%0 Journal Article %T Characterization of the Formability of High-Purity Polycrystalline Niobium Sheets for Superconducting Radiofrequency Applications %+ I-Cube Research %+ Institut de Recherche Dupuy de Lôme (IRDL) %+ Laboratoire d'Etude des Microstructures et de Mécanique des Matériaux (LEM3) %+ European Organization for Nuclear Research (CERN) %A Croteau, Jean-François %A Robin, Guillaume %A Cantergiani, Elisa %A Atieh, Said %A Jacques, Nicolas %A Mazars, Gilles %A Martiny, Marion %< avec comité de lecture %@ 0094-4289 %J Journal of Engineering Materials and Technology %I American Society of Mechanical Engineers %V 144 %N 2 %P 021004 %8 2022 %D 2022 %R 10.1115/1.4052557 %K forming limit diagram %K Marciniak test %K two-zone model %K niobium %K SRF %K mechanical behavior %K metals %K plastic behavior %Z Engineering Sciences [physics]/Mechanics [physics.med-ph]/Mechanics of materials [physics.class-ph]Journal articles %X The forming limit diagram (FLD) of high-purity niobium sheets used for the manufacturing of superconducting radiofrequency (SRF) cavities is presented. The Marciniak (in-plane) test was used with niobium blanks with a thickness of 1 mm and blank carriers of annealed oxygen-free electronic (OFE) copper. A high formability was measured, with an approximate true major strain at necking for plane strain of 0.44. The high formability of highpurity niobium is likely caused by its high strain rate sensitivity of 0.112. Plastic strain anisotropies (r-values) of 1.66, 1.00, and 2.30 were measured in the 0 deg, 45 deg, and 90 deg directions. However, stress-strain curves at a nominal strain rate of ∼10 −3 s −1 showed similar mechanical properties in the three directions. Theoretical calculations of the forming limit curves (FLCs) were conducted using an analytical two-zone model. The obtained results indicate that the anisotropy and strain rate sensitivity of niobium affect its formability. The model was used to investigate the influence of strain rate on strains at necking. The obtained results suggest that the use of high-speed sheet forming should further increase the formability of niobium. %G English %2 https://ensta-bretagne.hal.science/hal-03648243/document %2 https://ensta-bretagne.hal.science/hal-03648243/file/mats_144_2_021004.pdf %L hal-03648243 %U https://ensta-bretagne.hal.science/hal-03648243 %~ UNIV-BREST %~ ENSTA-BRETAGNE %~ CNRS %~ UNIV-UBS %~ ENSAM %~ UBS %~ ENIB %~ UNIV-LORRAINE %~ IRDL %~ LEM3-UL %~ ENSTA-BRETAGNE-MECA %~ ENSTA-BRETAGNE-PTR3-IRDL %~ TEST3-HALCNRS %~ HESAM %~ HESAM-ENSAM %~ IRENAV %~ LAMPA %~ LCPI %~ LABOMAP %~ LISPEN %~ MSMP