BRITTLE FRACTURE

BRITTLE FRACTURE

what is brittle fracture?

Basically, brittle fracture is a rapid run of cracks through a stressed material. The cracks usually travel so fast that you can't tell when the material is about to break. In other words, there is very little plastic deformation before failure occurs. In most cases, this is the worst type of fracture because you can't repair visible damage in a part or structure before it breaks.
In brittle fracture, the cracks run close to perpendicular to the applied stress. This perpendicular fracture leaves a relatively flat surface at the break. Besides having a nearly flat fracture surface, brittle materials usually contain a pattern on their fracture surfaces. Some brittle materials have lines and ridges beginning at the origin of the crack and spreading out across the crack surface.
Other materials, like some steels have back to back V-shaped markings pointing to the origin of the crack. These V-shaped markings are called chevrons. Very hard or fine grained materials have no special pattern on their fracture surface, and amorphous materials like ceramic glass have shiny smooth fracture surfaces. Chevron Fracture Surface (Callister p. 185)
Radiating Ridge Fracture Surface (Callister pg. 186, copyright by John Wiley & Sons, inc.)

Types of Brittle Fracture

The first type of fracture is transgranular. In transgranular fracture, the fracture travels through the grain of the material. The fracture changes direction from grain to grain due to the different lattice orientation of atoms in each grain. In other words, when the crack reaches a new grain, it may have to find a new path or plane of atoms to travel on because it is easier to change direction for the crack than it is to rip through. Cracks choose the path of least resistance. You can tell when a crack has changed in direction through the material, because you get a slightly bumpy crack surface.