Ensuring safety and reliablity through non-destructive testing
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 sustainability and increase the likelihood of failure. Ultimately, this could lead to devastating consequences for the environment or serious threaten the safety of people.
Our research is developing new methodologies to provide quantitative measurements, improve accuracy and provide treaceability to non-destructive testing methods. We evaluate the ability of selected NDT techniques to identify, size and locate defects in a range of advanced materials during manufacture. These methods include:
- Ultrasonic C-scan - The C-scan 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 are developing procedures which are designed to place the use of C-scan techniques on a sound and traceable basis.
- Thermography - Thermography is the detection of sub-surface features from the way in which heat propagates through an object, is also being researched to make the analysis more traceable to length standards
- 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 and internal features without the need to disassemble a component. Our work to validate the identification and size of subsurface defects includes quantifying localised differences in attenuation under x-ray illumination, the limits in the resolution and penetration of the x-rays for different materials, the effect of surface roughness on dimensional measurement, the identification of interfaces within the component and reviewing different tomographic techniques for 3D reconstruction.
We are improving the development of high resolution detection capability for a range of NDT techniques such as X-ray computed tomography, ultrasonics and laser shearography that will enable step changes in the accuracy of physical characterisation of material form, integrity and homogeneity.
We are completing international benchmarking exercises for through-thickness permeability and textile preform compressibility. This work is linked to a collaborative Engineering Doctorate with Bristol University and the National Composites Centre and will transfer laboratory based techniques for in situ monitoring of liquid moulding processes to application in industrial scale processes.
Digital image correlation
DIC is a general term for comparing images, and at NPL it is used to describe our research into innovative non-contact optical techniques for measuring strain and displacement of both macro and microstructures. Our work is making this method more reliable and applicable to a wider range of applications and imaging methods. We are comparing the results taken from optical, thermal and radiographic images, and improving the accuracy of non-contact strain, and full field residual stress measurement.
As part of grant funded projects we are working with experts in robotics to develop better and safer ways to use the methods in inhospitable environments. We are working on machine learning to identify surface features and defects automatically and developing algorithms to detect defect signatures in a single pass, alleviating the need for multiple images. We have also undertaken work on railway tunnels, roads, bridges, waterways, power distribution networks, buildings and nuclear applications.