Full-Field Displacement Measurement Method of Metal-As-Insulation Pancake at Liquid Nitrogen Temperature

In situ measurement of metal-as-insulation (MI) high temperature superconductor (HTS) pancake deformation gives insight to its actual mechanical state. Measurement of hoop strain for inner / outer turn of MI pancake is usually made by strain gauges. This measurement is however local and faces electromagnetic compatibility (EMC) and thermal issues. Non-contact full-field displacement measurement is an interesting alternative solution. This technique is based on digital image correlation (DIC), which derives the displacement field in specified region of interest (ROI) by correlation between the deformed state image and the reference state image. In this article, we present a novel DIC experiment setup for displacement measurement of MI pancake in cryogenic cooling. The setup is validated by a cooling test of 304 stainless steel disc. Then, it is used for cooling test of MI pancake made of co-wound copper beryllium - 304 stainless steel tapes. Both tests are done at 80 K by conduction cooling using liquid nitrogen. Finally, experimental results are compared to numerical results obtained from an analytical formulation of the mechanical equilibrium using generalized plane strain assumption.