The application of sintered NdFeB permanent magnets mainly relies on their magnetic properties. However, due to different usage environments and conditions, in addition to magnetic performance requirements, there are also mechanical and chemical performance requirements for the magnets. For example, some permanent magnets are used in high-speed rotating machinery and must withstand large centrifugal forces, are used in vibration environments, withstand extremely high acceleration (3g~5g), or are subject to stress when installing the magnets. It may peel, fall off, corners or crack, etc., so it is natural to have requirements for the mechanical properties of the magnet.

- Tensile strength (tensile strength) refers to the strength limit when the external force is pulling force
- Compressive strength refers to the strength limit when an external force is pressure
- Bending strength refers to the strength limit when an external force is perpendicular to the axis of the material and causes the material to bend.

The figure below is a comparison of the magnetic energy product (BH)m and fracture toughness of various permanent magnet materials. We can find that sintered NdFeB has the highest magnetic energy product (BH)m, and the fracture toughness is still comparable to Sm2Tm17, SmCo5, and ferrite permanent magnets, because they are all permanent magnet materials based on intermetallic compounds and belong to Brittle materials. Bonded rare earth permanent magnet materials, Fe-Cr-Co, and magnetic steel have the best fracture toughness, but their magnetic energy product (BH)m is much lower than that of sintered NdFeB.

1. Fracture toughness usually reflects the strength when cracks expand in the material. The unit is MPa·m1/2. The fracture toughness test of materials requires a tensile testing machine, stress sensor, extensometer, signal amplification dynamic strain gauge, etc. In addition, the sample must be made into a thin sheet.
2. Impact strength (impact fracture toughness) reflects the energy absorbed by the material during the fracture process under the action of impact stress. The unit is J/m2. The measured value of impact strength is too sensitive to the size, shape, processing accuracy, and test environment of the sample, and the dispersion of the measured value will be relatively large.
3. The flexural strength is measured by the three-point bending method. Because the sample is easy to process and the measurement is simple, it is most commonly used to describe the mechanical properties of sintered NdFeB magnets.

1. The Nd content has a certain influence on the strength of sintered NdFeB. Experimental results show that under certain conditions, the higher the Nd content, the higher the strength of the material.
2. Adding other metal elements has a certain impact on the strength of sintered NdFeB. When a certain amount of Ti, Nb, or Cu is added, the impact fracture toughness of the permanent magnet is improved; when a small amount of Co is added, the flexural strength of the permanent magnet is improved.