Probing aerospace with X-rays and neutrons

Materials World magazine
24 Sep 2018

Professor Helmut Schober, Director, Institut Laue-Langevin, France, explores how the aerospace industry is reaching new heights with neutron and X-ray probing.

The development of advanced materials is essential to the progression of the aerospace industry, which, through space exploration, has provided many improvements to quality of life on Earth. For instance, the first satellites enabled the foundation of telecommunications systems, global positioning and weather forecasting capabilities. Yet even down here on Earth, aerospace technologies have impacted daily life – tensile fabrics, originally developed for spacesuits, are now commonly used to build airports, sports stadiums and shopping malls.

They are lightweight, durable and fireproof – the melting point can exceed 350°C. Another innovative material that has emerged from space is a strong, clear, smooth ceramic called poly-crystalline alumina, initially developed as protection against heat-seeking missiles. However, it also turned out to be perfect for invisible braces, which have become highly popular. Attempts to find materials with the properties to withstand harsh environments for aerospace have led to the development of intriguing materials that have gone on to improve our everyday lives.

The most significant advancements are likely to arise from a deeper understanding of the structure and characterisation of the materials at hand. Acknowledging the advantages that cutting-edge investigative techniques might provide the industry, two major European aerospace companies have announced their intentions to partner with the world’s flagship neutron and synchrotron research facilities.

Aerospace meets big science

Keen to take on board the opportunity to use neutrons and X-rays to improve the materials at their fingertips are OHB System AG and MT Aerospace AG – German sister companies that have a combined 85 years of experience in developing aerospace technologies and materials. OHB System AG specialises in the production of satellites for Earth observation and navigation, and human space exploration and scientific activity.

MT Aerospace AG is a technological leader in the production of lightweight metal and composite engineering for aerospace, in fields such as space vehicles and satellites. Offering knowledge, tools and experience, are the Institut Laue-Langevin (ILL) and European Synchrotron Radiation Facility (ESRF), the world’s leading neutron and X-ray probing facilities, respectively. The goal of their agreement is to identify and tackle the greatest challenges facing materials development, such as the ability to function in extreme variations of temperature, and to help secure their place as market leaders.

By teaming up with the ILL and ESRF, the industry players have been given an opportunity to gain an enhanced understanding of specific components within materials. The ILL and ESRF combine to form a toolkit
on a singular site in Grenoble, France, for the probing
of materials to reveal atomic and molecular structures. ILL uses world-class instruments for conducting
neutron research.

Home to leading neutron research, the facility provides multiple techniques for penetrating deep inside samples to investigate the atomic structure. Offering complementary research capabilities, ESRF provides advanced X-ray beams for probing materials, providing extensive structural details of the sample.

These research facilities will inform the choice of materials for new technologies that may, in turn, revolutionise the aerospace industry. A dedicated
group of engineers and scientists from ILL and ESRF will also be on hand to assist all aspects of the project, from identifying challenges through to experiments
and reporting.

Optimising the use of existing materials to ensure they perform at their highest capability will ensure that only the best technologies make it into space. Maximising structural awareness through the development of innovative new materials will help OHB System AG and MT Aerospace AG remain at the top of their field regarding scientific developments.

Bringing X-rays and neutrons together

Neutron beams are useful for probing materials, thanks to the specific properties of neutrons themselves. As they are electrically neutral, they interact with the nuclei of atoms within a sample, allowing researchers to visualise the position of atoms. Neutrons also have a magnetic dipole, allowing the magnetic effects of the samples to be observed. Additionally, experimental environments for neutron probing can be tailored to test the material under various conditions – extreme temperatures, pressures and magnetic and electric fields can be generated. In some experiments, the wavelength and energy of neutrons in the beam can be adjusted to optimise the penetration power of the neutrons, and as a result the ILL provides an excellent tool for gaining a deep understanding of the most complex materials. In contrast, the X-ray probes at ESRF, produced by a synchrotron radiation source, provide extensive detail of the structure based on interaction with electrons, rather than neutrons, in the same sample.

One manner by which neutron and X-ray probing can contribute to aerospace specifically is by investigating precise components of the aerospace products, such as valves or tank structures in rockets, and electronic components and circuit boards in satellites. Many of these are composed of alloys, where a mixture of metals might combine to form an overall stronger or lighter material, ideal for aerospace. Neutrons are perfect for examining these, as neutron beams are able to distinguish the lighter metals from the heavier ones, and understand the exact composition of the alloy.

Neutron and X-ray investigation can also help aerospace manufacturers assess whether their building and maintenance processes are suitable for the product. By examining stress within the metal components throughout development, they can ensure their chosen methods are not having a detrimental effect on the longevity and function of the product.

Critically, as neutron and X-ray beams both provide a non-destructive way of examining the structures, the technology can be scrutinised without damage. It is critical that these can be examined without compromising their competence, as common subjects of inspection include engine blades, aircraft wings and devices for rocket ignition, all of which must remain intact to ensure their safety.

A key use of probing to test technology components is evaluating their stress in response to parameters that the material might encounter during a rocket launch or deployment in space. This can be conducted in real-time, providing the most accurate reproduction of the material in use. In-situ measurements at the ILL enable the stress level of a material to be determined under various load conditions, including extreme temperatures, statics, dynamics and acoustics.

Neutrons are sensitive tools for determining strain
of materials at the atomic level. The neutron beam is able to achieve significant penetration depth, so that residual stress deep inside structures can be measured. This increases our knowledge of the strength and toughness of the material, and may provide an early signal of potential failure, which in the aerospace industry would be particularly catastrophic. Awareness of the stress level of components under a range of conditions will support judgements of the optimal material choice and manufacturing process for aerospace technology to ensure it has the highest possible efficiency and reliability.

A new frontier for materials science

These developments will assist companies in the global competition to develop advanced aerospace materials. In satellite manufacturing, constantly pushing for innovation is of vital importance. Companies must always be developing new concepts, systems and processes. As modern manufacturing systems advance, progressive understanding of new prototypes and established materials is essential to ensure their applications are optimised.

The material challenges placed on space technology are substantial – they must be very hardwearing to hold up in the extreme conditions of space. The industry seeks lighter materials that can withstand rougher environments, remaining functional under a variety of hostile conditions. The types of technologies required for space missions are also very diverse. High-performance materials are needed for vehicle structures, propellant tanks and propulsion systems, lightweight, deployable and inflatable structures for space infrastructures and crew habitats, and systems for reducing launch mass and volume of parts, such as antennae and booms to be deployed in space. Consequently, the quality requirements are exceptionally demanding, and each and every material included must be of the highest standard.

In modern materials research it is important to use the best possible tool for the investigation under consideration. The extreme environmental conditions placed on samples being probed at the ILL and ESRF provide thorough testing. Materials can be characterised over all relevant length scales, from the atomic to the micrometre scale. This will identify with great accuracy any weaknesses or margins of improvement, ultimately leading to the most effective materials in the industry.

The partnership between the European aerospace leaders and flagship research facilities demonstrates the great advantage that may arise from establishing a relationship with mutually beneficial goals – pooling resources is the best way for organisations to stay ahead of the game. This partnership is one that optimises the seamless flow of scientific research into industry, allowing all players involved to perform at their highest standard and see direct advances as a result of their efforts. The aerospace industry will receive access to the knowledge and research capabilities of the global leaders in neutron and X-ray investigation, and the research facilities will benefit from the combined 85 years’ industry insights boasted by OHB System AG and MT Aerospace AG.

Aerospace materials research is evolving to take advantage of the continued developments in investigative techniques at big science facilities. The opportunity these advances provide, for organisations to better understand their products at a deeper level than previously achievable, should not be overlooked. Companies that trail behind regarding the development of new technologies, or that fail to implicate recent scientific progress, are unlikely to be those that remain at the top of their field.

The agreement signed between ILL, ESRF and the German aerospace firms, to join forces in the field of advanced characterisation of aerospace materials, is likely to successfully identify and tackle industry challenges. Should the partnership continue to be fruitful, other similar agreement will undoubtedly follow, enhancing the flow of knowledge between science and industry for the benefit of all.