Bending Behavior of High-Strength Conductor

Conductors in pulsed magnets in the U.S. National High Magnetic Field Laboratory (MagLab) are rectangular cross section wires of relatively large thickness. During the manufacture of the magnets, some of these conductors are wound to small-diameter coils (less than 15 mm). Because of the large thickness and the small bending radii for winding, the wires undergo large bending strain, sometimes causing breakage. We studied the bending behavior of high-strength conductor wires. In most materials, maximum bending strain can usually be calculated from elongation values obtained in tensile tests. In this paper, however, the maximum bending strain exceeded the elongation of most of our high-strength wires; therefore, we could not estimate bending strain from elongation. The large bending strain that occurs during the manufacture of coils in pulsed magnets causes an increase in residual strain and a decrease in packing factor. Due to the anticlastic effect, the cross section of the wire changes from rectangular to keystone-shaped, with the keystone angle up to 10 degrees. This introduces gaps into the coils, thus reducing the magnetic field by an amount that must be taken into an account. In both tensile-and compressive-strained regions, we observed significant microstructure changes. Certain properties, such as tensile mechanical strength and electrical conductivity, depend directly on microstructure. This paper summarizes our work on both geometry and microstructure evolution in conductors exposed to different bending strain values.