Experts in precision parts processing tell you that all defects in materials, including microcracks, small pores and places where impurities are concentrated, and places where the organization is loose, can be the source and cause of cracks, which is called crack source. Any crack is caused by the material from the source of the crack under the action of external force. The source of cracks is often small and cannot be detected with the naked eye. However, under the microscope, you can see many small cracks, pores and impurities. These are the origins of cracks.
The source of the crack is brought in by the abrasive tool during the production process. No material can be completely free of defects, but the number and degree are different. Although we have made various efforts in process operations, internal defects are still better than metal materials. A lot. But this is not to say that if the product is defective, cracks will definitely occur. The important thing is that the product cannot undergo plastic deformation like metal under the action of external force. It is easy to concentrate the stress on a certain part, so that this part of the defect-the source of the crack is quickly transformed into a crack. Once the internal crack is formed and reaches a certain critical size, it is very easy to expand. The internal stress immediately concentrates on the tip of the crack and expands to both sides of the tip. It cannot absorb the external force through the change of its shape like metal. The incoming energy can only be used to generate new surfaces to absorb this part of the energy. The expansion of cracks means the formation of two new surfaces.
Experts in precision parts processing tell you that the cracks grow rapidly and the new surface grows rapidly until the cracks are formed or broken, so that all the applied energy is transformed into the energy produced by the new surface. This is the process of crack formation. The formation and expansion of cracks occurred in a very short period of time, or even an instant, and it can be said to be an instant disintegration. The property of an abrasive tool that cannot withstand strong vibration and impact is called brittleness. The measure of brittleness can be expressed by the energy required to form a unit of new surface, which is called fracture work. The greater the work of fracture, the greater its toughness. The work of fracture of ceramic grinding wheels is very small, only one-thousandth of that of copper. That is to say, the brittleness of abrasive tools is large and cannot withstand the impact. Therefore, whether it is a semi-finished product or a finished product, Handle with care to avoid cracks and waste caused by collisions. The brittleness of the grinding wheel is not only reflected in its inability to withstand beatings, that is, poor mechanical shock resistance, but also in its poor thermal shock resistance, which is also called poor thermal vibration resistance. Mechanical shock resistance and thermal shock resistance are similar and different. They have the same damage performance. They both cause cracks inside the product and promote the rapid expansion of the cracks, and finally lead to complete cracks.
Experts in precision parts processing tell you that mechanical shock is caused by external forces, while thermal shock is due to thermal stress generated inside the product. Thermal shock resistance is not only related to the mechanics, but also related to the thermal conductivity and thermal expansion of the product itself. The performance has a great relationship. During the heating process, the temperature difference between the surface and the inside of the product, that is, the temperature difference, causes the various parts of the product to have different expansion and contraction rates, thus generating thermal stress. If the heat conduction ability is high, the temperature difference caused by each part of the product can be reduced, the expansion and contraction rate of each part is small, and the influence of thermal stress generated can also be reduced.