ELASTOPLASTIC STRESS-ANALYSIS OF NB3SN SUPERCONDUCTING MAGNET

The plastic behavior of a superconducting material is investigated and the corresponding elastoplastic formulation for the distribution of s tress and strain in a superconducting solenoid magnet is presented. Th e analysis calculates stress and strain at the midsection, where tange ntial stress exhibits its maximum value and shear stress is negligible . The prediction of stress and strain is essential for both the mechan ical and electrical design of high-field superconducting magnets conta ining Nb3Sn superconductor. The concept of plasticity is introduced fo r the first time in the context of magnet design for Nb3Sn conductor n d compared to alternative approaches using conventional elasticity the ory. Individual coil sections of a superconducting magnet can be reinf orced by an outer section of structural material, the effect of which is included in this formulation. The results show that the elasticity approach using the ''secant modulus method'' does not fully predict th e strain distribution; however, it call be used to approximate the str esses. It is shown that for an accurate strain prediction the true non linear elastoplastic nature of the superconducting materials should be considered and proper yield criteria should be used. The inaccurate p rediction of strains (tangential or radial) can affect critical curren t density and the evaluation of the reinforcements. (C) 1996 American Institute of Physics.