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3D Digital Image Correlation at cryogenic temperature

3D Digital Image Correlation at cryogenic temperature

Visualisation of the displacement field as a function of the applied forceGTT is constantly looking at ways to increase its systems’ performance and efficiency by improving its testing and validation methods.

As part of its approach for the validation of new CCS technologies, the GTT Prefabrication laboratory recently acquired a new measurement system called 3D Digital Image Correlation in order to improve the design of its new technologies. 3D Digital Image Correlation is a contactless optical measurement method that achieves high precision over relatively large studied areas. The analysis and interpretation of this global data in the form of displacement fields and strain fields make it possible to improve the correlation between Thermomechanical Tests and Numerical Models. It also improves the identification of mechanical stresses of CCS components under in-service loads.

To date, although some laboratories are familiar with Digital Image Correlation, there has been very little experience in using this method during mechanical tests at cryogenic temperatures. It was therefore a challenge for GTT to be able to adapt this measurement method to our cryogenic testing facilities.Lighting set-up

After acquiring this measurement system, the engineers and technicians in the Prefabrication laboratory of GTT used their expertise and know-how in Instrumentation and Thermomechanical Tests to develop a “defrost” system synchronised with the associated photographic equipment and test machine data. A system for mounting the cameras and specific lighting allows for the observation of the behaviour of the sample with high precision behind the window of the cryogenic chamber.

Tests were successfully carried out on samples of Mark III technology sub-assemblies made up of various materials (Reinforced Polyurethane Foam and Plywood), representing several study plans at different cryogenic temperatures (down to -163°C: the operating temperature of the primary membrane on a LNG carrier).

These first tests were conclusive and made it possible to refine and improve existing numerical models. It also allowed GTT to understand better the behaviour of the systems with regard to in-service stresses. The analysis and interpretation of this global data in the form of displacement fields and deformation fields enhance the correlation between Thermomechanical Tests and Numerical Models and the knowledge about the cryogenic behaviour of the systems as well.

Correlation Tests/Calculations

One of the major challenges in developing membrane containment systems is the ability to properly model and understand the mechanical behaviour of its complex structure. Made of thin metallic or composite materials subject to cryogenic temperatures, static and dynamic loads, the containment systems require some design analyses going far beyond what we could find in the literature or in any classic design approach.

These new capabilities of the GTT laboratory offer a wide range of new possibilities in all the innovation activities. The better measurement of the behaviour of the technologies during in-service conditions will allow the design teams to strengthen their understanding of all the accumulated return of experience of the systems. Such a breakthrough, pushing back the current state-of-the-art allows the engineers to refine their assessment of the system design margins which could result in further optimization when developing new technologies. This new testing method provides more accurate measures of all the local effects and behaviours of the structure. All the finite element models with their modelling assumptions can now be recalibrated according to those more accurate measures. By doing so, the innovation processes will be improved and may result in shorter lead-times for new technology development and large scale tests. This new in-house-testing facility fully supports the innovation teams in their continuous efforts to provide the industry with higher performance systems relying on enhanced design features.

 

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