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Description
During the production of Nb3Sn coils for the Hi-Lumi LHC, some differences have been observed in coil performance in coils that follow a mostly identical fabrication process. Post mortem analysis on underperforming coils has indicated conductor degradation in regions of high stress/strain gradients as a result of filament cracking. To better understand the mechanisms for this behavior, a comparative analysis of two coils was completed to see if the bonding strength in the region of interest varies by a substantial amount. Tests devised included an apparent shear strength test using a punch and die for the coil wedge interface and a bending strength test of the coil cross section which shows difference in bond behavior at the pole. This information is compared to expected behavior in operation via FEA.
