Fracture

With brittle fracture (also brittle fracture ) is called a suddenly occurring material failure. It occurs ( typical examples: glass, ceramics, ice) especially in hard and brittle materials with low ductility and toughness. Brittle fractures occur without or with little plastic deformation in the gap breakdown voltage is exceeded. Since most metals ductile break, you will find this form of fracture only for some metals and only under certain stress conditions. For brittle fracture tend pig iron, chromium, molybdenum, tungsten, beryllium and zinc, but brittle fractures can also occur in ductile metals, such as very low temperatures ( see transition temperature) at a multiaxial stress state, which also results in thick-walled components, and at very high rates of deformation ( impact effect, explosion).

Brittle materials are characterized in the stress-strain diagram by a steep increase of Hooke's straight, it will execute at the end of the fracture without plastic deformation. The fracture start is done by small errors, where a stress concentrator. The crack can propagate at the speed of sound in the material and usually occurs by cleavage at specific crystallographic lattice planes - heaped on low-index planes ( see Miller indices ) - on. One speaks in this case of a transgranular fracture path. Less often occur in brittle fractures with intergranular course; these are then observed when relatively large amounts of precipitates or inclusions are located at the grain boundaries.

The brittle fracture can be based on the fracture surface, due to typical features seen. A transgranular fracture pattern in the fracture surface has a crystalline appearance, since the grains are broken up into different layers with different orientations (which is similar to the appearance of the candy sugar ). Another frequently occurring feature is the so-called Chevronmuster. It has a plurality of break layers lying at different heights of the material. The surface shows a fan- like pattern, starting at the crack origin outwardly extending, with deep furrows and ridges. The Chevronmuster, visible to the naked eye or a magnifying glass, is always an indication of brittle fracture, suggesting a shock as crack cause. The occurrence of brittle fracture is thus no single indication of inferior workmanship or manufacturing quality.