withstood repeated temperature cycling between + and - 100ºC. The Bristol team believe that the technology is compatible with existing fabrication techniques and could be in production within around five years but others are less convinced. Scott White, a materials engineer at the American University of Illinois at Urbana- Champaign, believes that the resin patches on earthbound spacecraft would burn off in the intense heat of re- entry and even for uses in orbit current resins leave much to be desired. The Bristol team concede that the epoxy ingredients would not solidify if mixed in the wrong ratio and ESA materials scientist Christopher Semprimoschnig notes that the substances can easily become contaminated and that there is a need to guarantee the longevity of the materials as they will have to repair damage after lying dormant for maybe one or two years in space.

Another limitation is that it is difficult to run glass tubes through a composite component in more than two dimensions. Thus, whilst glass micro- plumbing could easily spider through the surface layer of a panel it could not easily be installed through its entire thickness. Nevertheless, these early trials suggest that the technique has promise and the next steps by the Bristol group are to develop stronger materials containing the filaments and to test them in even more extreme conditions, such as at very high temperatures. According to Semprimoschnig “We have taken the first step but there is at least a decade to go before this technology finds its way onto a spacecraft";.