Custom Magnets
The application of sintered NdFeB permanent custom magnets are mainly to use their magnetic properties. However, due to different use environments and conditions, in addition to magnetic properties, there are also requirements for mechanical and chemical properties.
For example, some permanent custom magnets are used in high-speed rotating machinery and must withstand large centrifugal forces, or are used in a vibration environment or under extremely high acceleration (3g~5g) conditions, or when the custom magnets are installed, they are subject to stress and may peel off, lose edges, corners, or crack, etc., so it is natural to have requirements for the mechanical properties of the magnets.
Was sind die mechanischen Eigenschaften von Materialien?
The mechanical properties of materials generally include strength, hardness, plasticity and toughness, and these mechanical property parameters have different physical meanings.
Strength refers to the maximum ability of a material to resist the destructive effects of external forces. Strength is divided into the following according to the different forms of external forces:
Tensile strength (tensile strength), which refers to the strength limit when the external force is tensile
Compressive strength, which refers to the strength limit when the external force is compressive
Flexural strength, which refers to the strength limit when the external force is perpendicular to the axis of the material and causes the material to bend after the action
Hardness refers to the ability of a material to locally resist the pressure of a hard object into its surface. It is an indicator for comparing the hardness of various materials. The higher the hardness, the stronger the ability of the metal to resist plastic deformation.
Plasticity refers to the ability of a solid substance to resist deformation under a certain external force. It is the ability of a material to permanently deform without being destroyed under the action of an external force
Toughness refers to the ability of a material to absorb energy during plastic deformation and rupture. The better the toughness, the less likely it is to have a brittle fracture. In materials science and metallurgy, toughness refers to the ability of a material to resist breaking when it is subjected to a force that causes it to deform. It is the ratio of the energy that a material can absorb before breaking to its volume.
Mechanische Eigenschaften von gesintertem NdFeB
Sintered NdFeB is a brittle material, and its mechanical properties are hard and brittle, that is, high strength and low toughness. There is almost no plastic deformation before fracture, that is, it breaks in the elastic deformation stage.
The figure below is a comparison of the magnetic energy product (BH)m and fracture toughness of various permanent custom magnets materials. We can find that sintered NdFeB has the highest magnetic energy product (BH)m, while the fracture toughness is still comparable to that of Sm2Tm17, SmCo5, and ferrite permanent magnets, because they are all permanent custom magnets materials based on intermetallic compounds and are brittle materials. Bonded rare earth permanent custom magnets 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.
Brittle materials often use three indicators to describe the mechanical properties of materials:
Fracture toughness, usually reflects the strength of the material when cracks expand, and the unit is MPa·m1/2. The fracture toughness of the material should be tested with a tensile tester, stress sensor, extensometer, signal amplification dynamic strain gauge, etc. In addition, the sample should be made into a thin sheet.
Impact strength (impact fracture toughness) reflects the energy absorbed by the material during the fracture process under the impact stress, and the unit is J/m2. The measured value of impact strength is too sensitive to the size, shape custom magnets, processing accuracy and test environment of the sample, and the measured value dispersion will be relatively large.
Bending strength is the bending fracture strength of the material measured by the three-point bending method custom magnets. 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 custom magnets.
DongMaidi found some scholars who combined different tests to give the approximate fluctuation range of the mechanical performance indicators of sintered NdFeB. Because it is a brittle material, the test data dispersion is relatively large.
The high strength and low toughness of sintered NdFeB permanent magnet materials are determined by their own crystal structure. In addition, the following two factors will affect the bending strength of sintered NdFeB custom magnets and are also ways to improve its strength.
The Nd content has a certain effect on the strength of sintered NdFeB custom magnets. The experimental results show that under certain conditions, the higher the Nd content, the higher the material strength.
The addition of other metal elements has a certain effect on the strength of sintered NdFeB custom magnets. When a certain amount of Ti titanium, Nb niobium or Cu copper is added, the impact fracture toughness of the permanent magnet is improved; when a small amount of Co cobalt is added, the bending strength of the permanent magnet is improved.
The insufficient comprehensive mechanical properties of sintered NdFeB are one of the important reasons that limit its application in a wider range of fields. If the toughness of the product can be improved while ensuring that the magnetic properties are improved or unchanged, sintered NdFeB will play a greater role in military, aerospace and other fields and enter a new period of development.
These are important mechanical properties of materials, especially in engineering and material science. Here’s a brief overview of each:
1. Fracture Toughness: This measures a material’s ability to resist crack propagation. It’s crucial for understanding how a material will behave under stress and is particularly important in applications where safety and reliability are critical custom magnets, such as in aerospace and construction. Higher fracture toughness means the material can withstand the presence of flaws and cracks without failing.
2. Impact Strength: This property indicates a material’s ability to absorb energy during a high-impact or sudden force application. It’s measured using tests like the Charpy or Izod impact tests custom magnets. Materials with high impact strength can withstand sudden impacts or shocks without breaking, making them suitable for applications where they might be subjected to unexpected forces.
3. Flexural Strength: This measures a material’s ability to resist deformation under load. It’s often assessed through a bending test, where a material is subjected to a force that causes it to bend until it breaks custom magnets. High flexural strength means the material can support larger loads or withstand greater bending without failing.
Each of these properties is critical in different contexts:
Fracture Toughness is essential for predicting failure in critical structural components.
Impact Strength is important for materials used in environments prone to sudden impacts or shocks.
Flexural Strength is crucial for components that will be subjected to bending or flexing forces.
When selecting a material for a specific application, you’ll want to consider all these properties to ensure it meets the performance requirements.
Understanding fracture toughness, impact strength, and flexural strength is crucial for selecting the right materials for various applications. Here’s a more detailed look at each property:
Fracture Toughness
Definition: Fracture toughness (often denoted as \( K_{IC} \)) is a material property that describes the ability of a material to resist crack propagation. It is a measure of the material’s resistance to fracture in the presence of pre-existing flaws or cracks.
Importance: High fracture toughness indicates a material can endure higher stress and resist crack growth, making it suitable for critical components where safety is paramount.
Testing: Typically measured using standardized tests like the ASTM E399 for metals or ASTM C1337 for ceramics. The material is tested with a pre-cracked specimen under a controlled stress to determine the critical stress intensity factor.
Impact Strength
Definition: Impact strength measures a material’s ability to absorb energy during a sudden impact or shock. It reflects the material’s toughness and resilience.
Importance: High impact strength is essential for materials used in applications where they are exposed to sudden forces or impacts, such as automotive parts, protective gear, or construction materials.
Testing: Common tests include the Charpy impact test and the Izod impact test. These involve striking a notched specimen with a pendulum hammer and measuring the energy absorbed by the material.
Flexural Strength
Definition: Flexural strength (also known as bending strength) measures a material’s ability to withstand deformation under load. It indicates how well a material can resist bending forces.
Importance: High flexural strength is important for components subjected to bending stresses, such as beams, bridges, and structural elements.
Testing: Typically assessed using a three-point or four-point bending test, where a material sample is supported at two or more points and a load is applied at the center. The maximum stress the material can withstand before breaking is recorded.
Comparing the Properties
Fracture Toughness is most relevant for materials that will experience stress concentrations or flaws.
Impact Strength is crucial for applications where materials face sudden or dynamic loads.
Flexural Strength is key for materials that need to endure bending or flexural stresses.
When designing or selecting materials for specific applications, you must consider these properties together with other factors such as thermal stability, corrosion resistance, and cost to ensure optimal performance and safety.
