Nonlinear Ultrasonic Stimulated Infrared Thermography (NUSIT)

Micro-cracks in aircraft primary structures or nuclear plants can easily spread over long periods of time and, if undetected, may lead to catastrophic failure conditions. Non-destructive evaluation (NDE) techniques are a necessary tool to guarantee that a component is free of any harmful damage. Thermosonics (also known as ultrasonic stimulated thermography) is an NDE technique that uses an infrared camera to image material defects by detecting the frictional heating at crack surfaces when a part under inspection is vibrated. These vibrations are produced by a high-power ultrasonic horn being pressed against the surface of the component under investigation. Thermosonics has the advantages of being rapid, affordable and more sensitive to micro-cracks detection than traditional infrared thermography. However, the ultrasonic horn used in thermosonics is a crude means of exciting vibrations. The mechanical contact between the material and the horn typically results in an uncontrolled generation of vibrations, which makes thermosonics results non-reproducible and, therefore, this technique not reliable.

NUSIT proposes a reliable and reproducible alternative to thermosonics by developing a novel hybrid NDE inspection method, here named as nonlinear vibro-thermography, obtained by a combination of nonlinear ultrasonic techniques and thermography. Nonlinear ultrasonic methods measure the material nonlinear effects caused by the interaction of ultrasonic waves with the "clapping" motion or the frictional contact between micro-crack surfaces. As a result of this interaction, other frequency components of the single input frequency can be generated. These new frequencies indicate that a damage is present within the material. Nonlinear ultrasonic methods will provide in NUSIT a reliable means to select the input frequency that will enhance these material nonlinear effects. This will allow high sensitivity to micro-cracks detection and repeatability. Traditional thermography will be then used to image the frictional heating at the damage location. The input frequency selection process will also be optimised in NUSIT by analysing the concept of nonlinear local defect resonance for input power reduction.

This eighteen-month project will be mainly focused on assessing real-life material damage such as corrosion micro-cracks in metallic structures and impact flaws in composite materials. To accomplish these objectives, NUSIT is supported by the Nuclear National Laboratory and Rolls-Royce that are providing a set of steel nuclear storage canisters with corrosion micro-cracks and impact damaged composite aero-engine components as in-kind contribution. Nonlinear vibro-thermography will produce a step-change in the non-destructive inspection of both metallic and composite materials by ensuring rapid and affordable inspection of large areas and complex geometries, reliable excitation and high sensitivity to the presence of micro-structural flaws. The overall aim of NUSIT will be to take nonlinear vibro-thermography out of the laboratory and introduce it successfully into industry.

The successful implementation of nonlinear vibro-thermography as a novel non-destructive evaluation (NDE) inspection system will ensure significant reduction in maintenance time and costs as well as the increase of safety due to the high sensitivity and reliability in detecting material defects for aeronautic, nuclear and high value manufacturing industries. The UK has 17% of the global aerospace market share with revenue of £24 billion and is responsible for 3.6% national employment. With the international civil aerospace market forecast to grow to $4 trillion by 2030, the UK market has the opportunity to grow to $352 billion by 2030. The civil nuclear industry also plays a pivotal role in the UK economy as it employs around 85,000 people of which 45,000 work at power plants and 40,000 in the supply chain. In addition, as noted by EPSRC, the development of novel material inspection techniques has been identified as a national priority area by the Department for Business Innovation and Skills. NDE techniques play a significant role in High Value Manufacturing as highlighted by Innovate UK. The UK is world-leading in NDE development having 24 of the 183 key NDE companies, with a global turnover in 2012 of about £5.6bn.

Industrial: Rolls-Royce and the Nuclear National Laboratory will benefit directly from the outcome of NUSIT. Indeed, by improving the efficiency of aircraft maintenance operation, extending the damage tolerance boundaries of aircraft components and reducing the materials usage, NUSIT will contribute to decrease CO2 emissions for commercial aircraft by 50% per passenger-kilometre. Such a reduction should enable a lighter, more fuel efficient next generation of aircraft in the next 5-20 years. This project will also contribute to reduce the operations and maintenance costs for nuclear power plants, which are usually realised during planned maintenance and refuelling outage periods and account for nearly 91% of planned energy loss. A technology live demonstrator will be built in collaboration with the Nuclear National Laboratory and Rolls-Royce towards the end of the project to showcase the proposed nonlinear vibro-thermography system. Input from both Rolls-Royce and the Nuclear National Laboratory will be available throughout the project via quarterly meetings with senior NDE specialised personnel. Ciampa will work with the University of Bath's Research Innovation Services, to conduct a review of Intellectual Property (IPs) developed in this project and, if applicable, to protect it through patent, copyright and design registration processes. Potential beneficiaries/partners will be sought through the ongoing collaborations with the Nuclear National Laboratory, Airbus, Rolls Royce and AgustaWestland UK, as well as the industrial partners of the EU FP7 ALAMSA and Horizon 2020 EXTREME projects.

Policy: The UK is committed to reduction of emissions. Results from NUSIT that enable such reductions will help deliver such commitments.

Public: The general public will see health benefits from reduced emissions and financial benefits as reduced flight costs are converted to reduced ticket prices. Lighter aircraft may also result in less powerful engines being required and subsequently a reduction of noise near airports. The technological advances of NUSIT will reflect in higher quality of structured inspection that mitigate the risk of a latent nuclear safety event and provide public risk awareness and acceptance for nuclear power. Open access publication and public data storage will ensure all information relating to NUSIT is directly available to the public and to any aerospace or nuclear related UK companies.

Staff: Ciampa and the PDRA will develop transferable knowledge of ultrasonic and thermography NDE inspection technologies and data interpretation/processing through collaborations and visits to industrial partners.