The image shows the discontinuities
in the local displacement field and
the associated cracking identified by
DIC during the loading of a concrete
structure. NPL, in partnership with Airbus, AWE,
Stresscraft, British Energy and
LaVision, has demonstrated the
world’s first application of using
DIC for the measurement of residual
stress with the incremental hole drilling
technique.
 

Digital Image Correlation (DIC) is 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:

• Material behaviour
• Examining the evolution and uniformity of strain
• The mapping of strain fields around features and defects
• Crack tip and crack propagation studies
• Dynamic vibrational analysis
• High temperature strain mapping
• Miniaturised testing
• Deformation of large structures
• Structural health monitoring
• Finite Element (FE) validation

NPL has worked with both Blue Chip companies and SMEs to apply DIC to the characterisation of materials and the monitoring of engineering components. We have recently expanded the technique to include a wide range of applications in the civil
engineering and nuclear industries.

How DIC works

DIC works by comparing images of a component or testpiece at different stages of deformation and tracking blocks of pixels to measure surface displacement and build up full field 2D and 3D deformation vector fields and strain maps. Different DIC analysis solutions have been developed to obtain sub-pixel resolution. The strain resolution is typically 100 μΣ and is ideally suited to plastic deformation studies.

The DIC correlation process is not restricted to optical images and can also be applied to other datasets such as surface roughness maps, and complex 3D MRI and X-ray tomography datasets.

Applications

The range of potential applications for DIC is huge and its practical application is both simple and cost effective. Images can be obtained from a wide variety of sources including conventional CCD or consumer digital cameras, high-speed video, microscopes, macroscopes, the SEM and AFM. NPL has delivered a wide range of DIC solutions to customers including:

• Quantifying strain field inhomogeneities during mechanical testing
• Validation of FE models in the biaxial testing of polymer composites
• Thermal expansion and distortion of electronic components
• Deformation and cracking in reinforced concrete structures
• Measuring the mechanical properties of nuclear graphite
• Integration with hole drilling technique for novel residual stress measurement
• Damage development in silk print screens 3D shape measurement on air bags
• Characterising the deformation of biological tissues
• High temperature strain measurement in thermomechanical fatigue testing
• Interfacing with NPL microtesting equipment for microscale strain measurement

Download DIC flyer

Contact

Customer Service tel: +44 20 8943 8681
E-mail: materials_enquiries@npl.co.uk