The Tensile Strength of Neodymium Iron Boron Magnets: Weibull Analysis and the Implications for PM Motor Design

This paper examines the tensile strength of sintered Neodymium Iron Boron magnet material and challenges the convention that it is weak and must be held at a low stress or in compression. A deeper understanding of its failure stresses may allow motor power densities to be increased. Magnets are found to be stronger than manufacturers claims, leading to a potential 68% increase in maximum speed for the same rotor dimensions on an example motor. Uni-axial tensile tests and 4-point bend tests were conducted on over 30 replicates to determine the tensile and flexural strength of the material. From the data it is concluded that Neodymium magnets exhibit a statistical strength that is better represented by a Weibull distribution, rather than the single ultimate tensile strength presented by manufacturers. The authors propose that with careful selection or pre-testing, magnets could be used under greater tension within electric motors, which can lead to higher power densities.