Nanocomposites take flight - HiPerNano 2012 report

Materials World magazine
,
4 Jun 2012

A vast amount of high performance nanocomposite research is being conducted, but where can the technology be applied in engineering? Ledetta Asfa-Wossen went to HiPerNano 2012 in London, UK, to find out.

Nanocomposite inks have been used in paintings for almost 3,000 years. They exist in nature in the form of abalone shell and bone, but even now the challenge of how to implement nanocomposites for advanced engineering on a mass scale remains.

The UK’s energy policy has set up a tough agenda for the electricity supply industry. The 2020 targets require the UK to increase electricity generation from renewable sources to 15% (currently 3%). By 2050, 80% of CO2 needs to be reduced, with a 34% reduction by 2022. Wind and ocean resources are plentiful given the UK’s location, but energy needs to be harvested, transported and distributed.

According to Dr Fabrice Perrot, nanocomposites could provide advanced insulation materials for the manufacture of next generation high voltage direct current (HVDC) power transmission equipment. ‘HVDC insulation materials could further redistribute renewable energy for high-cost converter stations and marine cables and increase power reliability. They are essential for long-term growth of onshore and offshore HVDC systems in the UK and Europe, which rely on point-to-point and multi-terminal HVDC schemes.’

Power to the people

Perrot noted other benefits, such as an increase in dielectric strength and voltage endurance, flexibility to control permittivity (AC) and conductivity (DC), thermal stability and mechanical strength. ‘In practise, this could mean more compact power equipment, flexibility in design and extended lifetimes.’ At present, nanodielectrics remain a relatively new area. Little is known about how to characterise or assemble these materials.

To test this idea, grid research and technology centre ALSTOM are heading up a £1m consortium-led project, NanocompEIM, to demonstrate, manufacture and scale up nanocomposite electrical insulation materials. The project is to span 30 months and will aim to gain understanding and practical experience of the production of nanodielectric materials for potential application in HVDC transmission equipment (most of which will also be relevant for HVAC equipment).

Working smart

A further energy issue that could be solved by nanoengineering is smart coatings for drag reduction. ‘Typically around 50% of fuel burn for a commercial airliner in cruise conditions is used just to overcome skin friction,’ explained David Birch of the University of Surrey, UK.

A substantial proportion of the drag penalty incurred by a number of marine vehicles, including submarines, is also due to skin friction. A smart surface capable of sensing and reacting to local flow conditions could reduce drag. However, limitations in sensor and actuator technology have so far hampered any practical development of these smart surfaces. At the University of Surrey, a team is investigating what elements need to be controlled when considering drag. Understanding turbulent boundary layers, for example, is key. ‘To control anything actively, you need an effective sensor to detect the structure. But there are often low sensitivity or temperature issues. Small-scale, high-sensitivity pressure sensors have proven extremely difficult to produce. Covering a decent-sized airliner with sensors using this process could cost £5bln.’

A high performance nanomaterial would be an ideal method to locally control and detect change in material property and surface shear on an aircraft as it is very thin and highly elastic (strains of 10–50%). In addition, it is electrically conductive and can be applied inexpensively over large areas. Birch continued, ‘At the moment, there are poor material choices available. Sensors are fragile, very expensive and have a high defect rate. Actuators need to be small (around 100um) and have fairly high bandwidth.’

John Godman of Agusta Westland Research and Innovation Dept UK, discussed how nanomaterial surfaces could provide a better solution for rotorcrafts that need to reduce vibration, noise and emissions and maximise payload range, or on rotor blades to delay stall. Helicopters need to sustain extreme environments such as erosion or brownout, often at 35 degrees and an altitude of 6,000ft. Ice and rain also present mechanical problems such as engine ingestion. But, even with a range of promising applications, qualification and product certification will stall material development in sectors where safety is paramount. A lab-scale project can take up to 1–3 years, to complete prototyping 5–11 years, and in engineering time is money.