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Description
High power-density motors are required to meet demand for increasing interest in aircraft electrification. To reach these requirements high current density and lightweight conductors are required in the motor windings. With liquid cryogen on-board, low temperatures (20 K with LH2) are achievable where very high purity normal metals benefit from resistance ratio (RR) values of up to 1000. This high RR occur not only due to high purity, but also low levels of defects (including grain boundaries and dislocations). High-purity Aluminum (HPAL) is one such material where 99.999% or higher purity allows for highly competitive ampacity. However, HPAL intrinsically possesses low yield and tensile strength and requires a strengthening matrix for use in applications. Previous efforts in developing a multifilamentary HPAL composites were successful with an Al-alloy as the metal matrix which increased composite strength without degrading HPAL purity, but faced degradation in RR values in electric windings due to an anomalous magnetoresistance contribution. We show in this work the higher resistivity matrix mitigated this anomalous magnetoresistance while maintain the ability to recover the RRR of the HPAL filaments after cold work. A second issue seen in previous HPAL composites was the presence of RR degradation with cycling. However, the new composite design utilizes a metal matrix with a higher elastic modulus in order to enable higher stress before RR degradation. In this work we measure the effect of cyclic mechanical deformation on RRR in HPAL composites at low temperatures in a new testing fixture. We further our measurements and analysis of cryogenic mechanical testing by measuring at various temperatures of interest in electric aircraft applications.
This work was performed under NASA Phase 1 SBIR
