Structural health and condition monitoring is vital to ensure that large structures – such as bridges, tunnels and power plants – are safe and stable throughout their lifespans. Any defects that develop could compromise structural integrity, reduce operational lifetimes and increase the likelihood of failures if not detected. To prevent this from happening, critical structures are periodically inspected, measuring and recording any changes in position, shape or performance to track and assess their structural health. This enables the early detection of any potential problems, which can then be addressed promptly to avoid further issues, helping to extend the service lifetimes of critical components and infrastructure, even in the harshest environments, while avoiding potentially serious safety and environmental consequences.
NPL offers condition monitoring solutions for structures including railway tunnels, nuclear power plants, roads, bridges, waterways, power distribution networks and buildings. These applications are part of by NPL’s non-destructive evaluation (NDE) services, and are complemented by non-destructive testing (NDT).
DIC is a general term for comparing images. This versatile analytical tool is used extensively in experimental mechanics across a diverse range of applications.
At NPL, the term is used to describe an innovative non-contact optical technique for measuring strain and displacement of both micro- and macrostructures in civil engineering projects. These typically include structural health monitoring of tunnels, roads and bridges, in nuclear industries where access is limited, and on energy grid locations.
The objects monitored can range in size from micrometres – measured by scanning electron microscopy – to millimetres, and even kilometres, generated using panoramic image capture techniques at resolutions of >250 gigapixels. Images are compared to assess external surface deformation, in-plane displacements (height, if using 3D DIC), and in-plane strain and shear, which are often caused by thermal or mechanical changes to an object, surface corrosion, weathering or damage. These observations can then be used to derive field displacement and strain parameters.
NPL is focused on enhancing DIC and applying the technique to a wider range of applications and imaging methods, comparing the results from optical, thermal and radiographic images.
We offer both short- and long-term DIC monitoring techniques that enable feature recognition and detection of common structural defects, including scoping options to reduce the risk to individual organisations. Bespoke solutions are frequently required, which must be compliant with relevant regulations and meet all health and safety requirements. Following a site risk assessment, large-scale DIC services can be devised to quantitatively monitor structures and track changes over time. This can involve prototype design and development, and/or bespoke machinery design and build. Examples include the development of a digital imaging for condition asset management (DIFCAM) system for a railway tunnel examination trolley for Network Rail, and a high accuracy inspection system for long-term monitoring of nuclear waste storage at Sellafield, a fully UKCA-marked finished product.
Research is also underway to develop methods that combine imaging data with sub-surface techniques, such as ground penetrating radar. This will allow common structural faults to be detected by imaging, while sub-surface data will enable the identification of potential causes of the defect. Alongside this, grant-funded projects include collaborations with experts in robotics to develop better and safer ways to use image analysis techniques in hazardous and inhospitable environments. NPL is also investigating machine learning and AI approaches to identify surface features and defects automatically, as well as developing algorithms that can automatically detect defect signatures in a single pass, avoiding the need for multiple images in some cases.
As the UK's National Metrology Institute, NPL aims to promote advances in metrology, using its years of experience and wide-ranging expertise in condition monitoring – complemented by extensive knowledge of NDT and NDE applications –to ensure the structural health of crucial infrastructure. This comprehensive skill set, combined with state-of-the-art facilities, perfectly positions NPL to meet the needs of safety-critical structural health monitoring applications.
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