Giving confidence in performance
Defects and irregularities in the materials of safety-critical components and large structures like bridges, tunnels and power plants can compromise structural integrity, reduce lifetime and increase the likelihood of failure. Ultimately, this could lead to devastating consequences for the environment or serious threaten the safety of people.
Our work provides customers with the confidence they need when designing, building and maintaining structures. We help to monitor structural health and integrity and extend the lifetime of structures, even in the most hazardous environments.
NDT provides a means of identifying damage and irregularities in materials and is often the only means of obtaining information about the current 'health' of a structure. It can be used to detect and size in-service and manufacturing defects. NDT is used for on-line production quality control through to in-service inspection, structural health monitoring (SHM) and life management.
NPL has extensive NDT and surface analysis instrumentation and expertise able to support industry in materials characterisation, product development, and long-term performance assessment and damage monitoring. NPL aims to promote the advancement of metrology underpinning non-destructive testing, condition monitoring and diagnostic engineering (including structural health monitoring) for design and quality assurance purposes.
The C-scan has a resolution of 1mm and is capable of scanning composites panels 600 mm x 600 mm. The system is operated in a water immersion tank.
This technique is used to detect, measure and characterise a wide range of manufacturing and in-service defects in composite materials and is routinely used in the aerospace industry. We have developed procedures which are designed to place the use of C-scan techniques on a sound and traceable basis.
X-ray computed tomography (XCT) and radiography
X-ray analysis of an object, either in 2D or reconstructing images in 3D allows the measurement of the geometry of external (surface) and internal features without the need to disassemble a component. Localised differences in attenuation under x-ray illumination to provide a cross-sectional picture of the density of a component from which variations caused by pores or inclusions can be identified. It is useful for complex components where it might be difficult to use other techniques but there are limits in the resolution and penetration of the x-rays for different materials.
The way in which heat propagates through objects can be used to detect sub-surface features and some types of failures without needing to cross-section the objects under study. The object can be heated in a variety of ways, and an infra-red camera is used to image the heat distribution and is propagation in to the surface. One of the features that makes this technique so attractive is that it can operate close to room temperature and is totally non-contact.
Digital image correlation (DIC)
DIC is a general term for comparing images but at NPL is is used to describe an innovative non-contact optical technique for measuring strain and displacement of both macro and microstructures. It offers a versatile analytical tool that is now being used extensively in experimental mechanics in a diverse range of applications. We have recently expanded the method to include applications in the civil engineering and nuclear industries, performing NDE on buildings and tunnels. We have also developed algorithms to automatically detect defect signatures in a single pass in some cases, alleviating the need for multiple images.