4.8. Grinding Brittle Materials

The designation “brittle”, often used in manufacturing, characterises a certain ma­terial group according to their mechanical properties. High brittleness, i. e. low fracture-resistance, and hardness represent a combination of material properties that, on the one hand, influences the range of uses of these materials, but also de­termines their machinability and workability properties.

Several factors influence the mechanical behaviour of a material. Firstly, there is the atom arrangement of the solid body. This can have an amorphous or a crys­talline structure. In the case of amorphous structures, the atoms are arranged ran­domly. Glasses and many plastics and rubbers are amorphously structured. We speak of a crystalline structure if the atoms form a regular three-dimensional lat­tice. Ceramics can exhibit both structures. The dominant atomic bond type is deci­sive for the inclination toward ductile or brittle material behaviour. Covalent bonds lead to limited electron movement potential. For plastic forming processes, position changes are, however, extremely necessary. For this reason, large amounts of covalent bonds facilitate brittleness and hardness, while metallic bonds (ionic bonds) cause ductile material behaviour.

From the basic properties are derived those branches in which brittle materials have a significant function today (Fig. 4-16).

Characteristics

• Low fracture toughness

• Low fracture strain

• Temperature resistance

• Chemical resistance

• High Hardness

Fig. 4-16. Properties of brittle materials and typical areas of application

In this chapter, we will consider high-performance ceramics, glasses and sili­con as examples of brittle materials.